by Paul Gilster | Nov 25, 2015 | Astrobiology and SETI |
KIC 8462852 is back in the news. And despite a new paper dealing with the unusual star, I suspect it will be in the news for some time to come, for we’re a long way from finding out what is causing the unusual light curves the Planet Hunters group found in Kepler data. KIC 8462, you’ll recall, clearly showed something moving between us and the star, with options explored by Tabetha Boyajian, a Yale University postdoc, in a paper we examined here in October (see KIC 8462852: Cometary Origin of an Unusual Light Curve? and a series of follow-up articles).
To recap, we’re seeing a light curve around this F3-class star that doesn’t look anything like a planetary transit, but is much more suggestive of debris. Finding a debris disk around a star is not in itself unusual, since we’ve found many such around young stars, but KIC 8462 doesn’t appear to be a young star when looked at kinematically. In other words, it’s not moving the way we would expect from a star that has recently formed. Moreover, the star shows us none of the emissions at mid-infrared wavelengths we would expect from a young, dusty disk.
Jason Wright and the team at the Glimpsing Heat from Alien Technologies project at Penn State have taken a hard look at KIC 8462 and discussed it briefly in a recent paper (citations for both the Boyajian and Wright papers are at the end of this entry). It seems entirely reasonable to do what Wright did in referencing the fact that the light curve we see around the star is what we would expect to see if an advanced civilization were building something. That ‘something’ might be a project along the lines of a ‘Dyson swarm,’ in which huge collectors gather solar energy, or it could be a kind of structure beyond our current thinking.
We all know that the media reaction was swift, and we saw some outlets acting as if Wright had declared KIC 8462 an alien outpost. He had done no such thing, nor has he or the Penn State team ever suggested anything more than continuing investigation of this strange star. What seems to bother others, who have scoffed at the idea of extraterrestrial engineering, is that Wright and company have not explicitly ruled it out as a matter of course. The assumption there is that no other civilizations exist, and therefore we could not possibly be seeing one.
I come down on the side of keeping our options open and studying the data in front of us. We have a lot of work ahead to figure out what is causing a light curve so unusual that at least one of the objects briefly occulting this star caused a 22 percent dip in its flux. That implies a huge object, evidently transiting in company with many smaller ones. There seems to be no evidence that the objects are spherically symmetric. What’s going on around KIC 8462?
A new paper from Massimo Marengo (Iowa State) and colleagues looks at what Tabetha Boyajian identified as the most likely natural cause of the KIC 8462 light curves. All I have at this point is the JPL news release and a release from Iowa State — the paper has not yet appeared online — describing evidence for a swarm of comets as the culprit. The study, which has been accepted at Astrophysical Journal Letters relies on Spitzer data dating from 2015, five years later than the WISE data that found no signs of an infrared excess.
Image: This illustration shows a star behind a shattered comet. Is this the explanation for the unusual light curves found at KIC 8462852? Image credit: NASA/JPL-Caltech.
If there had been a collision between planets or asteroids in this system, it was possible that the WISE (Wide-field Infrared Survey Explorer) data, taken in 2010, reflected conditions just before the collision occurred. Now, however, we can rule that out, because Spitzer, like WISE, finds no excess of infrared light from warm dust around KIC 8462. So the idea of planet or asteroid collisions seems even less likely. Marengo, according to the JPL document, falls back on the idea of a family of comets on an eccentric orbit. He’s also aware of just how odd KIC 8462 is:
“This is a very strange star,” [Marengo] said. “It reminds me of when we first discovered pulsars. They were emitting odd signals nobody had ever seen before, and the first one discovered was named LGM-1 after ‘Little Green Men… We may not know yet what’s going on around this star, but that’s what makes it so interesting.”
It would take a very large comet indeed to account for the drop in flux we’ve already seen, but a swarm of comets and fragments can’t be ruled out because we just don’t have enough data to make the call. I assume Marengo also gets into the fact that a nearby M-dwarf (less than 900 AU from KIC 8462, is a possible influence in disrupting the system. The comet explanation would be striking if confirmed because we have no other instances of transiting events like these, and we would have found these comets by just happening to see them at the right time in their presumably long and eccentric orbit around the star.
Image: Left: a deep, isolated, asymmetric event in the Kepler data for KIC 8462. The deepest portion of the event is a couple of days long, but the long “tails” extend for over 10 days. Right: a complex series of events. The deepest event extends below 0.8, off the bottom of the figure. After Figure 1 of Boyajian et al. (2015). Credit: Wright et al.
