Hygiea, Vesta, and Ceres

New ground-based observations with ESO’s SPHERE instrument on the Very Large Telescope have revealed that the surface of the asteroid Hygiea lacks a large impact crater. Because it was formed from one of the largest impacts in the history of the asteroid belt, astronomers were expecting to find at least one large, deep impact basin, similar to the one on Vesta (bottom right in the central panel).

The new study also found that Hygiea is spherical. That would mean that it rather than Ceres is the smallest dwarf planet in the Solar System. Hygiea’s diameter is just over 430 km, a bit less than half that of Ceres (950 km).

Image Credit: ESO

Dwarf Planet 2007 OR10

2007 OR10 is the largest unnamed body in the solar system, and it was visible by the K2 mission’s of the repurposed Kepler spacecraft late 2014. The apparent movement of the faint dwarf planet (follow the arrow) among the stars is caused by the changing position of Kepler in its orbit around the Sun. The diffuse light sweeping across view is a reflection from the much brighter planet Mars passing nearby.

Video Credits: Konkoly Observatory / László Molnár and András Pál

Five Dwarfs

Dwarf PlanetsA dwarf planet is a planetary-mass object that isn’t a planet nor a natural satellite of a planet. It is in direct orbit around the Sun, and it is massive enough for its shape to pulled into a sphere by its own gravity. However, unlike all of the major planets, it has not cleared the neighborhood around its orbit.

The International Astronomical Union (IAU) currently recognizes five dwarf planets: Ceres, Pluto,  Makemake, Eris, and Haumea. They’re pictured above (from top left):
Ceres as seen from the Dawn spacecraft. It’s the dwarf planet in the asteroid belt.
Pluto as photographed by New Horizons.
Makemake as viewed by the Hubble Space Telescope.
Eris and its moon Dysnomia as seen by the Hubble.
Haumea with its moons, Hiʻiaka and Namaka as seen by the ground-based Keck telescope.

Image Credit: Wikimedia

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