Images of 42 of the Biggest Asteroids in the Solar System

A huge team of astronomers have combined forces to use the European Southern Observatory’s Very Large Telescope (ESO’s VLT) to provide the sharpest view ever of 42 of the largest objects in the asteroid belt, located between Mars and Jupiter.

Fittingly, the collection of images was released on the 42nd anniversary of the publication of “The Hitchhiker’s Guide to the Galaxy” by Douglas Adams. In the book, the number 42 is the answer to the “Ultimate Question of Life, the Universe, and Everything.” These 42 images represent some of the sharpest views ever of these objects  — which might contribute to answering these ultimate questions!

Plus, there’s a great poster of the asteroids, too:

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 kilometres in diameter, including 20 larger than 200 kilometres. 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. You can find larger versions of this image and more at this link from ESO.

“Only three large main belt asteroids, Ceres, Vesta and Lutetia, have been imaged with a high level of detail so far,” said Pierre Vernazza, from the Laboratoire d’Astrophysique de Marseille in France, who led the asteroid study, published in Astronomy & Astrophysics, “as they were visited by the space missions Dawn and Rosetta of NASA and the European Space Agency, respectively. Our ESO observations have provided sharp images for many more targets, 42 in total.”

Sixty-seven astronomers contributed to the effort, and in their paper the scientists explained that their main goal was to be able to reconstruct the 3D shapes and garner the density of their target asteroids. They were able to use the extremely sensitive Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument mounted on the VLT.

“Our SPHERE data along with light curve data have been used to constrain the rotational parameters (spin axis and period) and have allowed us to reconstruct a first 3D shape of every target,” the team wrote in their paper.

“ELT observations of main-belt asteroids will allow us to study objects with diameters down to 35 to 80 kilometers, depending on their location in the belt, and craters down to approximately 10 to 25 kilometers in size,” said Vernazza. “Having a SPHERE-like instrument at the ELT would even allow us to image a similar sample of objects in the distant Kuiper Belt. This means we’ll be able to characterize the geological history of a much larger sample of small bodies from the ground.”

Most of the 42 objects in their sample are larger than 100 km in size; in particular, the team imaged nearly all of the belt asteroids larger than 200 kilometers, 20 out of 23. The two biggest objects the team probed were Ceres and Vesta, which are around 940 and 520 kilometers in diameter, whereas the two smallest asteroids are Urania and Ausonia, each only about 90 kilometers.

In reconstructing the objects’ shapes, the team found 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, such as the dog-bone-shaped asteroid Kleopatra.

Computing the densities of the objects revealed that the asteroids’ composition varies significantly across the 42 objects. The best theory for explaining the differences is that the various bodies originated in different areas of the Solar System. For example, the results support that the least dense asteroids formed in the remote regions beyond the orbit of Neptune and migrated to their current location.

Read more about the team’s work here.