So, despite PR headlines like Strange Star Likely Swarmed by Comets, I think we have to take a more cautious view. We’re dealing with a curious star whose changes in flux we don’t yet understand, and we have candidate theories to explain them. We’re no more ready to declare comets the cause of KIC 8462’s anomalies than we are to confirm alien megastructures. At this point we should leave both natural and artificial causes in the mix and recognize how long it’s going to take to work out a viable solution through careful, unbiased analysis.
The Marengo paper is Marengo, Hulsebus and Willis, ”KIC 8462852: The Infrared Flux,” Astrophysical Journal Letters, Vol. 814, No. 1 (abstract). I write about it this morning only because it is getting so much media attention — more later when I can go through the actual paper. The Boyajian paper is Boyajian et al., “Planet Hunters X. KIC 8462852 – Where’s the flux?” submitted to Monthly Notices of the Royal Astronomical Society (preprint). The Wright paper is Wright et al., “The ? Search for Extraterrestrial Civilizations with Large Energy Supplies. IV. The Signatures and Information Content of Transiting Megastructures,” submitted to The Astrophysical Journal (preprint).
by Paul Gilster | Nov 10, 2015 | Astrobiology and SETI |
Plasma physicist James Benford, CEO of Microwave Sciences, is well known here on Centauri Dreams. Today he is joined by his son Dominic, whose work focuses on the development of ultrasensitive technologies for far-infrared through millimeter-wave astronomy. The younger Dr. Benford is Program Scientist for NASA’s WFIRST mission, which is designed to conduct major surveys in the near-infrared to answer fundamental questions on the nature of dark energy, the distribution of dark matter, the occurrence of planets around other stars, and even to enable the direct imaging of planetary systems. Previously, Dominic was Chief Scientist for the Cosmic Origins Program Office, as well as Deputy Mission Scientist for WISE, the Wide-field Infrared Survey Explorer. In today’s entry, the Benfords look at the SETI Institute’s recent observations of KIC 8462852 and analyze the detectability of power beaming at these distances.
by James and Dominic Benford
The recent report from the SETI Institute of radio observations of the anomalous star KIC 8462852 has immediate implications. That report concluded that, using the Allen Array, no narrowband radio signals were found above a few hundred Janskys in 1 Hz channels and no “wideband” signals above 100 Janskys are seen in 100 kHz channels. This is for observations taking place for 2 weeks, observing half the time. This implies about 180 hours of observations, although only about 1% of the time is spent at any individual frequency.
The purpose of the observations is to see whether the anomalous star is the site of a super-civilization that might be incidentally radiating sufficient power that we can observe, i.e., leakage radiation. They might even be intentionally producing signals for us to detect. The easiest way to do that is to ‘piggyback’, to put a message onto the power beams.
The thresholds they have reported, above which no signals are present, have implications for the presence of power beams in the anomalous star system. Beaming power on astronomical scales has been a frequent topic on this site and it has long been pointed out that the beaming of power for various purposes could be observable at astronomical distances.
The missions suggested for power beaming involve Earth-to-space applications such as launching spacecraft to orbit or raising satellites from a lower orbit to a higher one. Several workers have studied interplanetary missions, meaning space-to-space transfers of cargo. Finally, launch into the outer solar system and for interstellar precursors and ultimately for starships has also been quantified.
We have examined the thresholds in light of concepts proposed for beaming power in and around our solar system. By comparing the reported thresholds set by the SETI Institute, the non-observation of leakage signals at their stated thresholds implies the following:
- Orbit raising missions, which require lower power, are not detectable at the thresholds of the Allen Array.
- Launch from a planetary surface into orbits would be bright enough to be seen by the 100 kHz observations. However, the narrow bandwidth 1 Hz survey would not see them.
- Interplanetary transfers by beam-driven sails should be detectable in their observations, but are not seen. This is for both the narrow 1 Hz and for the “wideband” 100 kHz observations.
- Starships launched by power beams with beamwidths that we happen to fall within would be detectable, but are not seen.
These results must be qualified by noting:
- Power beaming is not an isotropic endeavor, and so the geometry of the transmitter and the intended recipient will produce a conjunction from our point of view only episodically. The observations were conducted for only a limited time and further observations would provide a more stringent constraint.
