According to a paper published in the latest issue of Nature, researchers at the University of California, Berkeley and Cornell University have come up with a new, simpler explanation for the mysterious cigar-shaped "interstellar object" Oumuamua, discovered in 2017: a small comet that emits a thin shell of hydrogen that cannot be detected by telescopes, pushing it to accelerate.
Oumuamua's unusual appearance and characteristics have puzzled scientists.
On October 19, 2017, scientists in Hawaii, USA, discovered an object Oumuamua that sailed over the Earth, and its unusual appearance and characteristics puzzled scientists, many believing that it was an alien spacecraft powered by an engine.
Oumuamua moves very fast, at about 97,200 mph (156428 km/h). Scientists believe that this speed cannot be produced by gravity from the sun.
Further analysis revealed that Oumuamua's shape was unusually slender, like a cigar, and tumbled through space.
These observations suggest that the object is not bound to the sun's gravity and is therefore the first object to be observed from outside the solar system.
Although it accelerates in a similar way to other comets, it is also much smaller than usual, measuring only 377 feet (115 meters) in length.
This, combined with the fact that it is quite far from the sun, means that it will not be able to produce enough water vapor to give the non-gravitational thrust it exhibits.
In addition, it has no characteristic tail or coma, leading the SETI Institute, which searched for extraterrestrial intelligence, to believe that Oumuamua could be "an alien artwork."
The trajectory of Oumuamua's flight over the solar system.
New research by researchers at the University of California, Berkeley and Cornell University shows that Oumuamua is a comet propelled by undetectable hydrogen gas.
Lead author Dr. Jenny Bergner said the comet was actually an iceberg made up of solid hydrogen or nitrogen because the material could be vaporized at Oumuamua's distance from the sun.
The team looked at past experiments to understand how energetic particles, such as cosmic radiation from interstellar space, would affect ice trapped inside comets.
They found that they could penetrate tens of meters of rock, reach deep in the ice locked inside, and convert it into hydrogen.
Hydrogen will remain inside the rock until the comet reaches the vicinity of the sun, where the heat will change the structure of the solid ice and cause the gas to be expelled.
As Oumuamua is close to the sun, hydrogen gas is emitted inside, pushing it to accelerate.
Models show that this force to expel the gas will be enough to accelerate the small object out of its hyperbolic orbit around the sun.
Co-author Dr Darryl Seligman said the study's results could be disappointing because Oumuamua is not an alien spacecraft, but it is exactly what should happen to an interstellar comet.
Comets are balls of ice, dust and rock, which astronomers call "dirty snowballs." Comets usually come from rings of frozen material at the outer edge of our solar system called the Oort cloud.
As various gravitational forces drive them out of the Oort Cloud, they move inward into the solar system, becoming more pronounced as they approach the heat emitted by the Sun.
As they approach, the comets melt, releasing a stream of water vapor, dust and other molecules that are blown away from their surfaces by solar radiation and plasma.
This manifests itself as cloudy and outward-facing tails and gives them an outward kick that slightly changes the shape of their orbit around the Sun.
Also surrounding the comet is a thin, gas-filled atmosphere with more ice and dust called "comets."
Text/Nandu reporter Chen Lin