A new study published in Nature confirms that ‘Oumuamua’s peculiar acceleration is due to the release of molecular hydrogen gas.
According to astrochemist Jennifer Bergner of the University of California at Berkeley and astrophysicist Darryl Seligman of Cornell University, this is further evidence that a cigar-shaped piece of rock that broke away from a nascent planet has set off to wander the galaxy.
‘Oumuamua first appeared in the field of view of astronomers in October 2017. After it made its closest pass to the Sun, the object made a loop and accelerated, leaving the solar system.
Scientists have not seen anything like it, so the object still continues to be of interest to astronomers.
First, its form surprises. Oumuamua is as long as a cigar, up to 400 meters long. No other comet or asteroid in the solar system has this shape.
In addition, Oumuamua rotates in the direction of travel. And, although the object does not appear to contain ice and does not emit gases, its trajectory cannot be explained solely by the influence of gravity.
The release of gases from comets as their ice sublimes gives the comets an additional source of acceleration, which is what astronomers observed at ‘Oumuamua. This suggests that it looks like a comet and an asteroid.
Scientists believe that ‘Oumuamua is probably a fragment that broke away from a young planet (planetesimal) that collided with a large object.
Such collisions are common in the emerging planetary system. For example, it is believed that our Earth collided with another object the size of a planet, while breaking off a piece from which the Moon was formed. In the case of Oumuamua, a fragment of the planetesimal was thrown out of its system altogether.
In 2020, Seligman co-authored a paper stating that the ‘Oumuamua acceleration can be explained by the sublimation of molecular hydrogen.
Molecular hydrogen is very difficult to detect in space because it does not emit or reflect light. If ʻOumuamua was emitting molecular hydrogen, we would not be able to see it in the way we usually see only traces of cometary activity.
On the other hand, there were doubts that ‘Oumuamua was a molecular hydrogen iceberg, so Bergner and Seligman turned to simulations to figure out how an object could contain (and sublimate) molecular hydrogen.
As a result of the simulation, it turned out that the sublimation of water ice by itself would only produce up to 50 percent of the observed acceleration.
Now ‘Oumuamua is at a great distance from us and is moving fast. The object is no longer visible even with powerful telescopes.
So the question of whether the team is right about molecular hydrogen will remain open.