In late 2017, astronomers around the world scrambled to study an enigmatic interstellar visitor – the first ever seen – that briefly came within range of their telescopes. The object’s discoverers dubbed it ‘Oumuamua—a Hawaiian term that roughly translates to “scout.” It was the first “visitor” from outside our Solar System.
It was discovered by Robert Weryk using the Pan-STARRS telescope at Haleakalā Observatory, Hawaii, on 19 October 2017, approximately 40 days after it passed its closest point to the Sun on 9 September. When it was first observed, it was about 33 million km from Earth (about 85 times as far away as the Moon), and already heading away from the Sun.
ʻOumuamua is a small object estimated to be between 100 and 1000 metres long, with its width and thickness both estimated to range between 35 and 167 metres. It has a red color, similar to objects in the outer Solar System.
Despite its close approach to the Sun, ʻOumuamua showed no signs of having a coma (a kind of “steam” coming from the object due to the local temperature). It has exhibited non‑gravitational acceleration, since the speed it gained couldn’t be explained by gravitational forces.
ʻOumuamua’s light curve, assuming little systematic error, presents its motion as “tumbling”, rather than “spinning”, and moving sufficiently fast relative to the Sun that it is likely of an extrasolar origin. Extrapolated and without further deceleration, ʻOumuamua’s path cannot be captured into a solar orbit, so it would eventually leave the Solar System and continue into interstellar space. ʻOumuamua’s planetary system of origin and the age of its excursion are unknown.
The unavoidably cursory examinations of this celestial passerby showed it had several properties that defied easy natural explanation.
‘Oumuamua’s apparent shape – which was like a, at least, 100-meter-long cigar – did not closely resemble any known asteroid or comet. Neither did its brightness, which revealed ‘Oumuamua was at least 10 times more reflective than one of our solar system’s typical space rocks – shiny enough to suggest the gleam of burnished metal.
Radio measurements
In December 2017, astronomer Avi Loeb of Harvard University, an adviser to the Breakthrough Listen Project, cited ʻOumuamua’s unusually elongated shape as one of the reasons why the Green Bank Telescope in West Virginia would listen for radio emissions from it to see if there were any unexpected signs that it might be of artificial origin, although earlier limited observations by other radio telescopes such as the SETI Institute’s Allen Telescope Array had produced no such results. On 13 December 2017, the Green Bank Telescope observed the object for six hours across four bands of radio frequency. No radio signals from ʻOumuamua were detected in this very limited scanning range, but observations are ongoing.
Avi Loeb
Avi Loeb is no stranger to controversy. the prolific Harvard University astrophysicist has produced pioneering and provocative research on black holes, gamma-ray bursts, the early universe and other standard topics of his field. But for more than a decade he has also courted a more contentious subject— namely, space aliens, including how to find them.
Until relatively recently, Loeb’s most high-profile work in that regard was his involvement with Breakthrough Starshot, a project funded by Silicon Valley billionaire Yuri Milner to send laserboosted, gossamer-thin mirrorlike spacecraft called “light sails” on high-speed voyages to nearby stars.
In late 2018 Loeb and his co-author Shmuel Bialy, a Harvard postdoctoral fellow, published a paper in the Astrophysical Journal Letters arguing that ‘Oumuamua had been nothing less than humanity’s first contact with an artifact of extraterrestrial intelligence. The paper has been a smash hit with journalists but has fallen flat with most of Loeb’s astrobiology-focused peers, who insist that, while strange, ‘Oumuamua’s properties still place it well within the realm of natural phenomena. To claim otherwise, Loeb’s critics say, is cavalier at best and destructive at worst for the long struggle to remove the stigma of credulous UFO and alien-abduction reports from what should unquestionably be a legitimate field of scientific inquiry.
First Sign of Intelligent Life beyond Earth
Loeb has now taken his case to the public with the book Extraterrestrial: The First Sign of Intelligent Life beyond Earth, which is just as much about the author’s life story as it is about ‘Oumuamua’s fundamental mysteries.
In an interview with the Scientific American Loeb reacts as follows to his critics: “Although I should say that I think my critics who are most vocal with nasty remarks on Twitter and elsewhere are relatively mediocre scientists. Most really good scientists would not behave that way – they would make arguments for or against my claims, and that would be enough. Nasty remarks don’t make sense—except, well, deep inside, I would not be surprised if many of these critics are actually quite intrigued by this possibility that ‘Oumuamua is artificial. But they don’t want to admit it. So they loudly say the opposite. Unfortunately, my situation is different from that of the young postdocs who I’ve worked with because they need to apply for jobs. I’m sure that people have approached them and said, “Look, this is dangerous for you.” And so they froze and basically stopped working on anything related. This isn’t surprising. If you create a hostile intellectual culture where something like SETI is not being honored, then young, bright people will not go there. But don’t step on the grass and then complain it doesn’t grow as you stand on it. Don’t block brilliant researchers from working on SETI and then say, “Look, nothing is being found. SETI is a failure!”
Another explanation
Alan Jackson and Steve Desch, published in March 2021 an artricle in the Journal of Geophysical Research in which they suggested ’Oumuamua could be a comet, but a different one to those we know as a mixture of stardust, iced water and or iced carbon dioxyde. Their conclusion is that the substance is iced nitrogen.
That’s not a strange tought: Pluto’s surface is similar, so perhaps it is just a piece of a planet similar to Pluto.
“Of course it is not strange people immediately think of alien origin, since it is our first visitor from outside our Solar System.” is Desch’s comment in a press issue. “It took us 3 years to find a possible explanation. And that’s a lot, but at the same time it was also too early to justify the alien explanation.”
Loeb did not yet response to this explanation.