by Paul Gilster | May 13, 2016 | Culture and Society |
As we move into the outer Solar System and beyond, the possibility exists that we may encounter an extraterrestrial species engaged in similar exploration. How we approach first contact has been a theme of science fiction for many years (Murray Leinster’s 1945 story ‘First Contact’ is a classic treatment). In the essay below, Ken Wisian looks at how we can develop contact protocols to handle such a situation. A Major General in the US Air Force (now retired) with combat experience in Iraq, Afghanistan and the Balkans, Ken brings a perspective seasoned by command and a deep knowledge of military history to issues of confrontation and outcomes, building on our current rules of engagement to ask how we will manage an encounter with another civilization, one whose consequences would be momentous for our species.
By Ken Wisian Ph.D
Galactic Ventures LLC, Austin, Texas
Abstract
How do two ships approach each other in a first contact setting? When it happens it will be a pivotal moment for human history. The slightest mistake or misperceived intention could cascade into violence. Therefore even future deep space robotic probes, let alone a true interstellar ship whether crewed by humans or AI, should incorporate courses of action for this possibility,
The development of first contact protocols is obviously rife with unknowns since we only have a one-planet historical data set build on; nevertheless we must proceed. The bulk of the thinking on first contact so far has focused on a remote contact via electromagnetic signal exchange (SETI) or finding non-sentient microbiota (aka Apollo post-mission quarantine), but what if we stumble upon another intelligence in space? Admittedly, this may not be the most likely course of action, but as we start to move deeper into space it is an increasing possibility. Through centuries of trial and error, protocols have been developed for military ship and aircraft encounters on Earth. These earth protocols provide as good a basis as we have for building extraterrestrial first contact protocols.
This paper will review human rules of encounter currently used and build a set of simple rules for a ship-to-ship encounter in space based on the assumption that there is no effective communication prior to or during the encounter.
1. Introduction
How do you approach a totally unknown entity in such a way as to not provoke a hostile reaction? This is not as easy a question as it might first appear. We are loaded with human-cultural preconceptions that are frequently subconscious. An example; smiling in humans is universally regarded as a friendly gesture, but in some primates and most species on earth (with a face that is) showing your teeth is a dominance/aggressive/threat gesture. And this difference here on earth exists between closely related species – who is to say how divergent the interpretation of gestures might be between species that evolved in different star systems? Another example is the white flag. Most industrialized states recognize it as a sign of surrender, some also would recognize its use to request parley, but it is far from universal in time or across cultures even today on earth. Thus nothing can be taken for granted and substantial on-the-spot sound judgement will be required.
Why worry about the vanishingly small chance of an unanticipated first contact? Risk management both in the military and civilian world considers not just the probability of an event, it also considers the potential consequences. In the case of a first contact, the odds of such an event are nearly vanishingly small, but they are cancelled out (and then some) by the off-the-chart potential impact of an encounter unintentionally entering an instantaneous, violent escalation spiral. Thus it is critically important that humans think through first contact in space before it happens.
Science fiction (SF) deals frequently with first contact scenarios. The volume of material is immense – far too much to even briefly review here. SF has explored, often quite well and with great “outside the box” thinking probably every conceivable scenario. So while there are no specific SF references here, the body of SF work informs all aspects of this paper.
We have a limited knowledge base from which to start and extrapolate general rules for first encounters, namely one technological species – homo-sapiens. This situation presents a danger that we must guard against as best we can; anthropomorphic bias. Given that potential bias, we will none the less start by looking at what humans do in the closest analog we currently have for first encounters; the meeting of unknown, neutral or potentially hostile ships and or aircraft. Through trial and (often fatal) error there are now well-defined rules of conduct for these situations (up to the level of international law).
The human-human contact experience is perhaps our best foundation upon which to build a set principles and protocols for a potential encounter in space. The envisioned scenario; two ships meeting in space rest on several assumptions.
Assumptions:
1. No effective telecommunication. There may be attempts to communicate via electromagnetic or other means, but understanding has not been achieved, thus we are without effective communication – “comm-out”.
2. Neither side is overtly hostile, but both are guardedly cautious.
3. At least one of the ships involved has “reasonable” maneuvering capability.
a. This will most likely be an “endpoint” encounter, in a solar system. An encounter in transit in deep interstellar space would likely mean neither ship has the ability to stop and/or maneuver in order to match vectors and effect a rendezvous.
Not a scenario assumption, but an important point is that these protocols apply just as well to Artificial Intelligence (AI) crewed ships as they do to human crewed ships. Also, ships is taken to include space stations or other similar outposts. Even probes without true AI can incorporate complex, branched Courses Of Action (COAs) for dealing with encounters. For instance, detection of radiation anywhere in a wide range of EM frequencies that does not correlate with known astronomical sources would be a target to slew all sensors to and report on. At that point, depending on level of sophistication, you enter COAs for determining artificiality etc.
