Endless World Reconnaissance

Mars Caves?
Image courtesy NASA/JPL/University of Arizona

Looking like space slug hidey-holes, huge pits gouge a bright, dusty plain near the Martianvolcano Ascraeus Mons in a picture taken between October 1 and November 1 by NASA's Mars Reconnaissance Orbiter (MRO).


Released in December, the image is among a series of new views snapped by MRO's HiRISE camera that show intriguing geological features on Mars. Each image covers a strip of Martian ground 3.7 miles (6 kilometers) wide and can reveal a detail about as small as a desk—and so far no sign of Star Wars monsters.

MRO's sister orbiter, Mars Odyssey, first noticed the two deep pits—which are about 590 feet (180 meters) and 1,017 feet (310 meters), respectively—a year earlier using its infrared camera, THEMIS. (Related: "Seven Great Mars Pictures From Record-Breaking Probe.")

"When compared to the surrounding surface, the dark interiors of the holes gave off heat at night but were cool by day," said Alfred McEwen, principal investigator on the HiRISE camera.

"So we then decided to target these with MRO because this thermal information may be evidence for these being caves—but the jury is still out on that."

(See "Mars Has Cave Networks, New Photos Suggest.")

The MRO has been studying Mars since 2006, beaming back more data than all other past and current missions to the planet combined.


Down the Martian Hole
Image courtesy NASA/JPL/University of Arizona

A sharp close-up of the the larger Martian pit revealed sediment and boulders (seen in a picture taken in fall 2010 by the Mars Reconnaissance Orbiter's HiRISE camera), as well as hints of sand that was blown inside and trapped in the deepest and darkest parts of the hole, according to NASA.

The holes are believed to be vertical shafts that cut through lava flows along the edges of the Ascraeus volcano. Similar features called pit craters—the result of the ground collapsing above a void—can be found on Hawaii's volcanoes. (See "Mars Volcanoes May Re-Erupt, Hawaii Comparison Shows.")

Scientists are still debating if these are genuine pits, which are simply vertical shafts in the ground, or caves—holes that lead into hidden horizontal undergound passageways.

"The big question is if these are in fact caves," principal investigator McEwen said. "And do they provide some sort of micro-environment that could have supported life on Mars in the past?"


Youthful Pit on Mars
Image courtesy NASA/JPL/University of Arizona

Car-size boulders punctuate the bottom of the smaller Martian pit (pictured in a fall 2010 HiRISE image). A bright sand dune laced with windblown ripples covers the sloping western side of the hole.

The two pits are believed to be relatively young, according to NASA. As the pits age, the slopes become shallow and widen as they material at the edges collapses inward.

"There are probably thousands of the older ones, and the younger ones like these, which are very steep and dark, may number be up to dozens," principal investigator McEwen said.

(Related: "Mars Has Liquid Water Close to Surface, Study Hints.")


Martian Mud Volcanoes
Image courtesy NASA/JPL/University of Arizona

Among other recently released pictures from NASA's Mars Reconnaisance Orbiter are these images of apparent mud volcanoes on in Acidalia Planitia, a large basin in Mars's northern lowlands (seen in a fall 2010 HiRISE picture).

Mud volcanoes—which also exist on Earth—form when wet, pressurized sediment buried at depth erupts onto the surface. (Related photo: "'Medusa' Worms Found in Mud Volcano.")

The Martian mud volcanoes might be prime targets in the search for past life on the red planet, according to NASA. (See Mars pictures.)

"If this mud is produced at depth, it could have brought up organic materials that may show biosignatures of some sort of ancient life on Mars," principal investigator McEwen said.

(Also see "Does Mars Methane Indicate Life Underground?")Scar in Martian Lava
Image courtesy NASA/JPL/University of Arizona

A gigantic trough (center) slices through Mars's Tharsis volcanic region in a fall 2010 picture by HiRISE.

Called a graben, the 1.2-mile-wide (2-kilometer-wide) depression formed when a block of the planet's crust dropped down between two faults. In this case, the tectonic movement left nearly vertical walls—each about a kilometer (0.6 mile) deep—on either side. (See another picture of a Mars graben.)

"From the scarcity of craters inside the graben, it's estimated to be less than a billion years old," principal investigator McEwen said. "This one is nicely defined because it cuts a well-preserved lava flow."