[meteorite-list] NASA Radar Finds Ice Age Record in Mars' Polar Cap

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=6519

NASA Radar Finds Ice Age Record in Mars' Polar Cap
Jet Propulsion Laboratory
May 26, 2016

Scientists using radar data from NASA's Mars Reconnaissance Orbiter (MRO) 
have found a record of the most recent Martian ice age recorded in the 
planet's north polar ice cap.

The new results agree with previous models that indicate a glacial period 
ended about 400,000 years ago, as well as predictions about how much ice 
would have been accumulated at the poles since then.

The results, published in the May 27 issue of the journal Science, help 
refine models of the Red Planet's past and future climate by allowing 
scientists to determine how ice moves between the poles and mid-latitudes, 
and in what volumes.

Mars has bright polar caps of ice that are easily visible from telescopes 
on Earth. A seasonal cover of carbon-dioxide ice and snow is observed 
to advance and retreat over the poles during the Martian year. 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 remains covered 
by a relatively thin layer of carbon dioxide ice even in southern summertime.

But Mars also undergoes variations in its tilt and the shape of its orbit 
over hundreds of thousands of years. These changes cause substantial shifts 
in the planet's climate, including ice ages. Earth has similar, but less 
variable, phases called Milankovitch cycles.

Scientists use data from MRO's Shallow Subsurface Radar (SHARAD) to produce 
images called radargrams that are like vertical slices though the layers 
of ice and dust that comprise the Martian polar ice deposits. For the 
new study, researchers analyzed hundreds of such images to look for variations 
in the layer properties.

The researchers identified a boundary in the ice that extends across the 
entire north polar cap. Above the boundary, the layers accumulated very 
quickly and uniformly, compared with 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.

On Earth, ice ages take hold when the polar regions and high latitudes 
become cooler than average for thousands of years, causing glaciers to 
grow toward the mid-latitudes. In contrast, the Martian variety occurs 
when -- as a result of the planet's increased tilt -- its poles become 
warmer than lower latitudes. During these periods, the polar caps retreat 
and water vapor migrates toward the equator, forming ground ice and glaciers 
at mid-latitudes. As the warm polar period ends, polar ice begins accumulating 
again, while ice is lost from mid-latitudes. This retreat and regrowth 
of polar ice is exactly what Smith and colleagues see in the record revealed 
by the SHARAD radar images.

An increase in polar ice following a mid-latitude ice age is also expected 
from climate models that show how ice moves around based on Mars' orbital 
properties, especially its tilt. These models predict the last Martian 
ice age ended about 400,000 years ago, as the poles began to cool relative 
to the equator. Models suggest that since then, the polar deposits would 
have thickened by about 980 feet (300 meters).

The upper unit identified by Smith and colleagues reaches a maximum thickness 
of 1,050 feet (320 meters) across the polar cap, which is equivalent to 
a 2-foot-thick (60-centimeter-thick) global layer of ice. That is essentially 
the same as model predictions made by other researchers in 2003 and 2007.

"This suggests that we have indeed identified the record of the most recent 
Martian glacial period and the regrowth of the polar ice since then. Using 
these measurements, we can improve our understanding of how much water 
is moving between the poles and other latitudes, helping to improve our 
understanding of the Martian climate," Smith said.

After 10 years in orbit, Mars Reconnaissance and its six science 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."

The Italian Space Agency provided the SHARAD instrument on Mars Reconnaissance 
Orbiter and Sapienza University of Rome leads its operations. JPL, a division 
of the California Institute of Technology in Pasadena, manages the mission 
for NASA's Science Mission Directorate in Washington. Lockheed Martin 
Space Systems of Denver built the orbiter and supports its operations.


News Media Contact

Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278
guy.w.webster at jpl.nasa.gov 

Written by Preston Dyches
NASA-JPL News Office 

2016-135