Free Astronomy Magazine January-February 2020

38 JANUARY-FEBRUARY 2020 SPACE CHRONICLES ment on the VLT, which is one of the most powerful imaging systems in the world, we could resolve Hygiea’s shape, which turns out to be nearly spherical,” says lead researcher Pierre Vernazza from the Labora- toire d’Astrophysique de Marseille in France. “Thanks to these images, Hy- giea may be reclassified as a dwarf planet, so far the smallest in the Solar System.” The team also used the SPHERE observations to con- strain Hygiea’s size, putting its diam- eter at just over 430 km. The smallest dwarf planet yet in the Solar System A stronomers using ESO’s SPHERE instrument at the Very Large Telescope (VLT) have revealed that the asteroid Hy- giea could be classified as a dwarf planet. The object is the fourth largest in the as- teroid belt after Ceres, Vesta and Pallas. For the first time, astronomers have observed Hygiea in sufficiently high resolution to study its sur- face and determine its shape and size. They found that Hygiea is spherical, poten- tially taking the crown from Ceres as the smallest dwarf planet in the Solar System. As an object in the main as- teroid belt, Hygiea satisfies right away three of the four requirements to be classified as a dwarf planet: it orbits around the Sun, it is not a moon and, unlike a planet, it has not cleared the neigh- bourhood around its orbit. The final requirement is that it has enough mass for its own gravity to pull it into a roughly spherical shape. This is what VLT observations have now revealed about Hygiea. “Thanks to the unique capa- bility of the SPHERE instru- by ESO T his is what VLT observations have now revealed about Hygiea. [ESO/P. Vernazza et al./ MISTRAL algorithm (ONERA/CNRS)]