by Paul Gilster | Aug 20, 2021 | Deep Sky Astronomy & Telescopes |
Anomalies in our models are productive. Often they can be explained by errors in analysis or sometimes systematic issues with equipment. In any case, they force us to examine assumptions and suggest hypotheses to explain them, as in the case of the unusual acceleration of stars that has turned up in two areas. Greg Matloff has written about one of them in these pages, the so-called Parenago’s Discontinuity that flags an unusual fact about stellar motion: Cool stars, including the Sun, revolve around galactic center faster than hotter ones.
This shift in star velocities occurs around (B-V) = 0.62, which corresponds to late F- or early G-class stars and extends down to M-dwarfs. In other words, stars with (B-V) greater than 0.61 revolve faster. The (B-V) statement refers to a color index that is used to quantify the colors of stars using two filters. One, the blue (B) filter, lets only a narrow range of wavelengths centered on blue colors through, while the (V) visual filter only passes wavelengths close to the green-yellow band. Hot stars have (B-V) indices closer to 0 (or negative); cool M-dwarf stars come out closer to 2.0. Proxima Centauri’s (B-V) number, for example, is 1.90. The (B–V) index for the Sun is about 0.65.
What the Soviet space scientist Pavel Parenago (1906-1960) had observed is that cooler stars, at least in the Sun’s neighborhood, revolve about 20 kilometers per second faster around the galactic center than hotter, more massive stars. Work in the 1990s using Hipparcos data on over 5,000 nearby main sequence stars clearly showed the discontinuity. An early question was whether or not this was an effect local to the Sun, or one that would prove common throughout the galaxy.
Image: Soviet space scientist Pavel Parenago. Credit: Visuotin? Lietuvi?.
The answer came in the form of a paper by Veniamin Vityazev (St. Petersburg State University) and colleagues in 2018. The scientists hugely expanded the stars in their sample by using the Gaia Data Release 1 dataset,. The Gaia release included some 1,260,000 stars on the main sequence and a further 500,000 red giants. As we saw yesterday, the Gaia mission, which launched in 2013, is continuing to gather data at the Earth-Sun L2 Lagrange point, using astrometric methods to determine the positions and motions of a billion stars in the galaxy.
You may remember that the Vityazev paper (citation below) and its consequences was the subject of a 2019 dialogue in these pages between Greg Matloff and Alex Tolley (see Probing Parenago: A Dialogue on Stellar Discontinuity). And for good reason: The Gaia dataset allowed the Russian scientist and colleagues to demonstrate that Parenago’s Discontinuity was not a local phenomenon, but was indeed galactic in nature. All of this naturally leads to questions about the mechanisms at work here — Matloff’s interest in panpsychism as one explanation is well known and discussed in his book Starlight, Starbright (Curtis, 2019).
But in a new paper with Matloff, Roman Ya. Kezerashvili (New York City College of Technology) and Kelvin Long (Interstellar Research Centre, UK) point to another noteworthy datapoint. The extensive Gaia dataset showed a feature that turned up in the Hipparcos data as well. There was what the authors call a ‘strange bump in the curve of galactic revolution velocity versus (B-V) color index between (B-V) ? 0.55 and (B-V) ? 0.9…’ This would take in stars of the spectral classes G1 through K2, and the authors add that the bump is apparent only in the direction of stellar galactic revolution, like Parenago’s Discontinuity itself. Is this to be construed as a subset of the discontinuity or a separate effect? We don’t yet know.
What we do have is apparent acceleration in the direction that stars rotate around the galaxy, an unusual effect that adds up: In a billion years, the positional shift between a star without this acceleration vs. with the acceleration is about 1,500 light years.
This second apparent acceleration has yet to be confirmed by other researchers, as the authors acknowledge. But as we await that result, the new paper investigates the physical processes that could account for it. If we consider a star expelling material in a specific direction, we can model the system by analogy to a rocket and its expelled fuel, and thus examine velocity change with the Tsiolkovsky rocket equation. From the paper:
There are a number of physical mechanisms responsible for expelling mass during the stars’ life. These include but may not be limited to: unidirectional or focused electromagnetic (EM) flux, solar wind, accelerated solar wind, coronal mass ejections (CMEs), unidirectional neutrino flux, and solar wind thermonuclear fusion. Each mechanism can be treated as an exhaust velocity Vex with a mass flow rate so that the acceleration of the star is analogous to a rocket thrust F = VexMs.
What stands out here is how big the force F = 1016 N — the force needed to accelerate stars like the Sun to this level — is from our terrestrial perspective. It is the equivalent of the force exerted by two billion 106 kg rockets, each accelerating at 3g. Backing out to cosmic scale, though, the force appears less daunting, being 5 orders of magnitude less than the mutual gravitational force between the Earth and the Sun.
The mechanisms of mass loss are many and varied, as noted above, and the paper goes to work on eight of them:
- Unidirectional or focused stellar electromagnetic flux
- Galactic cannibalism
- Stellar mass loss by thermonuclear fusion
- Non-isotropic stellar wind
- Accelerated unidirectional stellar wind
- Coronal mass ejections
- Unidirectional neutrino flux
- Solar wind thermonuclear fusion
Note how many of these demand an existing advanced technology to implement them. In fact, of the eight, only two have solutions that are what Matloff calls ‘mechanistic;’ i.e. operational within nature without technological intervention. These are galactic cannibalism and stellar sass loss by thermonuclear fusion. Neither show promise as a cause for stellar acceleration of this order.
Galactic cannibalism refers to interactions between dwarf galaxies and large galaxies like the Milky Way, with the satellite galaxies being absorbed. This adds to the mass of the primary galaxy and may increase star orbiting velocities, but the authors discount the process because stellar nurseries are also accelerated by galaxy mergers, just as pre-existing stars. Stellar mass loss by thermonuclear fusion due not only to fusion within the core but via the stellar wind — which is in any case omnidirectional — likewise fails to produce the observed acceleration effect across classes of stars.
The other six options all involve the application of advanced technologies to create stellar motion in a specific direction, and some of these don’t work either. Unidirectional coronal mass ejections, for example, even if they could be shaped as thrust, fail to provide the needed energies. What emerge as viable candidates are the combined effects of a unidirectional neutrino jet and an accelerated unidirectional stellar wind “in conjunction with the unidirectional photon jet ejected from the star and non-isotropic stellar wind.” Thus on the accelerated unidirectional stellar wind:
Consider the case of a dual-purpose Dyson/Stapledon megastructure constructed around a star. Confirmation of the existence of such a megastructure would constitute evidence for the existence of a Kardashev Level 2 or higher civilization. A fraction of the star’s radiant output is used to accelerate a fraction of the star’s stellar wind as a unidirectional jet.
Obviously these options take us into science fiction territory, such as the recent Greg Benford/Larry Niven collaboration beginning with Bowl of Heaven (Tor, 2012), where a star in directed motion carries with it a vast environmental shell. So as an example of just one way to do all this, let me quote from an article Benford wrote for Centauri Dreams in 2014 (see Building the Bowl of Heaven):
Our Bowl is a shell more than a hundred million miles across, held to a star by gravity and some electrodynamic forces. The star produces a long jet of hot gas, which is magnetically confined so well it spears through a hole at the crown of the cup-shaped shell. This jet propels the entire system forward – literally, a star turned into the engine of a “ship” that is the shell, the Bowl. On the shell’s inner face, a sprawling civilization dwells…
The jet passes through a Knothole at the “bottom” of the Bowl, out into space, as exhaust. Magnetic fields, entrained on the star surface, wrap around the outgoing jet plasma and confine it, so it does not flare out and paint the interior face of the Bowl — where a whole living ecology thrives, immensely larger than Earth’s area.
Image: Moving a star as depicted in Bowl of Heaven. Credit: Don Davis.
But the idea of moving stars via technology has a long pedigree. As just one example, let me quote Fritz Zwicky, that fiercely independent and prescient thinker, from an article he published in June, 1961 in Engineering and Science:
In order to exert the necessary thrust on the sun, nuclear fusion reactions could be ignited locally in the sun’s material, causing the ejection of enormously high-speed jets. The necessary nuclear fusion can probably best be ignited through the use of ultrafast particles being shot at the sun. To date there are at least two promising prospects for producing particles of colloidal size with velocities of a thousand kilometers per second or more. Such particles, when impinging on solids, liquids, or dense gases, will generate temperatures of one hundred million degrees Kelvin or higher-quite sufficient to ignite nuclear fusion. The two possibilities for nuclear fusion ignition which I have in mind do not make use of any ideas related to plasmas, and to their constriction and acceleration in electric and magnetic fields…
So could an advanced culture pull this off? The authors are quick to point out that the eight mechanisms they evaluate do not exhaust the range of possibilities, but thus far the physical mechanisms under investigation fail the test unless assisted by a technology. The first order of business, of course, will be to verify the apparent stellar acceleration and then to ponder stellar kinematics in their combined light.
But while we can envision advanced cultures developing the tools to move individual stars, as breathtaking as the concept seems, it appears unlikely in the extreme that entire stellar classes are being moved about simultaneously by megastructures or other technologies.
I think the existence of an explanation within the realm of nature has to be assumed. The question, of course, is just where it is to be found. This spirited paper, cheerfully speculative, contains an open call to the community to investigate anomalous stellar accelerations and produce other hypotheses explaining this curious behavior.
