Malin Space Science Systems banner

Mars Global Surveyor
Mars Orbiter Camera

8 Years at Mars #2: New Crater Might Have Formed During The 1980s

MGS MOC Release No. MOC2-1221, 20 September 2005

MOC2-1221a: Small crater with dark, rayed ejecta was not present in 1976; rate at which ejecta faded from 1999 to 2005 suggests mid-1980s age.
Three views, one from Viking 2 orbiter on 28 September 1976, one from MGS MOC on 5 October 1999, and one from MGS MOC on 11 January 2005; the 1999 and 2005 views show the small, fresh crater that may have formed in the 1980s.
50% size (652 KB) -- Full size (2.2 MB) -- Full size with no annotation (2.3 MB) -- Animated GIF
NASA/JPL/Malin Space Science Systems
MOC2-1221b: Comparison of MOC wide angle views with Viking 2 view.
Three context views of the location of the small fresh crater, one from Viking 2 in 1976, one from MGS MOC in 1999, and one from MGS MOC in 2005; the Viking image shows that the crater did not exist in 1976.
50% size (340 KB) -- Full size (1.0 MB) -- Full size with no annotation (1.0 MB) -- Animated GIF
NASA/JPL/Malin Space Science Systems
MOC2-1221c: Context, Ulysses Patera volcano in U.S. Geological Survey mosaic of Viking Orbiter images.
Viking orbiter view showing Ulysses Patera volcano, and context of the new crater that formed there.
Full size (325 KB)

One of the basic tenets of planetary geology is that impact craters have accumulated on planetary surfaces at roughly a constant rate since the early history of the Solar System. This appears to have been the case for small craters on the surface of the Moon, as shown by measurements of the length of time that lunar rocks created by small impacts have been exposed to cosmic rays, as determined by laboratory measurements of samples returned to Earth by the Apollo astronauts. This principle should permit the number of craters found on a planetary surface to be used to determine the age of that surface, if the rate at which new craters form is known.

Scientists have only been able to estimate the cratering rate of Mars by scaling the lunar cratering rate based on the proximity of Mars to the asteroid belt, and by performing calculations based on orbital mechanics.

Another way to establish the cratering rate of Mars would be to use long-term observations, say, from orbiting spacecraft, to actually locate brand new craters. Here we report on the discovery of a crater that appears to have formed on Mars in the past 20 or so Earth years, and we use it and several other similar craters to estimate the present cratering rate on Mars.

The new crater is located on the southern rim of the summit crater, or caldera, of the intermediate-sized martian volcano, Ulysses Patera (figures MOC2-1221a and MOC2-1221c, above). 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.

The top two figures (MOC2-1221a, MOC2-1221b) show 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 first figure (MOC2-1221a) shows an enlargement of the Viking image, as compared with much higher spatial resolution MOC narrow angle camera images. The second figure (MOC2-1221b) shows the Viking image compared to low resolution MOC wide angle camera views. 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. The actual contrast between the ejecta blanket and the undisturbed volcano summit materials is actually much less than it appears to be in these processed images, and the amount of fading is also much less. 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.

The rate at which dark surfaces lighten on Mars is not uniform over the whole planet, but we have found a number of other craters with dark ejecta that have faded during the MGS mission, and estimate that these craters probably formed within the past 100 years. 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 pictures derived from 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 pictures derived from 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. The pictures derived from the 2005 MOC image, S02-00470, were acquired when sunlight came from the upper left and the sub-solar latitude was near 14.7°N. The Viking image mosaic in MOC2-1221c was produced by the U. S. Geological Survey.

Reference Material:

  • Another spectacular, relatively young crater in the Tharsis region of Mars was shown in a MOC release on 11 February 2002. In this case, the crater is larger and already existed when it was first imaged at low spatial resolution by Mariner 9 (1972) and the Viking orbiters (1976-1980): Fresh Impact Crater and Rays in Tharsis

Tips for Media Use

Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, California. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, California and Denver, Colorado.