The alien star probably has a band of eccentric comets. (NASA/JPL-Caltech) 
 
 If you were still holding out hope for aliens hanging out around KIC 8462852, I've got some bad news for you. Researchers at Iowa State University think they've found an explanation for the star's weird behavior. Spoiler alert: It's not aliens. 
 
 In October, scientists spotted a distant star that was blinking in an unusual fashion. Unlike most of the stars spotted by the Kepler telescope — which keeps an eye on fluctuations in light to help detect planets passing in front of distant suns — this one was dimming irregularly. 
 
 [Why NASA’s top scientist is sure that we’ll find signs of alien life in the next decade] 
 
 Experts pointed out that the star's light was winking in and out of view in a way that could presumably possibly be the result of some massive orbiting alien structure. The scientists didn't really think that our space telescopes had caught sight of an "alien megastructure," but there's no harm in hoping. 
 
 Since then, the Search for Extraterrestrial Intelligence (SETI) institute has turned its radio telescopes to the strange star — and they haven't heard any of the radio signals we'd expect from the goings-on of an intelligent civilization. 
 
 [Scientists caught a new planet forming for the first time ever] 
 
 A cluster of comets had been floated as one possible explanation. Now, in a study published in the Astrophysical Journal Letters, Massimo Marengo of Iowa State University (along with his doctoral student Alan Hulsebus and former student Sarah Willis, now a researcher at the Massachusetts Institute of Technology’s Lincoln Laboratory) suggests it's the most likely one. 
 
 Marengo and Co.'s work didn't actually rule out an alien megastructure, but it did rule out other, more likely explanations — like massive planetary or asteroid collisions. Looking at the star in infrared light didn't reveal the hot dust one would expect from such violent activity. That makes the most likely (non-alien) explanation a set of cold comets — ones that have been orbiting the planet for a while, causing different levels of dimming based on their assorted sizes and transit periods. 
 
 "This is a very strange star," Marengo said in a statement. "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.'” 
 
 Pulsars turned out to be very weird — but they weren't aliens, either. 
 
 "We may not know yet what's going on around this star,” Marengo said. “But that's what makes it so interesting." 
 
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 Mars might get rings just like Saturn’s one day ||||| AMES, Iowa – Was it a catastrophic collision in the star’s asteroid belt? A giant impact that disrupted a nearby planet? A dusty cloud of rock and debris? A family of comets breaking apart? Or was it alien megastructures built to harvest the star’s energy? 
 
 Just what caused the mysterious dimming of star KIC 8462852? 
 
 Massimo Marengo, an Iowa State University associate professor of physics and astronomy, wondered when he saw all the buzz about the mysterious star found by citizen scientists on the Planet Hunters website. 
 
 Those citizen scientists were highlighting measurements of star brightness recorded by NASA’s Kepler spacecraft. Tiny dips in a star’s brightness can indicate a planet is passing in front of the star. That’s how Kepler astronomers – and citizen scientists using the internet to help analyze the light curves of stars – are looking for planets. 
 
 But this star had deep dips in brightness – up to 22 percent. The star’s brightness also changed irregularly, sometimes for days and even months at a time. A search of the 150,000-plus stars in Kepler’s database found nothing like this. 
 
 So Marengo and two other astronomers decided to take a close look at the star using data taken with the Infrared Array Camera of NASA’s Spitzer Space Telescope. They report their findings in a paper recently published online by The Astrophysical Journal Letters. 
 
 Their conclusion? 
 
 “The scenario in which the dimming in the KIC 8462852 light curve were caused by the destruction of a family of comets remains the preferred explanation …,” wrote the three – Marengo; Alan Hulsebus, an Iowa State doctoral student; and Sarah Willis, a former Iowa State graduate student now with the Massachusetts Institute of Technology’s Lincoln Laboratory. 
 
 Questions about the star were launched last month when a research team led by Tabetha Boyajian of Yale University reported on the star in the Monthly Notices of the Royal Astronomical Society. The astronomers reported how citizen scientists tagged the star’s deep and irregular dips in brightness as “bizarre” and “interesting.” 
 
 Boyajian and the other researchers looked at the data and investigated several possible causes. They wrote the “most promising theory” was a barrage of crumbling comets passing in front of the star. 
 
 In a subsequent paper submitted to The Astrophysical Journal, Jason Wright and colleagues at Penn State University speculated about other causes, including alien megastructures built to harvest energy while orbiting the star. 
 
