Using the Very Large Telescope (TGT), recent observations of the Asteroid Hygiea, show that its dimensions place it in fourth position of the largest objects in the main asteroid belt, after Ceres, Vesta and Pallas.
It is thanks to the SPHERE instrument installed on the TGT that the astronomers were able to study the celestial object for the first time.
They were able to see its surface and determine its shape and size.
The mysterious Hygiea has a spherical shape and presumably displaces Ceres from its rank as the smallest dwarf planet in the solar system.
In fact, the asteroid immediately satisfies three of the four conditions necessary to qualify it as a dwarf planet: it orbits around the Sun, it is not a moon and, unlike a planet, it does not did not clean the surroundings of its orbit.
The fourth condition is that it has sufficient mass for its own gravity to give it an almost spherical shape.
The new observations made using TGT make this clear.
The SPHERE instrument installed on the TGT has unique features that make it one of the most powerful imaging systems in the world and has helped determine the shape of Hygiea: an almost spherical shape.
Pierre Vernazza, Laboratory of Astrophysics of Marseille in France
The diameter of Hygiea would be about 430 km.
Pluto, the most famous of the dwarf planets, has a diameter of 2400 km. That of Ceres is around 950 km.
Few impact craters
Observations revealed that the Hygiea surface showed no evidence of a large impact crater, as scientists expected.
It should be known that Hygiea is the main member of one of the largest families of asteroids made up of nearly 7000 objects originating from one and the same parent body.
Astronomers therefore expected that the event that led to the formation of this large family had left a visible mark, deep and extended on the surface of Hygiea.
This result is a real surprise. We expected to see the presence of a large impact crater, like the one on the surface of Vesta.
Pierre Vernazza
Only two craters could be identified with certainty on the images covering 95% of the total area of Hygiea.
None of these two craters could result from the impact that gave birth to the Asteroid family of Hygiea, whose volume is close to that of an object of 100 km in diameter. They are far too small.
Miroslav Brož, Institute of Astronomy at Charles University
New theory
With the help of numerical simulations, astronomers have established that the spherical shape of Hygiea and its large family of asteroids are probably the result of a major frontal collision with a large projectile with a diameter between 75 km and 150 km occurred about 2 billion years ago and is responsible for the complete destruction of the parent body.
The details of this work are published in the journal Nature Astronomy.
