jeudi 13 juillet 2017

Mars and the Amazing Technicolor Ejecta Blanket & 'Elementary, My Dear Deposit...'

NASA - Mars Reconnaissance Orbiter (MRO) logo.

July 13, 2017

Mars and the Amazing Technicolor Ejecta Blanket

This image from NASA's Mars Reconnaissance Orbiter shows the exposed bedrock of an ejecta blanket of an unnamed crater in the Mare Serpentis region of Mars. Ejecta, when exposed, are truly an eye-opening feature, as they reveal the sometimes exotic subsurface, and materials created by impacts (close-up view). This ejecta shares similarities to others found elsewhere on Mars, which are of particular scientific interest for the extent of exposure and diverse colors. (For example, the Hargraves Crater ejecta, in the Nili Fossae trough region, was once considered as a candidate landing site for the next NASA Mars rover 2020.)

The colors observed in this picture represent different rocks and minerals, now exposed on the surface. Blue in HiRISE infrared color images generally depicts iron-rich minerals, like olivine and pyroxene. Lighter colors, such as yellow, indicate the presence of altered rocks.

The possible sources of the ejecta is most likely from two unnamed craters. How do we determine which crater deposited the ejecta?

A full-scale image shows numerous linear features that are observed trending in an east-west direction. These linear features indicate the flow direction of the ejecta from its unnamed host crater. Therefore, if we follow them, we find that they emanate from the bottom of the two unnamed craters. If the ejecta had originated from the top crater, then we would expect the linear features at the location of our picture to trend northwest to southeast.

The map is projected here at a scale of 50 centimeters (19.7 inches) per pixel. [The original image scale is 50.8 centimeters (20 inches) per pixel (with 2 x 2 binning); objects on the order of 153 centimeters (60.2 inches) across are resolved.] North is up.

'Elementary, My Dear Deposit...' 

In this image, NASA's Mars Reconnaissance Orbiter (MRO) observes an impact crater with associated bright deposits that at first glance give the appearance of seasonal frost or ice accumulations. MRO has an onboard spectrometer called CRISM that can distinguish between ices and other minerals. Unfortunately, there is currently no coverage of this particular spot. However, it can be deduced through several lines of evidence that this is, in fact, not ice.

Just like Earth, Mars experiences seasons that change as the planet orbits the Sun. Seasonal changes are most apparent at the higher latitudes. As these regions in each hemisphere enter their respective summer seasons, the Sun rises higher in the Martian sky causing frost and ice to sublimate, and illuminate more features across the landscape. As the high latitudes of each hemisphere move toward their respective winters, the days (called "sols") grow shorter and the sun hangs low on the horizon, giving rise to prolonged periods of cold, darkness, and frost accumulation.

First, it should be noted that at the time this image was taken, the Southern hemisphere is at the end of the summer season, so any frost or ice deposits have long since sublimated away. Second, numerous HiRISE images of seasonal targets show that ice accumulates on pole-facing slopes. The deposits in question are situated on a slope that faces the equator, and would not accumulate deposits of frost. Thus, it can be concluded that these exposures are light-toned mineral deposits.

The map is projected here at a scale of 25 centimeters (9.8 inches) per pixel. [The original image scale is 25.5 centimeters (10 inches) per pixel (with 1 x 1 binning); objects on the order of 77 centimeters (30.3 inches) across are resolved.] North is up.

Mars Reconnaissance Orbiter (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):

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


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