Oumuamua can be formed mainly from solid nitrogen, similar to the surface of Pluto. According to a new study conducted at Arizona State University by planetary scientists Alan Jackson and Steven Desch, the characteristics of the mysterious object indicate that it is probably a block from a planet in another solar system.
The results, published in the Journal of Geophysical Research: Planets, provide more information about the formation of exoplanets and the evolution of galaxies. “Until now, we had no way of knowing whether other solar systems had planets like Pluto, but now we have seen a piece of a pass through Earth,” commented Desch to Advancing Earth and Space Science (AGU), the science outreach association. The celestial body was discovered in 2017 by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) observatory in Hawaii (USA) and drew the attention of the scientific community due to its more flattened shape.
The object entered the Solar System at a speed of 87.3 kilometers per second, a rate slightly lower than expected and which indicates that it has not been more than 1 billion light years in space. “It was probably pulled off the surface by an impact about half a billion years ago and driven out of its original system,” said Jackson.
Oumuamua was probably not flat when it first appeared, however, during its journey, it suffered a kind of cosmic ray erosion. This factor caused the loss of more than 95% of its mass at the moment of its closest encounter with the Sun. “Being made of frozen nitrogen also explains its unusual shape. As the outer layers of nitrogen ice evaporated, the shape of the body became progressively flatter, ”he explained.
Initially, it was speculated that it could be a comet, but unlike any other observed in the Solar System. The pair of astronomers then hypothesized that the object would be composed of different types of ice; thus, they calculated the sublimation rate (change from solid to gaseous state) as Oumuamua passed through the Sun, in addition to analyzing its mass, shape and reflectivity.
The determining factor for not qualifying for this classification was the failure to detect an exhaust gas from the rocket effect – which would have a “tail” appearance -, common in these types from the vaporization of their ice structure by sunlight.
“We knew we were right when we finished calculating which albedo [how reflective an object is] would make Oumuamua’s movement match the observations. This value ended up being the same as the surface of Pluto or Triton [the largest moon of Neptune], bodies covered by nitrogen ice ”, added the researcher.