- Even the “wideband” observation is actually quite narrow compared with the kinds of sources that would be used in power beams, based on our current understanding of microwave physics. For the applications discussed here, the 100 kHz bandwidth observed would be about 10 to 100 millionths of the center frequency of the Beamer. But high-power devices are inherently not designed for such narrow bandwidths.
- The frequencies we would use for power beaming are in the millimeter band, so are outside the microwave range the Allen Array observed.
Therefore the observations by the Allen Array are not sufficiently broad to produce firm conclusions about realistic Beamers.
Readers are encouraged to consult the original paper: Harp et al., “Radio SETI Observations of the Anomalous Star KIC 8462852” (preprint). Previous discussions on this matter can be found in the following reports:
“A Path Forward for Beamed Sails”: https://centauri-dreams.org/?p=20962
“Seeing Alien Power Beaming”: https://centauri-dreams.org/?p=34133
“Microwave Beaming: A Fast Sail to Mars”: https://centauri-dreams.org/?p=1176
“The Case for Beamed Sails”: https://centauri-dreams.org/?p=20924
by Paul Gilster | Nov 6, 2015 | Astrobiology and SETI |
I’ve mentioned before that I think the name ‘Tabby’s Star’ is a wonderful addition to the catalog. It trips off the tongue so much more easily than the tongue-twisting KIC 8462852, and of course it honors the person who brought this unusual object to our attention, Yale University postdoc Tabetha Boyajian. 1480 light years away, Tabby’s Star is an F3 with a difference. It produces light curves showing objects transiting across its face, some of them quite large, and the search is on to find an explanation that fits within the realm of natural causes.
Five articles about Tabby’s Star have already appeared in these pages, with the most likely explanation being some kind of cometary activity, an answer that seems to satisfy no one. We’ve also consulted both Boyajian’s paper on the subject and a paper by Jason Wright and colleagues out of the Glimpsing Heat from Alien Technologies project at Penn State. The light curves we’re looking at do fit the scenario of a ‘Dyson swarm,’ a cluster of power-collecting surfaces that an advanced civilization might create to extract maximum energy from its star.
Thus we can’t rule out the possibility of an extraterrestrial civilization, but no one is claiming that we’ve found one. The point is that in terms of Dysonian SETI, which looks for signs of another civilization’s activity in our astronomical data, Tabby’s Star is the most interesting target we’ve found, so it only makes sense to investigate it. Assuming we do deduce a natural cause for its signature, we will have learned something about an unusual astrophysical process, and that is all to the good. The sole driver here is to investigate and find out what is happening.
The SETI Institute has a natural interest in all this and has been deploying the Allen Telescope Array on Tabby’s Star for more than two weeks. Now we have an update on what the Institute has found. The effort used the Array’s 42 antennas north of San Francisco to look for narrow-band signals (approximately 1 Hz in width) that could be part of an interstellar beacon. In general, SETI at radio and optical frequencies (SETI, that is, of the non-Dysonian kind) looks for this kind of signal, a deliberate attempt by a civilization to declare its presence.
Image: Allen Telescope Array. Credit: Seth Shostak, SETI Institute.
But the SETI Institute also looked for broadband signals, an interesting choice. Here we are asking whether, if there really is an enormous astro-engineering effort going on around this star, there would be spacecraft sent out to service it. Our own investigations into quick travel around the Solar System point to microwave beaming as a feasible solution, the basis for an interplanetary infrastructure. Such intense microwave beams might well be visible, a kind of ‘leakage’ from the civilization’s activities that implies nothing about communication.
Here’s the result, from the SETI Institute’s paper on the work (Jy stands for jansky, a unit of density used in radio astronomy):
The observations presented here indicate no evidence for persistent technology-related signals in the microwave frequency range 1 – 10 GHz with threshold sensitivities of 180 – 300 Jy in a 1 Hz channel for signals with 0.01 – 100 Hz bandwidth, and 100 Jy in a 100 kHz channel from 0.1 – 100 MHz.
So no clear evidence for either kind of signal between 1 and 10 GHz. The paper goes on:
These limits correspond to isotropic radio transmitter powers of 4 – 7 1015 W and 1020 W for the narrowband and moderate band observations. These can be compared with Earth’s strongest transmitters, including the Arecibo Observatory’s planetary radar (2 1013 W EIRP [effective isotropically radiated power]). Clearly, the energy demands for a detectable signal from KIC 8462852 are far higher than this terrestrial example (largely as a consequence of the distance of this star).
