Centauri Dreams
Imagining and Planning Interstellar Exploration
Kepler 107: Collision of Worlds
It seems increasingly clear that the factors that govern what kind of a planet emerges where in a given stellar system are numerous and not always well understood. Beyond the snowline, planets draw themselves together from the ice and other volatiles available in these cold regions, so that we wind up with low-density gas or ice-giants in the outer parts of a stellar system. Sometimes. Rocky worlds are made of silicates and iron, elements that, unlike ice, can withstand the much warmer temperatures inside the snowline. But consider:
While we now have 2,000 confirmed exoplanets smaller than three Earth radii, the spread in their densities is all over the map. We’re finding that other processes must be in play, and at no insubstantial level. Low-density giant planets can turn up orbiting close to their stars. Planets not so dissimilar from Earth in terms of their radius may be found with strikingly different densities in the same system, and at no great distance from each other.
Which takes us to a new paper from Aldo S. Bonomo and Mario Damasso (Istituto Nazionale Di Astrofisica), working with an international team including astrophysicist Li Zeng (CfA). The collaboration has produced a new paper in Nature Astronomy that uses the planetary system around the star Kepler-107 to probe another possible formative influence: planetary collisions. Kepler-107 may be flagging a process that occurs in many young systems.
Image: The figure shows one frame from the middle of a hydrodynamical simulation of a high-speed head-on collision between two 10 Earth-mass planets. The temperature range of the material is represented by four colors grey, orange, yellow and red, where grey is the coolest and red is the hottest. Such collisions eject a large amount of the silicate mantle material leaving a high-iron content, high-density remnant planet similar to the observed characteristics of Kepler-107c. Credit: Zoe Leinhardt and Thomas Denman, University of Bristol.
Let’s take a deeper look at this curious system. The two innermost planets at Kepler-107 have radii that are nearly identical — 1.536 and 1.597 Earth-radii, respectively. They both orbit close to the host, a G2 star in Cygnus of about 1.25 solar masses, with orbital periods of 3.18 and 4.90 days. The scientists used the HARPS-N spectrograph at the Telescopio Nazionale Galileo in La Palma to determine the planets’ masses, and because they were working with known radii (thanks to Kepler’s observations of these transiting worlds), they were able to determine their densities. And now things get interesting.
For the innermost planet shows a density of 5.3 grams per cubic centimeter, while the second world comes in at 12.65 grams per cubic centimeter. The inner world, Kepler-107b, is thus about the same density as the Earth (5.5 grams per cubic centimeter), while Kepler-107c shows a much higher number (for comparison, water’s density is 1 gram per cubic centimeter).
The outer of the two is the denser world and by more than twice the inner world’s value, and given the proximity of their orbits, coming up with stellar radiation effects that could have caused mass loss is difficult to do, for such radiation should have affected both in the same way. The remaining strong possibility is that a collision between planets played a role in this system.
“This is one out of many interesting exoplanet systems that the Kepler space telescope has discovered and characterized,” says Li Zeng. “This discovery has confirmed earlier theoretical work suggesting that giant impact between planets has played a role during planet formation. The TESS mission is expected to find more of such examples.”
And this from the paper, which notes the possibility of extreme X-ray and ultraviolet flux in the young system, but dismisses it as operational here, at least to explain the discrepancy:
This imbalance cannot be explained by the stellar XUV irradiation, which would conversely make the more-irradiated and less-massive planet Kepler-107b denser than Kepler-107c. Instead, the dissimilar densities are consistent with a giant impact event on Kepler-107c that would have stripped off part of its silicate mantle.
Image: The video shows a hydrodynamical simulation of a high-speed head-on collision between two 10 Earth-mass planets. The temperature range of the material is represented by four colors grey, orange, yellow and red, where grey is the coolest and red is the hottest. Watch Video. Credit: Zoe Leinhardt and Thomas Denman, University of Bristol.
We can produce Kepler-107c, then, by a collision that results in a high-density remnant. We have apparent evidence for collisions even in our own Solar System. The composition of Mercury, with a dense metallic core and thin crust, may point to this; only Earth is more dense in our system. So too could the emergence of Earth’s moon through a planetary-sized impactor striking our planet. We can also see in the obliquity of Uranus — the planet’s axis of rotation is skewed by 98 degrees from what we would expect — the possibility that, as advanced in some theories, a large object struck the planet long ago.