Image: Confronting the unknown. A still from Steven Spielberg’s Close Encounters of the Third Kind. Credit: EMI Films / Columbia Pictures.
2. Current human protocols
There are internationally accepted protocols for encounters between ships and correspondingly between aircraft. Some are based on international law and custom (Law of the Seas), some are rules by governing bodies (International Civil Aviation Organization). Similar laws and rules exist also within the boundaries of individual countries. Regardless of origin, they follow broadly similar, mostly common sense (at least to us nowadays) paths based on centuries of experience. Underlying much of this is an unwritten intent to minimize potential misunderstanding that could lead to violence. This point is critical for our purposes. It is difficult enough to minimize misunderstanding and escalation within our own species, it could be significantly more difficult to do the same when civilizations from different stars meet.
Much of the law and customs for ships at sea pertain to piracy or the right of a country to inspect a ship to ensure that it is conducting legal business (particularly in territorial waters). Even here though reasonable cause is required for more than a cursory inspection. The rules governing intercept of aircraft are more slanted towards the need to immediately protect a country from devastating attack that can result from a craft moving at or above supersonic speed and thus can lead much more quickly to lethal action.
In all air and sea cases there is a hierarchy of communication means used to establish meaningful dialog between ships from straightforward radio communication to flag and light signals up to and including weapons fire – the shot across the bow, so yes, even gunfire can be a form of communication. With aircraft there are no flags, but brief maneuvers (such as rocking wings) can be used for communication.
For ships at sea, there are rules for avoiding collision such as pass to the right (starboard). There is also a rule that the most maneuverable ship has primary responsibility to avoid collision. For example a functional ship at sea that comes upon a ship adrift, unable to maneuver, besides having a responsibility to help, is responsible to maneuver so to avoid collision. Correspondingly, the less maneuverable ship is obligated to maintain constant speed and heading or come to a stop. For aircraft meeting aircraft there is a similar most maneuverable has primary responsibility to avoid collision rule, so for instance a powered aircraft has responsibility to avoid a hot air balloon.
For military aircraft or ships meeting other military ships or aircraft there are additional guidelines that are critical for avoiding escalation. First is to avoid collision courses or aggressive maneuvers such as those designed to put one in a (better) shooting position. Right along with that are restrictions on pointing guns or (and this gets tricky) putting support systems such as radars into modes such as target track that are standard preparatories to firing weapons. Radar modes have become particularly problematic as technology has advanced; many weapon system no longer require a distinctive target tracking mode in order to shoot. Furthermore electromagnetic jamming during an intercept is a potentially hostile act. These rules unfortunately are not universally followed and not following them has resulted in very serious international incidents to the present day.
3. Excursion into past human civilizational first contacts
The past record of human civilization first contacts is a well-trodden area of history and will only briefly be covered as it pertains to extraterrestrial scenarios – the longer term consequences such as disease transfer and cultural domination will not be addressed. Less commonly studied though are the details and consequences of the actual first contact. The bottom line is that first encounters have often, though not always turned violent and in such cases the side with a major technological advantage usually wins. Commonly Western Europeans with well advanced gunpowder technology encountering stone or bronze/iron age technologies have won most violent encounters, but have sometimes been overcome bu numbers. The question of why encounters have turned violent and the cause is much more ambiguous – some encounters have been peaceful, but in many cases territoriality and xenophobia have been prompt causes for violence. Who can say for sure that any species encountered may not have these traits (even more markedly than humans)? Perhaps more disturbing, there are human cultures that consider war/killing a necessary prerequisite to full citizen status. Fortunately none of these cultures are dominant on earth today, but what if such a culture achieved an interstellar civilization?
4. Towards a protocol
The above review of human encounter situations and history gives us a good starting point for thinking about alien ship to ship encounters. First a few general principles to go with the assumptions already laid down at the beginning. These principles are distilled from the human contact procedures above which in turn are built upon millennia of experience.
Contact principles
- 1. Be predictable
- 2. Avoid any appearance of hostile intent
- 3. Attempt communication
These seem straightforward, but #2 has many subtleties and #3 is a very complex subject which is beyond the scope or this paper or the expertise of the author.
The principles are in priority order; communicating is far less important than the closely related ideas of being predictable and not showing hostile intent. These principles are broadly applicable in human experience. For example besides applying at the level of international affairs, these are also appropriate at the level of individuals for an encounter with law enforcement around the world, driving a car, or encountering strangers on the street.
What has not been stated before is the underlying motivation for these principles and that is to avoid putting the other party into a position where they have to make a snap judgement about your intent. In human interactions between two wary parties ambiguity of intent is almost always interpreted in the most hostile way (unless the parties have a considerable experience base, which in a first contact they will not, that allows them to presume accidental ambiguity versus hostility). It is also important to note that for the foreseeable future, considering that we have only just become a spacefaring species, we are most likely to be the less technologically advanced of the two encountering civilizations and thus it becomes particularly important that we not precipitate any escalation that we are very likely to lose.
