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

Dusk is Coming for Dawn

The Dawn spacecraft is about to wrap up it’s11-year mission which has included visits to the asteroids Vesta and Ceres. It’s now in a low orbit around Ceres gathering images and other science data, but in few months, it will run out of fuel for it’s attitude control thrusters. It will no longer be able to keep it’s antenna pointed toward Earth and, contact will be lost. The spacecraft will remain in orbit around Ceres.

The Gentle Reader may remember those intriguing bright spots that mystified observers as Dawn approached Ceres. They turned out to be mineral deposits in a large crater named Occator. The images above are close ups of some of those deposits taken from an altitude of 35 km. The top picture is a mosaic of multiple images of the formation called Cerealia Facula in Occator Crater. The bottom is of Vinalia Faculae also in Occator.

Image Credits: NASA

Organic Compounds Found on Ceres

organics-on-ceresThis enhanced color image was made with data from the Dawn spacecraft. It shows the area around a crater on the dwarf planet Ceres named Ernutet. The areas which show up as bright red are associated with evidence of organic material. Organic molecules are interesting to scientists because they are necessary, though not sufficient, components of life on Earth. This discovery adds to the growing list of bodies in the solar system where organic molecules have been found.

Image Credit: NASA

Ceres and Ammonia

Ceres from 240 kmThe Dawn spacecraft has moved into its lowest planed orbit around the dwarf planet Ceres. This picture of a chain of craters called Gerber Catena was take from an altitude of 385 km.

In early December, the Dawn science team announced that the bright material found in such notable craters as Occator is consistent with salt and suggested that a type of magnesium sulfate called hexahydrite may be present. The Dawn team has also found that ammoniated clays are present on Ceres. Because ammonia is abundant in the outer solar system, this could mean that Ceres was formed in the vicinity of Neptune and migrated inward during the early life of the Solar System.

Curiouser and curiouser.

Image Credit: NASA

Those Bright Spots on Ceres

Ceres has more than 130 bright spots. Most of them are associated with impact craters. Researchers at the Max Planck Institute for Solar System Research in Göttingen, Germany, suggest that the bright material could be a type of magnesium sulfate called hexahydrite. Epsom salt is another form of magnesium sulfate. Their theory is that these salt-rich areas were left behind as water-ice sublimated. Impacts from asteroids could have uncovered the mixture of ice and salt from a subsurface layer containing briny water-ice.

The Dawn spacecraft is still in orbit around Ceres. Perhaps additional data will validate this theory.

Video Credit: NASA

Mapping Ceres

CR-7881This color-coded map was assembled using topographic data from the Dawn mission. It shows the highs and lows of the surface of dwarf planet Ceres. It is labeled with names of features that have been approved by the International Astronomical Union. Click on the map to embiggen it.

Image Credit: NASA

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

Grumpy and Dopey were unavailable for comment.

More Pictures of Ceres

VLTThese images are the best ground-based observations of the dwarf planet ever. They were taken using the SPHERE instrument on ESO’s Very Large Telescope.

Ceres orbits in the asteroid belt between Mars and Jupiter, a region known as the Main Belt. It was the first asteroid to be discovered in 1801 and is the largest body in the Main Belt. It is now classified as a dwarf planet. It’s surface area is about the size of India and several of the intriguing bright spots can be seen in these new images. They’re being looked at more closely by the Dawn spacecraft currently orbiting Ceres.

Image Credit: ESO

A Mountain on Ceres

MountainThe Dawn spacecraft has returned images of this tall, conical mountain on Ceres. The mountain is located in the southern hemisphere and is about 6 km high. Its perimeter is sharply defined, and there almost no accumulated debris at the base of the brightly streaked slope.

This image was taken from an altitude of 1470 km. Dawn will spend the next couple of months mapping the planet from that height. Next, it will move to within 375 km of the surface.

BTW, there’s still no word on those bright spots.

Image Credit: NASA