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All Rights Reserved Subscribe | Sign In BETA This is a BETA experience. You may opt-out by clicking here More From Forbes Jan 29, 2021,02:00am EST Ask Ethan: Could We Be Living In A Steady-State Universe? Jan 28, 2021,10:00pm EST You Should Know About The Weird 'Sextuple' Star System Just Found By NASA Where Six Suns Eclipse Each Other Jan 28, 2021,05:00pm EST Another Close Call: U.S. Weather Radars Are Vulnerable To Destructive Storms Jan 28, 2021,02:50pm EST Mysterious Deaths At Dyatlov Pass May Finally Be Solved After 62 Years Thanks To A Computer Simulation Jan 28, 2021,02:39pm EST Dogs Learn Words Quickly, But Only After Playing With Toys Jan 28, 2021,02:00pm EST 8 Insights From A 160 Year Study On Artists, Musicians, Actors And Authors Jan 28, 2021,09:00am EST New Science: Why Our Brains Spend 50% Of The Time Mind-Wandering Jan 27, 2021,10:00pm EST The 3 Things We Need To Do To Find Intelligent Life On Nearby Alien Planets Jan 27, 2021,06:09pm EST As Global Covid Cases Surpass 100 Million, A New Player Enters The game: Hope Edit Story Jan 28, 2021,02:00am EST| The Uncensored Guide To 'Oumuamua, Aliens, And That Harvard Astronomer Starts With A Bang Ethan SiegelSenior Contributor Starts With A Bang Contributor Group Opinions expressed by Forbes Contributors are their own. Science The Universe is out there, waiting for you to discover it. * Share to Facebook * Share to Twitter * Share to Linkedin This very deep combined image shows the interstellar object 'Oumuamua. This very deep combined image shows the interstellar object 'Oumuamua at the centre of the picture. ... [+] It is surrounded by the trails of faint stars that are smeared as the telescopes tracked the moving interloper. This image was created by combining multiple images from ESO's Very Large Telescope as well as the Gemini South Telescope. The object is marked with a blue circle and appears to be a point source, with no surrounding dust. ESO/K. Meech et al. In 2017, an astronomical event occurred that was unlike any other: for the first time, we observed an object that we are certain originated from beyond our Solar System. Initially, its origin was a hot topic of contention. Was it a comet, albeit one with an unusual orbit? Was it an asteroid, on account of the fact that it didn't develop a notable tail? Or was it something entirely unique: a visitor from elsewhere in the galaxy, and the first example of an entirely new class of object? Named 'Oumuamua -- Hawaiian for "messenger from the distant past" -- it became a spectacular discovery, and a window into what objects exist throughout interstellar space. But one scientist, enamored with his own hypothesis and ignoring the large amounts of research done by other professionals who specialize in this particular field, has embarked on a public crusade to convince the world of the most far-fetched explanation for this natural phenomenon: aliens. For the better part of the past four years, Harvard astronomer Avi Loeb has appeared all over the media to gather public support for an idea that absolutely defies the scientific evidence. Contrary to the narratives you'll find elsewhere, including in Loeb's new book, Extraterrestrial: The First Sign of Life Beyond Earth, this is not a possibility worth taking seriously as a scientist. A straightforward look at the evidence shows us why. The orbits of planets, comets, and more are governed by the law of universal gravitation. The orbits of the planets and comets, among other celestial objects, are governed by the laws of ... [+] universal gravitation. The objects that are gravitationally bound to our Sun all have an eccentricity of less than 1, while those that become unbound will have their eccentricities cross over to be greater than 1. An eccentricity over 1.06 or so indicates an origin from beyond our Solar System. Kay Gibson, Ball Aerospace & Technologies Corp According to the law of gravity, every object that's gravitationally influenced by the Sun will take one of four orbital paths: * circular, with an eccentricity of 0, * elliptical, with an eccentricity greater than 0 but less than 1, * parabolic, with an eccentricity exactly equal to 1, * or hyperbolic, with an eccentricity greater than 1. Before 2017, we had seen a few objects with eccentricities that were 1 or greater, but only by a tiny amount: values like 1.0001 or so. Even with a kick from Jupiter, the fastest-moving Solar System object ever seen only reached an eccentricity of 1.06. This corresponds to an object escaping the Sun's gravity, but only by a tiny amount. By the time an object like this makes it to interstellar space, it will only have a speed of ~1 km/s or less. MORE FOR YOU A 10 Billion-Year-Old 'Super-Earth' Has Been Found In Our Galaxy That Suggests Ancient Lifeforms Are Possible This Week's 'Wolf Moon' Kicks-Off A Year Of Three 'Supermoons,' A 'Blue Moon' And A 'Blood Moon' Mysterious Deaths At Dyatlov Pass May Finally Be Solved After 62 Years Thanks To A Computer Simulation But for 'Oumuamua, it was an entirely different story. It immediately became clear that this object was something special, as its eccentricity was about 1.2, corresponding to an escape speed that was more like 26 km/s. It was the fastest-moving naturally occurring object to leave the Solar