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Martian “Bomb Sag” a Clue to Wetter Times

A volcanic rock sits in a 1" deep crater near Home Plate

Spirit may be settled in for its eternal sleep, but the data it’s returned is still helping researchers piece together clues to Mars’ watery past!

The image above, a false-color view from the “Home Plate” region where Spirit now sits, points to a feature geologists call a “bomb sag”. Bombs are a term for rocks ejected from volcanic eruptions, and a sag is the crater that’s formed when said rocks impact the ground. A team of researchers led by Michael Manga from the University of California, Berkeley, used this photographic evidence to recreate what the conditions of Mars’ air and soil may have been like during the time of the bomb sag’s formation.

What they found, after running several physical experiments using materials of different composition, was that the sag seen here was likely formed during a time when the atmosphere was thicker – and the soil wetter.

“The downward deflection of beds seen on Mars is consistent with water-saturated sediment in the laboratory experiments,” states the team’s paper, published Jan. 5 in Geophysical Research Letters. In addition, Manga et al. concluded the atmosphere in the region must have been (based on the rock’s mass and velocity before impact) at least 20 times thicker than it is today.

Since the Home Plate region is believed to have once been a hydrothermal vent, these findings are in line with what the area must have been like at one point in the planet’s distant past. Still, the team stresses that these results are based on one finding in one area and are not necessarily conclusive.

Read more about this on ASU’s Red Planet Report.

(Also, check out an excellent program by National Geographic in honor of Spirit, the Mars Exploration Rover that really defied all odds right up until the end.)

Research credit: Manga, M., A. Patel, J. Dufek, and E. S. Kite (2012). Image NASA/JPL-Caltech.


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