NASA’s MRO spacecraft finds record of Martian ice age in polar cap
Scientists using radar data from NASA’s Mars Reconnaissance Orbiter (MRO) have found evidence of the most recent Martian ice age recorded in the Red Planet’s north polar ice cap. The new findings agree with previous climate models that indicate a glacial period ended about 400,000 years ago, as well as predictions about how much ice would have accumulated at the poles since then.
The new findings, which were published in May 27 issue of the journal Science, are helping researchers to refine models of the Martian climate by allowing them to determine how ice moves between the poles and mid-latitudes, and in what volumes. Mars has polar caps of ice that are bright and easily visible from Earth-bound telescopes. A seasonal cover of carbon dioxide ice and snow has been observed advancing and retreating over the Martian poles.
During summertime in the planet’s north, the remaining northern polar cap is all water ice; the southern cap is water ice as well, but it remains covered by a relatively thin layer of carbon dioxide ice even in southern summertime.
Mars has undergone variations in its tilt and the shape of its orbit over hundreds of thousands of years. Earth has similar, but less variable, phases known as Milankovitch cycles.
Researchers use data from MRO’s Shallow Subsurface Radar (SHARAD) to capture images called radargrams that are like vertical slices through the layers that make up the Martian polar icecaps. For the recently-published study, scientists analyzed hundreds of radargrams to search for variations in the properties of the layers.
The scientists discovered a boundary in the ice that extends across the whole of the north pole cap. Above the boundary, the layers accumulated much more quickly and uniformly than the layers below them.
“The layers in the upper few hundred meters display features that indicate a period of erosion, followed by a period of rapid accumulation that is still occurring today,” said planetary scientist Isaac Smith, the study’s lead author. Smith led the work while at Southwest Research Institute in Boulder, Colorado, but is now at the Planetary Science Institute in Tucson, Arizona.
Ice ages on Earth begin when the polar regions and higher latitudes become cooler than average for thousands of years, causing glaciers to advance towards the mid-latitudes. Ice ages on Mars occur differently due to the planet’s increased tilt. They begin when the polar regions become warmer and the polar ice caps retreat, causing water vapor to migrate towards the equator, forming ground ice and glaciers. As the warm polar period ends, polar ice begins to accumulate while ice is lost from mid-latitudes. This retreat and regrowth of polar ice have been seen in SHARAD radar images.
The MRO spacecraft was launched from Cape Canaveral Air Force Station’s Space Launch Complex 41 atop an Atlas v 401 rocket on August 12, 2005. After 10 years in orbit, the spacecraft and all six of its scientific instruments are still in excellent shape.
“The longevity of the mission has enabled more thorough and improved radar coverage of the Martian poles,” said Richard Zurek, the mission’s project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California. “Our long life in orbit and powerful 3-D analysis tools are allowing scientists to unravel Mars’ past climate history.”
Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.