Earth’s Icy Cousin

Mars has a low atmospheric pressure today, only about 0.6% that of Earth. It is also much colder than Earth, with an average temperature near 82 degrees (Fahrenheit) below freezing! It’s nearly impossible for liquid water to exist under these conditions; it would either freeze from the cold or boil away from the low pressure. Water does, however, exist on Mars today; it can be found mixed into the soil and trapped in large ice caps at the poles. The ice caps are about 2 miles thick and together have a volume similar to that of the Greenland ice sheet. Using radar images to probe below the surface, researchers at the University of Arizona study variations within these ice caps and what that means for how Mars’ climate has changed over time.

A Watery Past

Crossing the highlands of Mars are branching networks of valleys that, from above, look like the rivers of Earth; they can reach up to 2,485 miles in length, longer than the Mississippi River! High-resolution images of the martian surface taken by the HiRISE instrument operated by LPL have been used to study stacks of sediment left behind by the water that once flowed through these valleys—similar to the alluvial fans and deltas laid down by rivers on Earth. Minerals observed on the surface could only have formed in the presence of water. While the rivers on Mars have long since dried up, LPL Professor William Boynton discovered that there is frozen water near the surface of Mars today.

Towering Infernos

Olympus Mons is the largest volcano in the solar system. At 15.5 miles high and 370 miles wide, Olympus Mons is 2.5 times taller than Mount Everest and nearly large enough to cover Arizona. The Tharsis region surrounding Olympus Mons and three other mega volcanoes may have been a hotspot of volcanic activity over Mars’ long history. Volcanic activity has occurred from around four billion years ago to as recently as a few million years ago.

University of Arizona Legacy

Launched in 2005, the High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter is the most powerful camera ever sent to another planet and was originally led by LPL Regents Professor Alfred McEwen. This mission is one of several missions to Mars for which the University of Arizona has played a significant role. LPL Professor Peter Smith was the primary investigator on both the imager for Mars Pathfinder launched in 1996 and for the Phoenix Mars Lander, the first university-led mission to Mars, launched in 2007.


MASS: 6.4x10^23 kg 11% that of Earth
DIAMETER: 6,792 km 53% that of Earth
SURFACE GRAVITY: 3.7 m/s2 38% that of Earth
AVG. DISTANCE TO SUN: 228 million km 1.5 au

Illustration of Mars surface features: glacier, mountains and a terraced crater with a cross section showing possible subsurface water ice.