Image: David Bowman (Keir Dullea) and a famous monolith, from Stanley Kubrick’s 2001: A Space Odyssey. Credit: Metro-Goldwyn-Mayer.
First, be predictable. Being predictable is taken to mean with respect to maneuvering primarily. If it is possible to determine that one ship has a decided maneuver advantage on the other, then rendezvous can be attempted with the ships adopting the convention of the most maneuverable ship takes primary responsibility for a safe rendezvous. In these cases gradual, deliberately slow maneuvers would be employed even if there is capability to rapidly affect course changes. With regards to maneuvers there are multiple COAs available. The simplest is to make no changes to what you are doing; if “coasting” – continue, if drive engines are engaged, continue at current setting. Alternatively, you might want to stop engines (this is not the same as stopping in space, which is probably not a practical thing to do (for that matter what frame of reference would you use to determine “stop”)). Regardless unless there is an overriding need (discussed shortly), maintain heading (in three dimensional terms – maintain vector).
What if one ship is approaching an orbital situation – remember that an encounter will most likely be at the endpoint of an interstellar journey. In such a case, in order to avoid catastrophe it might be necessary to start or continue maneuvers to achieve a safe, stable orbit, but this brings with it a slightly elevated risk misunderstanding. In this situation we would be forced to rely on the other parties’ ability to perceive the obvious need to conduct maneuvers. Note the potential for unintended consequences; for a ship that would need to “flip” end-to-end in order to reverse its engines and thrust, you would not want to “sweep” your thrust vector across the other ship and therefore place them in a position of having to decide if you are about to use you most destructive weapon (main drive) on them.
Secondly, avoid any appearance of hostile intent. This is a much more problematic issue than being predictable. The main problem with avoiding appearance of hostile intent is the perception problem. In any encounter between entities that do not share a common culture, there can be serious misinterpretations of intent and meaning, as exemplified by the smile and white flag examples earlier.
If a ship is equipped with weapons you would obviously not want to point them at the other ship. If practical stowing or deactivating them is good, but this then poses another question: would you want to have weapons that require time to activate completely deactivated, thus costing valuable time to spin up if things go bad?
Besides weapons, other non-destructive systems are used by the military; jammers and expendable decoys for example. These would obviously not want to be triggered (but what might be the difference between jamming and a high-powered attempt at communication?).
“But we are peaceful and will not be going armed into space” you say. Any conceivable ship will have technology/systems that are dual-use. The main drive of any self-powered interstellar ship will obviously be extremely high energy and could be used as a weapon of great range and destructive power, thus even a peaceful braking maneuver (with the drive off) that sweeps the business end of the drive towards the other ship, could prompt a swift reaction. Other systems that must be accounted for include communication systems; radios or lasers strong enough to communicate across interstellar distances could be very destructive at short range. So what is one to think when you see a high power laser move to point at you? Perhaps part of a communication protocol would be to only use low-power omnidirectional radio until good understanding is established. Shielding to protect ship and crew from radiation and or collisions has obvious military application – do you reduce its power, turn it off, or leave it in normal on mode? Can you? What if there is an active collision prevention system that destroys or pushes objects out of the way – that has major weapon potential. Is it safe to turn it off?
Tertiary considerations. Avoid looking like you are hiding (aircraft that turn off transponders are usually considered to have hostile or at least illegal intent). Turn on lights and anything else that makes you easily visible (but will this in turn blind any of the other ships sensors?). In your turn you will obviously use every sensor available to learn about the other ship, but passive sensors are probably best until goodwill is firmly established – an active radar scan may look like targeting to another party (just as targeting and search modes of radars are often indistinguishable in modern aircraft). A decoy, a probe, or a vessel containing materials to allow for communication and understanding, might be indistinguishable from a bomb, when launched from a ship.
Lastly, at what range do these actions need to start? As early as practical, probably at detection of the other ship. Your need to be predictable starts when they can see you and that is probably at least at the point when you can see them, if not much earlier.
5. Conclusion
What can be determined from the above discussion is that there are vast unknowns in any potential extraterrestrial encounter in space where effective communication is not established in advance. In these circumstances there are good principles to follow – be predictable, display no hostile intent, and attempt to establish communication, but the specific actions involve many gray areas where judgement, assumptions, or just plain hope, will be the guide. For any ship making an interstellar journey the scenarios must be “gamed” extensively in advance, but any COAs or checklist for an encounter should only be a guide/starting point. Flexibility, sound judgement and quick learning will be very important in these circumstances. The number one goal is to not put the other party in the position of having to make an instantaneous judgement about your intent.
by Paul Gilster | May 12, 2016 | Exoplanetary Science |
What’s a movie director supposed to do about gravity? In The Martian, we see Matt Damon moving about on Mars with a gait more or less similar to what he would use on Earth, despite Mars’ 0.38g. Harrison Ford changes worlds but never strides in The Force Awakens. About the gravitational challenges of 1953’s Cat Women of the Moon, the less said the better. Even so, we can chalk all these problems up to the fact that both top directors and their B-film counterparts are forced to film at the bottom of a gravity well, so a certain suspension of disbelief is at least understandable.
