Hygiea may soon be getting a classification promotion from asteroid to dwarf planet. High-resolution pictures were studied by astronomers who discovered that Hygiea actually has a spherical shape which is an extremely important qualification for being labelled a dwarf planet.
Prior to finding out that it has a spherical shape, Hygiea already met three of the four requirements in order to be classified as a dwarf planet – it orbits the sun; it isn’t a moon that orbits another planet; and it hasn’t pushed other objects out of its orbit. And now astronomers have confirmed that it has a round shape, meaning that it had enough mass for its gravity to mold it into that shape. Robert Massey, who is from the U.K.’s Royal Astronomical Society, told Newsweek, “It’s an unusual situation, as Hygiea appears to be smaller than the minor planets Vesta and Pallas, but is more spherical.”
Hygiea is the fourth biggest rock in the Asteroid Belt between the orbits of Mars and Jupiter. According to the team of astronomers that was led by Pierre Vernazza from the Laboratoire d’Astrophysique de Marseille in France, Hygiea has a diameter of a little more than 267 miles, making it less than one-fifth of the width of Pluto (approximately 1,491 miles in diameter).
The team was surprised to have found only two impact craters on its surface. “This result came as a real surprise as we were expecting the presence of a large impact basin, as is the case on Vesta,” Vernazza said. The asteroid’s parent body was thought to have been between 46 and 93 miles wide before a huge impact broke it apart into thousands of pieces, ultimately causing the creation of Hygiea.
If Hygiea moves up from asteroid to dwarf planet status, it would officially be our Solar System’s smallest dwarf planet, stealing the title from Ceres that has a diameter of nearly 590 miles.
But for now, Hygiea is still officially classified as an asteroid, as the International Astronomical Union (the same group that demoted Pluto to a dwarf planet) has to review all of the evidence and take a vote on whether or not it will be promoted to dwarf planet status. (Pictures of Hygiea can be seen here.)
In a statement from the European Southern Observatory (ESO) that manages the SPHERE instrument that captured the high-resolution photos, Vernazza stated, “Thanks to these images, Hygiea may be reclassified as a dwarf planet, so far the smallest in the solar system,” adding, “Thanks to the VLT and the new generation adaptive-optics instrument SPHERE, we are now imaging main belt asteroids with unprecedented resolution, closing the gap between Earth-based and interplanetary mission observations.” Their study was published in Nature Astronomy and can be read in full here.