NASA Mars Reconnaissance Orbiter HiRise Image: Martian Sand Dunes in Spring

Mars’ northern-most sand dunes are beginning to emerge from their winter cover of seasonal carbon dioxide (dry) ice. 

Dark, bare south-facing slopes are soaking up the warmth of the sun.

The steep lee sides of the dunes are also ice-free along the crest, allowing sand to slide down the dune. 

Dark splotches are places where ice cracked earlier in spring, releasing sand. Soon the dunes will be completely bare and all signs of spring activity will be gone.

This image was acquired by the HiRISE camera aboard NASA's Mars Reconnaissance Orbiter on Jan. 16, 2014. 

The University of Arizona, Tucson, operates the HiRISE camera, which was built by Ball Aerospace & Technologies Corp., Boulder, Colo. 

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter Project for the NASA Science Mission Directorate, Washington.

Image Credit: NASA/JPL-Caltech/Univ. of Arizona

Caption: Candy Hansen

Mars HiRise Image: Spring on Mars

Spring on Mars. This image provided by NASA/JPL and the University of Arizona shows barchan (crescent-shaped) sand dunes in the North Polar region on Mars. 

In this image, taken during the northern spring season, the dunes and ground are still covered in seasonal frost.

The speckled appearance is due to the warming of the area.

As the carbon dioxide frost and ice on the dunes warms, small areas warm and sublimate (turn from solid to gas) faster, creating small jets that expose/deposit dark sand and dust onto the surface. 

Notice that there are no spots on the ground between the dunes - that is because the ground stays more uniformly cold, unlike the darker dune sand.

Picture: NASA/JPL/University of Arizona/AFP/Getty

Spring On Titan Brings Sunshine And Patchy Cloud

Titan's northern hemisphere is set for mainly fine spring weather, with polar skies clearing since the equinox in August last year. Cassini's VIMS instrument has been monitoring clouds on Titan continuously since the spacecraft went into orbit around Saturn.

Now, a team led by Sebastien Rodriguez (AIM laboratorry - Universite Paris Diderot) has used more than 2000 VIMS images to create the first long-term study of Titan's weather that includes the equinox, using observational data.

Dr Rodriguez will be presenting the results at the European Planetary Science Congress in Rome on Wednesday 22nd September.

Together with Saturn in its 30-years orbit around the Sun, Titan has seasons that last for 7 terrestrial years. The team has observed significant atmospheric changes between July 2004 (early summer in the southern hemisphere) and April 2010, the very start of northern spring.

The images showed that cloud activity has recently decreased near both of Titan's poles. These regions had been heavily overcast during the late southern summer until 2008, a few months before the equinox.

"Over the past six years, we've found that clouds appear clustered in three distinct latitude regions of Titan: large clouds at the north pole, patchy cloud at the south pole and a narrow belt around 40 degrees south.

However, we are now seeing evidence of a seasonal circulation turnover on Titan - the clouds at the south pole completely disappeared just before the equinox and the clouds in the north are thinning out. This agrees with predictions from models and we are expecting to see cloud activity reverse from one hemisphere to another in the coming decade as southern winter approaches," said Dr Rodriguez