The paper is Kezerashvili, Matloff & Long, “Anomalous Stellar Acceleration: Causes and Consequences,” JBIS Vol. 74 (2021), pp. 269-275 (full text). The Vityazev paper is V. V. Vityazev et al., “New Features of Parenago’s Discontinuity from Gaia DR1 Data,” Astronomy Letters 44, 629-644 (2018). Abstract.
by Paul Gilster | Apr 26, 2019 | Deep Sky Astronomy & Telescopes |
The publication of a paper called “New Features of Parenago’s Discontinuity from Gaia DR1 Data” by V. V. Vityazev and colleagues brought us a new look at an unusual observation. Parenago’s Discontinuity refers to the fact that red, cooler stars move faster in the direction of galactic rotation than blue, hotter stars, based on Hipparcos data. But is the phenomenon just a chance, local observation? Fortunately, a much larger dataset from the Gaia mission has now become available, and it is this that the Vityazev paper addresses in terms of Parenago’s finding. The following dialogue between Greg Matloff and Alex Tolley goes to work on the Vityazev document. Dr. Matloff has pointed to the Discontinuity as a possible marker of consciousness among low temperature stars, where molecular bonds can form.
Could motion be a matter of agency in such stars? Greg explored the idea in his book StarLight, StarBright. Now Alex digs into the Vityazev paper and questions whether Greg is right that his controversial theory can be falsified given our data. Various mechanisms for stellar motion are explored, ranging from coronal mass ejections to possibilities that are downright Stapledonian. How exactly would a civilization go about moving stars? I am preserving the dialogue format of the original correspondence as a case in point of serious differences being discussed in a way that both disputants have found valuable.
By Greg Matloff and Alex Tolley
Alex: Greg, in your 2012 Centauri Dreams post Star Consciousness: An Alternative to Dark Matter, you made the claim that there was an alternative explanation to dark matter for the velocity of stars around the galactic center. Your hypothesis was some sort of psychokinesis effect generated by consciousness, even if a primitive one. You used the Parenago Discontinuity (PD), which showed that velocity was related to star type, to suggest that fast stars were cool and that these cool stars could have chemistry, allowing some sort of consciousness. The 2015 Centauri Dreams post Greg Matloff: Conscious Stars Revisited further elaborated on this hypothesis.
The first problem I have with the data you used is that there was no plateau of velocity, but rather a peak, unlike the classic Parenago Discontinuity, which showed a plateau. This would imply that star types reach a peak velocity, then decline. Why would there be such an effect if consciousness was the driver of some psychokinetic effect? A possible explanation could be the amount of material that could be expelled to propel the stars.
The issue was left on whether the Parenago Discontinuity was purely a local, rather than galactic effect. We awaited the Gaia data.
The Vityazev paper using Gaia data confirmed that the Parenago Discontinuity was indeed non-local and that the peak effect around B-V of 0.7 seen with the earlier data you presented was indeed correct. As you had hung the hypothesis on the Parenago Discontinuity, this confirmation with the larger data did not falsify the interpretation that stars might be conscious.
The Hipparcos satellite measured the distances to hundreds of thousands of stars. It also measured the magnitude of each star through two filters:
A blue filter, yielding a B (for “blue”) magnitude
A greenish filter, yielding a V (for “visual”) magnitude (the human eye has highest sensitivity in the green)
Now, astronomers call the difference between the B and V magnitude of a star its (B-V) color, or sometimes just “color” for short. Remember how magnitudes work: large numbers mean “faint”, and small numbers mean “bright”. What is the “(B-V) color” of a hot star?
Figure 5 in the Vityazev paper seems to offer the basis for the more likely explanation of the PD results.
The figure 1b graph (left) shows the PD with the Gaia data. The figure 5 chart (right) shows that the PD effect is correlated with stellar age, rather than stellar temperature. The cooler stars in the sample are actually younger than G stars at the age peak. The shape of the B-V vs age graph matches the B-V vs azimuthal velocity (V) graph. This seems to me to suggest that velocity is therefore related to age, and more likely due to some physical factor related to time.
This seems to me to be the most parsimonious relationship and should be chosen by Occam’s razor. The stellar conscious hypothesis has to account for this age relationship and explain why the coolest stars that should have good consciousness and can, for unknown reasons and unknown mechanisms, chase around the galaxy faster than large, hotter stars, nevertheless go more slowly than G-type stars.
Why stars increase velocity with age still needs elucidation and modeling. However, the Vityazev paper has broken down the many components of stellar kinematics. This should provide a nice set of constraints for validating computational models.
Greg: The fact that Parengo’s Discontinuity is apparently non-local supports my hypothesis and does not support density waves. I have gone through the Messier, Herschel, and NGC Catalogues and reported my results in several publications. No known diffuse nebula in our galaxy or the Clouds of Magellan is large enough to drag along stars over a ~1,000 light-year radius sphere. The fact that stars seem to move faster along the direction of galactic motion as they age is very interesting, but it does not bear upon my original hypothesis that the discontinuity occurs at the point where molecules come in to stellar spectra. It is in my data as well as the data in the paper, so I presume that it is correct. I had originally ignored it because it does not bear on the original hypothesis. I presented in my original letter to Paul and others the causes I could think of to explain this phenomenon. But please, don’t hesitate to present others.
I am pretty happy right now because I predicted a non-local Parenago Discontinuity and this has apparently been verified. No one else, to my knowledge, had made this prediction. The local alternative explanations are now extinct. But science works by constructing alternative explanations for a phenomenon and testing them. Please do so. Try your hand at galaxy-wide possible alternative explanations. I can think of a few that won’t work. I am very interested in what you and others come up with and look forward to a dialogue of competing ideas.
Alex: The chart below is a rough conversion of the B-V values to age (from Figure 5) and the velocity from figure 1b. This seems to show that the Parenago Discontinuity might be a phenomenon based on using a variable (stellar type) that isn’t really related to the star’s velocity. Using age provides an approximately linear trendline with an R-squared of 0.93.
I accept that this velocity might be hard to explain (I am certainly not able to comment on this) but the relationship of age to velocity does seem to point to a simpler explanation for V based on natural forces, rather than requiring agency.
This older reference looked at A and B stars and examined the velocity differences based on age. There were clear differences based on age, rather than stellar type. While this doesn’t invalidate your hypothesis, they do have a physical explanation on why age impacts star velocity. To my mind, such approaches should be examined further before resorting to more exotic explanations. With the Gaia data, astronomers involved in kinematics studies now have a trove of high-quality data to test their models. I would be looking amongst that cadre for cutting-edge modeling.
Greg: Nice analysis! What I tried to do is put all the cards, as I see them, on the table. I am not and never have been an advocate for psychokinesis. But science seems willing to accept the Multiverse, which can perhaps not be verified. It accepts dark matter and invokes many properties for this stuff even though it remains hidden. I have discussed PK and the Geller/Randi controversy with people on both sides and find nothing wrong with their arguments. So I believe, with David Kaiser of MIT and others, that the case should be reopened. If a weak PK force can be demonstrated to the satisfaction of the scientific community, it should be considered an option.
I also believe that the stellar age variation has little to do with Parenago’s Discontinuity. Why does the discontinuity appear at the same place where molecules come in to stellar spectra?? And why indeed is it a discontinuity instead of a smooth curve? Invoking strange (and unknown) stellar variability to explain it is certainly an exotic explanation!
One of the problems with what we are discussing comes from the fact that I was checking the metaphysics of Olaf Stapledon, a sci-fi author and philosopher, and attempting to see if there is something scientific behind his discussion in Star Maker. If I were starting afresh, I would title my work (as I have done in subsequent papers) “A Test of Self-Organization on the Galactic Scale?”, since astrophysicist Erich Jantsch uses “self-organization” as a possible explanation of consciousness. Alternatively, I might go with the terminology of philosophers such as David Chalmer and title my papers “Is Panpsychism a Science?”
I think that the work that you have done on (B-V) vs. star age from the Gaia Release 1 sample is invaluable and should be included in our published dialogue. I hope very much that our debate leads to further work with future Gaia data releases.
Alex: Let me give you a perspective from a biologist’s point of view. The Parenago Discontinuity might have an analogy to living vs non-living, where living things can be observed to grow, move (or have tropisms), reproduce, etc. Let us assume that cooler stars have some sort of motility which is driven by a “need”, perhaps acting something like a bacterium. Bacteria can be observed to move faster in their medium if they have flagella. A biologist would ask “what is the evolutionary advantage of movement given the cost” and might hypothesize that this leads to faster food discovery, or a phototropism, or evasion of larger predators. In the case of cool stars, I would be asking similar questions. Why is V (azimuthal velocity) the key variable, rather than a different direction (U, W)?
Given that V is affected by star type, what is the advantage of moving faster in one direction? One might hypothesize that this facilitates sweeping up of neutral gas clouds more effectively, but this would be even better if the stars moved in the opposite direction. Are the stars perhaps self-organizing into “flocks” and what we are seeing is the movement of the flock which is currently going in the V direction? With bacteria, we know that it is flagella that allow movement through the medium. With stars, one mechanism is with a Shkadov drive to asymmetrically create thrust. Another might be directed coronal mass ejections (CMEs). In the former case, it is not the star that is sentient, but more likely a separate intelligence, a more Stapledonian idea.
Therefore another hypothesis is that stars are being driven by a galactic wide intelligence[s] to reach a certain unified velocity for some reason. The age relation to velocity then makes sense if the Shkadov drives need billions of years to reach the needed velocity. For what purpose?
