Release Date: 20 September 2005
Here we report on the discovery of a crater that appears to have formed on Mars in the past 20 or so Earth years. The new crater is located on the southern rim of the summit crater, or caldera, of the intermediate-sized martian volcano, Ulysses Patera. The 100 kilometer-wide (~62 miles) diameter volcanic shield, located near 2.5°N, 121.3°W, is one of the Tharsis volcanoes, and is partly buried by younger lava flows. The summit caldera is about 55 kilometers (~34 mi) in diameter. This image mosaic shows comparisons of the location of the new crater in a Viking 2 orbiter image taken in 1976, with views taken by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) in 1999 and 2005. The image on the left, shows an enlargement of the Viking image, as compared with much higher spatial resolution MOC narrow angle camera images on the right. The new crater, about 25 meters (~82 ft) across, is marked by a distinct dark, rayed ejecta pattern, which is seen to have faded somewhat between 1999 and 2005. The amount that the crater's rays faded between 1999 and 2005 can be used to help to estimate how many years ago the crater formed. We know from many examples that disturbed surfaces on Mars are dark (for example, dark slope streaks, dust devil tracks, and the tracks created by the Mars rover, Spirit), and that they lighten with time. Using these other examples to estimate how dark the ejecta of the Ulysses crater was originally, and the amount it has faded in six years, suggests that the crater formed in the early to mid 1980's. Although our sample is very small (the MOC narrow angle camera has imaged only just over 4 percent of Mars), it appears that the recent cratering rate for craters between 25 and 100 m diameter on Mars is about 3-6 x 10-8 craters/km2/yr (0.000000003 to 0.000000006 craters per square kilometer per Earth year), which is about 5 times lower than previous estimates. In the 1976 Viking 2 image 049B85, sunlight illuminates the scene from the left/lower left and the sub-solar latitude was near 7.3°S. In the 1999 MGS MOC image, M08-01170, sunlight comes from the lower left and the sun sub-solar latitude was at about 15.4°S. In the 2005 MOC image, S02-00470, sunlight comes from the upper left and the sub-solar latitude was near 14.7°N.
Image Credit: NASA/JPL/MSSS