The paper gives us some of the details about Kepler 107:
…the difference in density of the two inner planets can be explained by a giant impact on Kepler-107 c that removed part of its mantle, significantly reducing its fraction of silicates with respect to an Earth-like composition. The radius and mass of Kepler-107 c, indeed, lie on the empirically derived collisional mantle stripping curve for differentiated rocky/iron planets… Smoothed particle hydrodynamics simulations show that a head-on high-speed giant impact between two ~10M? exoplanets in the disruption regime would result in a planet-like Kepler-107 c with approximately the same mass and interior composition… Such an impact may destabilize the current resonant configuration of Kepler-107 and thus it likely occurred before the system reached resonance. Multiple less-energetic collisions may also lead to a similar outcome.
Another possibility discussed by the authors: Planet c may have formed closer to the parent star and later crossed Kepler-107b in its orbit. But the authors note that to dampen the orbital eccentricities this would have produced, this scenario is unlikely to have had time to operate.
The paper is Bonomo & Zeng, “A giant impact as the likely origin of different twins in the Kepler-107 exoplanet system,” Nature Astronomy 04 February 2019 (abstract).
Gravitational Wave Astronomy: Enter the ‘Standard Siren’
Recently we’ve talked about ‘standard candles,’ these being understood as objects in the sky about which we know the total luminosity because of some innate characteristic. Thus the Type 1a supernova, produced in a binary star system as material from a red giant falls onto a white dwarf, causing the smaller star to reach a mass limit and explode. These explosions reach roughly the same peak brightness, allowing astronomers to calculate their distance.
Even better known are Cepheid variables, stars whose luminosity and variable pulsation period are linked, so we can measure the pulsation and know the true luminosity. This in turn lets us calculate the distance to the star by comparing what we see against the known true luminosity.
This is helpful stuff, and Edwin Hubble used Cepheids in making the calculations that helped him figure out the distance between the Milky Way and Andromeda, which in turn put us on the road to understanding that Andromeda was not a nebula but a galaxy. Hubble’s early distance estimates were low, but we now know that Andromeda is 2.5 million light years away.
I love distance comparisons and just ran across this one in Richard Gott’s The Cosmic Web: “If our galaxy were the size of a standard dinner plate (10 inches across), the Andromeda Galaxy (M31) would be another dinner plate 21 feet away.”
Galaxies of hundreds of billions of stars each, reduced to the size of dinner plates and a scant 21 feet apart… Hubble would go on to study galactic redshifts enroute to determining that the universe is expanding. He would produce the Hubble Constant as a measure of the rate of expansion, and that controversial figure takes us into the realm of today’s article.
For we’re moving into the exciting world of gravitational wave astronomy, and a paper in Physical Review Letters now tells us that a new standard candle is emerging. Using it, we may be able to refine the value of the Hubble Constant (H0), the present rate of expansion of the cosmos. This would be helpful indeed because right now, the value of the constant is not absolutely pinned down. Hubble’s initial take was on the high side, and controversy has continued as different methodologies yield different values for H0.
Hiranya Peiris (University College London) is a co-author on the paper on this work:
“The Hubble Constant is one of the most important numbers in cosmology because it is essential for estimating the curvature of space and the age of the universe, as well as exploring its fate.
“We can measure the Hubble Constant by using two methods – one observing Cepheid stars and supernovae in the local universe, and a second using measurements of cosmic background radiation from the early universe – but these methods don’t give the same values, which means our standard cosmological model might be flawed.”
Binary neutron stars appear to offer a solution. As they spiral towards each other before colliding, they produce powerful gravitational waves, ripples in spacetime, that can be flagged by gravitational experiments like the Laser Interferometer Gravitational Wave Observatory (LIGO) and Virgo. Astronomers can then compare the gravitational wave observation with the detected light of a binary neutron star merger, a result that produces the velocity of the system
Image: Artist’s vision of the death spiral of the remarkable J0806 system. Credit: NASA/Tod Strohmayer (GSFC)/Dana Berry (Chandra X-Ray Observatory).
We’re closing on a refined Hubble’s Constant, and researchers on the case, led by Stephen Feeney (Center for Computational Astrophysics at the Flatiron Institute, NY) think that observations of no more than 50 binary neutron stars should produce sufficient data to pin down H0. We’ll then have an independent measurement of this critical figure. And, says Feeney, “[w]e should be able to detect enough mergers to answer this question within 5-10 years.”