One idea might be to facilitate more frequent stellar encounters allowing biological civilizations to disperse more easily among the stars. On the other hand, if the galaxy is an organism or superorganism, perhaps the Parenago Discontinuity is some process to organize older stars for some equivalent of a cellular process.
An obvious question suggests itself. If cooler stars are somehow able to direct their velocity, shouldn’t very cool stars, i.e. red dwarfs and brown dwarfs, also have that behavior? We don’t have enough examples of BDs to determine this, but it would provide another datum. One might extend this to gas giant planets too. While the ones we know about are bound to their stars, is it possible that planetary migration is a related phenomenon? Are “hot Jupiters” exhibiting similar behaviors?
Clearly one can speculate endlessly. If the relevant variable is time rather than stellar type, then this constrains mechanisms to those that require both time and a reason for the more uniform direction. With such a constraint, looking for a natural process that requires billions of years would seem to be the most fruitful direction. That velocity W (fig 1c) is fairly constant, but U (fig 1a) declines with stellar type suggests to me that physical forces are somehow directing the movement into the W direction, whether those forces are natural or artificial. The direction is apparently translating from U, towards the galactic center, to V, a transverse direction, rather like the Coriolis forces operating on weather patterns that “shape” the velocity profile.
If time is the relevant variable, then looking for young, cool stars should be the best way to test the hypothesis. If they are fast, then stellar type is the key variable, but if slow, then time. The Vityazev paper also has limited data for red giant stars. If anything, the G, K and M red giant stars have more uniform V than main sequence stars, i.e. they seem to conform more closely to the classic PD plateau. Whatever the mechanism, size is clearly not a variable as they have velocities comparable to the oldest G stars. Creating an age chart for these stars might also be instructive.
Unfortunately, even if age is the relevant variable, it doesn’t falsify your hypothesis. The mechanism of acquiring a high V might simply require time, whether a natural, external force or an inner, self-directed one. Just as with determining which animals are conscious (e.g. using the mirror test), we need a better test to be able to falsify your hypothesis. We may be in the position of trying to determine sentience of a herd of buffalo from a still photograph when what we need is video or many photographs over time.
PS: A back-of-the-envelope calculation shows that a star could attain the necessary velocity by directing its radiant energy (e.g. Shkadov drive), but not by directed coronal mass ejections. (calculation for our sun).
Greg: Wonderful! My feeling has always been that stars need not have a high level of consciousness–they could be like slime-mold amoeba or developing cells in embryos.
I suspect that Vityazev et al could not use the red giant Gaia data for the same reasons the Burnham’s validation of Parenago for giants looks so fluffy. Since most of these stars are very distant, astrometric parallax is impossible with Hipparchus and the early Gaia data.
Spectroscopic distance estimates using the HR diagram are accurate to 10% or less. Also, what is the local reference standard when the subject stars occupy a sphere thousands of parsecs in radius? Hopefully, future Gaia data releases will offer the possibility of greater accuracy.
Also, I have been thinking about your suggestion regarding unknown forms of stellar variability. My suggestions in the earlier emails–EM radiation anisotropy and unidirectional jets in mature stars–are two of these. Perhaps there are others!
Greg: The Shkadov thruster could of course be a form of anisotropic EM emission from the star. But could such a thruster develop in a purely materialistic setting not requiring a Kardashev Type 2 civilization in that star’s system or volition on the part of the star?
It is so strange that we are encountering so many fascinating intellectual insights at the same time that national governments are failing. Last Sunday we attended a talk by Tyler Volk, a biologist at NYU. He has constructed a geometric/architectural model of self-organization from the quark to universal levels. Tyler suspects that we are moving towards the planetary phase of our civilization and this is the use of apparent political dysfunction. I hope he is correct.
Alex: Greg, you write: “The Shkadov thruster could of course be a form of anisotropic EM emission from the star. But could such a thruster develop in a purely materialistic setting not requiring a Kardashev Type 2 civilization in that star’s system or volition on the part of the star?”
I would be skeptical about EM emission asymmetry as I would have thought this would be detectable. A Shkadov drive with mirrors would definitely have some observable effects. Even just some “magical” control over EM emissions should be detectable.
While CMEs are not energetic enough, a small star with large CMEs that are accelerated to c might just work. But again, I would think such a beam would be detectable. I agree with you that such EM or particle control would need K2 civilizations to manage. With so many stars that would be exhibiting such high V’s, just by chance we would detect some anomalies, and solve the SETI question too.
It also occurs to me that since our galaxy has experienced a collision with another galaxy or satellite in the remote past, with a corkscrew effect on velocities, is there any chance this might in some way be responsible for the Parenago Discontinuity?
Let me refer to a post here on Centauri Dreams titled Gaia Data Hint at Galactic Encounter. I could imagine that an old collision with another galaxy or similar massive object accelerated stars which retained their higher velocities while younger stars maintain the velocities of birth in a more stable galaxy post-collision. To get the age-related relationship, it suggests that the collision must have had its impact on velocity over billions of years. Perhaps the values of U, W and V can be used to determine the likely form of the collision?
Greg: Regarding the Shkadov thruster discussion, have you read the Benford/Niven novels Bowl of Heaven and Shipstar? These discuss an advanced version of this concept. I have given some thought to a galactic collision producing Parenago’s Discontinuity. According to the computer simulations done at Cornell (and likely other places), when the Milky Way collides with Andromeda to form Milkimedia (what a horrible name!), there will be widespread disruption of diffuse nebulae. This might result in a Spiral Arms Density Wave effect drawing lower-mass stars along faster than their more massive colleagues.
But the same simulations indicate that the combined galaxies lose their spiral shapes after merger. The ultimate result is a giant elliptical with few nebulae and a very low rate of star formation. Since this has clearly not occurred for the Milky Way galaxy (which is a nice barred spiral), it is reasonable to conclude that such a galactic merger did not happen. From what I understand, galactic cannibalism (where a big galaxy gobbles a smaller one) has less disruptive effects–the big guy retains its shape (which might be an argument for self-organization on the galactic scale.
Alex: From an engineering point of view, I think controlling the solar wind might be a lot easier than deflecting the EM with a solid mirror. I would envisage surrounding the star in a charged, superconducting “mesh” to trap the protons. These would be funneled to electromagnetic accelerators to emit the protons in a unified direction at near c velocity. That might be enough to accelerate the star over the needed timescales. The advantage is lower mass requirements and no impact on the star’s light emissions or spectrum. However, I would expect that the proton beam emitted would be detectable. Think of this drive as a giant ion engine coupled with a ramscoop that captures the protons from the star, rather than from the interstellar medium as in a Bussard ramjet.
The Centauri Dreams link I provided was for a proposed “impact” with a dwarf galaxy (the Sagittarius dwarf galaxy). Much smaller than M-31, and if there was an impact, it certainly hasn’t disrupted the shape of our galaxy. What is interesting is the analysis technique that teased out the spiral shape of the velocity-position phase space that was too subtle to visualize with pre-Gaia data. This sort of analysis might offer a better way to understand the stellar type/age vs velocity relationship. Figure 2 in the paper referenced in the article shows the structure in the azimuthal (V) direction vs the radius (I cannot interpret if this has any possible bearing at all on the Parenago Discontinuity, but the same analysis teasing out stellar type might well do. It might be worth contacting the principal author regarding this approach. Paper attached)
[The paper Alex is referring to is Antoja et al., “A Dynamically Young and Perturbed Milky Way Disk,” Nature 561 (2018), 360-362 (abstract / preprint).]
Greg: Nice paper! Thanks for it. But can this effect bear on an apparent near-linear relationship between galactic revolution velocity and star age? I think that such dwarf galaxy absorptions by the Milky Way are rare events. Regarding the Shakdov thruster, you are (I think) correct. But could we detect a proton flow necessary to increase V by ~1 km/s over a 10 billion year time interval? Certainly fuel for thought.
Alex: Given the large numbers of stars in the sample, I was thinking that the stellar type vs velocity relationships could be plotted for locations on the galactic disc. If they are all the same, that would tell a different story than if they differed in shape. There is a hint of this in the Vityazev paper where they plot thin vs thick disk stars that show differences. In other words, given the large sample size, it should be possible to show more granularity based on location than with the averaging that Vityazev computes.
Incidentally, I came to the same conclusion with regards to CMEs. However, even for our sun, the CMEs are within a single order of magnitude if they are accelerated to c. As the solar wind produces more protons overall than CME, the same approach might work. However, this approach has to work for all stars, so the mass loss of protons/star mass has to increase for cooler stars for this mechanism to describe the PD observation.
I am not aware of the idea of moving stars by trapping and accelerating the solar wind and flares, so possibly it is novel. I also wonder if it is possible to direct solar flares by manipulating the surface magnetic fields of the star so that they break and cause a flare in desired positions. As the star rotates, the magnetic field is broken when the alignment is correct, releasing the flare. The flare material still needs to be accelerated to have the desired thrust, so electric fields could do that, or something more like a linear particle accelerator. Definitely K2 or even K3 level engineering…or just maybe some phenomenon than a “living” star could manage.
Greg: The differences between disc star velocities and others in the Antoja et al paper is fascinating. I don’t think it bears on Parenago unless somehow large diffuse nebula were created in the galactic merger. These could have perhaps caused differential velocities between massive and less massive stars. But such nebula would have to be perhaps an order of magnitude larger in radius than those in today’s galaxy to encompass a stellar sphere with a radius in excess of 1,000 light years. A further problem is that these structures would have to dissipate in less than 1 billion years, leaving no trace.