What this initial search does is to place upper limits on anomalous emissions from Tabby’s Star. It tells us that we can rule out omnidirectional transmitters broadcasting narrow-band signals at approximately 100 times today’s total terrestrial energy usage, as well as broadband emissions of ten million times terrestrial energy usage. These numbers are high, as the Institute notes, but the paper goes on to say that required transmitter power for narrow-band signals could be reduced considerably if a signal were being beamed in our direction intentionally. It’s worth remembering, too, that any civilization of K2 status (capable of building a Dyson swarm) should have approximately 1027 watts to work with, the energy output of its star.
In any case, says Institute astronomer Seth Shostak, we keep looking:
“The history of astronomy tells us that every time we thought we had found a phenomenon due to the activities of extraterrestrials, we were wrong. But although it’s quite likely that this star’s strange behavior is due to nature, not aliens, it’s only prudent to check such things out.”
Exactly so. The authors add that the star will be the subject of observations for years to come.
Addendum: The Boquete Optical SETI Observatory in Panama is also going to be brought into the search, as per this story.
The paper is Harp et al., “Radio SETI Observations of the Anomalous Star KIC 8462852” (preprint). A SETI Institute news release is also available.
by Paul Gilster | Oct 26, 2015 | Astrobiology and SETI |
Back from my break, I have to explain to those who asked about what exotic destination I was headed for that I didn’t actually go anywhere (the South Pacific will have to wait). The break was from writing Centauri Dreams posts in order to concentrate on some other pressing matters that I had neglected for too long. Happily, I managed to get most of these taken care of, all the while keeping an eye on interstellar news and especially the interesting case of KIC 8462852 (for those just joining us, start with KIC 8462852: Cometary Origin of an Unusual Light Curve? and track the story through the next two entries).
Whatever the explanation for what can only be described as a bizarre light curve from this star, KIC 8462852 is a significant object. While Dysonian SETI has been percolating along, ably studied by projects like Glimpsing Heat from Alien Technologies, the public has continued to see SETI largely in terms of radio and deliberate attempts to communicate. Tabetha Boyajian and team, who produced the first paper on KIC 8462852, have put an end to that, ensuring wide coverage of the object as well as the notion that detection of an extraterrestrial intelligence might occur through observing large artificial structures in our astronomical data.
Meanwhile, the delightful ‘Tabby’s Star’ is beginning to emerge as a replacement for the star’s unwieldy designation. Coverage of the story has been all over the map. The term ‘alien megastructures’ has appeared in various headlines, while others have focused on the natural explanations that could mimic the ETI effect. The tension between natural and artificial is going to persist, and it’s the subject of Jason Wright and colleagues in their recent paper (submitted to The Astrophysical Journal), which asks that kinds of signatures an alien civilization’s activities could create, and what natural phenomenon could explain such signatures.
I think the Wright paper hits exactly the right note in its conclusion:
Invoking alien engineering to explain an anomalous astronomical phenomenon can be a perilous approach to science because it can lead to an “aliens of the gaps” fallacy (as discussed in §2.3 of Wright et al. 2014b) and unfalsifiable hypotheses. The conservative approach is therefore to initially ascribe all anomalies to natural sources, and only entertain the ETI hypothesis in cases where even the most contrived natural explanations fail to adequately explain the data. Nonetheless, invoking the ETI hypothesis can be a perfectly reasonable way to enrich the search space of communication SETI efforts with extraordinary targets, even while natural explanations are pursued.
Just so, and the lengthy discussions in the comments section here on the previous three articles on KIC 8462852 are much in that spirit. We do have the cometary hypothesis suggested in the original Boyajian paper as what had been considered the leading candidate, and Michael Million, a regular in these pages, has pointed to a paper from Jason Barnes (University of Idaho) and colleagues that looks at the phenomenon of gravity darkening and spin-orbit misalignment.
In this scenario, we have a star that is spinning fast enough to become oblate; i.e., it has a larger radius at the equator than it does at the poles, producing higher temperatures and ‘brightening’ at the poles, while the equator is consequently darkened. The transits of a planet in this scenario can produce asymmetrical light curves, a process the Wright paper notes, and one that Million began to discuss as early as the 17th in the comments here. That discussion was picked up in Did the Kepler space telescope discover alien megastructures? The mystery of Tabby’s star solved, which appeared in a blog called Desdemona Despair. The author sees the case as clear-cut: “There are four discrete events in the Kepler data for KIC 8462852, and planetary transits across a gravity-darkened disk are plausible causes for all of them.”
