Since being tugged into orbit around asteroid Vesta last July, NASA's Dawn spacecraft has pulled back the curtain on the object's surface characteristics, internal structure and wild temperature swings, revealing Vesta to be a complex world much like a miniature planet.

Artist's concept of the Dawn spacecraft at Vesta. Credit: NASA/JPL-Caltech
 
Dawn's mission at Vesta has been extended 40 days until Aug. 26. The extension will allow the spacecraft to spend more time in a low-altitude mapping orbit 130 miles from Vesta for additional studies of the asteroid's composition and gravity field, according to NASA.

The spacecraft will also be stationed in a high-altitude mapping orbit for longer than planned this summer.

"We are leveraging our smooth and successful operations at Vesta to provide for even more scientific discoveries for NASA and the world." said Robert Mase, Dawn project manager based at NASA's Jet Propulsion Laboratory. "This extra time will allow us to extend our scientific investigation and learn more about this mysterious world."

Financial and schedule reserves were built in to Dawn's mission to cover any problems at Vesta, but the mission has not encountered any major problems, permitting managers to extend the craft's stay at Vesta from July until August.

Dawn will depart Vesta in late summer, using its ion propulsion system to reshape its trajectory and reach the dwarf planet Ceres in February 2015.

Photos of Ceres (left) and Vesta (right) from the Hubble Space Telescope. These were the best images of the asteroids before Dawn's mission. Credit: NASA/ESA/J. Parker (Southwest Research Institute), L. McFadden (University of Maryland)
 
Before the Dawn probe arrived at Vesta, scientists only knew the asteroid as a fuzzy dot viewed through the apertures of telescopes. They had no idea about Vesta's landslides, lumpy gravity field, or the asteroid's surface appearance. Scientists did not even know what Vesta might look like once Dawn arrived in its vicinity.

"After more than nine months at Vesta, Dawn's suite of instruments has enabled us to peel back the layers of mystery that have surrounded this giant asteroid since humankind first saw it as just a bright spot in the night sky," said Carol Raymond, Dawn deputy principal investigator at JPL. "We are closing in on the giant asteroid's secrets."

Vesta is roughly spherical in shape, measuring about 359 miles by 285 miles. First identified in 1807, Vesta was the fourth asteroid ever discovered.

Images from Dawn reflect Vesta's diverse history, which included volcanism and collisions with other asteroids. Both types of processes shaped the Vesta surface researchers see today.

These composite images from the framing camera aboard NASA's Dawn spacecraft show three views of a terrain with ridges and grooves near Aquilia crater in the southern hemisphere of the giant asteroid Vesta. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
 
Dawn has investigated Vesta's volcanic past, which deposited molten rock across the asteroid's surface. The spacecraft has located breccias, a type of rock fused together by violent impacts with other objects in space, according to a NASA statement.

The craft's camera spotted evidence of landslides on the slopes of craters. It also appears fine grains of rock and soil kicked up by impacts settled in low-lying areas as a sea of dust.

"These results from Dawn suggest Vesta's skin is constantly renewing," said Maria Cristina De Sanctis, head scientist for Dawn's visible and infrared mapping spectrometer at Italy's National Institute for Astrophysics in Rome.

Dawn's visible and infrared mapping spectrometer detected temperatures differentials on Vesta's surface from colder than minus 150 degrees Fahrenheit to minus 10 degrees Fahrenheit. The sharp temperature swings over small areas suggest Vesta's surface quickly responds to sunlight, according to NASA.

The probe also measured Vesta's global gravity field, which yields information on the asteroid's internal structure. Vesta's gravity model shows which regions of the asteroid are denser than others.