Vesta and Ceres: born at the same time and yet so different

Asteroids, also known as minor planets, differ greatly in shape and size. Those with which we are more familiar are in almost all cases crater-strewn irregularly shaped bodies that can even have tiny moons. Most of them have a diameter of between 20 to 100 kilometres, a few up to 500 kilometres, but none are larger than Ceres: with its 1000- kilometre diameter, it makes up more than a third of the total mass of the asteroid belt.

Vesta, with a diameter of between 460 and 580 kilometres, is the third largest asteroid. It rotates around its own axis in five hours and 20 minutes, and requires 3.6 Earth years to complete an orbit around the Sun. As this asteroid is relatively close to the sun at 380 million kilometres, the light elements in the rock have evaporated and escaped into space.

It is assumed that only a very small percentage of water ice has remained, which is why planetary researchers describe Vesta as 'dry'. Spectroscopic observations with Dawn show that Vesta's crust consists of various types of rock. At the south pole, the collision with another asteroid has left a huge impact crater with a diameter of 460 kilometres and a depth of about 13 kilometres. Planetary researchers assume that the impact produced at least 50 smaller asteroids, which now follow their path around the Sun as 'Vestoids'. It is pretty certain that individual fragments have reached Earth. That is indicated by various meteorite finds in the Antarctic.

Data on the asteroid Vesta

Mass: 3.0 x 1020 kg
Size: 578 x 560 x 458 kilometres
Density: 3.9 g/cm3
Rotation period: 5.34 hours
Orbital period: 3.63 years
Average distance from the Sun: 353.3 million kilometres                                     

Ceres orbits the Sun in 4.6 Earth years and rotates around its own axis in just over 9 hours. At about 415 million kilometres, it is significantly further away from the Sun than Vesta. Its formation process was different as a result of the lower quantity of radiation from the Sun. Instead of evaporating completely, a large part of the light and volatile elements are still present in parts of the asteroid. It is assumed that Ceres has a considerable amount of water content, from 15 to 25 percent, and is therefore also referred to as a 'wet' asteroid. Planetary researchers estimate that the ice is hidden in a 100 kilometres thick layer in the mantle under the crust. Furthermore, there might be a thin atmosphere on the dwarf planet: astrobiologists even speculate that primitive life could have existed on Ceres in the past.

Data on the asteroid Ceres

Mass: 8.7 x 1020 kilograms
Size: 974 x 974 x 910 kilometres
Density: 1.98 g/cm3
Rotation period: 9.08 hours
Orbital period: 4.6 years
Average distance from the Sun: 413.9 million kilometres

The discovery of the Main Asteroid Belt 

It was on the night of New Year in Palermo in 1801 – in what was then the southernmost observatory in Europe – that Italian astronomer Giuseppe Piazzi discovered the dwarf planet Ceres. Before this discovery, eighteenth century scholars had wondered about the gap between Mars and Jupiter; after all, according to the empirical Titius-Bode law on the distances between the planetary orbits, there should have been a planet precisely in that location. With a diameter of 1000 kilometres, Ceres was, however, too small to close that gap on its own. So German astronomers continued their search.

Working together as a 'celestial police force' they noted one object after the other. Vesta was discovered in 1807 by the Bremen physicist and astronomer Heinrich Olbers. By the end of the nineteenth century, astronomers could proudly point to 463 recorded asteroids. Instead of a planet on the far side of Mars they had found the Main Asteroid Belt of the Solar System. Today we know almost half a million objects.

Last modified: 23/02/2012 10:49:03

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Contacts

Elke Heinemann
Deutsches Zentrum für Luft- und Raumfahrt (DLR) - German Aerospace Center

Tel.: +49 2203 601-2867

Fax: +49 2203 601-3249
Ulrich Köhler
Deutsches Zentrum für Luft- und Raumfahrt (DLR) - German Aerospace Center

Tel.: +49 30 67055-215

Fax: +49 30 67055-402

Vesta and Ceres vs Mars

Vesta, Ceres und Mars im Größenvergleich

Vesta and Ceres are small bodies. The planets of the Solar System were created from such fragments a long time ago. Both bodies are shown in a size comparison with Mars.

Up and down on Vesta's crater-strewn surface

Vesta

NASA's Dawn spacecraft obtained this image with the Framing Camera on 11 August 2011 using the clear filter. The image has a resolution of about 260 metres per pixel.

Piece of the Millbillillie eucritic meteorite, thought to come from Vesta

Stück des Eucrit%2dMeteoriten Millbillillie, der vermutlich von Vesta stammt

A piece of the Millbillillie eucritic meteorite, thought to come from Vesta, which fell to Earth on 15 October 1960 in the Wiluna district of Western Australia.

Structure of the dwarf planet Ceres

Unterschiedliche Schichten des Asteroiden Ceres

Planetary researchers estimate that Ceres has a considerable amount of water - 15 to 25 percent of its mass - which is hidden below the crust in the form of a 100 kilometre-thick water-ice mantle.

Links

  • DLR Institute of Planetary Research: Dawn - Image of the day
    (http://www.dlr.de/pf/en/desktopdefault.aspx/tabid-7622/)
  • Dawn Image Gallery
    (http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10506/)