 When the Iowa State astronomers studied the star with Spitzer infrared data from January 2015 – two years after the Kepler measurements – Marengo said they didn’t see much. If there had been some kind of catastrophe near the star, he said there would be a lot of dust and debris. And that would show up as extra infrared emissions. 
 
 Marengo said the study looked at two different infrared wavelengths: the shorter was consistent with a typical star and the longer showed some infrared emissions, but not enough to reach a detection threshold. The astronomers concluded there were no excess infrared emissions and therefore no sign of an asteroid belt collision, a giant impact on a planet or a dusty cloud of rock and debris. 
 
 So Marengo and his colleagues say the destruction of a family of comets near the star is the most likely explanation for the mysterious dimming. The comet fragments coming in rapidly at a steep, elliptical orbit could create a big debris cloud that could dim the star. Then the cloud would move off, restoring the star’s brightness and leaving no trace of excess infrared light. 
 
 And the alien megastructure theory? 
 
 “We didn’t look for that,” Marengo said. “We can’t really say it is, or is not. But what the star is doing is very strange. It’s interesting when you have phenomena like that – typically it means there’s some new physical explanation or a new concept to be discovered.” ||||| A star called KIC 8462852 has been in the news recently for unexplained and bizarre behavior. NASA's Kepler mission had monitored the star for four years, observing two unusual incidents, in 2011 and 2013, when the star's light dimmed in dramatic, never-before-seen ways. Something had passed in front of the star and blocked its light, but what? 
 
 Scientists first reported the findings in September, suggesting a family of comets as the most likely explanation. Other cited causes included fragments of planets and asteroids. 
 
 A new study using data from NASA's Spitzer Space Telescope addresses the mystery, finding more evidence for the scenario involving a swarm of comets. The study, led by Massimo Marengo of Iowa State University, Ames, is accepted for publication in the Astrophysical Journal Letters. 
 
 One way to learn more about the star is to study it in infrared light. Kepler had observed it in visible light. If a planetary impact, or a collision amongst asteroids, were behind the mystery of KIC 8462852, then there should be an excess of infrared light around the star. Dusty, ground-up bits of rock would be at the right temperature to glow at infrared wavelengths. 
 
 At first, researchers tried to look for infrared light using NASA's Wide-Field Infrared Survey Explorer, or WISE, and found none. But those observations were taken in 2010, before the strange events seen by Kepler -- and before any collisions would have kicked up dust. 
 
 To search for infrared light that might have been generated after the oddball events, researchers turned to Spitzer, which, like WISE, also detects infrared light. Spitzer just happened to observe KIC 8462852 more recently in 2015. 
 
 "Spitzer has observed all of the hundreds of thousands of stars where Kepler hunted for planets, in the hope of finding infrared emission from circumstellar dust," said Michael Werner, the Spitzer project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California, and the lead investigator of that particular Spitzer/Kepler observing program. 
 
 But, like WISE, Spitzer did not find any significant excess of infrared light from warm dust. That makes theories of rocky smashups very unlikely, and favors the idea that cold comets are responsible. It's possible that a family of comets is traveling on a very long, eccentric orbit around the star. At the head of the pack would be a very large comet, which would have blocked the star's light in 2011, as noted by Kepler. Later, in 2013, the rest of the comet family, a band of varied fragments lagging behind, would have passed in front of the star and again blocked its light. 
 
 By the time Spitzer observed the star in 2015, those comets would be farther away, having continued on their long journey around the star. They would not leave any infrared signatures that could be detected. 
 
 According to Marengo, more observations are needed to help settle the case of KIC 8462852. 
 
 "This is a very strange star," he 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.'" 
 
 In the end, the LGM-1 signals turned out to be a natural phenomenon. 
 
 "We may not know yet what's going on around this star," Marengo observed. "But that's what makes it so interesting." 
 
 Ames manages the Kepler and K2 missions for NASA's Science Mission Directorate. JPL managed Kepler mission development. Ball Aerospace & Technologies Corp. operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder. 
 
 JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. 
 
 Caltech manages JPL for NASA. 
 
