Using the Spectro-Polarimetric High Contrast Exoplanet REsearch (SPHERE) instrument mounted on ESO’s Very Large Telescope (VLT), astronomers conducted a high-angular resolution imaging study of 42 large asteroids in the main asteroid belt, located between Mars and Jupiter. Their results appear in the journal Astronomy & Astrophysics.
“Only three large Main Belt asteroids, Ceres, Vesta and Lutetia, have been photographed in high level of detail so far, as they have been visited by NASA’s Dawn and ESO’s Rosetta, respectively. “, said Dr Pierre Vernazza, astronomer. at the Astrophysics Laboratory in Marseille.
âOur ESO observations provided sharp images for many other targets, 42 in total. “
Most of the 42 objects are over 100 km (62 miles); in particular, astronomers have imaged almost all asteroids in the belt over 200 km (124 miles), 20 of the 23 asteroids.
The two largest objects they probed were Ceres and Vesta, which are approximately 940 km (584 miles) and 520 km (323 miles) in diameter, while the two smaller asteroids are Urania and Ausonia, each about 90 km (56 miles).
By reconstructing the shapes of the objects, the team realized that the observed asteroids are mainly divided into two families.
Some are almost perfectly spherical, like Hygiea and Ceres, while others have a more peculiar, “elongated” shape, their undisputed queen being the “dog bone” asteroid Kleopatra.
By combining the shapes of the asteroids with information about their masses, Dr. Vernazza and his colleagues found that the densities change significantly in the sample.
The four least dense asteroids studied, including Lamberta and Sylvia, have densities of around 1.3 g / cm3, approximately the density of coal.
The tallest, Psyche and Kalliope, have densities of 3.9 and 4.4 g / cm3, respectively, which is greater than the density of diamond (3.5 g / cm3).
This large difference in density suggests that the makeup of asteroids varies considerably, giving astronomers important clues as to their origin.
“Our observations strongly support the substantial migration of these bodies since their formation,” said Dr. Josef HanuÅ¡, astronomer at Charles University.
“In short, such a great variety in their composition can only be understood if the bodies originate from distinct regions of the solar system.”
In particular, the results support the theory that the less dense asteroids formed in remote regions beyond Neptune’s orbit and migrated to their current location.
P. Vernazza et al. 2021. VLT / SPHERE imaging survey of the largest asteroids in the main belt: final results and synthesis. A&A 654, A56; doi: 10.1051 / 0004-6361 / 202141781