But your suggestion of using future Gaia data releases to dig deeper in stellar kinematics is excellent. I hope that someone will check if Parenago’s Discontinuity works for a star sample at a distance, say, of 10,000 light years.
I have done some rough calculations to see if a directional stellar wind or directional coronal mass ejections (CMEs) could accelerate a Sun-mass star by about 1,000 m/s in 1 billion years. Both seem to fail by a few orders of magnitude. But it is most intriguing that stellar flares (and presumably CMEs) are more common in less massive red dwarfs than in Sunlike stars.
Alex: BoE calculation for thrust of solar wind:
For our sun, redirecting the solar wind to a single direction would only result in the sun traveling ~3 m/s after 1 billion years. However, if the particles were accelerated by 3 orders of magnitude to c, that increases the velocity to 3 km/s. Over 5 billion years, that gets you to 15 km/s, which is in the range of the V needed for the Parenago Discontinuity graph. So physically possible. My first thought is that this would be an engineering solution, rather than a natural one – that is K2 – K3 civilizations. The bias in my thinking is that only human engineering can create craft that can travel at supersonic and hypersonic speeds. Birds cannot even manage 0.1 km/s, while our engineering can propel craft in air 1-2 orders of magnitude faster.
I do have a question about the relative emissions of EM and particles from different stellar types. Isn’t the mass loss vs initial star mass going to be the basically the same for all stellar types? If so, wouldn’t all stellar types reach the same velocity by the time they reach the end of their main sequence period? The Parenago Discontinuity relationship suggests mass or age is important, which implies that the acceleration must be approximately constant for all stars. This would imply, naively perhaps, a force more like gravity, that is exerted over the age of the star. It cannot be a point source outside the galaxy; otherwise the rotation of the galaxy would keep changing the direction of the force. Could it possibly be invoked by the [dark] matter in or surrounding the galaxy? Can this force be computed to suggest a possible cause?
Greg: Very interesting speculation. It’s so funny–we needed Gaia to get beyond a few hundred light years. And this early paper of Gaia results (and I am sure many others) will inspire people to generate designs for even more capable space observatories. It seems that every question we investigate and answer results in hundreds of new questions.
I would hesitate to invoke dark matter. It seems to be a catch-all for everything not understood in the universe. I will check out mass loss rates for distant star types. But I don’t know if we have reliable data.
Alex: What is relevant is whether the acceleration is related to stellar type or not. A large, hot star may lose a lot of mass, but it has to accelerate a more massive object. If a star loses X% of its mass over its lifetime, and if the wind speed is fairly uniform across such stars then the final velocity should be much the same for all star types over their lifetimes. The PD requires that this is not the case.
Greg: I just did a Google for “Mass Loss from Main Sequence Stars”. Apparently, this quantity directly depends upon star surface temperature.
I think our dialog has been very fruitful. When I submitted my first paper on the subject to the Journal of the British Interplanetary Society, I had to contend with 4 reviewers. Some of these favored the concept of stellar volition but argued about the inclusion of psychokinetics as a possible explanation. I am neutral regarding this topic, as I have discussed but I am still impressed by the vehemence of the arguments pro and con decades after the Geller/Randi affair. So the fact that accelerated CMEs can provide acceleration of G-type stars (as I agree after a few calculations) indicates that there is an alternative option. I will at some point write up my work on accelerated CMEs and send you the results.
Late this afternoon, weather permitting, we will journey to the Hayden Planetarium, which is hosting a Dutch astronomer who will talk about the latest Gaia results on galactic stellar kinematics. I suspect that Parenago’s Discontinuity is not on the agenda, but I will let you know.
Alex: I note that the Gaia data include all the information needed to create samples of stars within a radius of a position. This could be used to explore the type/mass vs V graphs at the higher granularity that I suggested, particularly radius from the galactic center. This would help confirm that the Parenago Discontinuity is truly global within the dataset and not some averaging, or whether there is spatial structure to the distributions. It may take some computational effort, but it might shed light on possible natural explanations of the PD observation. Sample sets would be easy to crunch on a PC, and the results compiled as a map. For example, the slope of V vs type or mass as a color-coded map.
I was also thinking about the gravity solution. It may work if a point object makes continual passes in the galactic plane. Older stars would experience more passes and if V is due to gravity dragging the stars along during a pass, then this would account for their higher V. A prediction would be that the slope of V would depend on how far from the source the stars are. Dare I say a denser clump of dark matter in a highly elliptical orbit about the galactic center? Data and some modeling would be needed to test this idea.
Out of this discussion, Greg Matloff incorporated many of Alex Tolley’s contributions and produced the short essay below looking at how stars could be accelerated to account for the Parenago Discontinuity.
Physical Methods of Effecting Main Sequence Star Acceleration
Greg Matloff, Nov. 16 2018
Using the Gaia DR1 dataset, Vityazev et al. have investigated Parenago’s Discontinuity for a sample of 1,260,071 main sequence stars [1]. The minimum mean distance for O-k stars in this data release is estimated as 0.15 kiloparsecs, which indicates that the diameter of the sphere containing the subject stars equals or exceeds 1,000 light years. Local explanations for Parenago’s Discontinuity clearly fail.
The analysis reveals that Parenago’s Discontinuity is real. Stars redder than (B-V) about equal to 0.6, which corresponds to spectral class F9 or G0 move faster in their orbits around the center of the Milky Way galaxy than hotter, more massive, bluer stars. Their results are in substantial agreement with the results from Allen’s Astrophysical Quantities and Hipparcos data for a much smaller stellar sample (with a diameter of about 500 light years) presented by Matloff [2].
But Vityazev et al. discuss for the first time a feature present in both data sets. Main Sequence stars apparently speed up in their galactic trajectory as they age. This velocity increment amounts to an increase of about 2 km/s in 8 billion years. The acceleration is approximately equal to 8 X 10-15 m/s2. For a solar-mass star (2 X 1030 kg), the average force exerted on or by the star during the 8 billion year time interval is 1.6 X 1016 N.
Reference 2 presents a number of possible causes for the discontinuity in galactic stellar orbital velocity around (B-V) = 0.6. The analysis presented here considers possible mechanisms that a star might employ to maintain a constant acceleration over a multi-billion year time interval.
1. Acceleration by Nonisotropic Stellar Electromagnetic Emissions
Consider here the possibility that a minded star can control the direction of its electromagnetic emissions. The solar luminosity (Lsun) is 3.9 X 1026 W [3]. Modifying Eq. ((7.2) of Ref. 4, the maximum stellar-radiation pressure acceleration for a Sun-mass star (Msun) is Lsun/ (Msun c) for a unidirectional stellar wind, where c is the speed of light in vacuum (3 X 108 m/s). Substituting in this equation, the maximum solar acceleration from this process is about 7 X 10-13 m/s2.
This acceleration is about 100 times the required stellar acceleration to effect the 1 km/s during a 1-billion year time interval. But if the Sun accelerates using this process, the Solar Constant might vary on an annual basis by up to 1%. Solar Luminosity has been measured to vary by a much smaller amount during the Sun’s 11-year activity cycle.
But the Sun and other main sequence stars generate neutrinos as well as photons as they convert hydrogen into helium deep in the solar (stellar) interiors [3]. Neutrinos have linear momentum as well as very small mass. The solar momentum flux is hard to study because of the very low cross-section of neutrino interactions with detectors. Perhaps stellar neutrino fluxes are not isotropic.
2. Acceleration by Nonisotropic Solar Wind
From Ref. 3, p. 427, the average solar wind velocity is 500 km/s (5 X 105 m/s) and the solar wind carries about 2 million tons of solar matter per second (2 X 109 kg). If all of this material were concentrated in a unidirectional jet, the force exerted on the Sun or Sunlike star is 1015 Newtons. This force is 1/16 the force required for stellar acceleration. This proposed method of stellar acceleration therefore fails.
3. Acceleration by Coronal Mass Ejections
Coronal mass ejections (CMEs) are generally associated with solar flares. Their frequency varies with the solar activity cycle. On average, the mass ejected by CMEs in a Sunlike star amounts to a few percent of the mass ejected in the solar wind and the velocity of a typical CME varies from a few hundred km/s to a few thousand km/s [5]. Unidirectional flares therefore fail as a stellar accelerating mechanism.
4. Acceleration by an Accelerated Solar Wind
Consider next the possibility that a minded Sunlike star can apply its magnetic field to accelerate a unidirectional solar wind to 0.1c (3 X 107 m/s). For the solar wind mass listed above, the kinetic energy of the jet is approximately 1024 W, which is less than 1% of the solar constant. If all of the solar wind is in the jet, the approximate force on the star is 6 X 1016 N. This is about 4X greater than the average force required to accelerate the star.
5. Might the Gravitational Constant of Galactic Mass Vary With time?
Elementary physics students learn that the velocity of an object orbiting a central body varies directly with the square root of the product of the central body’s mass and the Universal Gravitational Constant G. It might be argued that increases in galactic mass or G over billion-year time scales might account for the higher galactic-orbital velocities of older stars.
Surprisingly, as reviewed in an on-line essay by Rupert Sheldrake, experimental measurements of G show some variation [6]. But according to Lorenzo Iorio, such variations are likely caused by experimental errors because the orbits of solar system planets seem relatively constant [7].
A recently published study based upon the Gaia data set demonstrates that within the last 900 million years, at least one dwarf galaxy has passed through and possibly merged with the Milky Way [8]. So it is safe to conclude that the mass of our galaxy may not be constant over multi-billion-year time scales.
