Though not as massive or colourful as planets, asteroids have a lot to teach us about our local corner of the universe. That’s especially the case for asteroids close enough to be sampled — such as Bennu was in October 2020 — or when rocky fragments fall to Earth as meteorites.
Asteroids are the detritus left over from the creation of our solar system’s planets, and as such, they contain information about what things were like billions of years ago. NASA has counted over 1 million asteroids to date, and recently, the Very Large Telescope at the European Southern Observatory imaged 42 of the largest ones.
“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,” said Pierre Vernazza from the Laboratoire d’Astrophysique de Marseille in France in an ESO press release. Vernazza led a study on the asteroids published today in Astronomy & Astrophysics.
The Very Large Telescope makes observations in visible and ultraviolet light. It is actually made up of four unit telescopes, all of which sit high up in Chile’s Atacama Desert, one of the best places for looking at the sky. The images were taken using the SPHERE instrument on the telescope, which ordinarily does direct imaging of exoplanets, but in this case was able to get a great look at a number of asteroids in the main belt.
The recent work by Vernazza’s team improves the quality and quantity of images detailing asteroids’ sizes and structures. These images will help astronomers get better understanding of the solar system’s origin.
The asteroids range from the very dense ones, like Kalliope and Psyche, to some of the least dense, like Sylvia and Lamberta. The smallest two asteroids in this group are Ausonia and Urania, which each measure about 89 km wide. The largest asteroid, Ceres, is 940 km across, large enough that it is considered a dwarf planet.
All of these objects offer insights about the primordial soup that forged them; for example, the research team found that the least dense asteroids of the 42 most likely formed farther out than their denser brethren, somewhere beyond the orbit of Neptune, and eventually migrated inward to their current locations.
“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,” said Josef Hanuš of the Charles University in Prague and one of the authors of the study, in the ESO release.
And if you’re impressed by the Very Large Telescope, just wait until the Extremely Large Telescope becomes operational later in the 2020s. That telescope will gather 20 times more light than a unit of the Very Large Telescope, allowing astronomers to see fainter objects better than they currently can. (Alas, the Overwhelmingly Large Telescope never made it past the concept phase.)