Giant Hole on Mars Leaves NASA Scientists Confused

"Swiss cheese"-like terrain and a pit of unknown origins on Mars in an image taken by NASA's Mars Reconnaissance Orbiter NASA/JPL-Caltech/University of Arizona

Updated | The Mars Reconnaissance Orbiter (MRO) has circled our neighboring planet 50,000 times since its launch 11 years ago. In the process, the spacecraft has delivered some stunning and potentially important revelations: a giant volcano that went extinct at about the same time as the dinosaurs on Earth; what our planet would look like to Martians; and three possible landing sites for the Mars 2020 Rover. In short, MRO has done its job.

And yet, NASA has released yet another compelling image from the orbiting spacecraft. The picture shows a large hole that defies easy explanation.

Much of the Martian surface appears pock-marked. At the southern polar region, frozen carbon dioxide converted into its gaseous state under the Martian summer sun creates a Swiss cheese landscape. Astronomers have had images showing this pattern for about 10 years.

But in a new, late-summer image of the planet's southern hemisphere, a deeper-than-normal hole stands out. The feature is hundreds of yards wide and unlike anything in its surroundings. The summer sun shining on the planet reveals a reflecting gleam of ice at the bottom of the hole. And NASA scientists can't explain where this giant hole came from.

The image was taken with an instrument called the high-resolution imaging science experiment, or HiRISE, one of six instruments included with MRO. The camera works with visible wavelengths, just like human eyes, but with a telescopic lens that generates images at a resolution higher than any previous NASA mission has achieved. HiRISE can reveal objects as small as three feet in size with an unprecedented level of detail. The camera also uses near-infrared wavelengths that enable researchers to make mineral observations. Layers materials, gullies and channels can all be detected.

As of now, it is unclear whether the pit is a dent from something hitting the surface or a collapse. Meteorites, lava tubes and floods are all capable of creating a cratered surface, but this particular hole is still a mystery.

This story has been updated with additional details about the MRO camera.