System with such a speed, a phenomenon that would be impossible from even an ideal gravitational interaction with a planet like Jupiter or Neptune, which weren't in the path of 'Oumuamua at any point. Clearly, it must have originated from outside of our neighborhood. The Pan-STARRS1 Observatory atop Haleakala Maui at sunset. The Pan-STARRS1 Observatory atop Haleakala Maui at sunset. By scanning the entire visible sky to ... [+] shallow depth but frequently, Pan-STARRS can automatically find any moving object within our Solar System above a specific apparent brightness. The discovery of 'Oumuamua was made in exactly that fashion, by tracking its motion relative to the background of fixed stars. Rob Ratkowski Theoretically, this lines up with a population of objects we've long expected to be there, but hadn't found until now: the analogue of asteroids, comets, Kuiper belt objects, and Oort cloud objects from other solar systems. We've long known that objects like this routinely get ejected from our own cosmic backyard, and likely have for billions of years, dating all the way back to the formation of the Sun and the planets. We've witnessed other solar systems forming similarly, and we've fully anticipated that there ought to be millions or even billions of these objects for every star in our galaxy. According to simulations and calculations, many of these objects should pass through our Solar System on an annual basis, but we wouldn't be able to identify them unless we started taking regular, almost nightly pictures of the entire sky to great sensitivity, over and over again. That's exactly what the Pan-STARRS telescope (above) -- the precursor to the Vera Rubin Observatory -- has been doing for years now, and it was that very telescope that discovered 'Oumuamua. It marks the first detection of an interstellar interloper, and that's the designation that scientists eventually settled on when it came to classifying this object. An animation showing the path of the interstellar interloper now known as `Oumuamua. An animation showing the path of the interstellar interloper now known as `Oumuamua. The combination ... [+] of speed, angle, trajectory, and physical properties all add up to the conclusion that this came from beyond our Solar System, but we were unable to discover it until it was already past Earth and on its way out of the Solar System. NASA / JPL - CALTECH Of course, the only reason we found this one is that it managed to get so close to the Sun, a rare occurrence for objects such as this. It actually passed interior to Mercury's orbit: where our telescopes rarely scan, because you never want to run the risk of accidentally pointing your telescope at the Sun. We didn't actually discover it until it had crossed over to the other side of Earth's orbit, when it was on its way out of the Solar System. We found it when it was near its closest to Earth: 23,000,000 kilometers away. When it made its closest approach to the Sun, it was moving incredibly fast: up to 88 km/s, or three times the speed that Earth orbits the Sun. But we were lucky to image it at all. It was small (only about 100 meters long), faint, and very red in color, similar to the Trojan asteroids we see in orbit around Jupiter. Its color is different from the icy bodies we know of, failing to match up with comets, Kuiper belt objects, or even centaurs, and follow-up observations revealed a certain amount of boring-ness to 'Oumuamua, as it displayed no molecular or atomic absorption or emission features. In fact, if it weren't for two odd features about this object, there would have been very little to note about it, other than the fact that it exists and has the trajectory we observed. The light curve of 'Oumuamua, at right, and its inferred, tumbling shape and orientation. Because of the brightness variations seen in interstellar object 1I/ 'Oumuamua, where it varies by a ... [+] factor of 15 from its brightest to its faintest, astronomers have modeled that it is very likely an elongated, tumbling object. The size ratio of its long axis to its short axis may be approximately 8-to-1, similar to weathered, elongated rocks found at the bottom of rivers. nagualdesign / Wikimedia Commons The first odd feature about 'Oumuamua was noticed in October of 2017, shortly following its discovery. Because it was relatively close to Earth but also moving away very quickly, we only had a short window of time to do follow-up observations, and a series of telescopes set their sites on this interstellar oddity. Over a timescale of about 3.6 hours -- but not periodically like clockwork -- the object varied in brightness by about a factor of 15. Objects like comets or asteroids might vary by a few percent, or even a factor of 2, but a factor of 15 is unheard of. The leading explanation from models of this object is that it must be both elongated and tumbling, which would explain its regular, severe brightness variations. The reason this is such a good explanation is that unless there's some mechanism for obscuring the light from this object on one side, like an interstellar analogue of Saturn's two-toned moon Iapetus, or perhaps dust or outgassing, a change in the object's apparent size could explain the large brightness variations. It's not a surprise that this object would be tumbling, but seeing an