Vesta’s regolith influences surface features
Posted: 28 March 2012
The Framing Camera aboard NASA’s Dawn spacecraft has been returning some remarkable pictures of Vesta since its arrival at the giant asteroid in July 2011, and some of these were shown at the National Astronomy Meeting in Manchester this week.
Vesta is a differentiated body, which means that as it cooled early in its history, it formed layers and became roughly spherical. It is also covered in a thick layer of loose material known as regolith. Martin Hoffmann from the Max-Planck-Institute for Solar System Research revealed that the mixing of regolith on the surface can make it difficult to decipher the precise thermal evolution of Vesta. “We see some details, but it’s much more complicated to disentangle the effects by the impacts and the early processes by the differentiation that we see.”
An example of a double crater on Vesta. Image: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA.
The regolith on Vesta is much deeper than that of the Moon, and the Dawn scientists can use surface features to estimate this depth of the regolith, as well as see how it varies across the surface.
“If you have regolith which is porous and it’s very deep, then you have compaction patterns outside the impact craters which indicate how deep the regolith can be,” said Hoffman. “In other places these compaction patterns look very shallow, or are not present at all, so in these cases we expect that the regolith is not of that size as we see in other places.”
The thick blanket of porous regolith also means that craters on Vesta can be deeper overall than those on the Moon. This deep regolith has an interesting effect when two objects impact the asteroid at almost the same point on the surface; a double crater can be formed. This is unusual as it was expected that a second impact would destroy the first crater completely.
Hoffmann explained to Astronomy Now how the regolith can become compacted enough to preserve the original crater: “You have some sheet of regolith and then you have the first impact onto this very porous material. This impact causes a compaction pattern in a way that the outer layers are at some distance from the centre where we have most compacted area. Then if you have a later impact on this region this particular compacted area will be laid bare by the subsequent impact, and you can see both the old crater in its remnants where its compacted in parts and the new crater which only removed the surface but not the deeper layers.”
Double craters are a common sight on Vesta. “In many cases we have several of such features in different parts and also the location of where we can find such particular features tells us something about the distribution of the materials on the surface,” said Hoffmann.
Launched on 27 September 2007, Dawn began returning intriguing images of Vesta several months before entering orbit. Initially orbiting high above the asteroid to get a birds eye view, Dawn gradually spiralled down to a lower orbit to image Vesta in breathtaking detail. Once completing its mission at Vesta in July 2012, Dawn will head for spherical asteroid Ceres, where it will arrive in 2015.
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