Articles & Reviews
Authored by RSF Research Staff
Astronomers Analyze Anomalous Star System for Signs of Advanced Intelligent Civilization.
Evaluating Speculation Over Kepler Space TelescopeData that an Alien Megastructure may be Causing the Weird Spectral Occultation Signal of KIC 8462852.
By: William Brown
Exoplanet Detection; the Kepler Mission
The Kepler Mission is a NASA program to locate and identify habitable planets in our local region of the galaxy. This is done by analyzing the light from distant stars collected by the Kepler Space Telescope. As a planet passes in front of the star it is orbiting, referred to as a transit, the light from the star will undergo a very minute, albeit detectable reduction in luminosity (large planets are also potentially identifiable by the gravitational “wobble” they cause in the parent star).
This slight dip in the star’s luminosity is an identifiable signal of a planetary transit, generating a light curve — essentially a graph charting the momentary reduction in starlight over time. Much information can be gleaned from analysis of the light curve, such as the physical size of the transiting exoplanet, the periodicity of transit, and hence the location of the planet around the star -- a measure important for determining if the planet is within the so called “habitable zone” and the planet’s density (is it a solid “rocky” planet or something of a lower density).
Other signals are detectable as well, such as those caused by stellar flares, star spots, dusty planetary rings, exocomets, or as we will see, possible artificial structures. These are detectable largely because of the shape of the light curve produced. Whereas a uniformly round planet will produce a smooth and consistent “bell-shaped” dip in the light curve, other events will produce different or irregular signatures.
Identifying Potentially Habitable Planetary Systems
To date, using the Kepler Space Telescope NASA has identified 3,488 confirmed exoplanets, with 4,496 potential candidates ; and, excitingly, at least 52 potentially habitable Earth-sized planets . This of course should not be surprising, given that even conservative estimates based on Kepler survey data predicts at least a billion earth-like, habitable planets in our Milky Way galaxy alone. Indeed, data from exploratory programs such as the Kepler mission have shown that planetary systems are abundant (an earth-sized planet has even been spotted around our nearest neighbor, Alpha Centauri B).
Could an Enigmatic Signal be a Sign of an Advanced Extrasolar Civilization?
Given the abundance of habitable planets in our galaxy, shouldn’t we be observing signs of life as we begin to catalog and observe these numerous planetary systems (excluding the fact that evidence for such activity is abundant right here on Earth: Press Conference Former Air Force Officers)? For instance, the same techniques used to identify planets transiting in front of their parent stars can be used to identify artificial structures, by the irregular spectral occultation pattern they should produce. Imagine an alien civilization that is high up on the Kardashev scale, while they will almost definitely utilize the nearly limitless energy of the vacuum to power their advanced civilization, with such technological sophistication and abundant energy utilization they may undertake to construct stellar-sized structures.
Named KIC 8462852, a main-sequence star located approximately 1,500 light years from Earth in the constellation Cygnus, the light curve from the star has nearly inexplicable transit signals. In a paper submitted to the journal Monthly Notices of the Royal Astronomical Society, astronomers, including citizen scientists from the Planet Hunters crowdsourcing program, report: “Over the duration of the Kepler mission, KIC 8462852 was observed to undergo irregularly shaped, aperiodic dips in flux down to below the 20 percent level.”Such megastructures would produce an irregular drop in the light intensity of a star they are situated around, producing an identifiable signature of intelligent activity. Remarkably, astronomers are analyzing an enigmatic signal from a star in the Kepler data – a signal that seems to defy most natural-based explanations.
Kepler has collected data on this star steadily for four years (informally known as Tabby’s Star). Upon identification of the extremely unusual and inexplicable light curve of KIC 8462852 researchers proceeded with further observation, using telescopes such as that on Mount Mauna Kea in Hawai’i that can identify protoplanetary discs through their microwave (excess IR) signal -- such research has shown that there is no evidence for a planetary disc or self-ejected material (as occurs in Be stars) that could be producing the KIC 8462852 signal.
Detailed analysis shows that the anomalous light curve is not instrumental error. Kepler isn’t seeing things; the signal is real.
“We’d never seen anything like this star,” Tabetha Boyajian, a postdoctorate researcher at Yale University and lead author, told The Atlantic. “It was really weird. We thought it might be bad data or movement on the spacecraft, but everything checked out.”
“It looked like the kind of thing you might expect an alien civilization to build.”
Advanced algorithms are utilized to automatically identify many of the planetary transits from the Kepler data, however at present no software is quite as sophisticated as the pattern recognition capabilities of humans. As such, the Planet Hunters is a “crowd-sourcing” project wherein volunteers identify transits in Kepler’s stars. “This is a huge quantity of data, from over 150,000 stars in Kepler’s original field of view, and you can’t beat the human eye when identifying a true dip in starlight brightness.” The Planet Hunters described KIC 8462852 as “bizarre,” “interesting” and a “giant transit.” Indeed, the signal is highly puzzling, especially when attempting to explain it in terms of naturally occurring phenomena.
