These two maps are derived from images of asteroid 4 Vesta taken between November 28 and December 1, 1994 with the Wide Field Planetary Camera-2 (in PC mode) aboard NASA's Hubble Space Telescope. Hubble images show surface details as small as 35 miles across. The mid latitude region of Vesta, between about 16 degrees south and 48 degrees north, were favorably situated for viewing from Earth at the time the images were taken. Global coverage was obtained by taking multiple images as Vesta rotated on its axis with a 5.34 hour period. Vesta is 320 miles in diameter, and the map covers a surface area of 200,000 miles.
[Top] Surface Brightness Map of Vesta - This map shows that, unlike most asteroids, Vesta's surface is significantly varied with a dark hemisphere and a light hemisphere. The surface markings may represent ancient igneous activity such as lava flows and, in addition, regions where major impacts have stripped away the crust revealing mantle material below the crust. The name "Olbers" has been proposed for a conspicuous dark circular feature that is 120 miles across. The feature is named after astronomer H.W. Olbers, who discovered Vesta in 1807. The image was taken in blue light.
[Bottom] Surface Composition Map of Vesta - This false-color composite map of Vesta results show that all of Vesta's surface is igneous, indicating that either the entire surface was once melted, or lava flowing from its interior once completely covered its surface. The map shows that Vesta has two distinct hemispheres containing two different types of solidified lava called basalts.
Current interpretations suggest the red-colored hemisphere has been heavily excavated by impacts which have exposed the subsurface material. This area is interpreted to be composed of a type of basalt (rich in the mineral pyroxene) which forms when lava cools and solidifies below a planet's surface. The hemisphere colored yellow-green may be the remains of Vesta's ancient crust formed near the time of the beginning of the solar system. This region is interpreted to be composed of a type of basalt which is comprised by a mixture of the minerals pyroxene and feldspar. This type of basalt is formed by lava which cools and solidifies on the surface of a planet. The region identified as "Olbers," and another dark green region at longitude +80 degrees, appear to have a more complex history. They could be regions where very deep impacts have punched through the basaltic crust to expose darker material from the upper mantle of Vesta, and mix it with the crustal lavas.
This map was produced from separate images in blue (439 nm), orange (673 nm), red (953 nm), and near-infrared (1024 nm) light. The map is produced in false colors to highlight regions of geologically interesting regions on Vesta's surface.
NASA's Hubble Space Telescope images of the asteroid Vesta are providing astronomers with a glimpse of the oldest terrain ever seen in the solar system and a peek into a broken off section of the "mini-planet" that exposes its interior.
Hubble's pictures provide the best view yet of Vesta's complex surface, with a geology similar to that of terrestrial worlds such as Earth or Mars. The asteroid's ancient surface, battered by collisions eons ago, allows astronomers to peer below the asteroid's crust and into the past.
Astronomers also believe that fragments gouged out of Vesta during ancient collisions have fallen to Earth as meteorites, making Vesta only the fourth solar system object, other than Earth, the Moon and Mars, where scientists have a confirmed laboratory sample. (About 50-60 other meteorite types are suspected to have come from asteroids, but positive identifications are more difficult to make.)
"The Hubble observations show that Vesta is far more interesting than simply a chunk of rock in space as most asteroids are," said Ben Zellner of Georgia Southern University. "This qualifies Vesta as the 'sixth' terrestrial planet."
No bigger than the state of Arizona, Vesta offers new clues to the origin of the solar system and the interior makeup of the rocky planets. "Vesta has survived essentially intact since the formation of the planets," Zellner said. "It provides a record of the long and complex evolution of our solar system."
Resolving features down to 50 miles across, Hubble reveals a surprisingly diverse world with an exposed mantle, ancient lava flows and impact basins. Though only 325 miles (525 kilometers) across, it once had a molten interior. This contradicts conventional ideas that asteroids essentially are cold, rocky fragments left behind from the early days of planetary formation.
Besides providing scientists with direct samples, Vesta's chipped surface allows Hubble to study the asteroid's rocky mantle, giving scientists a unique opportunity to see what a planet looks like below the crust. "Our knowledge of the interior composition of the other terrestrial worlds, the Moon, Mars, Venus, Mercury and even Earth, depends heavily on theory and inference," Zellner said. "Vesta allows us to actually see the mantle and study pristine samples in our laboratories."
Before these observations, only the smaller and less geologically diverse asteroids, Ida and Gaspra, have been observed in detail by the Jupiter-bound Galileo spacecraft. Unlike Vesta, these smaller objects are pieces torn off larger bodies by collisions that occurred perhaps only a few hundred million years ago.
The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).
Credit: Ben Zellner (Georgia Southern University) and NASA
Principal Investigator is Dr. Ben Zellner of Members of the science team include Dr. Rudolph Albrecht of the Space Telescope European Coordinating Facility, Dr. Richard P. Binzel of MIT, Dr. Michael Gaffey of Rensellaer Polytechnic Institute, Dr. Alex Storrs of Space Telescope Science Institute, Dr. Peter Thomas of Cornell, and Dr. Ed Wells of Computer Sciences Corporation.
EMBARGOED UNTIL: 2:00 PM EDT April 19, 1995
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PRESS RELEASE NO.: STScI-PR95-20