Nailing down the Hubble Constant will refine our estimates of the curvature of space and the age of the universe. Just a few years ago, who would have thought we’d be doing this by using neutron star interactions as what the researchers are now delightfully calling ‘standard sirens,’ allowing measurements that should solve the H0 discrepancy once and for all.
A final impulse takes me back to Hubble himself. The man had a bit of the poet in him, as witness his own outside perspective of our galaxy: “Our stellar system is a swarm of stars isolated in space. It drifts through the universe as a swarm of bees drifts through the summer air.” Found in The Realm of the Nebulae (1936).
The paper is Feeney et al., “Prospects for Resolving the Hubble Constant Tension with Standard Sirens,” Physical Review Letters 122 (14 February 2019), 061105 (abstract).
Breakthrough Propulsion Study
Ideas on interstellar propulsion are legion, from fusion drives to antimatter engines, beamed lightsails and deep space ramjets, not to mention Orion-class fusion-bomb devices. We’re starting to experiment with sails, though beaming energy to a space sail is still an unrealized, though near-term, project. But given the sheer range of concepts out there and the fact that almost all are at the earliest stages of research, how do we prioritize our work so as to move toward a true interstellar capability? Marc Millis, former head of NASA’s Breakthrough Propulsion Physics project and founder of the Tau Zero Foundation, has been delving into the question in new work for NASA. In the essay below, Marc describes a developing methodology for making decisions and allocating resources wisely.
by Marc G Millis
In February 2017, NASA awarded a grant to the Tau Zero Foundation to compare propulsion options for interstellar flight. To be clear, this is not about picking a mission and its technology – a common misconception – but rather about identifying which research paths might have the most leverage for increasing NASA’s ability to travel farther, faster, and with more capability.
The first report was completed in June 2018 and is now available on the NASA Technical Report Server, entitled “Breakthrough Propulsion Study: Assessing Interstellar Flight Challenges and Prospects.” (4MB file at: http://hdl.handle.net/2060/20180006480).
This report is about how to compare the diverse propulsion options in an equitable, revealing manner. Future plans include creating a database of the key aspects and issues of those options. Thereafter comparisons can be run to determine which of their research paths might be the most impactive and under what circumstances.
This study does not address technologies that are on the verge of fruition, like those being considered for a probe to reach 1000 AU with a 50 year flight time. Instead, this study is about the advancements needed to reach exoplanets, where the nearest is 270 times farther (Proxima Centauri b). These more ambitious concepts span different operating principles and levels of technological maturity, and their original mission assumptions are so different that equitable comparisons have been impossible.
Furthermore, all of these concepts require significant additional research before their performance predictions are ready for traditional trade studies. Right now their values are more akin to goals than specifications.
To make fair comparisons that are consistent with the varied and provisional information, the following tactics are used: (1) all propulsion concepts will be compared to the same mission profiles in addition to their original mission context; (2) the performance of the disparate propulsion methods will be quantified using common, fundamental measures; (3) the analysis methods will be consistent with fidelity of the data; and (4) the figures of merit by which concepts will be judged will finally be explicit.
Regarding the figures of merit – this was one of the least specified details of prior interstellar studies. It is easy to understand why there are so many differing opinions about which concept is “best” when there are no common criteria with which to measure goodness. The criteria now include quantifiable factors spanning: (1) the value of the mission, (2) the time to complete the mission, and (3) the cost of the mission.
The value of a mission includes subjective criteria and objective values. The intent is to allow the subjective factors to be variables so that the user can see how their interests affect which technologies appear more valuable. One of those subjective judgments is the importance of the destination. For example, some might think that Proxima Centauri b is less interesting than the ‘Oumuamua object. Another subjective factor is motive. The prior dominant – and often implicit – figure of merit was “who can get there first.” While that has merit, it can only happen once. The full suite of motives continue beyond that first event, including gathering science about the destinations, accelerating technological progress, and ultimately, ensuring the survival of humanity.
Examples of the objective factors include: (1) time within range of target; (2) closeness to target (better data fidelity); and (3) the amount of data acquired. A mission that gets closer to the destination, stays there longer, and sends back more data, is more valuable. Virtually all mission concepts have been limited to fly-by’s. Table 1 shows how long a probe would be within different ranges for different fly-by speeds. To shift attention toward improving capabilities, the added value (and difficulty) of slowing at the destination – and even entering orbit – will now be part of the comparisons.
