When the first interstellar comet ever observed in the Solar System was discovered in 2017, one feature inspired wild conjecture was its unusual orbit in which some even believed that it was an extraterrestrial spaceship.
Now, an astrochemist discovered a simpler explanation and verified it with an astronomer. Science Daily reported that cosmic rays changed water to hydrogen in the comet's outer layers in interstellar space, wherein outgassed hydrogen gave the little comet a boost as it approached the Sun.
Discovery of 'Oumuamua Comet
Comets are ice rocks that were left over from the Solar System's formation about 4.5 billion years ago. They may inform scientists about the circumstances that existed at the time the Solar System formed. Interstellar comets can also provide information about the circumstances around other stars that are encircled by planet-forming disks.
In the past, it seemed impossible to observe comets from outside the Solar System, but then the 'Oumuamua comet came along. Using the Pan-STARRS1 telescope, operated by the Institute for Astronomy at the University of Hawaii in Manoa, scientists found the comet on October 19, 2017.
According to NASA, it was the first interstellar object in the Solar System ever observed other than dust grains. A second comet named 2I/Borisov was discovered in 2019, although it behaved like what common comets do.
The size of 'Oumuamua distinguished it from every other well-studied comet in the Solar System, Science Daily reported. When additional telescopes focused on 'Oumuamua, astronomers were able to plot its orbit and discover that it had already completed a lap around the sun and was on its way out of the solar system.
Also, astronomers noticed its slight acceleration away from the Sun which seems larger than seen for asteroids with the same characteristics as comets. When comets approach the Sun, the water and gases expelled from their surfaces form a luminous, gaseous coma and emit dust.
Typically, dust left in the comet's trail appears as one tail, while vapor and dust pushed by solar ray light pressure generates a second tail heading away from the sun, plus a little inertial push outward. Additional substances that can be released include imprisoned organic molecules and carbon monoxide. But they could not detect a coma.
Mystery Behind 'Oumuamua's Weird Orbit
Calculations revealed that the solar energy striking the comet would not be enough to sublimate water or organic molecules off its surface, resulting in the observed non-gravitational kick. With the incoming solar energy, only hypervolatile gases such as H2, N2, or carbon monoxide (CO) could generate enough acceleration to match observations.
The new research, titled "Acceleration of 1I/''Oumuamua from radiolytically produced H2 in H2O ice" published in the journal Nature by astrochemist Jennifer Bergner of the University of California, Berkeley, and astrophysicist Darryl Seligman of Cornell University, explains that the weird acceleration of 'Oumuamua can be attributed to the release of molecular hydrogen gas.
According to Science Alert, the scientists found that this explanation is plausible through the irradiation of a body rich in water ice. They wrote that 'Oumuamua began as an icy planetesimal irradiated at low temperatures by cosmic rays during its interstellar journey. Studies have shown that the processing of water ice can efficiently separate hydrogen.
The researchers remark that the sublimation of water ice would only create up to 50% of the measured acceleration. Molecular hydrogen, on the other hand, explains it fairly well.
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