The Sun sets at ESO’s Very Large Telescope (VLT) in this image, taken at the observatory on Cerro Paranal in the dry Atacama Desert of Chile. Credit: Iztok Bončina/ESO

Never before has such a large group of asteroids been imaged so sharply.

That’s the word from The European Southern Observatory using its Very Large Telescope in Chile.

Forty-two of the largest objects in the asteroid belt between Mars and Jupiter have been imaged. Taken in the whole, the observations reveal a wide range of peculiar shapes, from spherical to dog-bone. That imagery can help astronomers trace the origins of the asteroids in our Solar System.

High level of detail

“Only three large main belt asteroids, Ceres, Vesta and Lutetia, have been imaged with a high level of detail so far, as they were visited by the space missions Dawn and Rosetta of NASA and the European Space Agency, respectively,” explains Pierre Vernazza, from the Laboratoire d’Astrophysique de Marseille in France, who led the asteroid study published recently in Astronomy & Astrophysics.

This image depicts 42 of the largest objects in the asteroid belt, located between Mars and Jupiter.
Credit: P. Vernazza, et al.

The four least dense asteroids studied, including Lamberta and Sylvia, have densities of about 1.3 grams per cubic centimeter, around 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).

Object shapes

ESO’s VLT in Chile has made possible the reconstruction of the objects’ shapes. The team realized that the observed asteroids are mainly divided into two families. Some are almost perfectly spherical, such as Hygiea and Ceres, while others have a more peculiar, “elongated” shape, their undisputed queen being the “dog-bone” asteroid Kleopatra, explains an ESO statement.

“Our observations provide strong support for substantial migration of these bodies since their formation. In short, such tremendous variety in their composition can only be understood if the bodies originated across distinct regions in the Solar System,” explains Josef Hanuš of the Charles University, Prague, Czech Republic, one of the authors of the study. In particular, the results support the theory that the least dense asteroids formed in the remote regions beyond the orbit of Neptune and migrated to their current location.

This poster shows 42 of the largest objects in the asteroid belt, located between Mars and Jupiter (orbits not to scale). The images in the outermost circle of this infographic have been captured with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on ESO’s Very Large Telescope. The asteroid sample features 39 objects larger than 100 kilometers in diameter, including 20 larger than 200 kilometers. The poster highlights a few of the objects, including Ceres (the largest asteroid in the belt), Urania (the smallest one imaged), Kalliope (the densest imaged) and Lutetia, which was visited by the European Space Agency’s Rosetta mission.
Credit: ESO/M. Kornmesser/Vernazza et al./MISTRAL algorithm (ONERA/CNRS)




SPHERE sensitivity

These findings were made possible due to the sensitivity of the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument mounted on ESO’s VLT.

“With the improved capabilities of SPHERE, along with the fact that little was known regarding the shape of the largest main belt asteroids, we were able to make substantial progress in this field,” says co-author Laurent Jorda, also of the Laboratoire d’Astrophysique de Marseille.













To access the paper – “VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis,” go to:

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