 For more information about Kepler and Spitzer, respectively, visit: 
 
 http://www.nasa.gov/kepler 
 
 http://kepler.nasa.gov 
 
 http://www.nasa.gov/spitzer 
 
 http://www.spitzer.caltech.edu 
 
 News Media Contact 
 
 Whitney ClavinJet Propulsion Laboratory, Pasadena, California818-354-4673whitney.clavin@jpl.nasa.govMichele JohnsonAmes Research Center, Moffett Field, Calif.650-604-6982michele.johnson@nasa.gov2015-357 ||||| In one of the most unusual -- and highly unlikely -- first-contact scenarios, aliens would be able to recognize us by the level of greenhouse gas emissions we pump into our atmosphere. Not only that, according to a hypothesis put forward by researchers affiliated with NASA and Pennsylvania State University (though not directly tied with either institution), but aliens may use that as cause to wipe out the human race. In this bizarre set of circumstance, aliens view human advancement as a destructive force spiraling out of control. To avoid the threat of a future adversary, extraterrestrials clear out the competition. BLOG: TO SAVE THE GALAXY, DESTROY HUMANITY 
 
 Humans may rely primarily on fossil fuels as their primary means of energy, but that doesn't mean extraterrestrials in a far off civilization have the same power source. Solar power could be one option, though not quite with the same black panels we use on Earth. A super civilization could even tap into a black hole to meet its energy needs. If aliens are tapping to these cosmic bodies, that should make them all the more detectable from Earth. How would we know whether an alien race was relying on a black hole as a source of energy? As Discovery News' Ray Villard explains: "Tell-tale evidence would come from measurements that showed the black hole weighed less than 3.5 solar masses. That's the minimum mass for crushing matter into a black hole via a supernova core-collapse." 
 
 Have aliens already stopped by for a visit, even though we weren't at the door to meet them? If they have, shouldn't they have left something behind? An artificial object of alien origin could be lurking in our solar system without our knowledge. As Discovery News' Ray Villard explains: "In a paper published in the 1960s, Carl Sagan, using the Drake Equation, statistically estimated that Earth might be visited every few tens of thousands of years by an extraterrestrial civilization." Further out beyond our solar system, aliens may have left what essentially amount to interstellar billboards large enough to be seen by, say, a planet-hunting telescope like Kepler. These last two scenarios, of course, envision an extremely technologically advanced civilization well beyond the engineering capabilities of humankind. At the same time, humans have sent spacecraft beyond the solar system, including Pioneer 10 and 11 as well as Voyager 1 and 2. All of these spacecraft are equipped with what are essentially calling cards for the human race -- small plaques in the case of the Pioneer spacecraft and golden records for the Voyager spacecraft (seen here). SCIENCE CHANNEL: Top 10 Alien Sightings 
 
 For more than 25 years, the SETI Institute has been scouring the skies for signs of alien life. However, long before the institute was established, scientists have tried to catch a communication signal from another world. Scientists looking for alien signals use a combination of optical and radio telescopes, such as the one seen here. Dropping in on a signal without knowing the source of the communication is the tricky part, however, and researchers narrow down their search by targeting specific kinds of stars. With their citizen science program, SETI@home, the institute has enlisted three million additional observers analyzing data for traces of an alien signal. BLOG: MAN LOOKS FOR ALIENS, LOSES JOB 
 
 If aliens are looking for us, they're scanning the same, vast, dark and mostly empty expanse of space that we are. It's a good thing then that we're leaving the lights on to make it easier to find us. According to Abraham Loeb, of Harvard University and Edwin Turner, from Princeton University, by scanning the skies for artificial illumination as opposed to naturally occurring light sources, both human and extraterrestrial astronomers might be able to find signs of life. Existing telescopes would be able to see a city the size of Tokyo as far as the edges of our solar system. BLOG: CITY LIGHTS COULD REVEAL ET 
 
 Before we can began to search the skies, we have to start by narrowing down our options. Sticking within our own galaxy is a good start, since we're more likely to spot a neighbor closer to us than one further away. Astronomers may also elect to focus their attention on stars closer to the center of the Milky Way, where 90 percent of its stars are clustered. Furthermore, the stars here are a billion times older than the sun, giving life more time to develop biologically and technologically. Many stars are unsuitable for nurturing life, and even stars that do have the appropriate "spectral type" may host exoplanets inhospitable to life due to their location relative to their parent star, size or composition. These criteria would not only help us find aliens, but also help them find us. After all, Earth would stand out as a hospitable planet, according to a paper published in 2007 in Astrophysical Journal. 
 
