An interstellar object currently on its long journey from our solar system, despite its strange quirks, has a completely natural explanation. New research suggests that Oumuamua’s unusual acceleration may be 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 proof that the cigar-shaped piece of rock began as a planet seed and was then sent around the galaxy without being bound to Earth. . star. According to the researchers, it’s an elegant solution that can “explain many of Oumuamua’s specific properties without fine-tuning” or make extraordinary claims about the object’s nature.

Oumuamua first appeared on our horizon in October 2017, just a month after it made its closest approach to the Sun, completed a loop around the Solar System, and quickly flew back out of the Solar System on its journey through space. We haven’t seen anything like it in our home system since then, and it’s still of great interest to astronomers.

The first is its shape. Oumuamua is long and slender like a cigar, measuring up to 400 meters (0.25 miles) in length. No other comet or asteroid in the solar system has this shape.

— Oumuamua also spins on its side like a bottle when in motion. And while the object probably doesn’t contain ice or gases that we can detect as a comet does, its orbit cannot be explained by gravity alone, like the orbit of an asteroid.

Comets release gas as their ice sublimes, providing an additional source of acceleration to the comets, consistent with what astronomers have observed from ‘Oumuamua. This makes it look somewhat similar to both a comet and an asteroid.

In the years since his visit, scientists have determined that ‘Oumuamua is a fragment of a minor planet, possibly a forming asteroid that collided with another object. Such collisions are not unusual in a forming planetary system; Our own Earth is believed to have collided with another planet-sized object, breaking off the piece that made up the Moon. In the case of Oumuamua, the planetary fragment was completely removed from his system.

In 2020, Seligman was co-author of a paper that suggested that the acceleration of Oumuamua could be explained by the sublimation of molecular hydrogen (H2). Molecular hydrogen is very difficult to detect in space because it does not emit or reflect light; If ‘Oumuamua had emitted molecular hydrogen, we would be able to see it as we normally see traces of comet 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 returned to modeling to determine how the object might contain (and sublimate) molecular hydrogen.

They found that the explanation was plausible because of the irradiation of an object rich in water ice. When ionizing radiation hits an object, radiolytic processes split water molecules to form molecular hydrogen.

“In this model,” they write in their article, “Oumuamua began as an icy planetary state that was irradiated by low-temperature cosmic rays during its interstellar journey and warmed during its transit through the Solar System.”

Existing experimental data suggest that water treatment (H ₂ o) ice can emit H consistently and efficiently₂. most of H₂ it will remain trapped in the water matrix until it is heated to a certain temperature range; When water is heated and ignited, molecular hydrogen is released. The researchers note that sublimation of water ice alone would only account for 50 percent of the observed acceleration. But molecular hydrogen explains it quite clearly.

“Oumuamua” is now quite far away and is advancing rapidly; Now there is no more real way to take a closer look at it than the observations we already have. Therefore, whether the team is right about molecular hydrogen remains an open question. However, they say it fits the bill, and could test it by looking at other objects — small outer solar system bodies and other interstellar objects discovered in the future — that show non-gravity acceleration without telltale signs of comets. activity.

“Future detection of small objects with non-gravity acceleration and weak coma may provide insight into the origin of ‘Oumuamua,” Bergner and Seligman write, “although it has long since left the Solar System.”