Planetary Exploration


MOUNTAIN VIEW – A science team led by Adrian Brown of the SETI Institute has measured the seasonal changes in Mars northern ice cap, and finds a net deposition each year that’s slightly more than the thickness of a human hair.

This measurement will allow greater understanding of how much water is active (as opposed to being permanently frozen) in the martian water system today, and how future astronauts might use it. 

“Just like farmers on Earth, visitors to Mars will need to know about the water cycle, how it operates seasonally, where the water comes from, and where it’s being stored now,” says Brown. 

While Mars’ polar caps were first spotted in 1666, it wasn’t until nearly two centuries later that astronomer William Herschel made the suggestion that they might be analogous to the ice caps of Earth, and a potential source of water. 

Brown and his team used the spectrometer known as CRISM on the Mars Reconnaissance Orbiter to monitor the infrared absorption bands of ice in the northern polar cap.  In winter, the carbon dioxide at the Martian poles freezes, and every exposed surface cools down to -190 F.

But during the summer, the polar caps thaw and occasionally get up to a balmy -100 F. Water molecules start warming up and traveling around the cap.

The scientists tracked the movement of water ice and the nighttime snowfall events that happen during the north polar cap summer.  They were able to follow the movement of water around the cap by identifying a latitude at which the polar cap ice goes from a ‘subliming’ state in the middle of summer (losing ice cover) to when it reverts to the ‘condensing’ stage (accumulating ice) late in the season as the Sun gets lower.

Studying this pattern, they’ve worked out how much ice gets transported onto the Martian northern cap in a year.  It amounts to a thickness of 70 microns.  

Whatever ice remains at the end of summer becomes a permanent part of the cap, as it will be covered in dry ice as winter sets in. This is likely how the cap built up over time, and gives future Martian colonists an indication of how much ice they can renewably harvest each northern summer.

The ice deposition rate gives insights into martian climate history.  Future researchers will be able to drill cores into the cap that will give a longer perspective on the Red Planet’s climate record, similar to what we have been able to measure on Earth.  These future efforts might even find evidence of buried carbon or methane that’s trapped beneath the surface.  This may be the best approach to resolving the current controversy over the presence of methane in the martian atmosphere.  Methane could be an indicator of underground bacteria. 

Continued research into the behavior of the polar cap is a key that can open the door to a deeper understanding of Mars’ climate.

“This work speaks to both the past and future of an essential resource on the Red Planet,” notes Brown. 

The results are published in the journal, Icarus.

Images here:


MOUNTAIN VIEW – Recently discovered evidence of carbonates beneath the surface of Mars points to a warmer and wetter environment in that planet’s past.  The presence of liquid water could have fostered the emergence of life. 

A new study by James Wray at the Georgia Institute of Technology and Janice Bishop of the SETI Institute, as well as other collaborators, has found evidence for widespread buried deposits of iron- and calcium-rich Martian carbonates, which suggests a wetter past for the Red Planet. 

 “Identification of these ancient carbonates and clays on Mars represents a window into history when the climate on Mars was very different from the cold and dry desert of today,” notes Bishop.

The fate of water on Mars has been energetically debated by scientists because the planet is currently dry and cold, in contrast to the widespread fluvial features that etch much of its surface. Scientists believe that if water did once flow on the surface of Mars, the planet’s bedrock should be full of carbonates and clays, which would be evidence that Mars once hosted habitable environments with liquid water. Researchers have struggled to find physical evidence for carbonate-rich bedrock, which may have formed when carbon dioxide in the planet’s early atmosphere was trapped in ancient surface waters.  They have focused their search on Mars’ Huygens basin.

This feature is an ideal site to investigate carbonates because multiple impact craters and troughs have exposed ancient, subsurface materials where carbonates can be detected across a broad region. And according to study led James Wray, “outcrops in the 450-km wide Huygens basin contain both clay minerals and iron- or calcium-rich carbonate-bearing rocks.”

The study has highlighted evidence of carbonate-bearing rocks in multiple sites across Mars, including Lucaya crater, where carbonates and clays 3.8 billion years old were buried by as much as 5 km of lava and caprock.

The researchers, supported by the SETI Institute’s NASA Astrobiology Institute (NAI) team, identified carbonates on the planet using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), which is on the Mars Reconnaissance Orbiter. This instrument collects the spectral fingerprints of carbonates and other minerals through vibrational transitions of the molecules in their crystal structure that produce infrared emission. The team paired CRISM data with images from the High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) on the orbiter, as well as the Mars Orbiter Laser Altimeter (MOLA) on the Mars Global Surveyor, to gain insights into the geologic features associated with carbonate-bearing rocks.

The extent of the global distribution of martian carbonates is not yet fully resolved and the early climate on the Red Planet is still subject of debate. However, this study is a forward step in understanding the potential habitability of ancient Mars.

Preview of paper:



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