 Despite the occasional report of an extraterrestrial sighting, be it through a microscope revealing curious shapes in a meteorite or a photo of wispy lights taken at the blurry end of a camera lens, aliens have yet to make contact with humans. Even the White House yesterday put out a statement declaring that the federal government "has no evidence that any life exists outside our planet, or that an extraterrestrial presence has contacted or engaged any member of the human race." Humans may not yet have encountered life outside of our planet, but many scientists see it as an inevitability. In 1960, astronomer Frank Drake came up with the now eponymous equation which provided an estimate of the number of civilizations in our galaxy. Although scientists continue to debate the application of his formula as well as alternatives, Drake's own solution to the equation is 10,000 civilizations, suggesting intelligent, technologically advanced life outside our planet is common. How these different civilizations, including our own, find each other is an important question for anyone here on Earth looking for extraterrestrials. Explore how aliens might stumble upon our planet -- and how we might actually spot them first. BLOG: ARE UFOS ALIEN? NO! 
 
 Has Kepler revealed evidence for a technologically advanced civilization around a star only 1500 light-years away? That's one exciting, if unlikely, interpretation of recent transit data. 
 
 NASA’s Kepler Space Telescope is tasked with finding small, rocky worlds orbiting distant stars. However, exoplanets aren’t the only thing Kepler can detect — stellar flares, star spots and dusty planetary rings can also pop up in the mission’s observations. 
 
 But there’s also been speculation that Kepler may have the ability to detect more than natural phenomena; if they’re out there, Kepler may also detect the signature of artificial structures orbiting other stars. Imagine an advanced civilization that’s well up on the Kardashev scale and has the ability to harness energy directly from its star. This hypothetical alien civilization may want to construct vast megastructures, like supersized solar arrays in orbit around their host star, that could be so big that they blot out a sizable fraction of starlight as they pass in front. 
 
 13 Ways to Hunt Intelligent Aliens 
 
 When Kepler detects an exoplanet, it does so by sensing the very slight dip in starlight from a given star. The premise is simple: an exoplanet orbits in front of star (known as a “transit”), Kepler detects a slight dimming of starlight and creates a “lightcurve” — basically a graph charting the dip in starlight over time. Much information can be gleaned from the lightcurve, such as the physical size of the transiting exoplanet. But it can also deduce the exoplanet’s shape. 
 
 Normally the shape of an exoplanet isn’t particularly surprising because it’s, well, planet-shaped. It’s round. The physics of planetary formation dictate that a planetary body above a certain mass will be governed by hydrostatic equilibrium. But say if Kepler detects something that isn’t round. Well, that’s when things can get a bit weird. 
 
 For the most part, any dip in star brightness can be attributed to some kind of natural phenomenon. But what if all possibilities are accounted for and only one scenario is left? What if that scenario is this object appears to be artificial? In other words, what if it’s alien? 
 
 In a chilling article written by Ross Andersen of The Atlantic, at first glance, it seems we may be at this incredible juncture. 
 
 GALLERY: How Aliens Can Find Us (and Vice Versa) 
 
 A star, named KIC 8462852, has been found with a highly curious transit signal. 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.” 
 
 The research paper is thorough, describing the phenomenon, pointing out that this star is unique - we’ve seen nothing like it. Kepler has collected data on this star steadily for four years. It’s 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.” 
 
 The Planet Hunters volunteers are depended on to seek out transits in Kepler’s stars in the direction of the constellation Cygnus. 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.” They’re not wrong. 
 
 ANALYSIS: Could Kepler Detect Alien Artifacts? 
 
 Follow-up studies focus on two interesting transit events at KIC 8462852, one that was detected between days 788 and 795 of the Kepler mission and between days 1510 to 1570. The researchers have tagged these events as D800 and D1500 respectively. 
 
 The D800 event appears to have been a single transit causing a star brightness drop-off of 15 percent, whereas D1500 was a burst of several transits, possibly indicating a clump of different objects, forcing a brightness dip of up to 22 percent. To cause such dips in brightness, these transiting objects must be huge. 
 
 The transit data for KIC 8462852, featuring the obvious transit features D800 and D1500. Boyajian et al. 
 
 The researchers worked through every known possibility, but each solution presented a new problem. For example, they investigated the possibility of some kind of circumstellar disk of dust. However, after looking for the infrared signal associated with these disks, no such signal could be seen. 
 
 Also, the star is a mature F-type star, approximately 1.5 times the size of our sun. Circumstellar disks are usually found around young stars. 
 
 ANALYSIS: Alien ‘Star Engine’ Detectable in Exoplanet Data? 
 
 The researchers also investigated the possibility of a huge planetary collision: could the debris from this smashup be creating this strange signal? The likelihood of us seeing a planetary collision is extremely low. There is no evidence in data taken by NASA’s Wide-field Infrared Survey Explorer (WISE) that a collision happened, creating a very tiny window of opportunity between WISE’s mission end and the beginning of Kepler’s mission (of a few years) for an astronomically unlikely cosmic event like this to occur. 
 
