Some of the biggest asteroids in our solar system – sciencedaily

Using the Very Large Telescope at the European Southern Observatory (ESO’s VLT) in Chile, astronomers photographed 42 of the largest objects in the asteroid belt, located between Mars and Jupiter. Never before has such a large group of asteroids been photographed with such precision. The observations reveal a wide range of particular shapes, from spherical to dog bone, and help astronomers trace the origins of asteroids in our solar system.

The detailed images of these 42 objects are a leap forward in the exploration of asteroids, made possible by ground-based telescopes, and help answer the ultimate question of life, the Universe and everything. [1].

“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 Rosetta space missions and the European Space Agency “, explains Pierre. Vernazza, from the Laboratoire d’Astrophysique de Marseille in France, who led the asteroid study published today in Astronomy & Astrophysics. “Our ESO observations provided sharp images for many other targets, 42 in total.”

The previously small number of detailed observations of asteroids meant that, until now, key features such as their 3D shape or density had remained largely unknown. Between 2017 and 2019, Vernazza and his team set out to fill this gap by conducting an in-depth investigation of the major bodies in the asteroid belt.

Most of the 42 objects in their sample are over 100 km in size; in particular, the team photographed almost all of the asteroids in the belt over 200 kilometers, 20 of 23. The two largest objects the team probed were Ceres and Vesta, which measure between 940 and 520 kilometers in diameter. , while the two smaller asteroids are Urania and Ausonia, each only about 90 kilometers away.

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, the team found that the densities change significantly in the sample. The four least dense asteroids studied, including Lamberta and Sylvia, have densities of about 1.3 grams per cubic centimeter, roughly the density of coal. The highest, Psyche and Kalliope, have densities of 3.9 and 4.4 grams per cubic centimeter, respectively, which is higher than the density of diamond (3.5 grams per cubic centimeter).

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. In short, such an enormous variety in their composition can only be understood if the bodies originate from separate regions of the solar system,” says Josef Hanuš of Charles University. , Prague, Czech Republic, one of the authors of the study. 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.

These results were made possible by the sensitivity of the Spectro-Polarimetric High Contrast Exoplanet REsearch (SPHERE) instrument mounted on the ESO VLT. [2]. “With the improved capabilities of SPHERE, as well as the fact that little was known about the shape of the larger asteroids in the main belt, we were able to make substantial progress in this area,” explains co-author Laurent Jorda, also from the Laboratory of Astrophysics in Marseille.

Astronomers will be able to image even more asteroids in great detail with ESO’s next Extremely Large Telescope (ELT), currently under construction in Chile and ready to start operations later this decade. “ELT observations of the asteroids in the main belt will allow us to study objects up to 35 to 80 kilometers in diameter, depending on their location in the belt, and craters about 10 to 25 in size. kilometers, “says Vernazza. “Having a SPHERE-type instrument at the ELT would even allow us to image a similar sample of objects in the distant Kuiper Belt. This means that we will be able to characterize the geological history of a much larger sample of small soil bodies. . “

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Arline J. Mercier