vendredi 5 mai 2017

Seasonal Flows in Valles Marineris & Aging with Impacts












NASA - Mars Reconnaissance Orbiter (MRO) patch.

May 5, 2017

Seasonal Flows in Valles Marineris

Recurring slope lineae (RSL) are seasonal flows on warm slopes, and are especially common in central and eastern Valles Marineris, as seen in this observation by NASA's Mars Reconnaissance Orbiter (MRO). This image covers a large area full of interesting features, but the enhanced color closeup highlight some of the RSL.

Here, the RSL are active on east-facing slopes, extending from bouldery terrain and terminating on fans. Perhaps the fans themselves built up over time from the seasonal flows. Part of the fans with abundant RSL are dark, while the downhill portion of the fans are bright. The role of water in RSL activity is a matter of active debate.

The map is projected here at a scale of 50 centimeters (19.7 inches) per pixel. [The original image scale is 52.6 centimeters (20.7 inches) per pixel (with 2 x 2 binning); objects on the order of 158 centimeters (62.2 inches) across are resolved.] North is up.

Aging with Impacts

Mamers Valles is a long (approximately 1000 kilometers) sinuous canyon beginning in Arabia Terra and ending in the Northern lowlands of Deuteronilus Mensae. This image from NASA's Mars Reconnaissance Orbiter (MRO) features the southern facing slope of the canyon wall.

The northern half (top) has a rough, pitted texture with numerous impact craters, while the middle section shows the steep canyon wall. Streaks of slightly different colors show slope material eroding onto the canyon floor. Though the canyon itself was formed long ago, the material deposited on the canyon floor has been laid down over time, creating a much younger surface.

The difference in age of the surfaces can also be indicated by the presence or absence of impact craters. The longer a surface has been exposed, the more impact craters it will accumulate. Counting craters to determine age estimates of planetary surfaces has been used throughout the solar system. This method is based on the assumption that the youngest, freshly formed surfaces will have no impact craters, and as time progresses crater impacts will accumulate at a predictable rate. This concept has been calibrated using crater counts on the Moon and the measured age of the rocks brought back by the Apollo missions.

The map is projected here at a scale of 50 centimeters (19.7 inches) per pixel. [The original image scale is 59.2 centimeters (22.4 inches) per pixel (with 2 x 2 binning); objects on the order of 178 centimeters (33.8 inches) across are resolved.] North is up.

Mars Reconnaissance Orbiter or MRO

The University of Arizona, Tucson, operates HiRISE, which was built by Ball Aerospace & Technologies Corp., Boulder, Colo. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Mars Reconnaissance Orbiter Project for NASA's Science Mission Directorate, Washington.

Mars Reconnaissance Orbiter (MRO): http://www.nasa.gov/mission_pages/MRO/main/index.html

Images, Text, Credits: NASA/Tony Greicius/JPL-Caltech/Univ. of Arizona.

Greetings, Orbiter.ch

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