33. Possible Source for Martian Meteorite ALH 84001
ALH 84001 was blasted into space by an asteroid impact on Mars, but no one knows which martian crater marks the site of that impact. The source crater must be fresh and rather unweathered, because ALH 84001 left Mars only 16 million years ago (which is recent by martian geologic time). Because ALH 84001 is so old (4.5 billion years, slide #19), its source crater may be in the martian highlands (like slide #2), or could be in thin younger deposits over highland rocks. Dr. Nadine Barlow of the University of Central Florida has searched a catalog of 42,283 martian impact craters and has found only two fresh craters of the right shape and size — circular and less than 100 kilometers across, or elliptical and less than 10 kilometers across. Only two craters appeared suitable: This slide shows one of the two, which is 11.3 kilometers × 9.0 kilometers in size and has fresh, unweathered ejecta (see slides #7 and #8).
Viking Orbiter image, 11.7°S 243.3°W, courtesy of Dr. Nadine Barlow (University of Central Florida)