But it seems unlikely that either of these two variations can account for the reported increase in stellar galaxy-orbiting velocity with star age. After all, stellar birth nebulae orbit the Milky Way galaxy’s center as do the stars. Infant stars will therefore be accelerated in the same fashion as mature stars by such variations.
6. Conclusions
We see that several of the above suggestions succeed as possible methods of main sequence star acceleration. Perhaps the most intriguing, and the one that might inspire future research, is the possibility that stellar neutrino emissions need not be isotropic.
Psychokinetic (PK) effects have not been considered in the above treatment. Although it is unwise to eliminate PK from consideration for this application and others, it is wise to keep a distance until/unless it can be demonstrated in the laboratory in experiments that can be replicated by other researchers, including skeptics.
Acknowledgement
I greatly appreciate communications and interactions with Alex Tolley. His spirited comments and criticisms were instrumental in preparation of the above discussion.
References
1. V. V. Vityazev, A. V. Popov, A. S. Tsvetkov, S. D. Petrov, D. A. Trofimov and V. I. Kiyaev, “New Features of Parenago’s Discontinuity from Gaia DR1 Data”, Astronomy Letters, 44, 629-644 (2018).
2. G. L. Matloff, “Olaf Stapledon and Conscious Stars: Philosophy or Science?”, JBIS, 65, 5-6 (2012).
3. E. Chaisson and S. McMillan, Astronomy Today, 6th ed., Pearson/Addison-Wesley, San Francisco, CA (2008).
4. G. L. Matloff, Deep Space Probes, 2bd. ed., Springer-Praxis, Chichester, UK (2005).
5. P. Odert, M. Leitzinger, A. Hanslmeier, and H. Lammer, “Stellar Coronal Mass Ejections I. Estimating Occurrence Frequencies and Mass-Loss Rates”, arXiv:1707.02165v2 [astro-ph.SR] 31 Jul 2017.
6. R. Sheldrake, “How the Universal Gravitational Constant Varies.”, www.sheldrake.org. Also in R. Sheldrake, Science Set Free, Deepak Chopra Books, NY (2012).
7. L. Iorio, “Does the Newton’s Gravitational Constant Vary Sinusoidally with Time? Orbital Motions Say No”, arXiv:1504.07233v2 [gr-qc] 16 Dec 2015.
8. T. Antoja, A. Helm, M. Romero-Gomez, D. Katz, C. Babuslaux, R. Drimmel, D. W. Evans, F. Figueras, E. Poggio, C. Reyle, A. C. Robin, G. Seabroke, and C. Soubiran, “A Dynamically Young and Perturbed Milky Way Disk”, arXiv:1804.10196v2 [astro-ph.GA] 24 Sep 2018.
———
The Vityazev et al. paper is “New Features of Parenago’s Discontinuity from Gaia DR1 Data,” Astronomy Letters, Volume 44, Issue 10 (October 2018), pp 629-644 (abstract).
by Paul Gilster | Aug 14, 2018 | Exoplanetary Science |
Speaking of getting really, really close to a star, as we were yesterday in our discussion of the Parker Solar Probe, I couldn’t help but turn to new computer models of the ‘ultrahot Jupiter’ WASP-121b. I still find it delightful that the earliest exoplanet detections involved a category of planet that few scientists had imagined existed. These days we routinely discuss gas giants blisteringly close to their hosts, and even manage to extract information about their atmospheres through transmission spectroscopy, but few people expected such planets when we began to discover them.
In fact, Apollo 11’s Buzz Aldrin had a role to play in what may be considered to be the first prediction of the worlds we would start calling ‘hot Jupiters.’ Working with John Barnes on his novel Encounter with Tiber (Grand Central, 1996), Aldrin asked physicist Greg Matloff whether a hydrogen-helium atmosphere as found in a Jupiter-class world could survive in an inner stellar system. Here’s how Matloff recalls the discussion:
Although I was initially very skeptical since then-standard models of solar system formation seemed to rule out such a possibility, I searched through the literature and located the appropriate equation (Jastrow and Rasool, 1965)….To my amazement, Buzz was correct. The planet’s atmosphere is stable for billions of years. Since I was at the time working as a consultant and adjunct professor, I did not challenge the existing physical paradigm by submitting my results to a mainstream journal. Since “Hot Jupiters” were discovered shortly before the novel was published, I am now credited with predicting the existence of such worlds.
Indeed, for this was just at the time when 51 Pegasi b swam into our consciousness in 1995 (the book was finished but not yet published when the discovery was made). Now we knew that hot Jupiters were out there, and the radial velocity method of exoplanet discovery ensured that large planets close to their star would be the most likely to be detected in our earliest efforts.
The Realm of the ‘Ultrahot’
But hot Jupiters are but one variety of inner system gas giants. Today we can catalog a planet like WASP-121b as a member of a still more unique class of worlds, distinguishing between ‘hot Jupiters’ and those gas giants that come astoundingly close to their stars.
Dubbed ‘ultrahot Jupiters,’ these worlds reflect about as much light as charcoal. What distinguishes them is a temperature that on the dayside causes them to glow like an ember. Thus the image below, in which WASP-121b is simulated based on computer models that draw on observations of the planet conducted by the Spitzer and Hubble space instruments.
Image: These simulated views of the ultrahot Jupiter WASP-121b show what the planet might look like to the human eye from five different vantage points, illuminated to different degrees by its parent star. The images were created using a computer simulation being used to help scientists understand the atmospheres of these ultra-hot planets. Credit: NASA/JPL-Caltech/Aix-Marseille University (AMU).
The word ‘hellish,’ so often used to describe the surface of Venus, can with even more justice be applied to ultrahot worlds like this. They orbit closer to their host stars than Mercury does to the Sun, tidally locked and with temperatures that can range between 2,000 and 3,000 degrees Celsius. Even the nightside of such a world can reach 1,000 degrees Celsius, though as we’ll see, this makes enough of a difference to explain some anomalous observations.
For new work from Vivien Parmentier (Aix Marseille University, France) and colleagues goes into the question of why we find no water vapor in the atmospheres of these worlds. Hot Jupiters — gas giants in an inner system that experience dayside temperatures below 2,000 degrees Celsius — have been found with abundant water vapor in their atmospheres. But ultrahot Jupiters seem to lack it. One theory on why is that these planets formed with high levels of carbon instead of oxygen, but the new study points to the occasional traces of water that have been detected at the dayside-nightside boundary as a refutation of the idea.
Parmentier’s team, applying a model of brown dwarf atmospheres developed by co-author Mark Marley (NASA Ames), went to work on ultrahot Jupiter atmospheres as if they were the atmospheres of stars. After all, says Parmentier, “The daysides of these worlds are furnaces that look more like a stellar atmosphere than a planetary atmosphere. In this way, ultrahot Jupiters stretch out what we think planets should look like.”
The team used Spitzer observations of WASP-121b at infrared wavelengths to probe carbon monoxide levels in its atmosphere. CO molecules have a bond strong enough to withstand the dayside heat. The result: The planet’s atmosphere reveals a strong temperature gradient, burning hotter higher up than further down. A uniform atmosphere could have masked the signature of water molecules, providing one explanation for the apparent lack of water.
But the carbon monoxide work showed that the answer lies elsewhere. According to the study, hydrogen and oxygen atoms are indeed found on ultrahot Jupiters, but the strong irradiation on the dayside simply tears the water molecules apart. The researchers have placed WASP-121b in the context of recently published studies authored by Parmentier, co-author Michael Line (ASU) and others on fellow ultrahot Jupiters WASP-103b, WASP-18b and HAT-P-7b.
They have concluded that the fierce stellar winds of the dayside blow the broken water molecules onto the nightside, where they can recombine and condense into clouds before, inevitably, drifting back onto the dayside to undergo the destructive process again.
The paper sees the transmission spectrum of WASP-121b as being consistent with a solar composition atmosphere having partial cloud coverage. Within its dayside atmosphere, molecules are being continually sundered. And here is why we see no water:
Ultra hot Jupiters with dayside temperatures larger than 2200K are good targets for thermal emission measurements. However, the majority of the observed planets have weaker-than-expected spectral features in the 1?2µm range. Using the example of WASP-121b, we interpret this lack of strong features as being due to a combination of a vertical gradient in molecular abundances due to thermal dissociation, and to the presence of H? [the hydrogen anion, or negative ion of hydrogen] absorption at wavelengths shorter than 1.4µm.
Thermal dissociation affects all spectrally important molecules in the atmospheres of ultra hot Jupiters except CO. It creates a large vertical gradient in the molecular abundances. We show analytically that the presence of such a molecular gradient weakens the features in emission spectra. This is a qualitatively different effect than a global depletion of the abundances.
Image: Jupiter-like exoplanets are 99 percent molecular hydrogen and helium with smaller amounts of water and other molecules. But what their spectra show depends strongly on temperature. Warm-to-hot planets form clouds of minerals, while hotter planets make starlight-absorbing molecules of titanium oxide. Yet to understand ultrahot Jupiter spectra, the research team had to turn to processes more commonly found in stars. Credit: Michael Line/ASU.
What a place an ultrahot Jupiter must be. The idea of this kind of circulation in the atmosphere is given force by the previous detection by Hubble of clouds at the boundary between night and day. The same process may affect titanium oxide as well as aluminum oxide. Because the latter is the basis for the gemstone ruby, this JPL news release speculates that there could be clouds producing rains of liquid metals and fluidic rubies in the atmospheres of ultrahot Jupiters. That would make the ultrahot Jupiter about as exotic an environment as we can conceive.
