NASA's Dawn Mission Reveals Secrets of Protoplanet Vesta
Posted on May 13, 2012
NASA's Dawn spacecraft has provided researchers with the first orbital analysis of the giant asteroid Vesta. The large asteroid is also described as a protoplanet. Vesta, which is in the doughnut-shaped asteroid belt between Mars and Jupiter, is currently some 321 million miles from Earth. Dawn has been orbiting Vesta and collecting data about its surface since July 2011. Dawn will depart Vesta on August 26 for its next study target, the dwarf planet Ceres, in 2015. Vesta is shown as the smallest body among other similar bodies in the solar system in the above image.
The image above shows topography of the southern hemisphere of the giant asteroid Vesta and a map of Vesta's gravity variations that have been adjusted to account for Vesta's shape. The map on the left shows the outlines of the two ancient basins, Rheasilvia and Veneneia. You can see a larger version of the image here.
UCLA's Christopher T. Russell, a professor in UCLA's Department of Earth and Space Sciences and the Dawn mission's principal investigator, is the co-author of six papers recently published in the journal Science about Vesta.
Russell says, "Vesta looks like a little planet. It has a beautiful surface, much more varied and diverse than we expected. We knew Vesta's surface had some variation in color, but we did not expect the diversity that we see or the clarity of the colors and textures, or their distinct boundaries. We didn't find gold on Vesta, but it is still a gold mine."
Here are some highlights of the Vesta discoveries:
- Vesta has large mountains - the largest is more than twice the size of Mount Everest - which were formed by a major impact to the protoplanet's surface. Scientists thought most of Vesta outside the south polar region might be flat like the moon, yet some of the craters outside that region formed on very steep slopes and have nearly vertical sides, with landslides often occurring in the regolith, the deep layer of crushed rock on the surface.
- The asteroid's geologic complexity can be attributed to a process that separated the asteroid into a crust, mantle and iron core with a radius of approximately 68 miles (110 kilometers) about 4.56 billion years ago. The terrestrial planets and Earth's moon formed in a similar way.
- Russell and his scientific team expected to find a large crater on Vesta, but they were surprised to find two, with the larger one essentially on top of the smaller. The smaller crater covers roughly the distance from Los Angeles to Monterey, Calif.; the larger one would stretch from L.A. to San Francisco.
- The Dawn mission has witnessed a pattern of minerals exposed by deep gashes created by space-rock impacts to Vesta. This might support the idea that Vesta was once molten inside and had a sub-surface magma ocean.
- Vesta has an iron core, formed during the period in which the protoplanet was molten, at the earliest epoch of the solar system; Dawn's measurements of Vesta's gravitational field have confirmed this. This finding was expected because meteorites from Vesta have less iron than the solar nebula from which planetary building blocks formed.
- Vesta's surface contains many bright spots of varying size. A real surprise is that Vesta also has some areas as dark as coal. The dark and light markings form intricate patterns suggesting the dominance of impact processes in creating mixed layers in Vesta's regolith.
- The Vesta asteroid is one of the largest single sources for Earth's meteorites. Data confirmed that a distinct group of meteorites found on Earth did, as theorized, originate from Vesta. The signatures of pyroxene, an iron- and magnesium-rich mineral, in those meteorites match those of rocks on Vesta's surface. NASA says these objects account for about 6% of all meteorites seen falling on Earth.
This artist's concept shows the internal structure of Vesta. Dawn data indicates Vesta has an iron core that is about 68 miles in radius.
You can find many images of Vetsa in the gallery on NASA.gov.