But assuming that gravity invariably increases as planets get bigger can be misleading, as Fernando J. Ballesteros (Universitat de València) and Bartolo Luque (Universidad Politécnica de Madrid) demonstrate in a new paper in Astrobiology. We learn that some larger worlds in our own Solar System have gravity not all that different from the Earth. In fact, the surface gravities for Venus, Uranus, Neptune and Saturn weigh in at 0.91g, 0.9g, 1.14g and 1.06g respectively, although these worlds are 0.82, 14, 17 and 95 times Earth’s mass.
Image: Walking on the planet Takodana looks more or less like walking on Earth in The Force Awakens, although the bar scene there is more interesting. Credit: Disney/Lucasfilm/Bad Robot Productions.
How do we go about making these deductions? Usefully, we have plentiful planets to work with as a result of the Kepler mission, and the fact that Kepler works with transits is likewise helpful. A transit light curve can show us how much starlight is blocked by the planet, which provides an estimate of the planet’s size, assuming we have a pretty good idea of the central star’s size.
Radial velocity measurements can then be brought to bear, a technique that supplements the transit method by adding a lower boundary to the planet’s mass. Remember that this measurement depends upon the viewing angle, as we can’t always know the orientation of a given planet’s orbit; i.e., in straight radial velocity studies, we won’t know whether we’re looking at a solar system edge-on, or from directly above (the measurement is M x sin(i), with i corresponding to the viewing angle. With transiting planets, though, we have a better read on the viewing angle because we see the planet transit across its star.
With an idea about the size of a world and a sound estimate of its mass, we can work out the planet’s surface gravity (gs = GM/R2). Ballesteros and Luque plot the surface gravity vs. mass for a range of exoplanets, folding in data from our own Solar System, where measurements are, obviously, far more precise. Three ‘regimes’ emerge from this work:
- Rocky worlds with masses lower than Earth’s ME;
- A ‘transition zone’ including super-Earths, Neptunes, and some Solar System planets, with masses from one to hundreds of Earth masses;
- Gas giants, with masses above hundreds of Earth masses.
And it’s in the transition zone that things get interesting. Let me quote from the paper:
In the first regime, planetary radius grows with mass as R ~ M¼; therefore surface gravity grows as gs ~ M½ (faster than what would be expected for incompressible bodies, gs ~ M?). On the other hand, for gas worlds, planetary radius remains roughly constant (i.e., gas giants with very different masses have similar sizes due to electron degeneracy), so surface gravity grows linearly with mass, gs ~ M. But in the transition zone, we find some sort of plateau where planetary radius has the fastest growth, as R ~ M½, which thereby yields a constant surface gravity roughly similar to that of Earth.
Hence the similarity in surface gravity between Venus, Uranus, Neptune, Saturn and the Earth, a non-intuitive result given the differences between these planets in structure and composition. As the number of confirmed exoplanets grows — and we saw the largest single addition to the catalog ever yesterday — we are able to understand that having five worlds with roughly the same surface gravity is a general trend. Fitting these findings in with planet formation models will be a challenge that should ultimately improve our understanding of the processes at work.
The accretion process and the competition for materials during planetary formation impose severe constraints on feasible planets. Current models of population synthesis (Mordasini et al., 2015) are designed to take this into account and can address many of the observed features. However, such models fail to explain this plateau and predict instead a noticeable increasing trend in surface gravities in this region.
Hence the value of our steadily increasing exoplanet catalog as we contrast real planetary systems with the theories we apply to their formation. Thus, as Ballesteros and Luque note, watching Harrison Ford walking on the planet Takodana as if he were taking a stroll down Hollywood Boulevard is not a simple moviemaker concession to Earth’s gravity. In this case, what we’re learning about surface gravity makes such strolls plausible.
The paper is Ballesteros and Luque, “Walking on Exoplanets: Is Star Wars Right?” Astrobiology Vol. 16, No. 5 (2016). Abstract. Preprint on arXiv.
by Paul Gilster | May 11, 2016 | Exoplanetary Science |
If you look into the software that made possible yesterday’s exoplanet results, you’ll find that VESPA (Validation of Exoplanet Signals using a Probabilistic Algorithm) is freely available online. The work of Princeton’s Timothy Morton, who spoke at the announcement news conference, VESPA is all about calculating the probabilities of false positives for signals that look like transiting planets. Transits, of course, are what the Kepler space telescope has been about, catching the slight stellar dimming as a planet crosses across the face of a star.
