Like water draining from an unplugged bathtub, meltwater flowing through deep cracks in the Martian rock may explain the origins of the enormous Hebes Chasma canyon.
About 100,000 cubic kilometres of material had to be removed to form the scar, which is five times the width and depth of the Grand Canyon. But where that material went has been a mystery, as there are no surface channels through which water and sediment could have exited.
John Adams of the University of Washington in Seattle and colleagues proposed in 2009 that heat from magma beneath the surface caused ice held in the rock to melt and released water locked up in salts. The water then drained away through underground cracks, leaving a void into which the overlying rock collapsed, to form the canyon.
Now, a tabletop experiment has bolstered this theory. Martin Jackson of the University of Texas at Austin and colleagues filled a box with viscous silicone oil, representing a watery slush, and covered it with sand and small glass spheres. As the oil was allowed to drain out through slits in the box's floor, a structure resembling Hebes Chasma appeared (Geological Society of America Bulletin, DOI: 10.1130/B30307.1).
Water from the canyon may have erupted onto the surface again. This would account for a nearby valley called Echus Chasma that looks as if it was carved by water, but for which there is no other obvious source. "You've got signs that a huge amount of water just erupted out of nowhere from depth and flowed down, scouring out a valley," Jackson says.
Similar collapses might have helped form other giant canyons on Mars, perhaps including Valles Marineris, the solar system's largest, though other factors like tectonic stretching were likely involved too, Jackson says.
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