Clicking on the small images above, and the links listed below, provides access to details about how the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) was used to find 20 new, small impact craters that formed on Mars between May 1999 and March 2006. These craters allow the rate at which new craters are presently forming on Mars (the cratering rate) to be determined directly. This is the first time the present cratering rate on any object in the Solar System has been measured by direct observation of new craters forming. These captioned materials accompany publication of results regarding present-day impact cratering and gully activity on Mars in the 8 December 2006 issue of Science.

The first two releases tell how the MGS MOC science operations team discovered the first of the 20 new impact craters, and how the team then proceeded to survey the planet for more craters. Given the versatility of the MGS spacecraft and MOC operations activities, the entire survey—covering nearly all of the regions Amazonis, Tharsis, and Arabia Terra—was conceived, executed, and completed in just 5 months.

• How We Found the First of the Fresh Impact Sites that Formed During the Mars Global Surveyor Mission
  
  
• Procedure for Finding New Impact Sites on Mars Using the Mars Global Surveyor Mars Orbiter Camera

The third release features an extremely pretty impact crater that formed between December 2003 and November 2005. This crater displays extensive secondary impacts radiating several kilometers out from the impact site. Of the 20 new craters we found, this one has the best, most detailed MOC narrow angle camera image coverage.

• New Impact Crater in Arabia Terra

The fourth and fifth releases are rather amazing. The MGS MOC narrow angle camera has only imaged a little more than 5% of the martian surface. This 5% amounts to over 96,000 images. Within those images and that tiny 5% of the planet covered, two of the 20 new craters just happened to form at a location where there was a previous MOC narrow angle image. One of these is on the high northern flank of the volcano, Ulysses Patera. The other crater is so young that it may have formed after we first realized we could conduct this study—the impact occurred sometime between 21 December 2005 and 31 January 2006!

• One of Two Fresh Impact Crater Sites With Before and After Narrow Angle Mars Orbiter Camera Images
  
  
• Second of Two Fresh Impact Crater Sites With Before and After Narrow Angle Mars Orbiter Camera Images

The sixth and seventh releases show other interesting details; the first is a case where the impacting meteorite excavated a crater that penetrated to a material that is lighter in tone than that of the surface; thus, its ejecta is light-toned. The other crater is, like its counterparts, interesting in that it shows some asymmetry indicative of the direction from which the impacting object came; the crater also displays chains of secondary impacts radiating from the central crater.

• Fresh Crater in Arabia Terra With Light-Toned Ejecta
  
  
• New Impact Crater Formed Between April 2001 and December 2003

In addition to the seven captioned releases, a complete catalog of all 20 fresh impact sites can be downloaded as a PDF file:

• Catalog of New Impact Sites on Mars Formed May 1999 – March 2006

These releases concerning new impact craters on Mars are also accompanied by a set of materials regarding another subject of the Science paper of 8 December 2006, present-day gully activity on Mars.

Identifying new craters on Mars that formed since May 1999 allows Mars scientists to constrain the present-day impact cratering rate of the planet. It allows comparison of the actual cratering rate with what is derived from models that make assumptions about how the martian rate may have differed in the past from that of the Moon, how close Mars is located relative to the asteroid belt, how well the thin martian atmosphere filters out small incoming meteorites, and related factors. When extrapolated into the past, such models permit scientists to estimate the ages of martian surfaces from the accumulation of impact craters.

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