The numbers quickly get mind-boggling because while Natalie Batalha (NASA Ames), joined by Morton, NASA’s Paul Hertz and Kepler/K2 mission manager Charlie Sobeck (a colleague of Batalha at Ames) could point to 1284 newly confirmed exoplanets, they represent only a fraction of what must be in the Kepler field of view. Out of its over 150,000 stars, Kepler can only see the planets that transit their host stars, making this a problem of orientation. We now have 2300 confirmed exoplanets in the Kepler catalog, but it’s clear that countless stellar systems are simply unviewable because they’re not lined up so as to make the identifying transit.
But back to VESPA and the technique that made yesterday’s announcement possible. The problems of false positives are legion when you’re looking at a light curve suggestive of a planet. For one thing, a brown dwarf or extremely low mass star may pass between Kepler and the star. For that matter, a larger star in a binary system may just ‘graze’ the limb of the host star, sending a planet-like signal that has to be untangled from the true planetary count. With these and other possibilities, we’ve relied upon verification through follow-ups, usually performed through radial velocity checks or even direct imaging of exoplanets.
All of this takes time and is resource-intensive, serious issues given the number of candidates (4700) found since launch. Morton calls the false positive signals ‘imposters,’ describing the VESPA method, which allows researchers to quantify the probability that any candidate signal is in fact a planet without requiring the lengthy follow-up investigations cited above. Two different kinds of simulation come into play, one involving transit signals and their causes, the other simulating how common the ‘imposter’ signals are likely to be in the Milky Way.
Image: Kepler candidate planets (orange) are smaller and orbit fainter stars than transiting planets detected by ground-based observatories (blue). Credit: NASA Ames/W. Stenzel; Princeton University/T. Morton.
As this Princeton news release explains, the duration, depth and shape of a transiting planet signal are thus weighed against simulated planetary and false positive signals even as VESPA factors in the projected distribution and frequency of star types in the galaxy. Says Morton:
“If you have something that passes all those tests, then it’s likely to be a planet. We know small planets are common, so if Kepler sees a small-looking planet candidate and it passes the strict internal vetting, it’s more likely to be a planet than a false positive because it’s hard to mimic that signal with anything else… It’s easier to mimic something the size of Jupiter, and we know Jupiter-sized planets are less common. So the likelihood of a Jupiter-sized candidate actually being a planet that large is typically relatively low.”
VESPA works with information from both kinds of simulation to produce a reliability score between zero and one for each candidate signal. The candidates with a reliability greater than 99 percent are considered validated. The 1284 exoplanets announced yesterday all fit this standard, meeting what we can consider the minimum requirements for validation, while another 1327 candidates are considered likely to be planets although they do not score as high. 707 candidates turn out to be caused by non-planetary phenomena. It’s worth pointing out, too, that 984 candidates were revalidated — these had previously been verified by other methods.
Image: Since Kepler launched in 2009, 21 planets less than twice the size of Earth have been discovered in the habitable zones of their stars. The orange spheres represent the nine newly validated planets announcement on May 10, 2016. The blue disks represent the 12 previous known planets. These planets are plotted relative to the temperature of their star and with respect to the amount of energy received from their star in their orbit in Earth units. The sizes of the exoplanets indicate the sizes relative to one another. The images of Earth, Venus and Mars are placed on this diagram for reference. The light and dark green shaded regions indicate the conservative and optimistic habitable zone. Credit: NASA Ames/N. Batalha and W. Stenzel.
The announcement of 1284 confirmed exoplanets is the largest single announcement of new planets ever made, doubling the number of confirmed planets, with VESPA being used to calculate the reliability values of over 7000 signals from the latest Kepler catalog. This work gains additional weight as we consider the upcoming TESS (Transiting Exoplanet Survey Satellite) mission, which will be performing an all-sky survey of bright, nearby stars that will doubtless reveal tens of thousands of new candidates, all in need of confirmation.
Natalie Batalha recalled early work on transit photometry with a small robotic telescope at Mount Hamilton (CA), where researchers were plagued with false alarms, up to 70 percent of the signals proving to be non-planetary. Clearly, as Kepler became available, our methods increased greatly in accuracy, but as we move toward the final discovery catalog of this mission next year, we’ll be using methods like VESPA to continue sorting through candidate data, looking ahead not just to TESS, due to launch in 2017, but also the European Space Agency’s PLATO (PLAnetary Transits and Oscillations of stars ), designated for launch by 2024.