Table 1: Time on target for different fly by speeds and instrumentation ranges
Quantifying the time to complete a mission involves more than just travel time. Now, instead of the completion point being when the probe arrives, it is defined as when its data arrive back at Earth. This shift is because the time needed to send the data back has a greater impact than often realized. For example, even though Breakthrough StarShot aims to get there the quickest, in just 22 years, that comes at the expense of making the spacecraft so small that it takes an additional 20 years to finish transmitting the data. Hence, the time from launch to data return is about a half century, comparable to other concepts (46 yrs = 22 trip + 4 signal + 20 to transmit data). The tradeoffs of using a larger payload with a faster data rate, but longer transit time, will be considered.
Regarding the total time to complete the mission, the beginning point is now. The analysis includes considerations for the remaining research and the subsequent work to design and build the mission hardware. Further, the mission hardware, now by definition, includes its infrastructure. While the 1000 AU precursor missions do not need new infrastructure, most everything beyond that will.
Recall that the laser lightsail concepts of Robert Forward required a 26 TW laser, firing through a 1,000 km diameter Fresnel lens placed beyond Saturn (around 10 AU), aimed at a 1,000 km diameter sail with a mass of 800 Tonnes. Project Daedalus envisioned needing 50,000 tonnes of helium 3 mined from the atmospheres of the gas giant planets. This not only requires the infrastructure for mining those propellants, but also processing and transporting that propellant to the assembly area of the spacecraft. Even the more modest Earth-based infrastructure of StarShot is beyond precedent. StarShot will require one million synchronized 100 kW lasers spread over an area of 1 km2 to get it up to the required 100 GW.
While predicting these durations in the absolute sense is dubious (predicting what year concept A might be ready), it is easier to make relative predictions (if concept A will be ready before B) by applying the same predictive models to all concepts. For example, the infrastructure rates are considered proportional to the mass and energy required for the mission – where a smaller and less energetic probe is assumed to be ready sooner than a larger, energy-intensive probe.
The most difficult duration to estimate, even when relaxed to relative instead of absolute comparisons, is the pace of research. Provisional comparative methods have been outlined, but this is an area needing further attention. The reason that this must be included – even if difficult – is because the timescales for interstellar flight are comparable to breakthrough advancements.
The fastest mission concepts (from launch to data return) are 5 decades, even for StarShot (not including research and infrastructure). Compare this to the 7 decades it took to advance from the rocket equation to having astronauts on the moon (1903-1969), or the 6 decades to go from the discovery of radioactivity to having a nuclear power plant tied to the grid (1890-1950).
So, do you pursue a lesser technology that can be ready sooner, a revolutionary technology that will take longer, or both? For example, what if technology A is estimated to need just 10 more years of research, but 25 years to build its infrastructure, while option B is estimated to take 25 more years of research, but will require no infrastructure. In that case, if all other factors are equal, option B is quicker.
To measure the cost of missions, a more fundamental currency than dollars is used – energy. Energy is the most fundamental commodity of all physical transactions, and one whose values are not affected by debatable economic models. Again, this is anchoring the comparisons in relative, rather than the more difficult, absolute terms. The energy cost includes the aforementioned infrastructure creation plus the energy required for propulsion.
Comparing the divergent propulsion methods requires converting their method-specific measures to common factors. Laser-sail performance is typically stated in terms of beam power, beam divergence, etc. Rocket performance in terms of thrust, specific impulse, etc. And warp drives in terms of stress-energy-tensors, bubble thickness, etc. All these type-specific terms can be converted to the more fundamental and common measures of energy, mass, and time.
To make these conversions, the propulsion options are divided into 4 analysis groups, where the distinction is if power is received from an external source or internally, and if their reaction mass is onboard or external. Further, as a measure of propulsion efficiency (or in NASA parlance, “bang for buck”) the ratio of the kinetic energy imparted to the payload, to the total energy consumed by the propulsion method, can be compared.
The other reason that energy is used as the anchoring measure is that it is a dominant factor with interstellar flight. Naively, the greatest challenge is thought to be speed. The gap between the achieved speeds of chemical rockets and the target goal of 10% lightspeed is a factor of 400. But, increasing speed by a factor of 400 requires a minimum of 160,000 times more energy. That minimum only covers the kinetic energy of the payload, not the added energy for propulsion and inefficiencies. Hence, energy is a bigger deal than speed.
