“It is impossible to guess the purpose behind Oumuamua without more data,” said Avi Loeb, chairman of Harvard’s astronomy department. “If Oumuamua is a lightsail,” he added, “one possibility is that it was floating in interstellar space when our solar system ran into it, “like a ship bumping into a buoy on the surface of the ocean.”
Loeb and his collaborator, Shmuel Bialy, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics, have raised the exotic possibility that the first observed interstellar visitor to our solar system, Oumuamua, is an alien spacecraft. As they say in a paper to be published Nov. 12 in The Astrophysical Journal Letters, the object “may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization.”
“There is data on the orbit of this object for which there is no other explanation. So we wrote this paper suggesting this explanation,” said co-author Loeb. “The approach I take to the subject is purely scientific and evidence-based. As far as I know, there is no other explanation,” he said. “You can rule it out or in, based on additional data.”
The object ‘Oumuamua — Hawaiian for “messenger from afar arriving first” — is the first ever observed intruding in the orbits of our planets. The mysterious reddish, stadium-sized space object with its flattened, elongated shape was picked up by telescopes in October 2017 at the University of Hawaii’s Haleakalā Observatory, the National Aeronautics and Space Administration said. It is on its way out of the solar system and expected to never return. Scientists say other “interstellar” objects may have sailed by in the past, undetected.
It was monitored for signs of radio signals as weak as one-tenth of a cellphone-strength signal, but nothing was detected. Researchers said in December 2017 that it appeared to be a naturally formed, icy object covered with a dry crust.
Loeb noted that no photograph was ever taken of ‘Oumuamua. “We don’t have an image because we were not prepared.The importance of finding this object is that now we can make plans for the future and look more.”
After a careful mathematical analysis of the way the interstellar object sped up as it shot past the sun, the Harvard team say Oumuamua could be a spacecraft pushed through space by light falling on its surface — or, as they put it in the paper, a “lightsail of artificial origin” similar but far more advanced than that proposed by Breakthrough Starshot, an initiative that plans to send a fleet of tiny laser-powered lightsail craft to the nearest star system.
The diagram below, provided by the European Southern Observatory, shows the orbit of ‘Oumuamua as it passes through the solar system. ‘Oumuamua passed the distance of Jupiter’s orbit in early May 2018 and will pass Saturn’s orbit January 2019. It will reach a distance corresponding to Uranus’ orbit in August 2020 and of Neptune in late June 2024. In late 2025 ‘Oumuamua will reach the outer edge of the Kuiper Belt, and then the heliopause — the edge of the Solar System — in November 2038.
Loeb said the object is “peculiar” for a variety of reasons. One reason is that it has deviated from an orbit dictated by the sun’s gravity. It had “excess acceleration,” he said. Comets can have such acceleration because ice on them vaporizes when heated by the Sun, propelling them. But ‘Oumuamua had no tail like a comet. “The question arises as to what is causing the excess acceleration, the excess kick it has, and the possibility we suggest is the radiation from the sun which is pushing it,” he said.
The way the object moves, Loeb said, is consistent with a light sail a fraction of a millimeter in thickness that is tens of meters across. If “radiation pressure” is pushing the object, then ‘Oumuamua “represents a new class of thin interstellar material, either produced naturally or artificially,” the paper says. If it is artificial, “one possibility is that ‘Oumuamua is a lightsail, floating in interstellar space as a debris from an advanced technological equipment. “Alternatively, a more exotic scenario is that ‘Oumuamua may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization.”
Loeb said he’s gotten some strong reactions, with the strongest ones coming from people who haven’t read the paper, which he said “illustrates how much prejudice there is about this subject. I don’t see this any differently from a subject that’s right in the mainstream that everyone is working on. It’s exactly the same approach.”
Andrew Siemion, director of the Berkeley SETI Research Center and principal investigator for Breakthrough Listen, a program of astronomical observations looking for life beyond Earth said in an e-mail to the Boston Globe that the paper was “very intriguing. Observational anomalies like we see with Oumuamua, combined with careful reasoning, is exactly the method through which we make new discoveries in astrophysics — including, perhaps, truly incredible ones like intelligent life beyond the Earth.”
“It’s certainly ingenious to show that an object the size of Oumuamua might be sent by aliens to another star system with nothing but a solar sail for power,” Seth Shostak, a senior astronomer at the SETI Institute in Mountain View, California, said in an email. “But one should not blindly accept this clever hypothesis when there is also a mundane (and a priori more likely) explanation for Oumuamua — namely that it’s a comet or asteroid from afar.”
Coryn Bailer-Jones, an astronomer at the Max Planck Institute for Astronomy in Heidelberg, Germany, voiced similar objections. “In science,” he said in an email to NBC MACH , “we must ask ourselves, “Where is the evidence?, not “Where is the lack of evidence so that I can fit in any hypothesis that I like?”
“Why send a spacecraft which is doing this?” he said. “If it were a spacecraft, this tumbling would make it impossible to keep any instruments pointed at the Earth. Of course, one could now say it was an accident, or the aliens did this to deceive us. One can always come up with increasingly implausible suggestions that have no evidence in order to maintain an idea.”
Steven Beckwith, a professor of astronomy and director of the Space Science Laboratory at University of California Berkeley, noted that the object was now too far away for our current technology to actually verify its shape, “which means that any speculation cannot be confirmed or denied. So it’s a clever idea, but not obviously science in absence of an observational check.”
But Loeb called the conjecture “purely scientific and evidence-based,” adding, “I follow the maxim of Sherlock Holmes: When you have excluded the impossible, whatever remains, however improbable, must be the truth. A survey for lightsails as technosignatures [of extraterrestrial civilizations] in the solar system is warranted,” he said, “irrespective of whether Oumuamua is one of them.”
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