The paper is Morton et al., “False positive probabilities for all Kepler Objects of Interest: 1284 newly validated planets and 428 likely false positives,” Astrophysical Journal Vol. 822, No. 2 (10 May 2016). Abstract / preprint.
by Paul Gilster | May 10, 2016 | Uncategorized |
The unusual star designated KIC 8462852, and now widely known as ‘Tabby’s Star,’ continues to be an enigma. As discussed in numerous articles in these pages, KIC 8462852 shows anomalous lightcurves that remain a mystery. Recently Michael Hippke explored a related question: Was the star dimming over time, as postulated by Louisiana State’s Bradley Schaefer? The two sharply disagreed (references below), leading Hippke and co-author Daniel Angerhausen to re-examine their conclusions. Now, with further collaboration from Keivan Stassun and Michael Lund (both at Vanderbilt University) and LeHigh University’s Joshua Pepper, Hippke and Angerhausen have a new paper out, peer-reviewed and accepted for publication by The Astrophysical Journal. What follows are Michael Hippke’s thoughts over the controversy as it stands today, with the dimming of KIC 8462852 again in doubt.
by Michael Hippke
Tabetha Boyajian et al. released a paper on the preprint platform astro-ph in September 2015, which quickly got the Internet up to speed. Planet Hunters, an open community that searches data from the Kepler space telescope, found this unusual star that is now known as “Tabby’s Star”. It is observed to undergo irregularly shaped, aperiodic dips in flux of up to ~20%, much more than expected for any orbiting planets.
Media interest skyrocketed in October, when Jason Wright et al. released a preprint in which they discussed — among many other possibilities — the idea that the dips could originate from an alien race building a mega-size construction around the star, perhaps in the form of a “Dyson sphere”. Could it really be true that we found the first ever evidence of a powerful extraterrestrial civilization? A controversial discussion quickly ensued.
Further examination in other electromagnetic wavelengths only brought disappointing null results. The star was unremarkable in the infrared, showed no sign of artificial laser pulses, or radio emissions. The only somehow realistic astrophysical explanation was offered by Bodman & Quillan, who suggest the presence of a large family of comets, and which as of today are considered to be the “best” explanation.
Image: Cascading comets around a distant star (NASA/JPL/Caltech).
In January 2016, Bradley Schaefer released a preprint that examined historical photographic glass plates from the Harvard Observatory taken since 1889. His results seemed to show that “Tabby’s Star” had dimmed by 20% since that time, which was interpreted by many in the media as an indication of a quickly proceeding alien construction.
This was about the time when Daniel Angerhausen (an experienced astrophysicist at the NASA Goddard Space Flight Center) and I got interested. Our basic thought was: “If this were true, it would be the greatest thing in history!” We wanted to see the evidence with our own eyes, because honestly, we had big hopes ourselves. Initially. We think it is very human to be wanting to be part of something big, or at least seeing it happen. So, we had hopes that something big had been found, and we had the chance to see it happen.
So we dug into the Kepler data and found them rock-solid. These strange dips were really there! Also, we downloaded the historic Harvard data and plotted them. Schaefer had binned them in 5-year intervals, but behind these bins, there were actually over a thousand individual data points. When we plotted these on our screen, and overlaid a linear trend, we became very disappointed. The Harvard plates have an uncertainty (over 100 years) of order 0.1 to 0.2mag, and this was also visually evident. We had serious doubts that this dimming trend was valid.
We selected some comparison stars, which had similar scatter and trends, and decided that we would release our findings as a preprint on astro-ph. KIC 8462852 is a very special case not only scientifically but also in the way it was discussed in the community. It became one of the most publicly discussed astronomical objects. Many articles on this fascinating object (including its original detection) were published on astro-ph before peer review and some even called it a revolution in scientific discussion, making it real time and on various social media channels involving the public.
Bradley Schaefer himself gave at least 2 interviews on the day his (at that time not peer-reviewed) manuscript came out. Following his own arguments that “putting up unchecked and false claims is bad all the way around”, we had no other choice than putting our doubts on his results out immediately, so that the community, the involved media and the interested public did not have to wait many months for the formal rebuttal. We also decided to do this to keep the discussion public and have interested laymen follow it; we even gave a recipe to reproduce the data using the publicly available Harvard DASCH [Digital Access to a Sky Century @ Harvard] data for the interested reader [see KIC 8462852: No Dimming After All?].
The immediate reactions to our preprint were overwhelmingly negative, just as most of the other publications on KIC 8462852 have been. In retrospect, we attribute this to two very human factors. The first was that some of our previous assumptions and methods were indeed inconsistent and the choice of some comparison stars questionable. But errors are human, and everybody makes them at times! While we believe that these errors did reduce the clarity of our result, we still believed that the result itself was correct. This view was not shared by Bradley Schaefer, who published his reply on Centauri Dreams [see Bradley Schaefer: A Response to Michael Hippke]. The other issue we see was that most readers wanted to believe that this thing was real. Schaefer was an authority, while Hippke was described as a “novice”, and “proof by authority” seemed to weigh in.
As this time, we decided to do two things. First of all, we cut all media connections. Second, we started collecting all issues and questions raised by Schaefer, and many others in the community and here on Centauri Dreams. “Tabby’s Star” started off as a community project, and it continued to be one! The pure number of emails we received was enormous. Our favourite mail, which was received via hand-written paper mail actually, was by an American who said that he was once captured by these aliens himself and is a first-hand witness!
