Low Down on Vesta

The South Pole of the Asteroid Vesta
Image Credit: NASA / JPLCalTech / UCLA / MPS / DLR / IDA

The Dawn spacecraft is beginning to wrap up its mission surveying Vesta. It completed the 70 day Low Altitude Mapping Orbit (LAMO) portion of its mission in December, January and February. The mission has been so smooth that the 40 days of reserve observation time have not been used. They will now be applied to the low altitude study of the composition of the surface and mapping of the gravity field. Dawn is currently about 210 kilometers above the surface.

We will discuss some of these low altitude images here. For a full description of the Dawn mission, see here (pdf). See also the nssphoenix articles on the mission, orbital capture, the rotation of Vesta, and previous low altitude images.

Below is a list of key dates for Dawn:

  • Launch – September 27, 2007
  • Mars gravity assist – February, 2009
  • Vesta arrival – July, 2011
  • Vesta departure – July, 2012
  • Ceres arrival – February 2015
  • End of primary mission – July 2015

In January, scientists at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, completed models of the average global temperatures on the asteroid Vesta, and concluded that it is cold enough that ice could exist below the surface of the poles (see the article in the January 2012 issue of the journal Icarus).

Vesta is the second largest asteroid (after Ceres) in the belt between Mars and Jupiter. However, because of the axial tilt (27 degrees compared to Earth at 23 degrees), there are likely to be no locations where ice would remain frozen on the surface. This includes the 480 kilometer wide crater at the south pole (image above).

Below, left is Severina crater, a relatively young crater with sharp edges. It is approximately 25 kilometers in diameter located inc Vesta’s Rheasilvia quadrangle (see map at bottom), near Vesta’s south pole. On the rim is a newer small crater with sharp features.

Below, right is an older crater, degraded along the rim from bombardment from space. Many smaller young fresh craters pockmark the area, both inside and outside the old crater. The image was taken from an altitude of 272 kilometers, and is located in Vesta’s Oppia quadrangle.

Severina Crater on Vesta
Image Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

Smoothed Crater
Smoothed Crater on Vesta
Image Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

Below, left is Cornelia crater. Cornelia is a very young crater, about 15 kilometers in diameter, and located in Vesta’s Numisia quadrangle. The rim has partially collapsed, and the smooth surrounding area indicates that a large amount of fine-grained material was ejected during formation. The slumping material inside the crater is consistent with the fine-grained material in the ejecta.

Below, right, is a high resolution image of the surface in Vesta’s Oppia quadrangle, taken from an altitude of about 190 kilometers. Resolution is about 17.5 meters per pixel. The image is saturated with large and small craters, accumulated over billions of years. Sharp edged craters are young, and blurred, smoothed craters are old. Young craters are on top.

Cornelia Crater on Vesta
Image Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

High Resolution
High Resolution Surface on Vesta
Image Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

Map of Vesta
Quadrangle Maps for the Asteroid Vesta
Image Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

Above is a quadrangle map of Vesta, showing the locations of quadrangles referred to in the article here. Additional maps can be found here.