While many astronomers are cautioning that a more naturalistic explanation is probably the most likely, they are certainly not ruling out the possibility of an alien megastructure because of the anomalous nature of the signal. At one point, Michio Kaku spoke on CBSN where he outlined the process of elimination that led many serious astronomers to posit the possibility that the signal is the result of an alien megastructure.
While such a scenario may sound bizarre to many, it is not as unlikely a possibility as might be naively presumed. Humanity itself is observational evidence that the universe develops into intelligent life capable of technologically sophisticated civilizations. Given the known preponderance of habitable Earth-like planets, by what reasoning would we expect there not to be intelligent civilizations within the galaxy (and certainly in the hundreds of billions of other galaxies of the Universe)? This is well known to many scientists, and certainly to astronomers, which is one of the reasons some are not ruling out the possibility that the strange signal from KIC 8462852 is of intelligent origin -- an artificial megastructure.
Accordingly, researchers have positioned the Allen Telescope Array (ATA), a system of radio dishes about 300 miles (483 kilometers) northeast of San Francisco, to attempt detection of radio signals of unnatural origin coming from the unusual star system – another means of detecting intelligent extraterrestrial life. There have been no unusual signals detected in the frequency ranges thought most likely to be indicative of intelligent origin, 1-10 GHz. However, any signals produced in these frequency ranges are only the result of specific activity, such as intentionally beaming a signal directly at Earth, so no conclusions can be drawn from the lack of a signal detected in these ranges.
"So history suggests we're going to find an explanation for this that doesn't involve Klingons, if you will," the senior astronomer of SETI, Seth Shostak said of the KIC 8462852 mystery.
“But until such an explanation is found, the intelligent-aliens hypothesis will still be on the table, even if the ATA and other instruments like it come up empty. The lack of a detectable signal, after all, does not establish that KIC 8462852 is a lifeless system.”
Exploring More Prosaic Explanations
Scientists, as an inherently conservative and skeptical group, are exploring any potential explanation that can rule out the KIC 8462852 signal as being the result of intelligent activity by an advanced alien civilization. A few recent scientific papers have offered new theories about what may be producing the dip. One new idea is that an internal process within the star may be causing its global magnetic field to flip, leading to a change in flux . Another research paper suggests that, rather than comets passing in front of the star as earlier hypothesized, the lower fluxes are caused by dust clouds associated with massive parent bodies orbiting the host star .
Apart from thousands of ‘regular’ exoplanet candidates, Kepler satellite has discovered a few stars exhibiting peculiar eclipse-like events. They are most probably caused by disintegrating bodies transiting in front of the star. However, the nature of the bodies and obscuration events, such as those observed in KIC8462852, remain mysterious. A swarm of comets or artificial alien mega-structures have been proposed as an explanation for the latter object.
We explore the possibility that such eclipses are caused by the dust clouds associated with massive parent bodies orbiting the host star. We assumed a massive object and a simple model of the dust cloud surrounding the object. Then, we used the numerical integration to simulate the evolution of the cloud, its parent body, and resulting light-curves as they orbit and transit the star.
We found that it is possible to reproduce the basic features in the light-curve of KIC8462852 with only four objects enshrouded in dust clouds. The fact that they are all on similar orbits and that such models require only a handful of free parameters provides additional support for this hypothesis.
This model provides an alternative to the comet scenario. With such physical models at hand, at present, there is no need to invoke alien mega-structures for an explanation of these light-curves. 
Even so, with the data at hand, there are numerous problems with naturalistic explanations, such as the lack of detectable signs of large cometary bodies (analogous to the asteroid belt in our solar system). Even a one-off chance collision between recently orbitally destabilized planets does not garner much support from the data as the observed reductions in luminosity appear to be aperiodic (within the ~1,600 day observational period none of the signals appear to repeat).
However, the star will need to be observed for a longer period of time, another 1,600 days to see if any of the signals repeat. This will be very telling, for instance if there is a reduction in the signal it might indicate that the occultation is from cometary or planetesimal debris that is dissipating (keep in mind that this debris would have to be comparable in size to the star in order to produce the approximate 20% reduction in luminosity that is observed, Jupiter-sized planets by comparison do not even produce a 1% drop in the luminosity upon transit).
“We describe various scenarios to explain the mysterious events in the Kepler light curve, most of which have problems explaining the data in hand.”
One thing is certain, KIC 8462852 has piqued the interest of serious scientists and the general public alike, and many resources are being devoted to determining the nature of the anomalous signal. The detection and verification of an advanced extraterrestrial civilization will be no small event – it will mark one of the major findings of humanity and forever change the way we view and think about the cosmos.
More to Explore
 Avalanche Statistics Identify Intrinsic Stellar Processes near Criticality in KIC 8462852 -- https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.117.261101
 Mysterious eclipses in the light curve of KIC8462852: a possible
explanation -- https://arxiv.org/pdf/1612.06121.pdf