Most feedback was incredibly helpful, however. We gained several co-authors who contributed several more analyses, statistical tools and better ways to select comparison stars. We also got an invitation to the ASTROPLATE conference in Prague, where Michael Hippke met most of the glass photography community. We spent a whole week discussing calibration techniques, scanners, and fungus (one of the reasons why digitization of these plates is so important!). These fungi are actually called “gold disease” owing to their look on the glass. We enjoyed long evening talks about the millions of plates that still await their scientific use, and after all of this, had the chance to discuss our own findings in a presentation and discussion.
During all this, and afterwards, we continued the peer-review process at the Astrophysical Journal. We have published several papers in this journal before, and, as always, it was a very professional process. Yet, they appointed two referees instead of the usual one, and we went through several rounds of question-and-answer to nail down every detail. This took considerable time. Now the paper has been accepted for publication (and is updated on astro-ph). From the feedback we got, and given the much more detailed than usual review process, the study is probably one of the most solid and waterproof papers we ever published. We believe that it is established beyond any reasonable doubt that no dimming can be found within the uncertainties of 0.2mag per century.
Now, what does that mean for the mystery? Are there no aliens after all? Probably not! Still, the day-long dips found by Kepler are real. Something seems to be transiting in front of this star. And we still have no idea what it is!
The cool message here, however, is that we now for the first time in human history have technology that can at least in theory detect such things, with upcoming missions such as JWST and PLATO. To solve the mystery, there are now several more projects under way. The American Association of Variable Star Observers (AAVSO) has collected thousands of amateur astronomer observations to discover new dips. Others, such as the Las Cumbres Observatory Global Telescope (LCOGT) have joined the effort. Observing further dips in different colors can reveal information about the chemistry of the transiting object, which might confirm or reject a cometary origin. Who knows, perhaps these telescopes have already captured some exciting new data, and any day researchers might publish a paper that solves the mystery!
The paper is Hippke et al., “A statistical analysis of the accuracy of the digitized magnitudes of photometric plates on the time scale of decades with an application to the century-long light curve of KIC 8462852,” accepted at the Astrophysical Journal (preprint). A Vanderbilt news release is also available.
by Paul Gilster | May 9, 2016 | Uncategorized |
If you’ve been following the Breakthrough Starshot concept in these pages and elsewhere, you’ll know that it’s small at one end and big on the other. A beamed sail mission, it would use sails four meters to the side — quite small by reference to earlier beamed sail designs — driven by a massive phased laser array on the Earth. The array is projected to be a kilometer to the side, incorporating laser emitters working in perfect synchronization to produce what Pete Worden, formerly of NASA Ames, described in Palo Alto as “a laser wind of 50 gigawatts.” Worden is now executive director of Breakthrough Starshot.
As with the sail, so with the payload. We have no macro-scale spacecraft here but a ‘Starchip’ about the size of a postage stamp, making it a kind of futuristic smartphone containing not just cameras, communication equipment and navigation instruments but tiny thrusters. If you want to imagine something like this, you take trends in digital technology like Moore’s Law and extrapolate them forward, for this is a generation-length project aiming at an actual mission in, at minimum, thirty years, unless the concept studies find an irrevocable showstopper.
Sails and their Origins
As Breakthrough Starshot begins to organize and get its concept study launched, I’ve been looking back at its roots. Several things come to mind, the first of which is the kind of sail Robert Forward once talked about. In an earlier post, I talked about Starshot as “classic Bob Forward thinking rotated according to the symmetries of our new era,” and I think that’s about right. In the sense that Forward was the first to discuss putting a laser beam on a sail, the project draws undeniable inspiration from him. But it also takes his ideas in entirely new directions.
When I talked to Phil Lubin (UC-Santa Barbara) about Starshot, he referenced his Roadmap to Interstellar Flight paper, one that clearly draws on work he has been developing for the NASA Innovative Advanced Concepts (NIAC) office, where he received a 2015 grant. The ‘Roadmap’ paper, submitted to the Journal of the British Interplanetary Society, also makes use of another JBIS paper Lubin wrote called Directed Energy for Relativistic Propulsion and Interstellar Communications. And the Starchip concept itself has roots in Mason Peck’s continuing work on the tiny craft called ‘sprites’ at Cornell University.
Forward’s sail ideas were as large as the Breakthrough Starshot sail is small. Consider this: For a 1984 paper, he considered a vehicle massing 80,000 tons that would be brought up to half the speed of light by a sail fully 1000 kilometers across. A power station in the inner Solar System would power up a 75,000 TW laser system, and the beam would rely on a huge Fresnel lens in the outer system to keep it focused on the departing starship. Forward even imagined a ‘staged sail’ concept that would allow deceleration, rendezvous, and Earth return for his crew.
