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BBC: “Asteroid Vesta reveals its scars ” Dawn over Vesta expected to shed light on ancient origins
NASA’s Dawn space probe, after an almost four year trip, is now orbiting Vesta—one of the largest objects in the asteroid belt. Dawn will orbit Vesta until next year and then move on to the dwarf planet Ceres. Vesta and Ceres are the most massive bodies in the asteroid belt located between Mars and Jupiter. Dawn’s mission is to determine their actual mass, analyze their geological composition, and gather data for detailed topographical maps.
Ceres and Vesta are thought by many scientists to be protoplanets leftover from the rubble of the solar system’s formation. Their geological make-up is probably very different. Vesta is believed to have a metallic core and a history of volcanic activity. Vesta also has a massive crater near its south pole. Debris from this crater is thought to have reached Earth in the form of about 200 meteorites.
Three types of meteorites are believed to have come from Vesta: howardite, eucrite, and diogenites.
Three types of meteorites are believed to have come from Vesta: howardite, eucrite, and diogenites. All are crystallized from magma. Vesta is extremely bright, and these HED meteorites reflect light in the same way as Vesta’s surface, leading investigators to suspect the missing chunk of Vesta is their source. Equipment on Dawn should be able to determine the mineral and elemental composition of Vesta’s surface to a depth of about one meter. This information can be compared to the composition of the HED meteorites.
“We are beginning the study of arguably the oldest extant primordial surface in the Solar System,” said Dawn's principal investigator Christopher Russell. “The images received to date reveal a complex surface that seems to have preserved some of the earliest events in Vesta's history, as well as logging the onslaught that Vesta has suffered in the intervening eons.”
Russell refers to Vesta as the “oldest extant primordial surface” because radiometric analysis of HED meteorites has been interpreted to indicate that Vesta finished accreting in the first 5–15 million years1 of the solar system’s existence and spent the rest of its history getting remodeled by volcanic activity and collisions.
Radiometric dating of meteorites is the source of the estimated 4.6 billion year age of the solar system. In addition to the unproveable nature of the assumptions underlying these dating methods, such an age is in conflict with a variety of other observations about the earth and space.2 Furthermore, the nebular hypothesis explanation of the solar system’s origins has serious problems such as its failure to accurately account for angular momentum and the improbability that bits of debris would accrete together to form asteroids and planets.
Data coming from Dawn will be giving us information about Vesta’s present composition and allow us to make some guesses about the volcanic activity and collisions that have literally shaped it. But statements about its age or the events occurring during the birth of the solar system will be based on assumptions that should not be accepted as factual.
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