January 6th, 2013 by James Ayre
Vesta, one of the few remaining protoplanets in the solar system, is effectively a window into the early days of the solar system. This is primarily due to its relatively short period of geologic activity and its ‘frozen’ place in time since then. It was only imaged and studied in detail for the first time very recently by NASA’s Dawn space probe. Among all of its findings, perhaps the most intriguing has been the discovery of two very-large craters in Vesta’s southern hemisphere. These enormous impacts greatly changed Vesta’s shape and also its surface composition. Among other things, depositing strange, dark, carbonaceous material onto the protoplanet.
Researchers theorize that the same delivery of materials to the Earth via asteroids likely played a large part in the formation of the modern Earth. The asteroids bring with them elements such as carbon, “an essential building block for organic molecules.”
“Vesta is remarkable in many respects. With a diameter of approximately 530 kilometres, Vesta is the one of the few protoplanets in our solar system still intact today. Like other protoplanets, Vesta underwent complete melting approximately 4.5 billion years ago. However, most of the volcanic activity on Vesta is thought to have ceased within a few million years making it a time capsule from the early solar system. Dawn observations of Vesta have shown a surface with diverse brightness variations and surface composition. There is bright material on Vesta that is as white as snow and dark material on Vesta as black as coal.”
Understanding the strange dark material is the key to understanding the impacts that Vesta experienced early in its existence. Previous research has found that the dark material isn’t native to Vesta, and that it is extremely likely that it was brought there by asteroid impacts.
And now, new research has been done that represents the “most comprehensive analysis of this material so far. Compositional analysis, mapping, and modelling of dark material distribution on Vesta suggest that it was delivered during the formation of giant impact basins on Vesta.”
“First, we created a map showing the distribution of dark material on Vesta using the framing camera data and found something remarkable,” explains Lucille Le Corre from the Max Planck Institute for Solar System Research one of the lead authors of the study.
“Dark material was preferentially spread around the edges of the giant impact basins in the southern hemisphere of Vesta suggesting a link to one of the two large impact basins. A closer examination showed that the dark material was most probably delivered during the formation of the older Veneneia basin when a slow impacting asteroid collided with Vesta. Dark material from this two to three billion year old basin was covered up by the impact that subsequently created the Rheasilvia basin.”
“We believe that the Veneneia basin was created by the first of two impacts two to three billion years ago,” says Reddy. “In fact, impact modelling presented in the paper reproduces the distribution of dark material from such a low velocity impact.”
“HED meteorites are fragments of Vesta
Evidence for dark material is also found in the HED meteorites that come from Vesta. Some of the meteorites show dark inclusions that are carbon-rich. Colour spectra of dark material on Vesta are identical to these carbon-rich inclusions in HED meteorites. The link between dark material on Vesta and dark clasts in HED meteorites provides us with direct evidence that these meteorites are indeed from Vesta.”
“Our analysis of the dark material on Vesta and comparisons with laboratory studies of HED meteorites for the first time proves directly that these meteorites are fragments from Vesta,” says Le Corre.
The new research was just published in the journal Icarus.
Some more information on the Dawn mission:
“Dawn is a spacecraft of NASA tasked with the exploration and study of Vesta and Ceres, the two largest members of the asteroid belt. Launched on September 27, 2007, the probe entered orbit around Vesta on July 16, 2011. Dawn left Vesta on September 5, 2012, on a course for Ceres, which it is scheduled to reach in February 2015.”
“Managed by NASA’s Jet Propulsion Laboratory, Dawn is NASA’s first purely exploratory mission to use ion propulsion. The spacecraft was constructed with European cooperation, with components contributed by partners in Germany, Italy, and the Netherlands. Dawn was the first spacecraft to visit Vesta, and is scheduled to be the first to visit Ceres. If it successfully reaches Ceres, it will also be the first spacecraft to orbit two separate extraterrestrial bodies, using ion thrusters to travel between its targets. Previous multi-target missions using conventional drives, such as the Voyager program, were restricted to flybys.”
“There are three principal scientific drivers for the mission. Firstly, the Dawn mission can capture the earliest moments in the origin of the Solar System, enabling us to understand the conditions under which these objects formed. Secondly, Dawn determines the nature of the building blocks from which the terrestrial planets formed, improving our understanding of this formation. Finally, it contrasts the formation and evolution of two small planets that followed very different evolutionary paths, so that we can understand what controls that evolution.”
Image Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
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