The paper is Parmentier et al., “From thermal dissociation to condensation in the atmospheres of ultra hot Jupiters: WASP-121b in context.” submitted to Astronomy & Astrophysics (preprint).
by Paul Gilster | Mar 23, 2018 | Missions |
Gregory Matloff’s contributions to interstellar studies need scant introduction, given their significance to solar-and beamed sail development for decades, and their visibility through books like The Starflight Handbook (1989) and Deep Space Probes (2005). A quick check of the bibliography online will demonstrate just how active Greg continues to be in analyzing the human future in space, as well as his newfound interest in the nature of consciousness (Star Light, Star Bright, 2016). The paper that follows grows out of Greg’s presentation at the 2016 iteration of the Tennessee Valley Interstellar Workshop, where he discussed ways to advance deep space exploration using near term technologies like Falcon Heavy, in conjunction with the solar sail capabilities he has so long championed. Read on for an examination of human factors beyond lunar orbit and a description of a useful near-term mission that could reach an object much closer than Mars relying on both chemical and sail capabilities. Dr. Matloff is a professor of physics at New York City College of Technology, CUNY.
ABSTRACT
The possibility of applying the Space-X Falcon-Heavy booster to human exploration of the inner solar system is discussed. A human-rated Dragon command module and an inflatable habitat module would house and support the 2-4 person crew during a ~1 year interplanetary venture. To minimize effects of galactic cosmic rays, older astronauts should conduct the mission during Solar Maximum. Crew life support is discussed as is application of a ~1-km square solar photon sail. The sail would be applied to rendezvous with the destination Near Earth Object (NEO) and to accelerate the spacecraft on its return to Earth. An on-line NASA trajectory browser has been used to examine optimized trajectories and destinations during 2025-2026. A suitable destination with well established solar-orbital parameters is Asteroid 2009 HC. Because the NASA Space Launch System (SLS) has a greater throw mass than the Falcon-Heavy, the primary propulsion for NEO rendezvous and Earth return would likely be a chemical rocket. The sail would be used in this case as an abort mechanism and a back-up for the primary propulsion system. In either scenario, a single Falcon-Heavy or SLS launch would be adequate.
Keywords: NEO Exploration, Falcon-Heavy, Dragon, BEAM, GCR, ECLSS, SLS
Introduction
The United States is currently developing two separate approaches to launching inner solar system exploration by human crews beginning in around 2020: the NASA Space Launch System (SLS) and the commercial Space-X Falcon Heavy [1,2]. The advantage of the SLS is its greater throw-weight on interplanetary trajectories. A disadvantage of SLS is the cost permission and constraints imposed by the current state of the US federal government. Although Falcon-Heavy has less launch capacity than the SLS, this booster is a composite of three existing and mass produced Falcon-9 boosters. These have an excellent reliability record to date on NASA-sponsored resupply missions to the International Space Station (ISS) and commercial launches. Experiments indicate that the Falcon 9 first stage may eventually be recovered and reused, which promises to greatly reduce the cost of space missions to low Earth orbit (LEO) and beyond.
This paper concentrates upon interplanetary ventures using a single Falcon-Heavy launcher and a small crew (2-4 people). As well as a Dragon V2 capsule appropriately modified for interplanetary application (3), an inflatable Bigelow space habitat similar to the one to be launched to the ISS [4} in the near future will be used for crews habitability. Life support for the crew on their 1-2 year interplanetary venture will utilize recycling of oxygen and water. Food recycling by biological means will likely not be ready by 2020.
After the spacecraft is launched towards Mars, a state-of-the-art solar photon sail with a dimension of ~0.7 km will be unfurled. This will allow, as will be demonstrated, non-rocket accelerations of 1-2 km/s per month in the solar system region between Earth and Mars.
A recent comprehensive study of in-space radiation effects reveals that galactic cosmic radiation beyond LEO is reduced by a factor of ~5 above LEO, if missions are conducted during solar maximum. During solar flares and coronal plasma discharges, the crew could be protected by aligning the Dragon’s heat shield between the crew quarters and the Sun.
Human landings on Mars will not be possible using a single Dragon launch. But a host of Near Earth Objects of asteroidal and cometary origin and possibly the Martian satellites Deimos and Phobos will be open to human explorers.
But any human expedition beyond the Moon will likely require cruise durations of months to years. Solar and galactic cosmic radiation will certainly be a limiting issue. The possibilities and effectiveness of using the capsule and habitat mass for self shielding is discussed in the next section.
Falcon-Heavy Interplanetary Throw Mass and Cosmic Ray Shielding
According to Ref. 2, a Falcon-Heavy is capable of projecting 13,200 kg on a trans-Mars trajectory. From Ref. 3, the dry mass of a Dragon V2 capsule is 4200 kg and the endurance of this spacecraft is about 2 years in space. The mass of the BEAM inflatable module is 1360 kg [4].
From Ref. 3, the Dragon’s configuration can be approximated by a cone with a diameter of about 3.7 m and a height of about 6.1 m. From Ref. 4, the BEAM inflatable habitat can be approximated by a cylinder with a diameter of about 3.2 m and a length of about 4 m. Assuming that the base of the Dragon abuts one of the circular end caps of the BEAM, it is easy to demonstrate that the surface area of the spacecraft is about 100 m2. Assuming that all of the Falcon’s throw mass can be used for self-shielding against cosmic rays during an interplanetary venture, the approximate shielding areal mass thickness is 130 kg/m2 or 13 g/cm2.
There are two major sources of cosmic radiation beyond the Earth’s magnetosphere. These are eruptions of solar energetic particles (SEPs), which are most common during solar maximum and galactic cosmic rays (GCR), which are alway present. We first consider the effects of a 13 g/cm2 shield on SEPs.
Shielding From SEPs
A recent paper by an international team summarizes the latest results on cosmic ray shielding above LEO [5}. Figure 6 of that reference compares the Effective Dose Equivalent predicted to be incurred by an astronaut from four SEP events: a 20-year event, a 10-year event, a worst-case modeled event and a Carrington-event estimate. This data is plotted against aluminum shield thickness and compared with currently recommended European Space Agency (ESA) career dose limits. In all cases presented, a 13 g/cm2 aluminum shield is adequate.
Figure 7 of Ref. 5 presents similar information and compares predicted doses from the above SEP events with the 30-day and annual ESA limit. Once again, a 13 g/cm2 aluminum shield seems to be adequate, although the Carrington-event predicted dose rate is very close to the 30-day limit.
Therefore, SEPs do not seem to pose an insurmountable health risk to crews venturing beyond LEO with an equivalent a 13 g/cm2 aluminum shield. Additional shielding could be affected by orienting the Drago heat shield between crew and Sun during a major SEP event.
Shielding from GCRs
Galactic cosmic rays, on the other hand, pose a larger risk to the crew’s health. Since at least 1979, it was known that energetic galactic cosmic rays more massive than helium nuclei (high-Z GCR) are potentially dangerous to human health and very difficult to shield against [6]. Figure 1 of Ref. 5 reveals that during solar maximum, the modeled flux of galactic hydrogen and helium nuclei are reduced by a factor of 5-10 when compared with fluxes of the same ions during solar minimum. But the fluxes of galactic lithium and iron nuclei are apparently independent of the solar activity cycle.
Cucinotta and Durante estimate that during an interplanetary transfer, the high-Z GCR dose might be 1-2 mSv per day or 0.4-0.8 Sv per year [7]. From Tables 1 and 2 of McKenna et al, the NASA one-year dose limits for 40-year old female and male astronauts are respectively 0.7 and 0.88 Sv. For older astronauts, the limits are higher. Dose limits for men are higher than dose limits for women.
During a 1-year interplanetary voyage, the dose limits for 40-year old astronauts may be exceeded. Exposures beyond these recommended limits may result in a 3% increased risk of fatal cancers.
Health effects on interplanetary astronauts from high-Z galactic cosmic rays is an ongoing field of research. Mewaldt et al. also conclude that interplanetary voyagers will experience a higher galactic dose during solar minimum than during solar maximum. According to their study, a thin aluminum shield of about 3 g/cm2 may reduce solar minimum dose rates to the NASA LEO career limit of 50 cSv for a 1-year interplanetary round trip [8].
It should also be mentioned that it is not always possible to predict future GCR doses in interplanetary space from data obtained during previous solar cycles. Schwadron et al have noted that unusually high levels of GCRs were measured during a prolonged solar minimum in 2009 [9].
Crew Life Support on Interplanetary Ventures
We next consider the mass requirements to maintain a small crew (2-4 people) during a 1-2 year interplanetary expedition. According to the wikipedia entry on space-life-support systems and in substantial concurrence with one classic reference [10], daily average human metabolic requirements can be summarized:
oxygen: 0.84 kg
food: 0.62 kg
water: 3.52 kg.
If partial recycling were not built in to the mission, a two-person crew could not be supported in the proposed spacecraft for missions of one year or longer. Projections from International Space Station technology indicate that a near-term goal for water recycling is 85% and the oxygen recovery rate can be raised to 75% [11,12]. Applying these values for an interplanetary mission applying near-term recycling technology, the daily consumable requirement per astronaut is 0.21 kg oxygen, 0.62 kg food, and 0.53 kg of water. Each crew member consumes about 1.4 kg per day of these resources or about 500 kg per year. A 4-person crew therefore requires about 2,000 kg of these resources for a 360-day duration interplanetary voyage.
