New observations of the unusual asteroid Cleopatra have shown that it is barely held intact, and its satellites could have formed from material escaped from the surface.
(216) Cleopatra is one of the large asteroids of the main belt located between the orbits of Mars and Jupiter. It is well known for its unusual bone-like shape just over 200 kilometers long. For a long time, it was even believed that Cleopatra is a double asteroid. However, later observations showed that its two parts are connected by a narrow bridge. In addition, he has a pair of his own companions, named after the descendants of the Egyptian queen - Alexgelios and Cleoselene.
Size comparison: Asteroid Cleopatra against the backdrop of the northern Italian Apennine Peninsula / © ESO, M. Kornmesser, Marchis et al., 2021
This unusual system is the subject of two articles (1, 2), which the team of French-American astrophysicist Franck Marchis published in Astronomy & Astrophysics. In them, scientists report on new, clearest in history pictures of the asteroid, which made it possible to compile its detailed three-dimensional model, as well as the origin of its satellites.
For these observations, Markey and his co-authors used the European Southern Observatory (ESO) VLT telescope with the SPHERE adaptive optics system. The new images helped to clarify the size and mass of the asteroid. The length of Cleopatra turned out to be more than the previous estimates (270 kilometers), but the mass is one third less than it was believed until now (3 * 1015 tons). In addition, scientists examined the orbits of satellites rotating near the asteroid, which in reality also turned out to be far from the calculated ones.
Asteroid Cleopatra, captured by VLT in rotation at different angles / © ESO, MISTRAL algorithm (ONERA / CNRS), Vernazza, Marchis et al., 2021
The work showed that the density of Cleopatra is not so high (3, 38 g / cm3), and since the asteroid belongs to class M and consists of metals, it seems to have a high porosity. It is believed that such objects are formed from the remnants of molten material, which is ejected during the collision of celestial bodies, and remain not very stable.
For Cleopatra, the situation is especially dangerous, because she also stands out with a decent rotational speed, making a full revolution around its axis in less than five and a half hours. A little faster, and the "bone" would have fallen apart. But already comparatively weak influences are enough for the centrifugal force to do its job and fragments to come off the asteroid. Scientists suggest that this is how the moons Alexgelios and Cleoselena appeared.