For an example, consider the 1-gram StarShot spacecraft traveling at 20% lightspeed. Just its kinetic energy is approximately 2 TJ. When calculating the propulsive energy in terms of the laser power and beam duration, (100 GW for minutes) the required energy spans 18 to 66 TJ, for just a 1-gram probe. For comparison, the energy for a suite of 1,000 probes is roughly the same as 1-4 years of the total energy consumption of New York City (NYC @ 500 MW).
Delivering more energy faster requires more power. By launching only 1 gm at a time, StarShot keeps the power requirement at 100 GW. If they launched the full suite of 1000 grams at once, that would require 1000 times more power (100 TW). Power is relevant to another under-addressed issue – the challenge of getting rid of excess heat. Hypothetically, if that 100 GW system has a 50% efficiency, that leaves 50 GW of heat to radiate. On Earth, with atmosphere and convection, that’s relatively easy. If it were a space-based laser, however, that gets far more dicey. To run fair comparisons, it is desired that each concept uses the same performance assumptions for their radiators.
Knowing how to compare the options is one thing. The other need is knowing which problems to solve. In the general sense, the entire span of interstellar challenges have been distilled into this “top 10” list. It is too soon to rank these until after running some test cases:
- Communication – Reasonable data rates with minimum power and mass.
- Navigation – Aiming well from the start and acquiring the target upon arrival, with minimum power and mass. (The ratio of the distance traversed to a ½ AU closest approach is about a million).
- Maneuvering upon reaching the destination (at least attitude control to aim the science instruments, if not the added benefit of braking).
- Instrumentation – Measure what cannot be determined by astronomy, with minimum power and mass.
- High density and long-term energy storage for powering the probe after decades in flight, with minimum mass.
- Long duration and fully autonomous spacecraft operations (includes surviving the environment).
- Propulsion that can achieve 400 times the speed of chemical rockets.
- Energy production at least 160,000 times chemical rockets and the power capacity to enable that high-speed propulsion.
- Highly efficient energy conversion to minimize waste heat from that much power.
- Infrastructure creation in affordable, durable increments.
While those are the general challenges common to all interstellar missions, each propulsion option will have its own make-break issues and associated research goals. At this stage, none of the ideas are ready for mission trade studies. All require further research, but which of those research paths might be the most impactive, and under what circumstances? It is important to repeat that this study is not about picking “one solution” for a mission. Instead, it is a process for continually making the most impactive advances that will not only enable that first mission, but the continually improving missions after that.
Ad astra incrementis.
Planet Formation: How Ocean Worlds Happen
It’s hard to fathom when we look at a globe, but our planet Earth’s substantial covering of ocean is relatively modest. Alternative scenarios involving ‘water worlds’ include rocky planets whose silicate mantle is covered in a deep, global ocean, with no land in sight. Kilometer after kilometer of water covers a layer of ice on the ocean floor in these models, making it unlikely that the processes that sustain life here could develop — how likely is a carbon cycle in such a scenario, and without it, how do we stabilize climate and make an inhabitable world?
These are challenging issues as we build the catalog of exoplanets and try to figure out local conditions. But it’s also intriguing to ask what made Earth turn out as dry as it is. Tim Lichtenberg developed a theory while doing his thesis at the Eidgenössische Technische Hochschule in Zürich (he is now at Oxford), and now presents it in a paper in collaboration with colleagues at Bayreuth and Bern, as well as the University of Michigan. Lichtenberg thinks we should be looking hard at the radioactive element Aluminium-26 (26Al).
Go back far enough in the evolution of the Solar System and kilometer-sized planetesimals made of rock and ice moved in a circumstellar disk around the young Sun, eventually through the process of accretion growing into planetary embryos. In this era a supernova evidently occurred in the astronomical neighborhood, depositing 26Al and other elements into the mix. Using computer simulations of the formation of thousands of planets, the researchers argue that two distinct populations emerge, water worlds and drier worlds like Earth.
“The results of our simulations suggest that there are two qualitatively different types of planetary systems,” says Lichtenberg: “There are those similar to our Solar System, whose planets have little water. In contrast, there are those in which primarily ocean worlds are created because no massive star, and so no Al-26, was around when their host system formed. The presence of Al-26 during planetesimal formation can make an order-of-magnitude difference in planetary water budgets between these two species of planetary systems.”
Image: Planetary systems born in dense and massive star-forming regions inherit substantial amounts of Aluminium-26, which dries out their building blocks before accretion (left). Planets formed in low-mass star-forming regions accrete many water-rich bodies and emerge as ocean worlds (right). Credit: Thibaut Roger.
