March 18, 2011
Young And Old
left image from ESA Mars Express; right image from LRO nearside mosaic (NASA/GSFC/Arizona State University)
The European Space Agency has just released another superb image from the Mars Express orbiter. It shows a very familiar looking crater three or four times as long as it is wide. Every lunar observer will recognize the similarity to Schiller, although the ESA press release doesn't include such a mention. Gerhard Neukum, my colleague and a long time lunar expert, wrote the ESA caption, including the com- ment that it was probably caused by the impact of a train of projectiles. That is one possibility, but the 78 km long martian crater is young enough to preserve its ejecta blanket, which only extends to the sides of the elongated structure. That is a diagnostic sign of an oblique impact. The Moon's 180 km long Schiller looks almost identical in outline but its floor has been filled in, and part of it does have a linear central peak, another diagnostic sign of oblique impact. Lavas erupted into the Schiller-Zucchius Basin covered Schiller's ejecta, but I am sure it too only extended to the sides. It was noted 25 years ago that there are quite a few elongated craters on Mars, and Pete Schultz of Brown University suggested that a population of previous moons crashed to the surface of Mars, causing oblique impacts and elongated craters; Phobos and Deimos are elongated craters waiting to happen. The Moon has only one Schiller, it probably formed from a one-off (large) oblique impact event.
Rükl plate 71
Yesterday's LPOD: What is Hidden Below the Surface?
Tomorrow's LPOD: Twins Separated Before Birth