It is next necessary to estimate the mass of the Environmental Control and Life Support System (ECLSS) equipment, not including consumables, necessary to support the mission. In Table 4.3 of his monograph, Rapp estimates the mass of the water-recovery system for a 180-day transit to Mars at 1.4 metric tons or 1,400 kg and the mass of the oxygen recovery system at 0.5 metric tons or 500 kg for a 6-person crew [13]. We are here considering a smaller crew and the 180-day return voyage as well as the 180-day flight to the interplanetary destination. Since we have no idea regarding ECLSS reliability on a deep-space mission, we will assume here that the required mass of ECLSS equipment is 3,000 kg. Including the 2,000 kg requirement for oxygen, food and water, the total ECLSS mass is about 5,000 kg.
Application of a Near-Term Solar Photon Sail
From the above discussion, the mass of the Dragon is estimated at 4,200 kg and the BEAM habitat mass is 1,360 kg. Since the Falcon-Heavy can project 13,200 kg towards Mars and our ECLSS mass projection is 5,000 kg, the remaining mass amounts to 2,640 kg. If 640 kg is required for scientific equipment, 2,000 kg remains to be allowed. We will therefore assume that the sail mass is 2,000 kg.
As an example of a large solar-photon sail that could be constructed in the not very distant future, we consider a 90% reflective (REF) opaque 1-km2 sail with an areal mass density of 2 g/m2. The sail mass is 2,000 kg and the areal mass density of the spacecraft (?eff) is 0.0132 kg/m2.
The lightness factor (?) of a solar-photon sail is the ratio of solar radiation-pressure acceleration on the sail to solar gravitational acceleration. It can be calculated by modifying Eq. (4.19) of Ref.14 for a solar constant of 1,366 W/m2:
Substituting in Eq. (1) for sail reflectivity and spacecraft areal mass density, we find that ? = 0.11.
Since the Earth is in a near-circular solar orbit at a distance of 1 Astronomical Unit (1 AU = 1.5 X 1011 m) and the Earth’s solar-orbital velocity is about 30 km/s, the Sun’s gravitational acceleration on the spacecraft at a distance of 1 AU is about 0.006 m/s2. The solar radiation-pressure acceleration on the sail is therefore about 6.6 X 10-4 m/s2, if the sail is normal to the Sun at a distance of 1 AU from the Sun. Such a sail configuration can result in a daily velocity increment of about 57 m/s. Every month, the sail can alter the spacecraft velocity by about 1.6 km/s, if it is oriented normal to the Sun at a solar distance of 1 AU. At the orbit of Mars (1.52 AU), this sail oriented normal to the Sun can alter the spacecraft’s solar velocity each month by about 0.69 km/s.
The effectiveness of this configuration for non-landing missions to Mars can be evaluated using Table 4.2 of Ref. 15. The duration of a Hohmann minimum-energy Earth-Mars trajectory is given in that table as 259 days. Although application of the sail can shorten this a bit on the Mars-bound trajectory, sail or some other form of propulsion must be used to accomplish Mars rendezvous. Aerocapture with a deployed sail of this size will be difficult or impossible. Table 4.2 of Ref. 15 also presents Earth-Mars transit times for spacecraft flying a logarithmic spiral trajectory at a sail pitch angle relative to the Sun of about 35 degrees, as a function of lightness factor. For ? = 0.1, the time required for a return journey on such a trajectory is about 431 days. To accomplish logarithmic-spiral Earth-return trips from Mars approximating the Hohmann-trajectory duration with the spacecraft configuration considered here would require a substantial increase in sail area without an increase in spacecraft mass. More advanced sails, smaller crews, or less massive ECLSS would be required.
Application of Falcon/Dragon/BEAM for NEO Exploration
So the configuration presented here is marginal at best for Mars-vicinity missions such as exploration of the natural Martian satellites Phobos and Deimos. Instead, it might see more immediate application to near Earth objects (NEOs) orbiting the Sun close to the Earth’s solar orbit.
A suitable target NEO for such an expedition would be in a near-circular, low-inclination orbit approximately 1-AU from Earth. If the mission is timed appropriately, the Hohmann trajectory duration should be considerably less than the time required to reach Mars and the Falcon-Heavy payload should be greater than that estimated for a Mars mission. One NEO class of potential targets is Earth’s quasi-satellites in “corkscrew orbits” [16].
The principal use of the sail on the out-bound trajectory leg would be deceleration for rendezvous with the NEO. The sail would be used to accelerate the spacecraft for Earth rendezvous on the return trajectory leg. Although the Sail and BEAM inflatable habitat could be maneuvered into Earth orbit for possible reuse, the Dragon would return crew and payload (including NEO samples) to Earth in a ballistic reentry.
It is possible to investigate mission possibilities with the aid of the NASA on-line Trajectory Browser (trajbrowser.arc.nasa.gov). After accessing this site on May 23 and 25, 2015, we specified a mission to a NEO with a well established orbit during the next solar-max (2025-2026) to reduce crew exposure to GCRs. Two mission types were considered: a round-trip with a maximum duration of 360 days and a one-way, rendezvous mission with a maximum duration of 180 days. For the one-way rendezvous mission, the maximum delta-V for departure from a 200-km low-Earth orbit was 4 km/s. For the round-trip. the maximum delta-V was 5 km/s.
The results of this exercise are presented in Table 1 [following the references]. The destination NEO determined by the Trajectory Browser software is Asteroid 2009 HC. Browser output is summarized in Table 1. This table also includes physical data on this NEO from the NASA Jet Propulsion Laboratory NEO data base (ssd.jpl.nasa.gov).
It is assumed that the pre-rendezvous propulsion requirements will be met by the Falcon upper stage, since this configuration is capable of reaching Mars, a more distant destination. Since the post-injection delta-V is small and the sail’s characteristic acceleration at 1 AU is greater than 1 km/s, the sail can be used to match velocity with the destination NEO without significantly increasing pre-rendezvous mission duration.
Note from Table 1 that the difference between post-injection delta-V for one-way rendezvous and round-trip missions is less than 1 km/s. So it is safe to assume that use of the sail to power Earth-return maneuvers does not significantly increase mission duration.
Another way to consider use of the sail on the Earth-bound trajectory is to estimate time required for the sail to be used for orbital inclination adjustment or “cranking”. From Eq. (5-74 of McInnes’s monograph [15]), a sail operating at the optimal cone angle can change its inclination by
? i = 88.2 ? degrees/orbit. (2)
According to McInnes, Equation (2) is independent of solar-orbit radius. Inclination correction for Earth-return will add a few months to the duration of the round-trip mission.
Conclusions: Use of the Sail with the NASA Space Launch System on NEO-Visit Missions
From the work presented here, it seems that round-trip visits to selected Near Earth Objects with durations not much greater than one year can be accomplished using a single Falcon-Heavy launch and a combination of a Dragon spacecraft, an inflatable habitability module, state of the art partially closed environmental system and a state of the art square solar photon sail with a 1-2 km dimension.
To reduce the Galactic Cosmic Radiation risk to the 3-4 person crew, it is advisable to conduct lengthy voyages above Low Earth Orbit during periods near the maximum of the solar activity cycle and to position the Dragon heat shield facing the Sun to shield against solar flare events. It may also be advisable to select older astronauts to crew such interplanetary ventures.
If the NASA Space Launch System is available to conduct human visits to suitable NEOs, the sail could serve at least two functions. Because the SLS has 2-3X the throw mass of the Falcon-Heavy, the sail could be accommodated as a pre-rendezvous abort option or as a back-up to the SLS propulsion module for Earth-return maneuvers.
It should also be mentioned that with either launch alternative, the sail and inflatable could be steered into high-Earth orbit for reuse after the Dragon or Orion is directed on its Earth reentry path.
References
1. “NASA Fact Sheet: NASA Space Launch System”, www.nasa.gov/pdf/ 664158main_sls_fs_master.pdf
2. “Falcon Heavy”, www.spacex.com/falcon-heavy
3. “Dragon V2), en.wikipedia.org/wiki/Dragon_V2
4. “The Bigelow Expandable Activity Module (BEAM),” bigelowaerospace.com/beam
5. S. McKenna-Lawlor, A. Bhardwaj, F. Ferrari, N. Kuznetsov, A. K. Lal, Y. Li, A. Nagamatsu, R. Nymmik, M. Panasyuk, V. Petrov, G. Reitz, L. Pinsky, M. Shukor, A. K. Singhvi, U. Strube, L. Tomi, and L. Townsend, “Recommendations to Mitigate Against Human Health Risks Due to Energetic Particle Irradiation Beyond Low Earth Orbit/BLEO”, Acta Astronautica, 109, 182-193 (2015).
6. E. Bock, F. Lambrou Jr., and M. Simon, “Effect of Environmental Parameters on Habitat Structural Weight and Cost”, Chap. II-1 in Space Resources and Space Settlements, NASA SP-428, J. Billingham and W. Gilbreath eds., NASA Ames Research Center, Moffett Field, CA (1979).
7. F. A. Cucinotta and M. Durante, “Cancer Risk from Exposure to Galactic Cosmic Rays: Implications for Space Exploration by Human Beings,” Lancet Oncology, 7, 431-435 (2006).