 The only natural explanation favored by the researchers seems to focus on an intervening clump of exocomets. 
 
 “One way we imagine such a barrage of comets could be triggered is by the passage of a field star through the system,” write the researchers. 
 
 Indeed, they argue, there’s a nearby star that might have tidally disturbed otherwise dormant comets in the outermost regions of the KIC 8462852 star system. This small star is located around 1,000 AU from KIC 8462852 and whether it’s a binary partner or an interstellar visitor, its presence may have caused some cometary turmoil. Like the other scenarios, however, the exocomet explanation still falls short of being fully satisfactory. 
 
 This research paper focuses only on natural and known possible causes of the mystery transit events around KIC 8462852. A second paper is currently being drafted to investigate a completely different transit scenario that focuses around the possibility of a mega-engineering project created by an advanced alien civilization. 
 
 ANALYSIS: Our Super-Advanced Alien Neighbors are Missing 
 
 This may sound like science fiction, but our galaxy has existed for over 13 billion years, it’s not such a stretch of the imagination to think that an alien civilization may be out there and evolved to the point where they can build megastructures around stars. 
 
 “Aliens should always be the very last hypothesis you consider, but this looked like something you would expect an alien civilization to build,” Jason Wright, an astronomer from Penn State University, told The Atlantic. 
 
 Indeed, hunting down huge structures that obscure the light from stars is no new thing. The Search for Extraterrestrial Technology (SETT) is one such project that does just this. Only recently, a survey of the local universe focused on the hope of detecting the waste heat generated by a technologically advanced civilization, specifically a Type II Kardashev civilization. 
 
 On the Kardashev scale, a Type II civilization has the ability to utilize all the available energy radiating from a star. Using a vast shell or series of rings surrounding a star, a Dyson sphere-like structure may be constructed. This has the effect of blotting out the star from view in visible wavelengths, but once the solar energy has been used by the alien civilization, the energy is shifted to longer wavelengths and likely lost as infrared radiation. 
 
 ANALYSIS: Could We Detect an Alien Civilization’s Waste Heat? 
 
 This recent search for aliens’ waste heat drew a blank, reaching the conclusion that as there appears to be no alien intelligence cocooning stars to harvest their heat, there’s likely no Type II civilization nearby. 
 
 But as KIC 8462852 is showing us, there may be something else out there — possibly an alien intelligence that is well on its way to becoming a Type II civilization, which is setting up some kind of artificial structure around its star. 
 
 Of course, these mystery transit events are nowhere near “proof” of an alien civilization. In fact, it’s barely evidence and a lot more work needs to be done. 
 
 The next step is to point a radio antenna at KIC 8462852, just to see whether the system is generating any artificial radio signals that could indicate the presence of something we’d define as “intelligent.” Boyajian and Wright have now teamed up with Andrew Siemion, the Director of the SETI Research Center at the University of California, Berkeley, to get a radio telescope to listen into the star and if they detect an artificial signal, they will request time on the Very Large Array (VLA) to deduce whether any radio signals from that star are the chatter of an alien civilization. 
 
 It might be a long shot, and the phenomenon is more likely a clump of comets or some other natural phenomenon that we haven’t accounted for blocking star light from view, but it’s worth investigating, especially if there really is some kind of alien intelligence building structures, or perhaps, ancient structures of a civilization long-gone, around a star only 1,500 light-years away from Earth.
– KIC 8462852 is an odd and fascinating star, astronomers say—but it probably isn't host to an "alien megastructure," as some researchers suggested as a longshot possibility when the star and its highly unusual dimming pattern first came to attention. Instead, Iowa State University researchers who studied infrared light emitted by the star in the Cygnus constellation believe that the likeliest explanation is the "destruction of a family of comets," which caused dramatic changes in the light observed by the Kepler telescope as the fragments and debris cloud moved past the star in a long, elliptical orbit. The team didn't actually look for alien structures, but they were able to use the infrared data to rule out possibilities including a massive collision nearby, the Washington Post reports. The SETI Institute has also investigated the star, and found no trace of the radio signals that would suggest extraterrestrial technology was present, CNN reports. But even without aliens, nothing like what is happening around KIC 8462852 has ever been seen before and astronomers want to learn more. "This is a very strange star," lead researcher Massimo Marengo said in a NASA press release. "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," he added "But that's what makes it so interesting." (Closer to home, astronomers have discovered that Mars is destroying its own moon.)