The debate continues: “ Oumuamua could be a remnant of the Pluto-like planet

The mysterious pancake-shaped object dubbed ‘Oumuamua (Hawaiian for “messenger from afar coming first”) generated considerable controversy earlier this year with the publication of Harvard astronomer Avi Loeb’s bestselling new book, claiming that it could be a piece of alien technology. Now, two Arizona State University (ASU) astrophysicists argue that the secret to at least one aspect of the object’s unusual properties lies in solid nitrogen ice. They described their findings in two new papers published in the Journal of Geophysical Research: Planets.

As we previously reported, at the end of 2017 our solar system received its very first known interstellar visitor: a bizarre cigar-shaped object traveling at 44 kilometers per second. Since then, scientists have wondered about the origin and unusual characteristics of ‘Oumuamua. It was first discovered by the University of Hawaii’s Pan-STARRS1 telescope, which is part of NASA’s near-Earth object observation program to track asteroids and comets that come close to the Earth. Other telescopes around the world quickly sprang into action, measuring the different characteristics of the object.

Because it had a hyperbolic, or escape, orbit around the Sun, Oumuamua is unlikely to return our path. So astronomers only had a brief window of time to gather as much data as possible about the object before it set off on its merry way. For starters, “Oumuamua was accelerating away from our Sun much faster than could be explained by gravity alone, ie via a ‘rocket effect’ which is common in comets, caused by sunlight. vaporizing the ice that these bodies are made of. While its strange orbit initially classified it as a comet, imagery showed no indication of gas and dust being released, as is usually the case when a comet approaches the Sun. Its elongated cigar-shaped shape, combined with its relatively rapid rotation, led to an early suggestion that it could also be an asteroid.

Oumuamua sparked some media excitement again in October 2018, when Loeb and his post-doctoral fellow Shmuel Bialy submitted a preprint (since published) to the Astrophysical Journal. As we reported at the time, much of their analysis discussed the possibility of solar radiation pressure or momentum transfer of photons hitting an object. This is precisely the driving idea behind the “solar sails” that could one day power spaceships around our solar system or beyond. Loeb and Bialy closed their article with a more exotic and highly speculative scenario, suggesting that the object could in fact be a very thin solar sail – in particular, “a fully operational probe intentionally sent close to Earth by an alien civilization. “.

Loeb developed this hypothesis in his new book (released in January), Aliens: the first signs of intelligent life beyond Earth, arguing that “we should be open-minded and look for evidence rather than assuming that everything we see in the sky must be rocks.” The book received its fair share of rave reviews, with an appropriate degree of mild skepticism.

Others have been more severe in their assessment, such as astrophysicist Ethan Siegel, who wrote a strongly worded counter-argument to Forbes:

Although the spectral signatures of the object – its color, reflectivity, size, etc. – are consistent with a natural origin, Loeb only offers noisy and shameless speculations on extraterrestrials and diatribes on communal group thinking. Coupled with inadequate data, which is the only data we have, it is impossible to go wrong … There are literally hundreds of astronomers working in this field, and Loeb continues to ignore them all – their work, their data, their conclusions, and the full body of evidence at hand – instead focusing on his own idea which has no compelling data to back it up … [R]Instead of responding to their scientific objections, he stopped listening entirely to other astronomers, choosing instead to try his scientific case in the least scientific place imaginable: the tribunal of public opinion.

“Everyone is interested in extraterrestrials, and it was inevitable that this first object outside the solar system would make you think of extraterrestrials,” said Steven Desch of ASU, co-author of the two new articles, of the hypothesis. Loeb. “But it’s important in science not to jump to conclusions. It took two or three years to find a natural explanation – a piece of nitrogenous ice – that matches everything we know about ‘Oumuamua. It’s not so long in science, and well also soon to say that we had exhausted all natural explanations. “

Last year, a team of astronomers published an article suggesting that “ Oumuamua could be the fragment of another larger parent body – a comet or a long-lived debris disc, perhaps, or even a super-terrestrial planet – torn apart by tidal forces as it passed too close to its host star. Specifically, astronomers have shown that “ Oumuamua-type interstellar objects can be produced by vast tidal fragmentation during close encounters of their parent bodies with their host stars, and then ejected into interstellar space.

Desch and his co-author, ASU astrophysicist Alan P. Jackson, also suggest that “ Oumuamua probably came from another solar system, a fragment of an exoplanet destroyed by an impact about a half ago. -billion years, throwing him out of his parenting system. They suggest that the parents’ body likely had characteristics similar to Pluto’s. Specifically, Pluto, like Neptune’s moon Triton, is covered in nitrogen ice.

Desch and Jackson argue that “Oumuamua is also made up of solid nitrogen ice, which may explain the object’s strong push away from the Sun. They calculated the value of the body’s reflection to account for this strong push and how quickly various types of ice would sublimate. Solid nitrogen exactly matched their calculations. “Oumuamua being made of frozen nitrogen also explains its unusual flattened shape. “As the outer layers of nitrogen evaporated, the shape of the body would have become progressively more flattened, just like a bar of soap does when the outer layers are washed away with use,” Jackson explained. .

Oumuamua’s study has provided useful new information about planetary systems outside of our own solar system, according to Desch and Jackson, who hope such interstellar objects will be discovered as a new generation of telescopes are put into operation. line, including the Vera Rubin Observatory. / Large synoptic study telescope in Chile. “It is hoped that in ten years or so, we can acquire statistics on the types of objects that pass through the solar system, and whether the pieces of nitrogenous ice are rare or as common as we have calculated,” said Jackson. “Either way, we should be able to learn a lot about other solar systems and whether they have suffered the same types of collision stories as ours.

DOI: Alan P. Jackson et al., Journal of Geophysical Research: Planets, 2021. 10.1029 / 2020JE006706.

DOI: SJ Desch et al., Journal of Geophysical Research: Planets, 2021. 10.1029 / 2020JE006807 (About DOIs).

Ad image by William Hartmann