NANJING, Oct. 20 (Xinhua) -- An international study has revealed how Arrokoth, the most distant object ever visited by a man-made probe, takes the bizarre shape of a flattened snowman.
The Kuiper Belt is a disc-shaped region beyond Neptune that extends from about 30 to 55 astronomical units. An astronomical unit of measurement is equal to 149.6 million km, the mean distance from the center of the earth to the center of the sun.
On New Year's day of 2019, NASA's New Horizons spacecraft performed the farthest flyby in history as it approached Arrokoth in the Kuiper Belt. Images sent back revealed that Arrokoth, about 30 km in size, is a strange world with two flattened lobes aligned to its equatorial plane like a squashed snowman.
Researchers from the Purple Mountain Observatory under the Chinese Academy of Sciences, the Max Planck Institute for Solar System Research in Germany, and the Planetary Science Institute in the United States investigated how the shape came to be, finding that it may have been gradually boiled away by the heat of the sun in a time scale of about 1 to 100 million years.
During the formation of the Solar System, the region where Arrokoth is located could have been cold and dust-shaded. The low temperatures enabled volatile substances like carbon monoxide and methane to freeze onto dust grains and compose planetesimals, small solid objects that are thought to come together under gravitation to form a planet.
Arrokoth may have started as a merger between a spherical and an oblate body. Solar illumination would have raised Arrokoth's temperature after the nebular dust cleared and then driven off the condensed volatile substances inside.
The researchers pointed out that for a space body to change its shape as dramatically as Arrokoth, its rotational axis needs to be oriented in a special way. For Arrokoth, its rotational axis is almost parallel to the orbital plane which causes the poles to heat up the most. During its orbit around the sun, the frozen gases escape from the poles most efficiently, leading to a strong mass loss and flattening of the shape.
The study suggested that sublimation mass loss could be a ubiquitous process and a major cause in shaping the structure of Kuiper Belt objects. The findings have been published in the journal Nature Astronomy.
The distant Kuiper Belt is thought to be populated with hundreds of thousands of icy bodies and an estimated trillion or more comets. Scientists believe that Kuiper Belt objects, such as Pluto, preserve evidence about the early formation of the solar system. Enditem