Because planets grow from these early planetesimals, their composition is critical. If a great part of a planet’s water comes from them, then the danger of accreting too much water is always present if many of the constituent materials come from the icy regions beyond the snowline. But radioactive constituents like 26Al inside the planetesimals can create heat that can evaporate much of the initial water ice content before accretion occurs. Dense star-forming regions are more likely to produce planets that manifest these latter outcomes.
Lichtenberg and team examined the decay heat from 26Al in terms of this early planetesimal evolution, which would have led to silicate melting and degassing of primordial water abundances. Their simulations of planet populations delved into internal structures that varied according to disk structures, planetary composition, and initial location of planetary embryos. They produced statistical variations of incorporated water in planets that varied in radius and initial 26Al abundance. In all, the authors achieved what they believe to be a statistically representative set of 540,000 individual simulations over 18 parameter sets.
Image: This is Figure 3 from the paper. Caption: Fig. 3 | Qualitative sketch of the effects of 26Al enrichment on planetary accretion. Left, 26Al-poor planetary systems; right, 26Al-rich planetary systems. RP, planetary radius. Arrows indicate proceeding accretion (middle), planetesimal water content (bottom right, blue-brown) and live 26Al (bottom right, red-white). Credit: Lichtenberg et al.
We wind up with planetary systems with 26Al abundances similar to or higher than the Solar System forming terrestrial planets with lower amounts of water, an effect that grows more pronounced with distance from the host star, since embryos forming there are likely to be richer in water. Systems poor in 26Al are thus far more likely to produce water worlds. A remaining question involves the actual growth of rocky planets, as the paper notes:
If rocky planets grow primarily from the accumulation of planetesimals, then the suggested deviation between planetary systems should be clearly distinguishable among the rocky exoplanet census. If, however, the main growth of rocky planets proceeds from the accumulation of small particles, such as pebbles, then the deviation between 26Al-rich and 26Al-poor systems may become less clear, and the composition of the accreting pebbles needs to be taken into account.
The direction of future work to explore the question is clear;
… models of water delivery and planet growth need to synchronize the timing of earliest planetesimal formation, the mutual influence of collisions and 26Al dehydration, the potential growth by pebble accretion, and the partitioning of volatile species between the interior and atmosphere of growing protoplanets in order to further constrain the perspectives for rocky (exo-)planet evolution.
The paper is Lichtenberg et al., “A Water Budget Dichotomy of Rocky Protoplanets from 26Al-Heating,” Nature Astronomy Letters, 11 February 2019 (abstract). Thanks to John Walker for helpful information regarding this story.
Looking Back from System’s Edge
Sometimes the way we discover new things is by looking back, as witness the blue haze of Pluto. The image below comes, of course, from New Horizons, taken after the flyby and looking back in the direction of the Sun. Here we’re looking at a mosaic combining black and white LORRI images (Long Range Reconnaissance Imager) and enhancing them with lower-resolution color data from the Ralph/Multispectral Visible Imaging Camera (MVIC). The result, taken about 3.5 hours after closest approach, is in approximately true color.
Image: Pluto as seen by New Horizons from 200,000 kilometers after the flyby. The spectacular blue haze, extending to over 200 kilometers in altitude, is the result of sunlight acting on methane and other molecules in Pluto’s atmosphere to produce a photochemical haze. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
Ultima Thule likewise yields more of its secrets as we look at data from beyond the closest encounter. New Horizons’ latest target produced departure imagery fleshing out our view of the object’s shape by showing us parts of the KBO that were not illuminated by the Sun during the approach. We learn that the two lobes of Ultima Thule are not spherical at all, but rather that the larger lobe is flattened into a pancake shape, while the New Horizons team sees in the smaller lobe a resemblance to a dented walnut. Here is a video rendering of the data.
Image: Mission scientists created this “departure movie” from 14 different images taken by the New Horizons Long Range Reconnaissance Imager (LORRI) shortly after the spacecraft flew past the Kuiper Belt object nicknamed Ultima Thule (officially named 2014 MU69) on Jan. 1, 2019. The central frame of this sequence was taken on Jan. 1 at 05:42:42 UT (12:42 a.m. EST), when New Horizons was 8,862 kilometers (5,494 miles) beyond Ultima Thule, some 6.6 billion kilometers (4.1 billion miles) from Earth. The object’s illuminated crescent is blurred in the individual frames because a relatively long exposure time was used during this rapid scan to boost the camera’s signal level – but the science team combined and processed the images to remove the blurring and sharpen the thin crescent. This is the farthest movie of any object in our Solar System ever made by any spacecraft. Credit: NASA/Johns Hopkins Applied Physics Laboratory/Southwest Research Institute/National Optical Astronomy Observatory.
