Astronomers May Have Found The Smallest Dwarf Planet Named Hygiea

    SPHERE image of Hygiea
    A new SPHERE/VLT image of Hygiea, which could be the Solar System’s smallest dwarf planet yet. As an object in the main asteroid 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 neighbourhood around its orbit. The final requirement is that it have enough mass that its own gravity pulls it into a roughly spherical shape. This is what VLT observations have now revealed about Hygiea.

    A close examination of the asteroid belt between Mars and Jupiter may have given us the smallest dwarf planet in our Solar System. Named Hygiea, this asteroid that can be found orbiting the sun in the Asteroid Belt and is the fourth-largest asteroid in it; behind dwarf planet Ceres (945 Kilometers) and asteroids Vesta (525 Kilometers) and Pallas (512 Kilometers).

    Until now, our understanding and knowledge about Hygiea were abysmal, to say the least. It was thought to be a roughly oblong chunk of rock with diameters of 350 km one way and 500 km the other with a giant impact crater on one side. It was considered to be a relatively uninteresting piece of rock, although this has been changed upon closer examination by the Very Large Telescope.

    Hygiea is a relatively small, inconspicuous asteroid orbiting the sun in the asteroid belt. Here is a visual size comparison.

    With the help of the cutting edge technology of the SPHERE instrument on the VLT, astronomers could resolve the shape of Hygiea. The results from one of the most robust imaging systems in the world indicate that the shape of the asteroid is more spherical than we thought.     

    The new images will directly lead to the reclassification of Hygiea as a new dwarf planet, the smallest one yet. The unique measurements from the photos indicate that Hygiea has a diameter of about 430 kilometres, with a rotation period of 13.8 hours. Hygiea was suspected to be similar to Ceres in several aspects such as surface composition and density, but the new observations show that it is almost as spherical as Ceres as well.

    Ceres is another dwarf planet that can be found in the asteroid belt.

    Hygiea is not alone in its orbit. It travels with around 7000 small objects of similar composition. These objects are suspected of having been released from Hygiea over 2 Billion years ago when an impact is thought to have occurred. Thus, this group is known as the Hygiea family.

    The criteria for a celestial body to be officially counted as a dwarf planet comprises of four parametres. According to the IAU, it has to be in orbit around the sun, not around a planet; it can’t have cleared the neighbourhood of its orbit, and it must’ve attained hydrostatic equilibrium. Which means it must be more or less round in shape. Having cleared that four criteria with the recent images, Hygiea is well on its way to becoming a dwarf planet.

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