ESO astronomers have used the SPHERE instrument on the very large telescope to observe an asteroid called Hygiea. Observations suggest that Hygiea can be classified as a dwarf planet. The object is said to be the fourth largest asteroid after Ceres, Vesta and Paras.
Hygiea is a special planet that may have won the title from Ceres, making it the smallest dwarf planet in the solar system. The ESO team said Hygiea met three of the four requirements classified as dwarf planets. This includes it orbiting the sun, not orbiting the planet shimias like the moon, and not clearing its neighbors around orbit like a planet. The last requirement is that it has enough gravity to pull itself into a rough sphere. This is where the SPHERE instrument is used, and the team was able to determine that Hygiea was almost spherical. The instrument also measures the diameter of Hygiea, which is just over 430 kilometers.
Pluto is nearly 2,400 kilometers in diameter, while Ceres is nearly 950 kilometers in diameter. The team did not find the expected large impact crater on its surface, and it did have two impact craters, but neither was large and was not generated during the formation of Hygiea. The team estimates that Hygiea and the asteroid family may have been the result of a major head-on collision between the larger planet and a object 75 to 150 kilometers in diameter. The collision is believed to have taken place about 2 billion years ago.