(ORDO NEWS) — An interstellar object currently making the long journey back from our solar system has a perfectly natural explanation, despite its strange quirks.
‘Oumuamua’s unusual acceleration, a new study confirms, can be entirely attributed to the release of molecular hydrogen gas.
This, according to astrochemist Jennifer Bergner of the University of California at Berkeley and astrophysicist Darryl Seligman of Cornell University, is further evidence that the cigar-shaped chunk of rock started out as a planet seed and then set off to roam the galaxy without being tied to a star.
It’s an elegant solution that, the researchers write, “could explain many of ‘Oumuamua’s specific properties without fine-tuning” — or appeal to extraordinary claims about the object’s nature.
“Oumuamua first appeared on our horizons in October 2017, just a month after it flew closest to the Sun, looping and accelerating. return from the solar system on her ongoing journey through space.
We have not seen anything like this in our home system and are still very interesting to astronomers.
First is its form. “Oumuamua is long and thin, like a cigar, reaching 400 meters (0.25 miles) in length. No other comet or asteroid in the solar system has this shape.
‘Oumuamua also sort of spins as it goes, like a bottle on its side. And although the object does not appear to contain ice or emit gases that we can detect like a comet, its trajectory cannot be explained by gravity alone, like the trajectory of an asteroid.
The comet’s outgassing as their ice sublimation gives comets an additional source of acceleration, consistent with what astronomers have observed from ‘Oumuamua. This suggests that it is somewhat similar to both a comet and an asteroid.
In the years since his visit, scientists have determined that “Oumuamua is likely a shard that has broken away from a planetesimal, a small planet still in space.” a formation process that collided with another object.
Such collisions are not uncommon in an emerging planetary system; our own Earth is believed to have collided with another planet-sized object, breaking away from the chunk that formed the Moon. In the case of ʻOumuamua, a fragment of the planetesimal was completely ejected from his system.
In 2020, Seligman co-authored a paper suggesting that “Oumuamua acceleration could be due to the sublimation of molecular hydrogen (H 2 ).
Molecular hydrogen is very difficult to detect in space because it does not emit or reflect light; if ‘Oumuamua was emitting molecular hydrogen, we would not be able to see it the way we usually see traces of cometary activity.
On the other hand, it has been suggested that ‘Oumuamua is unlikely to be a molecular hydrogen iceberg, as researchers suggested in 2020, so Bergner and Seligman went back to modeling to determine how an object could contain (and sublimate) molecular hydrogen.
They found that the explanation was plausible thanks to the irradiation of a body rich in water ice.
When ionizing radiation hits an object, radiolytic processes break down water molecules to form molecular hydrogen.
“In this model,” they write in their paper, “Oumuamua began as an icy planetesimal that was irradiated by cosmic rays at low temperatures during its interstellar journey and experienced heating during its passage through the solar system.”
The existing body of experimental data indicates that aqueous (H 2 O) ice treatment can consistently and efficiently separate H 2. Most of the H 2 will remain in the water matrix until heated to a certain temperature range; as the water is heated and annealed, the molecular hydrogen escapes.
The researchers note that the sublimation of water ice itself gives only up to 50 percent of the observed acceleration. Molecular hydrogen, however, explains this quite accurately.
‘Oumuamua is now quite far away and moving fast; now there is no real opportunity to consider it closer than the observations that we already had.
So whether the team is right about molecular hydrogen remains an open question.
However, they say it fits the bill, and it can be tested by looking at other objects – small outer bodies in the solar system and other interstellar objects discovered in the future that show non-gravitational acceleration with no detectable traces of cometary activity.
“Future detections of small bodies with non-gravitational acceleration and weak coma may provide insight into the origin of ‘Oumuamua,” write Bergner and Seligman, “even though it has long since left the solar system.”
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