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

Prathamesh S. Pawar

S. P. Pune University, Pune

Processes on Mars

• In past-

• Volcanic- lava flows

• Sedimentary- fluvial, glacial & aeolian erosional-depositional landforms

• Impacts

• Mass movements- landslides, debris flows

…Processes on Mars

• No active geology on large scales

• Considered a “geologically dead” planet until recently

• Latest technological advancements led to high-res imaging of Martian surface which ultimately have led to discovery of active geological processes on very small scales

• Hence, Mars is active- but on smaller scales!

Currently active processes

• Aeolian processes- dust storms- fine sand/dust deposition as well as deflation

• Mass movements- debris flows, dust/sand avalanches

• Processes induced by dry ice frost/blocks

• Processes induced by meteoritic impacts

Now let’s take a look at some of the processes…

Dust Avalanches

• Most dramatic & rare event

• observed along steep cliffs in North Polar Layered Deposits and steep slopes of dunes & craters, happening in Martian summers.

• Triggering mechanism may be defrosting or meteoric impact

• Freeze & thaw in cracks of loose material may trigger their cascading along steep slopes.

Slope Streaks

• Dark colored streaks upto a few hundred meters wide & several km long on dune slopes & crater walls

• 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

Aeolian activity

• 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 show depositional processes

• Solar panels of rovers have been experiencing deposition as well as blowing of sand/dust upon them.

• 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.

• This sequence of images shows the changing appearance of Victoria Crater (top row) and a small portion of its north rim (bottom row) with tracks of the rover Opportunity.

• Strong surface winds during the global dust storm of July 2007 blew away the basaltic sand making up the wind streaks

Recurring Slope Lineae (RSL)

• RSL are dark debris flows up to a few meters wide & few hundred m long 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 of equator; 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.

Animation of 4 images of RSL in a crater on floor of central Valles

Marineris; scene 193 m wide

Gully formation & modification

• Gullies on Mars are of great interest as they appear to be active and resemble landforms that on the Earth are formed by water.

• Observations of gullies during the last decade show that repetitive activity occurs only during the winter seasons.

• 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 seem to be active only in winters

• Seasonally controlled & correlated with seasonal frost.

• This dune gully is found in Matara Crater (50°S). During winter, a new alcove and channel (white arrow) eroded during late winter, sending material downslope through the existing channel and out onto the fan (new deposits are the darker material on the dune surface). In both larger gullies, the existing channel was incised further into the apron. Frost coats the dune surface in both images, but defrosting has begun in the bottom one.

2010-Oct-04

2010-Aug-21

• This dune gully is in the northern hemisphere (70°N). During the winter, a new alcove (white arrow) eroded during winter, sending material downslope onto the frost (middle image). Once the frost had disappeared, the full apron and channel are visible.

2008-Jul-05 2009-Dec-20 2010-May-12

…Gully formation

• Gullies are also thought to be formed on dune slopes in polar regions because of sublimating dry ice blocks in summers.

• Sublimating dry ice blocks hovercraft down the dune slopes carving out shallow, long troughs.

• Gaseous CO2 may act as cushion to the hovercrafting blocks.

• Over many winters, downhill motion of broken dry ice blocks can perhaps form the large linear gullies (some up to 2km long) seen on Martian dunes.

Impacts

• 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.

• Many impacts expose underlying water ice, helping the scientists studying about water on Mars.

Thank you…

References and Images:NASA/JPL/University of Arizona

http://www.uahirise.org/