Image: Effects of rapid rotation on the shape of stars. Credit: Ming Zhao (Penn State).
Meanwhile, Centauri Dreams reader Jim Galasyn uncovered a paper by a team led by Shoya Kamiaka (University of Tokyo) studying gravity darkening of the light curves for the transiting system PTFO 8-8695, also studied by Barnes, which involves a ‘hot Jupiter’ orbiting a rapidly rotating pre-main-sequence star. Gravity darkening appears to be very much in play, and we can, as the Desdemona Despair blog does, cite the Barnes paper: “An oblique transit path across a gravity-darkened, oblate star leads to the long transit duration and asymmetric lightcurve evident in the photometric data [for the PTFO 8-8695 system].”
In Wright et al.’s “Signatures and Information Content of Transiting Megastructures” paper, which looks in depth at the natural sources of unusual light curves, these possibilities are discussed in relation to non-spherical stars, and this is worth quoting:
The dominant effect of a non-disk-like stellar aspect on transit light curves is to potentially generate an anomalous transit duration; the effects on ingress and egress shape are small. Gravity darkening, which makes the lower-gravity portions of the stellar disk dimmer than the other parts, can have a large effect on the transit curves of planets and stars with large spin-orbit misalignment, potentially producing transit light curves with large asymmetries and other in-transit features (first seen in the KOI-13 system, Barnes 2009; Barnes et al. 2011).
Another effect of a non-spherical star is to induce precession in an eccentric orbit. Wright also takes note of PTFO 8-8695, “which exhibits asymmetric transits of variable depth, variable duration, and variable in-transit shape.” Here astronomers were helped by the star’s age, which was soundly established by its association with the Orion star forming region. Wright adds that effects of this magnitude would not be expected for older, more slowly rotating objects.
The work on KIC 8462852 continues, and I also need to mention that the Allen Telescope Array focused in on this fascinating target beginning on October 16, even as the American Association of Variable Star Observers (AAVSO) published an Alert Notice requesting that astronomers begin observing the system. For more on this, see SETI Institute Undertakes Search for Alien Signal from Kepler Star KIC 8462852. Universe Today quotes the SETI Institute’s Gerald Harp as saying: “This is a special target. We’re using the scope to look at transmissions that would produce excess power over a range of wavelengths.” I’ll obviously be reporting on the paper that comes out of the ATA search.
The papers discussed today are Wright et al., “The ? Search for Extraterrestrial Civilizations with Large Energy Supplies. IV. The Signatures and Information Content of Transiting Megastructures,” submitted to The Astrophysical Journal (preprint); Barnes et al., “Measurement of Spin-Orbit Misalignment and Nodal Precession for the Planet around Pre-Main-Sequence Star PTFO 8-8695 From Gravity Darkening,” accepted at The Astrophysical Journal (preprint) and Kamiaka et al., “Revisiting a gravity-darkened and precessing planetary system PTFO 8-8695: spin-orbit non-synchronous case,” accepted at Publications of the Astronomical Society of Japan (preprint).
by Paul Gilster | Oct 16, 2015 | Astrobiology and SETI |
I had no idea when the week began that I would be ending it with a third consecutive post on Dysonian SETI, but the recent paper on KIC 8462852 by Tabetha Boyajian and colleagues has forced the issue. My original plan for today was to focus in on Cassini’s work at Enceladus, not only because of the high quality of the imagery but the fact that we’re nearing the end of Cassini’s great run investigating Saturn’s icy moons. Then last night I received Jason Wright’s new paper (thanks Brian McConnell!) and there was more to say about KIC 8462852.
Actually, I’m going to look at Wright’s paper in stages. It was late enough last night that I began reading it that I don’t want to rush a paper that covers a broad discussion of megastructures around other stars and how their particular orbits and properties would make them stand out from exoplanets. But the material in the paper on KIC 8462852 certainly follows up our discussion of the last two days, so I’ll focus on that alone this morning. Next week there will be no Centauri Dreams posts as I take a much needed vacation, but when I return (on October 26), I plan to go through the rest of the Wright paper in closer detail.
A professor of astronomy and astrophysics at Penn State, Wright heads up the Glimpsing Heat from Alien Technologies project that looks for the passive signs of an extraterrestrial civilization rather than direct communications, so the study of large objects around other stars is a natural fit (see Glimpsing Heat from Alien Technologies for background). Luc Arnold suggested in 2005 that large objects could be used as a kind of beacon, announcing a civilization’s presence, but it seems more likely that large collectors of light would be deployed first and foremost as energy collectors. We’ve also seen in these pages that a number of searches have been mounted for the infrared signatures of Dyson spheres and other anomalous objects (see, for example, An Archaeological Approach to SETI).
