NASA’s been busy lately. Not only has the new arsenic-eating microbe grabbed the headlines, but the agency recently released a batch of new images taken from Mars orbit by the Mars Reconnaissance Orbiter (MRO).Â Several of the photos feature two dark, rimless pits in the Tharsis volcanic region of the planet. Maybe it’s because I like a mystery, but these dark pits invite us to wonder what lurks beneath their rims and where they may lead. Under normal lighting, the photos show what look like black holes in the landscape. Special processing brings out the details of their shady interiors. In the top image you can see boulders strewn about, a small area of sand dunes to the far left and thick, layered crust. Scientists are still working to determine just how pits form on the planet.
The second photo shows how the pits look at a glance without enhancement or enlargement. Curious that they appear to be aligned with a chain of larger depressions that curves off to the right. The wispy boomerang-shaped deposit may consist of dark material that has been either blown out of the pits or from some other source and scattered about by the local winds.
On Earth, pit caves are vertical shafts formed by water erosion in limestone over a long period of time. Sinkholes form from water erosion as well and involve the removal of underground soil, sand or rock leaving the top layer vulnerable to collapse. No one knows for sure what mechanism created the Mars pits, but since the Red Planet was once wetter in the past, it’s possible that underground liquid water may have played a role. An alternative view is that pits may be collapse features in an underground lava tube. A lava tube forms when molten rock, flowing in a channel, develops a hard crust on its outside as it cools.Â Over time, as the lava cuts a deeper path, it becomes sealed from above by a slowly hardening roof of rock. Once the lava drains from the channel, a tube-like lava cave is left behind. Later, an unstable part of the roof can collapse, leaving a hole or skylight.
Cavers of the future will have plenty of exotic places to squeeze into as orbiting spacecraft continue to uncover more of these fascinating pits on our neighbors in the solar system.
More spectacular closeups of Mars – pits, gullies, polar ice and all – can be viewed at the MRO images site. Before we wrap up, check out the three 3D images of Martian crater pits below. If you really want to feel what it’s like to look into one of these holes, grab a pair of those red-blue 3D glasses and prepare to gasp.