“We’ve never seen something like this orbiting the Sun,” says mission PI Alan Stern, adding:
“We had an impression of Ultima Thule based on the limited number of images returned in the days around the flyby, but seeing more data has significantly changed our view. It would be closer to reality to say Ultima Thule’s shape is flatter, like a pancake. But more importantly, the new images are creating scientific puzzles about how such an object could even be formed.”
Image: New Horizons took this image of Ultima Thule on Jan. 1, 2019, when the NASA spacecraft was 8,862 kilometers (5,494 miles) beyond it. The image to the left is an “average” of ten images taken by the Long Range Reconnaissance Imager (LORRI); the sharper processed view is to the right. Credit: NASA/Johns Hopkins Applied Physics Laboratory/Southwest Research Institute/National Optical Astronomy Observatory.
Observing stars as they disappeared when Ultima Thule passed in front of them allowed scientists to further refine the shape. The illustration below shows the evolution of our understanding, as we’ve moved from the ‘snowman’ to the ‘pancake’ model.
“While the very nature of a fast flyby in some ways limits how well we can determine the true shape of Ultima Thule, the new results clearly show that Ultima and Thule are much flatter than originally believed, and much flatter than expected,” adds Hal Weaver, New Horizons project scientist from the Johns Hopkins Applied Physics Laboratory. “This will undoubtedly motivate new theories of planetesimal formation in the early solar system.”
Image: Scientists’ understanding of Ultima Thule has changed as they review additional data. The “old view” in this illustration is based on images taken within a day of New Horizons’ closest approach to the Kuiper Belt object on Jan. 1, 2019, suggesting that both “Ultima” (the larger section, or lobe) and “Thule” (the smaller) were nearly perfect spheres just barely touching each other. But as more data were analyzed, including several highly evocative crescent images taken nearly 10 minutes after closest approach, a “new view” of the object’s shape emerged. Ultima more closely resembles a “pancake,” and Thule a “dented walnut.” The bottom view is the team’s current best shape model for Ultima Thule, but still carries some uncertainty as an entire region was essentially hidden from view, and not illuminated by the Sun, during the New Horizons flyby. The dashed blue lines span the uncertainty in that hemisphere, which shows that Ultima Thule could be either flatter than, or not as flat as, depicted in this figure. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
2019 Symposium Call for Papers
6th Interstellar Symposium and Interstellar Propulsion Workshop – TVIW 2019
In collaboration with the National Aeronautics and Space Administration (NASA), the Tennessee Valley Interstellar Workshop (TVIW) hereby invites participation in its 6th Interstellar Symposium and Interstellar Propulsion Workshop -hosted by Wichita State University (WSU) and Ad Astra Kansas Foundation – to be held from Sunday, November 10 through Friday, November 15, 2019, in Wichita, Kansas. The 2019 TVIW has the following elements:
The NASA Workshop on Interstellar Propulsion will focus solely on physics-based propulsion technologies that have the potential to meet the goal of launching an interstellar probe within the next century and achieving .1c transit velocity: Beamed Energy Propulsion, Fusion, and Antimatter.
At this meeting, the state-of-the-art of each will be examined, competing approaches to advancing the Technology Readiness Level (TRL) of each will be presented by advocates and assessed by non-advocates for synthesis into a workshop report to serve as the blueprint for possible future interstellar propulsion technology development.
The Interstellar Symposium will focus on all other aspects of interstellar travel excluding the advanced propulsion technologies to be covered in the NASA Workshop on Interstellar Propulsion, such as power, communications, system reliability/maintainability, psychology, crew health, anthropology, legal regimes and treaties, ethics, exoplanet science (possible destinations), and related research.
Working Tracks are collaborative, small group discussions around a set of interdisciplinary questions on an interstellar subject with the objective of producing “roadmaps” and/or publications to encourage further developments in the respective topics. This year we will be organizing the Working Tracks to follow selected plenary talks with focused discussions on the same topic.
