An international team of astronomers have determined the properties of the surface layer of one of the Earth's natural quasi-satellites, the asteroid Kamoʻoalewa.
It turned out that this body could be covered with fine-grained regolith, similar to the lunar, and earlier could have been a fragment of the lunar surface, ejected during a major collision.
Quasisatellites are bodies in orbital resonance with the planet, and the eccentricity of their orbits is usually greater than the eccentricity of the planet's orbit.
A distinctive feature of such objects is the instability of the orbit over long time intervals, since they are located outside the Hill sphere, where the planet is able to hold its satellite, despite the attraction of the Sun.
Quasi-satellites exist in many planets of the solar system; six such bodies are known for the Earth today.
A group of astronomers led by Benjamin N. L. Sharkey from the University of Arizona has published the results of studies of the properties of the terrestrial quasi-satellite Kamoʻoalewa.
They used ground-based telescopes LBT (Large Binocular Telescope) and LDT (Lowell Discovery Telescope).
This body was discovered in 2016 as part of the Pan-STARRS sky survey, later scientists determined that it was not space debris, but an asteroid.
The orbit of Kamoʻoalewa is the most stable among all quasi-satellites of the Earth with a dynamic lifetime of several hundred years.
It is characterized by a semi-major axis within 0.001 astronomical units from the Earth, an eccentricity of only 0.1 and a moderate inclination of about 8 degrees to the plane of the ecliptic, and the period of revolution around the Sun is about a year.
The period of rotation around its own axis of this body is estimated at 28.3 hours.
Analysis of the spectra of the radiation reflected from the surface of the asteroid and their comparison with the spectra of various materials in the Solar System showed that silicate grains, 20–45 micrometers in size, found on the Moon during the Apollo 14 flight, are best suited for the role of the Kamoʻoalewa surface layer matter.
However, this does not guarantee that the asteroid is indeed covered by fine-grained regolith.
The spectral properties of the asteroid are incompatible with typical near-Earth asteroids and require additional features such as high metal content or extreme space weathering.
There can be several answers to the question about the origin of Kamoʻoalewa.
It can belong to objects approaching the Earth, be from an unknown quasi-stable population of Earth's Trojan asteroids, a fragment of the Moon ejected during the fall of a large body, or a fragment of a destroyed body that previously approached the Earth- Moon.
It is expected that further observations of Kamoʻoalewa using ground-based telescopes and its studies by the Chinese interplanetary mission ZhengHe will help to accurately establish the nature of the asteroid.