If you’re interested in this era and the work it produced, be aware that JBIS was a major venue for sail concepts in the 1980s. It was here that Gregory Matloff published his classic 1984 paper “Solar Sail Starships – The Clipper Ships of the Galaxy” (JBIS 34, 371-380), one that would be followed by a series of optimization papers in the same venue, and also developed in his book The Starflight Handbook (Wiley, 1989). The latter contains Forward’s endorsement, one I consider a classic in the book blurb business: “Don’t leave the Solar System without it!” Matloff became one of the leading theorists on sail design along with Forward’s explicitly named successor, writer and physicist Geoffrey Landis.
Here I need to remind those who haven’t already seen it that Landis’ new paper “Mission to the Gravitational Focus of the Sun: A Critical Analysis” (preprint) looks at problems at realizing the FOCAL concept, in particular dealing with the question of imaging capabilities. And we’ve looked recently at Claudio Maccone’s ideas on FOCAL for communications in Starshot and the Gravitational Lens.
You can see that what we have at play here is the evolution of technology making new space concepts possible. Indeed, part of the Breakthrough Starshot premise is that further evolution during the thirty year ‘window’ for the system to be developed will solve many of the intractable problems that face it. The list of issues, as we’ve seen in previous posts, is large, ranging from getting a huge phased laser array to perform to keeping the small sails on the beam for the agonizing two minutes of acceleration at 60,000 g’s. Not to mention getting data back to Earth.
Image: A futuristic beamed sail design as depicted by Adrian Mann (no relation here to Breakthrough Starshot). Thanks to Jim Benford for passing it along.
Space Sailing in Italy
Thinking about using the gravitational lens of the Sun for communications and imaging calls to mind the rich heritage solar sailing draws upon from Italian scientists. The gravitational lens mission that Maccone has come to call FOCAL can trace its origins back to the late 1980s. Here I should mention Quasat, which was conceived as an Earth-orbiting radio telescope based on an inflatable sail technology.
The Quasat notion came from Italian aerospace company Alenia Spazio. Gregory Matloff would thoroughly analyze the Quasat concept in a 1994 paper, discussing a high-reflectivity sail with an area of 10,000 square meters at a thickness of 2 μm, with an aluminum reflective layer with a thickness of 0.1 μm, carrying a 100 kg payload. Adapted for the gravity focus mission, the sail would, with the help of a close Solar gravity assist and perhaps an assist at Jupiter as well, reach the gravity focus at 550 AU in approximately sixty years.
A gravity focus mission is quite a stretch now and it was even more of one in the early 1990s, which is one reason the European team involved in the Quasat and other sail work turned to a project called Aurora. The effort was conceived at the International Astronautical Congress in Graz, Austria in 1993, with a core team led by Giovanni Vulpetti and including both Claudio Maccone and Italian engineer and author Giancarlo Genta. This turned out to be highly influential work, producing fifteen papers and presentations to European space agencies.
What became known as the Aurora Collaboration would produce a thin-film 250-meter square sail design that would venture to the heliopause and beyond at speeds about three times that of the Voyager probes. The issues it addressed were numerous, as explained in Solar Sails: A Novel Approach to Interplanetary Travel (Springer, 2008), written by Vulpetti, Les Johnson and Greg Matloff:
- Considering SPS propulsion for realistic extra-solar exploration;
- Investigating mission classes and related technological implications for significantly reducing the flight time, from departure to the target(s);
- Analyzing flight profiles; and
- Sizing sailcraft’s main systems for a technology demonstration mission to be proposed to the space agencies.
In a six-year period ending in 2000, the Aurora Collaboration would analyze telecommunications systems, the optical properties of sails, their optimized trajectories all the way out to the gravitational lens, communications options and the means of reducing the thickness of the sail. The group was an entirely self-supporting initiative whose work relied on the voluntary efforts of top scientists in the area of sail design. It would have later reverberations in NASA’s work on precursor interstellar missions and the European ESA/ESTEC heliopause probe.
I’m thinking about Aurora today particularly because I’ve just heard from Giovanni Vulpetti that he has made available a series of files of recent lectures he made at the University of Rome. Have a look at Dr. Vulpetti’s Astrodynamics and Propulsion website and click on Lectures to see over 400 slides dealing with sailcraft trajectories, thrust calculations, solar photon and plasma flow and a great deal more. Those of you interested in delving into the technical aspects of various sail configurations including magnetic sails will have plenty of material to work with here. Digging around in the site you’ll also find Vulpetti’s Problems and Perspectives in Interstellar Exploration paper now available in its entirety online.
What a pleasure it must be for the scientists who developed key sail concepts to see the actual deployment of sails like IKAROS in space. Now their work is being examined anew as we look for ways to continue reducing the size and thickness of sails, and ponder how best to get a propulsive beam onto a sail for acceleration up to a substantial percentage of the speed of light. Breakthrough Starshot continues to take the process forward as it launches its concept study, and in doing so draws upon a rich history of work in the service of space sailing.