Sagan Meetings. Carl Sagan famously employed this format for his 1971 conference at the Byurakan Observatory in old Soviet Armenia, which dealt with the Drake Equation. Each Sagan Meeting will invite five speakers to give a short presentation staking out a position on a particular question. These speakers will then form a panel to engage in a lively discussion with the audience on that topic.
Seminars are 3-hour presentations on a single subject, providing an in depth look at that subject. Seminars will be held on Sunday, November 10, 2019, with morning and afternoon sessions. The content must be acceptable to be counted as continuation education credit for those holding a Professional Engineer (PE) certificate.
Other Content includes, but is not limited to, posters, displays of art or models, demonstrations, panel discussions, interviews, or public outreach events.
Publications: Since TVIW serves as a critical incubator of ideas for the interstellar community, we intend to publish the work of TVIW 2019 in many outlets, including a complete workshop proceedings in book form.
No Paper, No Podium: If a written paper is not submitted by the final manuscript deadline, authors will not be permitted to present their work at the event. Papers should be original work that has not been previously published. Select papers may be submitted for professional publication, such as in the Journal of the British Interplanetary Society (JBIS).
Video and Archiving: All TVIW events may be captured on video or in still images for use on the TVIW website, in newsletters and social media. All presenters, speakers and selected participants will be asked to complete a Release Form that grants permission for TVIW to use this content as described.
ABSTRACT SUBMISSION
Abstracts for presented papers/presentations at TVIW 2019 may be submitted to either of two categories:
1. NASA Workshop on Interstellar Propulsion
2. Interstellar Symposium
Topics for Working Tracks, Sagan Meetings, Seminars, and Other Content are NOT solicited at this time.
Abstracts for the NASA Workshop on Interstellar Propulsion must relate to one of the three propulsion technologies of interest (Beamed Energy Propulsion, Fusion, and Antimatter) and should include the aspects of recent research, an assessment of the technology’s Technology Readiness Level (TRL) using NASA’s definitions found here, and a discussion of critical technical issues to be resolved with realistic, near-term technical development milestones identified (including relevant performance metrics).
Abstracts for the Interstellar Symposium must related to one or more of the many other interstellar mission related topics, such as power, communications, system reliability/maintainability, psychology, crew health, anthropology, legal regimes and treaties, ethics, exoplanet science (possible destinations), and propulsion technologies not explicitly called for in the NASA Workshop on Interstellar Propulsion.
Abstracts due: July 30, 2019.
All abstracts must be submitted online here.
PRESENTING AUTHOR(S) – Please list ONLY the author(s) who will actually be in attendance and presenting at the conference. (first name, last name, degree -for example, Susan Smith, MD)
ADDITIONAL AUTHORS – List all authors here, including Presenting Author(s) – (first name, last name, degree(s) – for example, Mary Rockford, RN; Susan Smith, MD; John Jones, PhD)
ABBREVIATIONS within the body should be kept to a minimum and must be defined upon first use in the abstract by placing the abbreviation in parenthesis after the represented full word or phrase. Proprietary drug names and logos may NOT be used. Non-proprietary (generic) names should be used.
ABSTRACT LENGTH – The entire abstract, (EXCLUDING title, authors, presenting author’s institutional affiliation(s), city, state, and text), including any tables or figures should be a maximum of 350 words. It is your responsibility to verify compliance with the length requirement.
Abstract Structure – abstracts must include the following headings:
- Title – the presentation title
- Background – describes the research or initiative context
- Objective – describes the research or initiative objective
- Methods – describes research methodology used. For initiatives, describes the target population, program or curricular content, and evaluation method
- Results – summarizes findings in sufficient detail to support the conclusions
- TRL Assessment and Justification (NASA Propulsion Workshop only)
- Development Roadmap (NASA Propulsion Workshop only)
- Near-term technical milestones and performance metrics (NASA Propulsion Workshop only)
- Conclusions – states the conclusions drawn from results, including their applicability.
Questions and responses to this Call for Papers, Workshops and Participation should be directed to: info@tviw.us
For updates on the meeting, speakers, and logistics, please refer to the website: https://tviw.us/2019-symposium/
TVIW is incorporated in the State of Tennessee as a non-profit education organization. TVIW is a tax-exempt, 501(c)(3) educational, non-profit corporation by U.S. Internal Revenue Service. For U.S. tax purposes, all donations to TVIW are fully tax deductible (as allowed by your local laws).
Copyright © 2019 Tennessee Valley Interstellar Workshop, Inc. (TVIW), All rights reserved.
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