Seasonal and Daily Changes on Mars Global and local dust storms; Dust devils; Eroded rock and dunes; Polar Caps and their variation by season; Layers within caps; Other cold-climate features; Cause of climate changes on Mars?

Global dust storms evolve in < 1 months, and last > 3 months

Dust Storms

Dust storm Polar cap Dust storm Africa Local dust storm on Mars Dust storm from Sahara

Dust devil tracks – evidence for local winds and surface fines

Wind-scoured rocks are called “Yardangs”

The material eroded from rocks forms many dunes. Show constant wind direction for long periods of time.

Wind erosion features on Mars

North Polar Cap Water (H2O) ice Low elevation

South Polar Cap Carbon dioxide (CO2) ice High elevation

Changing shape of the South Polar Cap due to seasons Frost Cap Winter Spring Summer MOLA data indicate that this eroding layer is about 10 cm thick

Polar Caps composed of hundreds of layers of ice and dust

Snow melt as possible mechanism for pit erosion

Polygonal ground as indicator of “freeze-thaw” process

So how do we get these longer seasonal changes on Mars? The obliquity of Mars may have varied from almost 0 – 60 degrees The precession may have changed climate dramatically in the past on timescales of 25,000 – 175,000 years

Temperature change on Mars due to change in eccentricity

Present and past climates of Mars may be very different Present – cold/dry Past – cold and moist

Results from Viking Lander Gaschromatograph - Mass spectrometer

Viking Biology Experiments Labeled release experiment, looked for signs of metabolism Pyrolytic release experiment, looked for signs of photosynthesis Gas exchange experiment, looked for signs of respiration

In 1996, possible “fossils” were found in a meteorite from Mars! ALH 84001 originated as a slowly-cooled igneous rock in the Martian crust, was excavated by an impact, altered by fluids, and finally sent to Earth by another impact. The consensus among most researchers is that these are not fossils but”ludae naturae” (playthings of nature), of inorganic origin.

More “pseudofossils” from Martian meteorite ALH 84001

Carbonates in Martian meteorite ALH 84001 formed by shock

Carbonate globules in Martian meteorite ALH 84001 are of inorganic origin