Oumuamua: asteroid or alien light sail, debate continues five years later

Mayank Chhaya-

This month it has been five years since a mysterious interstellar object, the first of its kind, that zipped through our solar system at a blistering 196000 miles or over 315000 kilometers an hour. Five years hence astronomers are still debating whether Oumuamua was an asteroid, a nitrogen iceberg, from another stellar system or an alien spacecraft, a light sail, sent by an advanced civilization.

Even as a new study ready for publication has concluded that the quarter mile-long, rocky, cigar-shaped, reddish hued object was not a light sail, the original proponent of the idea that it was potentially an alien light sail is firmly standing by it.

Called Oumuamua, which in Hawaiian means “a messenger that reaches out from the distant past”, was a quarter mile, rocky, cigar-shaped, somewhat reddish hued object that NASA said, “had been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with our star system.”

Oumuamua was discovered on October 19, 2017, after what NASA then said it slingshotted past the sun on September 9,2017. The passage of five years has not settled the debate over what it really was, and it is unlikely that there will be a definite final answer.

In 2018, researchers at the Harvard Smithsonian Center for Astrophysics had raised the extraordinary possibility that Oumuamua “may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization.”

The research paper was a serious attempt by Shmuel Bialy and Abraham Loeb of the Harvard center to explain many unusual features of the mysterious object. Ever since its appearance and exit, there has been serious speculation that it was not an asteroid. It was immediately pointed out that Oumuamua was indeed an interstellar object, meaning it came from outside our solar system, which in itself was unprecedented. With that as the tantalizing backdrop it was only natural to speculate whether it may have been an artificial object or, in other words, made and sent by an intelligent alien civilization.

One of the features much talked about has been its likely non-gravitational acceleration suggesting that it might have had its own power source.  One exciting suggestion in the paper was that ‘Oumuamua is a light sail, floating in interstellar space as a debris from an advanced technological equipment.” The paper’s authors also offered this showstopper,” Alternatively, a more exotic scenario is that ‘Oumuamua may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization.”

While Professor Loeb still firmly maintains that Oumuamua may have been an alien spacecraft, a new study, accepted for publication in the journal Astronomy and Astrophysics, has concluded that “‘Oumuamua is unlikely to be a light sail. The dynamics of an intruding light sail, if it exists, has distinct observational signatures, which can be quantitatively identified and analyzed with our methods in future surveys.”

The new study by Wen-Han Zhou, Shang-Fei Liu, Yun Zhang and Douglas N.C. Lin to be published in the journal Astronomy and Astrophysics offers rather complex calculations to conclude that Oumuamua was not a light sail sent by advanced civilization. The authors point out that, “Nevertheless, the spaceship hypothesis is based on the conjecture that the Solar System has always been ‘Oumuamua’s intended destination and that it has maintained its original course.”

On a remarkable note, Oumuamua reminded this journalist of the iconic science fiction writer Arthur C Clarke’s celebrated ‘Rendezvous with Rama’ about a strangely symmetrical and cylindrical object that comes into our solar system and indeed turns out to be an alien spaceship.

It was striking that Oumuamua showed up around the 100th birth anniversary of Clarke’s on December 16. Although the interstellar asteroid was discovered in October it broadly coincide with Clarke’s birth anniversary symbolically.

A passage from ‘Rendezvous with Rama’ where it first introduces the spaceship reads rather prescient now. Indians would be thrilled to know how it came to be named Rama by Clarke, who lived in Sri Lanka, the putative hub of Ravan, Rama’s arch adversary. Let me quote some passages from the novel.

In the novel the object is first identified as 31/439 and given that it is indeed an alien spaceship those who discovered feel compelled to christen it memorably. The year was 2130 by which Mars-based radars were discovering asteroids “at the rate of a dozen a day.”

The object was of an exceptional size. “From the strength of echo, the computers deduced a diameter of at least forty kilometers,” Clarke writes. The object was not on a normal asteroidal path. In a somewhat disconcertingly similar attribute to Oumuamua, Clarke writes, “It was a lonely wanderer among the stars, making its first and last visit to the solar system—for it was moving so swiftly that the gravitational field of the Sun could never capture it.” Oumuamua too is moving too fast to be captured by the Sun’s gravitational field.

In terms of nomenclature, Clarke writes, “Long ago astronomers had exhausted Greek and Roman mythology; now they were working through the Hindu pantheon. And so 31/439 was christened Rama.”

Alas, unlike Rama, Oumuamua did not appear to be an alien spaceship. The findings suggested that it had a coating of carbon-rich ices. The coating has been described as “organic gunk.” No radio signals were detected which would have given it a wholly remarkable feature of being an artificial object rather than just a random space rock. Its cigar shape caused some speculation about what it could be but so far no sign that it is anything other than the most likely explanation—a random space rock from a different star system.

Unlike a spaceship, which would glide in a controlled, measured fashion, Oumuamua was head over heels and wobbly

The new study is not expected to end the debate, particularly when Dr. Loeb steadfastly maintains the possibility of Oumuamua being an alien light sail.