HiRISE Updates Week of 2018 Nov 26

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HiRISE Updates Week of 2018 Nov 26

Post by bystander » Tue Nov 27, 2018 3:45 pm

Paul Geissler wrote:

The Changing Climate of Mars (ESP_056563_0960)

A story of changes in the climate of Mars is told by icy deposits. Remnants of a formerly extensive deposit composed of dry ice layered together with dust and water ice form what is known as the south polar residual cap.

This deposit is shrinking over time as the frozen carbon dioxide turns to vapor. Rounded valleys that give the deposit an appearance resembling Swiss cheese are enlarging over time, exposing an older surface below that is likely made up of water ice.

In the past, the South Pole of Mars was colder than it is today, with an average temperature below the freezing point of carbon dioxide gas. Carbon dioxide from the atmosphere condensed on the polar water ice cap, forming a layered deposit of dry ice together with trace amounts of dust and water ice. More recently, the South Pole of Mars has warmed to an average temperature greater than the freezing point of carbon dioxide gas, and the dry ice deposits are retreating.

Changes in the Martian climate can be produced by several factors that are internal to the planet. Variations in the tilt of Mars’ rotation axis—called obliquity—affect the amount of sunlight received at the poles, cooling them during periods of low obliquity and less direct sunlight. Changes in the reflectivity of the surface also affect temperature, because darker surfaces absorb more sunlight and are warmer than bright surfaces. Variations in dust storm activity also affect the climate, since a dusty atmosphere is warmer than a clear one. If the current conditions persist, the south polar residual cap could be gone in as little as one hundred years.
Livio Leonardo Tornabene wrote:

Looking at Martian Salts and Clays (PSP_005811_1470)

This 3D perspective view is a composite of both HiRISE and data from CRISM, another instrument onboard MRO. This view covers a small patch of ancient Martian real estate in Terra Sirenum.

CRISM collects spectral data that can be used as a chemical fingerprint for the upper most surface. This information suggests that this small patch of surface is covered with salts (chlorides) represented in green and water-rich clays that appear in blue.

CRISM colors can be added to high-resolution images to enhance our knowledge of these materials. They also match nicely with the surface features in our HiRISE image. For example, a fissure near the center of the image may be a a clue to the origin of the salts. The fissure may be a fracture where warm salt-laden water may have welled up, erupted and ponded on the surface. These waters then evaporated leaving the salt-rich deposits behind.

This is a stereo pair with PSP_006668_1470.
Mike Mellon wrote:

Spring Frost on a Cold World (PSP_007448_2475)

Winter on Mars comes with a blanket of carbon dioxide snow. During the spring “thaw,” this snow evaporates into the atmosphere, lingering longest in the shallow depressions such as the troughs of polygon patterned ground.

Enhanced color shows the carbon dioxide snow as bluish-white patches among areas of rusty red bare ground. We took this image in 2008 as a possible landing site for the Phoenix Lander that arrived on Mars later that same year.
Serina Diniega wrote:

Active Dunes in Wirtz Crater (ESP_021893_1315)

These gorgeous dunes are likely active, with ripples on their upwind slopes and dark streaks on their downwind slopes forming and changing due to wind-driven sand motion.

This motion will also keep the dune brink (the edge between the two slopes) and bottom edges sharply defined. The dark lines and squiggles on the dune slope are formed by passing dust devils.

This is a stereo pair with ESP_021603_1315.

Credit: NASA/JPL-Caltech/University of Arizona

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