• Mechanism of formation & triggering is debated; may form by similar processes as dust avalanches. • Most commonly believed to form by down-slope movement of extremely dry sand or very fine-grained dust in an almost fluid-like manner (analogous to a terrestrial snow avalanche) exposing darker underlying material. • Darkest slope streaks are youngest & can be seen to cross-cut & lie on top of older & lighter-toned streaks. • Lighter-toned streaks are streaks that are lightening with time as new dust is deposited on their surface. • Upto a few hundred meters wide & several km long.

• Most dramatic & rare event observed along steep cliffs in North Polar Layered Deposits and steep slopes of dunes & craters, happening in Martian summer. • Triggering mechanism may be defrosting, meteoric impact or freeze & thaw in cracks of loose material along steep slopes.

• The thin atmosphere of Mars, which is mostly made up of CO2 , is quite active with its sand storms & dust devils.

• Fading of slope streaks and rover tracks over long durations show week depositional process. • Following images show dome dunes in the Endeavour crater rapidly migrated (4–12 m/Mars year) in just 2 Martian seasons; some of the fastest translating Martian dunes detected to date.

• RSL are dark flows up to a few meters wide on steep, rocky slopes. • Known to be abundant in equatorial regions, especially deep in Valles Marineris. • Follow the sun: active on N-facing slopes when the Sun is to the north; active on S-facing slopes when the Sun is to the south. • Important candidate for finding liquid water on Mars. • Show depositional fans / aprons at their bases, unlike slope

streaks.

• Very slow activity; changes in at least 1 gully observed at about 15% MRO/HiRISE monitoring sites in southern hemisphere over a period of ~2 Martian years. • Changes in gullies include channel incision & substantial mass movements, which are thought to be driven by mass movements. • Not a candidate for liquid water activity as the gullies only active in winters; thus seasonally controlled & correlated with seasonal frost.

• Mars is bombarded by around 200 small asteroids or bits of comets per year forming craters at least 4 m across. • New craters are identified by their darker ejecta as compared to surroundings. • One of the triggering mechanisms for avalanches which cause the slope streaks.

It's easy to think of Mars as static, unchanging - a "geologically dead" planet, as is often mentioned. The first images taken at close approach to Martian surface came to us in 1965 from Mariner 4. Since

then, many more images have revealed features that, except for becoming clearer and more detailed as cameras improve, seem much the same as they did more than 40 years ago. But while this apparent

fixedness of the Martian surface might be true when compared to Earth, a closer look shows that slowly & on small scales, Mars remakes its image even today. HiRISE, onboard NASA’s MRO, with its ability

to see meter-sized features, is one of the best suited instruments to capture these changes. The closer we look at Mars, the more fascinating processes- active in both past & present- we find to study.

Impacts

Aeolian Activities

Slope Streaks

Gully Formation by Frost

Recurring Slope Lineae (RSL)

Active Mars A Glimpse at the Active Geological Processes on the Planet Mars

Prathamesh S. Pawar

S. P. Pune University, Pune Introduction

Dust Avalanches

2010-Oct-04 2010-Aug-21

• Observed in polar regions. • When warmed, dry ice blocks sublimate (go directly from solid to gas), rather than melt. This creates a cushion of gas beneath the block that makes it very easy for the block to slide or roll down the dune slope, carving out a shallow trough. • Over many winters, downhill motion of broken dry ice blocks can perhaps form the large linear gullies (up to 2km long!) seen on Martian dunes.

Gully Formation by Dry Ice Blocks

Reference and Images: NASA/JPL/University of Arizona: http://www.uahirise.org/