8. R. A. Mewaldt, A. J. Davis, W. R. Binns, G. A. de Nolfo, J. S. George, M. H. Israel, R. A. Leske, E. C. Stone, M. E. Wiedenbeck and T. T. von Rosenvinge, “The Cosmic Ray Radiation Dose in Interplanetary Space—Present Day and Worst-Case Evaluations”, Proceedings of the 29th International Cosmic Ray Conference, Pune, India, August 3-10, 2005, B. Sripathi Acharya, S. Gupta, P. Jagadeesan, A. Jain, S. Karthikeyan, S. Morris and S. Tonwar eds., ( Tata Institute for Fundamental Research, Mumbai, India, 2005), pp. 433-436.
9. N. A. Schwadron, A. J. Boyd, K. Kozarev, M. Golightly, H. Spence, L. W. Townsend and M. Owens, “Galactic Cosmic Ray Radiation Hazard in the Unusual Solar Minimum Between Solar Cycles 23 and 24”, Space Weather, 8, DOI: 10.1029/2010SW000567, (2010).
10. M. R. Sharpe, Living in Space: The Astronaut and His Environment, Doubleday, Garden City, NY (1969).
11. R. Carrasquillo, “ISS Environmental Control and Life Support System (ECLSS) Future Development for Exploration”, presented at 2nd Annual ISS Research and Development Conference (July 16-18, 2013).
12. M. Gannon, “NASA Wants Ideas to Recycle Precious Oxygen on Deep-Space Voyages”, www.space.com/25518-nasa-oxygen-recycling-space-tech.html (space.com, April 16, 2004).
13. D. Rapp, Human Missions to Mars: Enabling Technologies for Exploring the Red Planet, Springer-Praxis, Chichester, UK (2008).
14. G. L. Matloff, Deep-Space Probes: To The Outer Solar System and Beyond, 2nd ed., Springer-Praxis, Chichester, UK (2005).
15. C. R. McInnes, Solar Sailing: Technology, Dynamics, and Mission Applications, Springer-Praxis, Chichester, UK (1999).
16. P. Wajer, “Dynamical Evolution of Earth’s Quasi-Satellites 2004 GU9 and 2006 FV35”, Icarus, 209, 488-493 (2010).
Table 1. Details for a NEO Visit in 2025-2026
by Paul Gilster | Apr 22, 2015 | Sail Concepts |
by Andreas Hein
Centauri Dreams readers most likely know Andreas Hein as the head of Project Hyperion, an effort for Icarus Interstellar to examine the prospects for manned interstellar flight, but he has also written in these pages about the uploading of consciousness. Now working on his PhD at the Technical University of Munich, Andreas today tells us about a new Kickstarter campaign in support of Project Dragonfly. Developing under the auspices of the Initiative for Interstellar Studies (of which Andreas is deputy director), Dragonfly explores interstellar flight at the small scale, and as he explains below, leverages the advances in computing and miniaturization that designers can use to change the paradigm of deep space missions.
Humanity has existed for over 200,000 years. It is only about 200 years since we entered the age of industrialization, and in the last 50 years, we have discovered ways of going to the stars [1]. However, the approaches conceived required spaceships the size of a tanker and massive space infrastructures. Today we live in a time when we may soon have the technological capabilities to launch a spacecraft to the stars, but now the spacecraft may be no bigger than a suitcase. Project Dragonfly is the first design study for an interstellar mission based on a small, laser-propelled spacecraft. In this article, I will explain the background of Project Dragonfly and the rationale for the Project Dragonfly Design Competition and crowdfunding campaign.
Many previous approaches for going to the stars have depended on extremely large and heavy spacecraft, based on propulsion systems like nuclear fusion or antimatter. Existing concepts of fusion-propelled spacecraft are as heavy as skyscrapers. Accelerating all the fuel with the ship until it is exhausted is actually not a very efficient way to get to the stars. Project Dragonfly aims at a different approach: The basic idea is not new – it is, in fact, very old. For centuries, humans have travelled the seas using sailing ships. We also plan to use a sail. But a sail which is made of an extremely thin reflective surface. This sail would be illuminated by a laser beam from a laser power station somewhere in the Solar System [2]. The photons of the laser beam push the sail, just as the wind pushes the sail of a sailing ship. And through this push to the sail, the spacecraft slowly accelerates.
However, as the spacecraft does not use any on-board fuel, it can accelerate to very high velocities in the range of several percent of the speed of light. Furthermore, Project Dragonfly builds upon the recent trend of miniaturization of space systems. Just a few decades ago, thousands of people were involved in developing the first satellite, Sputnik. Today, a handful of university students are able to build a satellite with the same capability as Sputnik, one that is much cheaper and weighs hundreds of times less than the first satellite. Recently, NASA announced a prize for the development of interplanetary CubeSats [3].
We simply think further. What could we do with these technologies in 20 or 30 years? Would it be possible to build spacecraft that can go to the stars but are as small as today’s picosatellites or even smaller? It is time to explore and innovate.
Image: Swarm of laser-sail spacecraft leaving the solar system. Credit: Adrian Mann.
History of the Project
The idea behind Project Dragonfly emerged in early 2013 when I visited Professor Gregory Matloff in New York. Matloff, author of The Starflight Handbook, is one of the key figures in interstellar research with major contributions to the area of solar sails. We talked about different propulsion methods for going to the stars and realized that nobody had yet done a mission design for an interstellar laser-propelled mission. Soon after this conversation, Project Dragonfly was officially announced by the Initiative for Interstellar Studies (i4is), with Kelvin F. Long and myself as co-founders.
However, it took another year to get to the point where we were able to organize an international design competition in order to speed up our search for a feasible mission to another star, based on technologies of the near future. One of the challenges for defining proper requirements for the competition was the development of preliminary mission concepts in order to identify performance drivers and showstoppers. Once these preparations were finished, we could launch the competition. See my essay Project Dragonfly: The case for small, laser-propelled, distributed probes for an early competition announcement and scientific backgrounder.
Why a Competition?
Design competitions have a long tradition in the history of technology: The Longitude rewards for the precise determination of a ship’s longitude at sea (1714), the Daily Mail prize for crossing the English Channel by an airplane (1908), the Orteig prize for crossing the Atlantic with an airplane (1919), and more recently DARPA’s Grand Challenge, which focuses on developing autonomous vehicles (2004). These competitions defined a set of requirements — most importantly performance requirements — the technology would need to fulfill. The solutions were up to the entrants.
Competitions offer the advantage that almost anyone can participate. This opens up opportunities for new entrants and innovative solutions, with the potential to disrupt the existing technological landscape [4]. Of course, with Project Dragonfly we are not yet at the level of the “Grand Challenges”. Nevertheless, the so-called Alpha Centauri Awards were announced by Kelvin Long in 2013, offering several cash prizes for relevant areas in interstellar travel. The Project Dragonfly Design Competition is one of the areas for which the Alpha Centauri Prize will be awarded [5].
The objective of the Project Dragonfly Design Competition is to develop a feasible mission design for a small, laser-propelled interstellar mission. Four international university teams are currently working on studies for small, laser-propelled interstellar spacecraft: Cairo University, the Technical University of Munich, the University of California Santa Barbara (UCSB), and Cranfield University, working with the Skolkovo Institute of Science and Technology (Skoltech) in Moscow and the University Paul Sabatier (UPS) in Paris. The final design reports of the teams will cover all areas that are relevant to make the mission a success and to return scientific data: Instruments, communication, laser sail design, power supply, secondary structure, deceleration propulsion, etc. Furthermore, both technological as well as economic feasibility will be assessed by the teams.
Image: The Project Dragonfly design team at Cairo University, made up of aerospace and communication engineering students, is one of four working on laser sail design.
The teams will meet with members of i4is in London at the headquarters of the British Interplanetary Society this July in order to evaluate their designs. The results from the competition will serve as a basis for future technology development of such a mission.
Project Dragonfly Kickstarter Campaign
The Initiative for Interstellar Studies has now launched the first ever Kickstarter campaign for supporting an interstellar design competition. The funds raised during the campaign will allow us to support the student teams during the competition. The campaign began on the 15th of April and will run until May 14th. All supporters will receive unique and exclusive rewards for their pledges, among them T-shirts and posters with an image of the winning team’s spacecraft, painted by the grand master of space art, David A. Hardy. The campaign is further supported by renowned space artist Adrian Mann. Further awards consist of a 3D-printed version of the winning team’s starship as well as early access to team reports, a signed version of the Beyond the Boundary book edited by Kelvin F. Long, etc.
The campaign can be accessed via:
https://www.kickstarter.com/projects/1465787600/project-dragonfly-sail-to-the-stars
Thanks a lot in advance for your support. Let’s find a way to get to the stars in our lifetime!
Image: An evocative futurescape by space artist David A. Hardy.
References
[1] Dyson, F. J. (1968). “Interstellar transport.” Physics Today, 21(10), 41-45.
[2] Forward, R. L. (1984). “Roundtrip interstellar travel using laser-pushed lightsails.” Journal of Spacecraft and Rockets, 21(2), 187-195.
[3] Staehle, R., Blaney, D., Hemmati, H., Lo, M., Mouroulis, P., Pingree, P., … & Svitek, T. (2011, August). “Interplanetary CubeSats: opening the solar system to a broad community at lower cost.” In CubeSat Workshop, Logan, UT, USA (pp. 6-7).
[4] Calandrelli, E. D. (2013). An evaluation of short innovation contest implementation in the federal context (Masters’ Thesis, Massachusetts Institute of Technology).
[5] Hein, A.M., Project Dragonfly Design Competition website
http://www.i4is.org/news/dragonfly