object so thoroughly elongated, like a rock that's spent a very long time being weathered in a river or ocean, makes this object all the more interesting. The nominal trajectory of interstellar asteroid `Oumuamua, as computed from observations. The nominal trajectory of interstellar asteroid `Oumuamua, as computed based on the observations of ... [+] October 19, 2017 and thereafter. The observed trajectory deviated by an acceleration that corresponds to an extremely small ~5 microns-per-second^2 over what was predicted, but that's significant enough to demand an explanation. TONY873004 OF WIKIMEDIA COMMONS The second odd feature came when we tracked 'Oumuamua's path out of the solar system. What we expected, perhaps naively, is that it would follow a hyperbolic orbit, as though the only force acting on it would be gravitational. What we found, however, was that a normal, perfectly hyperbolic orbit didn't quite fit what we observed. It was as though there was an additional acceleration, as though something unobserved were pushing it, in addition to the influence of gravity. There are many reasons, of course, that an additional acceleration could occur. We've seen spacecrafts accelerate in exactly this fashion when they heat unevenly, and an asymmetric, rotating body fits that profile very well. Additionally, there could have been some form of outgassing coming from 'Oumuamua; the only feature we could even test for was a coma, which it lacked, but that only rules out an icy nature. Given its small size and great distance, we concluded it didn't have a halo of gas around it, but could say nothing about whether it had a diffuse jet of ejecta coming off of it: an eminent possibility. Even most asteroids in our Solar System contain substantial amounts of volatile compounds. Even most asteroids in our Solar System contain substantial amounts of volatile compounds, and can ... [+] often develop tails when they approach near the Sun. Even though `Oumuamua may not have had an identifiable tail or coma, there is very likely an astrophysical explanation for its behavior that is related to outgassing, and has absolutely nothing at all to do with aliens. ESA-ScienceOffice.org Since the discovery of 'Oumuamua, there have been many papers written about it by the astrophysics community, bringing together the lessons we learned from it, synthesizing our pre-existing theories with the new observations to create a holistic picture of what might be lurking in interstellar space. An individual object like 'Oumuamua will only pass so close to a star in the Milky Way once every ~100 trillion (10^14) years, or about 10,000 times the present age of the Universe. How did we get so lucky, then, as to see it? It's because of the sheer number of them. There may be, according to some estimates, as many as ~10^25 objects like this -- interstellar interlopers -- that are flying through our galaxy. Every so often, given the incredible number of these objects out there, they'll pass through our Solar System, up to a few times per year. If we have the right tools, scanning the sky often enough, comprehensively enough, pollution-free enough, and to faint enough magnitudes, we'll get to observe them. Many speculated that 'Oumuamua would be a one-off; as astronomer Gregory Laughlin quipped, "this was the time of 'Oumuamua's life." But just two years later, we found a second interstellar interloper: the very comet-like object, Borisov. Hubble Space Telescope observations of interstellar object 2I/ Borisov: time-lapse. This time-lapse series of Hubble Space Telescope observations of interstellar object 2I/Borisov ... [+] spans seven hours, and was taken with Borisov at a distance of 260 million miles. A blue, comet-like coma can clearly be seen as the object streaks past the background stars. At an extraordinary speed of more than 110,000 miles per hour, it is the fastest natural object to be detected in our Solar System thus far. NASA, ESA and J. DePasquale (STScI) Borisov, in August of 2019, became the second example of a significant object whose origin is beyond our Solar System, but it was very different from 'Oumuamua. Comparing the two, we find that Borisov was: * extremely eccentric, with an eccentricity of 3.35, nearly triple any other object, * very large, with a diameter of about 6 kilometers, versus 0.1-0.3 km for 'Oumuamua, * and distinctly comet-like, with a clear coma and a long tail, rich in cynaide and diatomic carbon gases. Borisov, unlike 'Oumuamua, has an appearance that was familiar to us. So why, then, were these two objects so different from one another? We have to recognize that there could be many answers to that question. Perhaps they're not that different, but 'Oumuamua was too small to measure in detail with the instruments we had in 2017. We discovered Borisov when it was on its way into the Solar System, giving us plenty of time to study it, but only saw 'Oumuamua when it was already on its way out. Perhaps they are different, because there are many populations of these objects out there: some are planetesimals, others are rocky and ice-free, some have been weathered by a journey of billions of years in interstellar space, etc. The way to answer a question like this is to build better instruments, collect more and superior data, increase our sample size, and