In the last two days we’ve seen why KIC 8462852 is causing so much interest among the SETI community. The possibility that we are looking at the breakup of a large comet or, indeed, an influx of comets caused by a nearby M-dwarf, is thoroughly discussed in the Boyajian paper. This would be a fascinating find in itself, for we’ve never seen anything quite like it. Indeed, among Kepler’s 156,000 stars, there are no other transiting events that mimic the changes in flux we see around this star. Boyajian and team were also able to confirm that the striking dips in the KIC 8462852 light curve were not the result of instrument-related flaws in the data.
So with an astrophysical origin established, it’s interesting to note that Boyajian’s search of the Kepler dataset produced over 1000 objects with a drop in flux of more than ten percent lasting 1.5 hours or more, with no requirement of periodicity. When the researchers studied them in depth, they found that in every case but one — KIC 8462852 — they were dealing with eclipsing binaries as well as stars with numerous starspots. The object remains unique.
Wright provides an excellent summary of the Boyajian et al. investigations. The Kepler instrument is designed to look for dips in the light curve of a star as it searches for planets. If the frequent dips we see at KIC 8462852 are indeed transits, then we must be looking at quite a few objects. Moreover, the very lack of repetition of the events indicates that we are dealing with objects on long-period orbits. One of the events shows a 22 percent reduction in flux, which Wright points out implies a size around half of the stellar radius (larger if the occulter is not completely opaque). The objects are, as far as we can tell, not spherically symmetric.
Let me quote Wright directly as we proceed:
The complexity of the light curves provide additional constraints: for a star with a uniformly illuminated disk and an occulter with constant shape, the shape of the occulter determines the magnitude of the slope during ingress or egress, but not its sign: a positive slope can only be accomplished by material during third and fourth contact, or by material changing direction multiple times mid-transit (as, for instance, a moon might). The light curves of KIC 8462 clearly show multiple reversals… indicating some material is undergoing egress prior to other material experiencing ingress during a single“event”. This implies either occulters with star-sized gaps, multiple, overlapping transit events, or complex non-Keplerian motion.
Image: Left: a deep, isolated, asymmetric event in the Kepler data for KIC 8462. The deepest portion of the event is a couple of days long, but the long “tails” extend for over 10 days. Right: a complex series of events. The deepest event extends below 0.8, off the bottom of the figure. After Figure 1 of Boyajian et al. (2015). Credit: Wright et al.
A giant ring system? It’s a tempting thought, but the dips in light do not occur symmetrically in time, and as Wright points out, we don’t have an excess at infrared wavelengths that would be consistent with rings or debris disks. Comet fragments remain the most viable explanation, and that nearby M-dwarf (about 885 AU away from KIC 8462852) is certainly a candidate for the kind of system disrupter we are looking for. That leaves the comet explanation as the leading natural solution. A non-natural explanation may raise eyebrows, but as I said yesterday, there is nothing in physics that precludes the existence of other civilizations or of engineering on scales well beyond our own. No one is arguing for anything other than full and impartial analysis that incorporates SETI possibilities.
Jason Wright puts the case this way:
We have in KIC 8462 a system with all of the hallmarks of a Dyson swarm… : aperiodic events of almost arbitrary depth, duration, and complexity. Historically, targeted SETI has followed a reasonable strategy of spending its most intense efforts on the most promising targets. Given this object’s qualitative uniqueness, given that even contrived natural explanations appear inadequate, and given predictions that Kepler would be able to detect large alien megastructures via anomalies like these, we feel [it] is the most promising stellar SETI target discovered to date. We suggest that KIC 8462 warrants significant interest from SETI in addition to traditional astrophysical study, and that searches for similar, less obvious objects in the Kepler data set are a compelling exercise.
As I mentioned, the Wright paper discusses the broader question of how we can distinguish potential artificial megastructures from exoplanet signatures, and also looks at other anomalous objects, like KIC 12557548 and CoRoT-29, whose quirks have been well explained by natural models. I want to go through the rest of this paper when we return to it in about ten days.
The paper is Wright et al., “The ? Search for Extraterrestrial Civilizations with Large Energy Supplies. IV. The Signatures and Information Content of Transiting Megastructures,” submitted to The Astrophysical Journal (preprint).
