Alien Pits Invite Exploration By Imagination

The inside of a rimless pit about 1,017 feet in diameter in the northern hemisphere of Mars. Pits, which form when part of a surface collapses, are different from the much more common craters, which are holes created from meteorite and asteroid impacts. Credit: NASA/JPL-Caltech/University of Arizona

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).  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.

Two dark, rimless pits are locatedin the Tharsis volcanic region of Mars. These pits are approximately591 feet and 1,017 feet in diameter. Credit: NASA/JPL-Caltech/University of Arizona

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.

High sun view of the lunar pit crater in the Sea of Tranquility revealing boulders on an otherwise smooth floor. The approximately 325 foot deep pit was probably formed as a "skylight" in an underground lava tube. Credit: NASA/GSFC/Arizona State University

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.  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.

A skylight offers a glimpse inside an active lava tube in Hawaii Volcanoes National Park. Credit: USGS

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.

Wide view of two Martian pits. Click on photos for larger versions.
Amazing view straight down the rabbit hole!
Picture yourself getting lowered down into this one as your powerful flashlight illuminates the fractured rocky walls.

5 Responses

  1. Jim Blue

    I would think that a meteor impact on the surface above a lava tube would easily create the openings we see.

    Excellent Blog !

    Thank you,

  2. Larry Dorau

    The 3d image really brings out the columnar nature of the rock where it has been sheared off by a sub surface collapse confirming that the cap rock is indeed lava. It looks like the hole gets wider as you go down and that could indicate erosion of softer rock below. A person would want to bring a big extention ladder.

    Good to see someone reporting on science discoveries. The general population is very receptive I think. The media types didn’t study science in school and give it a wide birth, to our detriment.

    Come back Spirit. Go Opportunity.

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