actually begin studying these interstellar objects in detail whenever they happen to pass close enough to be observed. Interstellar objects 1I/'Oumuamua and 2I/Borisov compared with known solar system objects. Compared with a number of other known objects with Solar System origins, the interstellar objects ... [+] 1I/'Oumuamua and 2I/Borisov appear very different from one another. Borisov fits in extremely well with comet-like objects, while 'Oumuamua appears completely depleted of volatiles. Discovering why is a task that still awaits humanity. Casey M. Lisse, presentation slides (2019), private communication As you can see, there's a rich scientific tapestry that the astronomical community is weaving about these new classes of objects. We expect the interstellar medium to be filled with remnants and ejecta from the hundreds of billions of solar systems throughout the Milky Way, and owing to the recent advances in our technology, we've finally started to detect them. We only have two such objects so far, but the coming years -- assuming that mega-constellations of satellites don't ruin our view -- should help us better understand and classify these objects. That is, unless we decide to take the fundamentally unscientific approach of Avi Loeb, and insist on considering an alien origin for the first of these objects. Loeb, who's been intimately involved with the Breakthrough Starshot project, has written papers with his postdocs and students insisting that 'Oumuamua is just as likely to be an alien spacecraft (that looks suspiciously like a light-sail) as it is to be one of the expected ~10^25 naturally occurring objects in our own galaxy. Despite the fact that the spectral signatures of the object -- its color, reflectivity, size, etc. -- are consistent with a natural origin, Loeb offers only loud, immodest speculation about aliens and diatribes about community groupthink. Coupled with inadequate data, which is the only data we have, he's impossible to prove wrong. Normally, structures like IKAROS, shown here, are viewed as potential sails in space. Normally, structures like IKAROS, shown here, are viewed as potential sails in space. By taking ... [+] advantage of the solar radiation pressure, an object like this could propel itself through space with a significant acceleration that departs from what gravity, alone, predicts. However, speculating that an asteroid-like object is an alien spacecraft is not worthy of serious scientific consideration. Wikimedia Commons user Andrzej Mirecki What is a responsible scientist to do in this situation? There are literally hundreds of astronomers who work in this field, and Loeb continues to ignore all of them -- their work, their data, their conclusions, and the full suite of evidence at hand -- instead focusing on his own idea which has no convincing data to back it up. He claims that he didn't court this public attention, but my own inbox shows that to be a lie. Prior to 2017, I had received 0 emails from Avi Loeb; since 2018, I have received 74 from him and even more from his students. All of them have been unsolicited; nearly all of them advertise his viewpoints about extraterrestrials, including the bizarre claim that astronomers are somehow resistant to considering the possibility of aliens. Given that planetary scientists are looking for life elsewhere in our Solar System, astronomers are searching for biosignatures on exoplanets and in interstellar materials, and that SETI continues to seek technosignatures, it's a claim that's countered by an enormous suite of evidence. Loeb was a once-respected scientist who made important contributions to astrophysics and cosmology, particularly when it came to black holes and the first stars. But his work on extraterrestrial signatures continues to be largely unappreciated by the community -- a position as justifiable as ignoring the comparable idea of Russell's teapot -- and rather than address their scientific objections, he's stopped listening to other astronomers entirely, instead choosing to try his scientific case in the most unscientific place imaginable: the court of public opinion. Loeb, like everyone, has the freedom to choose which hill his career and reputation will die on. While the possibility of aliens will certainly attract a large amount of public attention, these extraordinary claims that lack even modest supporting evidence will continue, deservedly so, to remain far out of the scientific mainstream. Follow me on Twitter. Check out my website or some of my other work here. Ethan Siegel Ethan Siegel I am a Ph.D. astrophysicist, author, and science communicator, who professes physics and astronomy at various colleges. I have won numerous awards for science writing ... Read More I am a Ph.D. astrophysicist, author, and science communicator, who professes physics and astronomy at various colleges. I have won numerous awards for science writing since 2008 for my blog, Starts With A Bang, including the award for best science blog by the Institute of Physics. My two books, Treknology: The Science of Star Trek from Tricorders to Warp Drive, Beyond the Galaxy: How humanity looked beyond our Milky Way and discovered the entire Universe, are available for purchase at Amazon. Follow me on Twitter @startswithabang. Read Less * Print * Reprints & Permissions [ ]