‘Oumuamua: explaining the mysterious acceleration – wissenschaft.de

It came from deep space and crossed our solar system in an almost bizarre way. Now researchers offer a plausible explanation for the previously mysterious acceleration of the interstellar comet ‘Oumuamua: according to this, hydrogen gas was released from the small celestial body by the heat of the Sun, causing it to thrust. The scientists explained that this “fuel” may have formed at Oumuamua from water ice under the influence of cosmic rays on its long journey through space.

In 2017, a celestial body appeared on the astronomy scene that has definitely become a celebrity. At first, telescope observations suggested that it was a comet or an asteroid in our solar system. But then it became clear from its unusual orbit and high speed that the celestial body christened ‘Oumuamua had come to us from the depths of space. Soon after flying over the sun, he disappeared there again.

With the exception of dust grains, this was the first interstellar object discovered by astronomers. Presumably, these celestial bodies were expelled from their home systems and then made their way through space. It’s clearly not as rare as one might think: another specimen was discovered in 2019: 2I/Borisov. But unlike this comet-like object, Oumuamua has remained shrouded in mystery.

What is the reason for the boost?

According to observational data, it is less than 200 meters in size and seems to have a strange shape – something between a cigar and a pie. It did not feature a fuzzy shell called a coma, and it did not have a tail like most comets. But the strangest aspect was the movement behavior that was observed. It was accelerated away from the sun in a way that astronomers can’t explain in terms of gravitational effects. There is even speculation that the UFO could be an extraterrestrial spacecraft.

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Calculations also showed that the solar energy hitting the comet would not be sufficient to provide an acceleration effect that could arise from bottled water. Given the incoming solar energy, only the release of volatile gases such as hydrogen, nitrogen, or carbon monoxide can provide sufficient acceleration. It therefore seemed possible that the comet consisted largely of solid and frozen forms of this material. But it remained a question about how the body formed from these materials.

But then Jennifer Bergner of the University of California, Berkeley, and Daryl Seligman of the University of Chicago came up with the idea that there could also be a simpler explanation: “A comet traveling through the interstellar medium is strongly affected by the effects and shapes of cosmic rays. Hydrogen. Our thinking was: If this happens, then Hydrogen can collect inside, so that as it enters the solar system and gets hotter, it outpaces the gases,” says Bergner. But could this generate the force needed to cause the observed acceleration?

Cosmic rays made hydrogen

To clarify this, the researchers conducted scientific research. They report that experimental research published in the 1970s, 1980s, and 1990s showed that when high-energy particles such as cosmic rays strike ice, molecular hydrogen (H2) is produced in abundance and trapped in the ice. According to them, cosmic rays penetrate tens of meters into the ice and can convert a quarter or more of water into hydrogen gas.

As the researchers point out, outgassing from this width would not play a role in comets, which are often several kilometers in diameter. “But because ‘Oumuamua is so small, we think enough force was already being generated to cause that acceleration,” says Bergner. Calculations indicate that structural changes in the ice due to the temperature rise near the Sun could release enough gas to affect Comet ‘Oumuamua’s orbit, either in the form of a focused jet or a fan-shaped spray.

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“The most important discovery is that ‘Oumuamua may be an ordinary interstellar comet that has undergone a rough treatment on its long journey,” says Bergner. The results thus support the theory that “Oumuamua originated in a distant star system as an icy body devoid of ‘alien’ features and then became an interstellar wanderer.

Source: UC Berkeley, professional article: Nature, doi: 10.1038/s41586-022-05687-w

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