Astronomy Picture of the Day
October 1, 2012


Credits: NASA/JPL-University of Arizona - Credits for the additional process. and color.: Dr Paolo C. Fienga/Lunar Explorer Italia/IPF

HiRISE acquired this dramatic views of the Martian moon, Phobos, on March 23, 2008. This observation (which has been catalogued as PSP_007769_9015) was acquired at a distance of approx. 5800 Km from Phobos, and it provides Surface Details at a 5,8 mt/pixel scale (with the object diameter of about 4000 pixels). The illuminated part of Phobos visible in the image is about 21 Km across. Images from previous Spacecraft have been of smaller pixel scale (for example, the NASA - Mars Global Surveyor Orbiter got data at 4 mt/pixel, because this Spacecraft came closer to Phobos), but the HiRISE images have greater signal-to-noise, making the new data some of the best ever for Phobos.

To the lower right portion of the frame, you can see the most prominent Surface Feature of this moon: the large Impact Crater Stickney. With a diameter of about 9 Km, it is the largest Surface Feature of Phobos. However, a number of Grooves, Surface Striations and Crater Chains are also well visible all over the moon. Although so many Grooves appear radial to Stickney, previous studies showed that, in fact, the Grooves radiate from a different point on Phobos and this circumstance led to several hypotheses about their formation. In the end, some scientists believe that the Grooves and Crater Chains are related to the formation of Stickney, while others think that they could have formed from Ejecta from impacts which actually occurred on Mars and that, some time later, collided with Phobos (consider the low Martian Gravity and do not forget that Phobos orbits only about 3700 miles above the Surface of Mars!). The Lineated Textures on the Walls of Stickney, as well as on other large Impact Craters, are Dust and Landslides formed from Surface Materials that slowly fell into the Crater Interiors.

This picture (which is the NASA - Original Mars Reconnaissance Orbiter enhanced-color frame identified by the serial n. PSP_007769_9015) has been additionally processed and then re-colorized in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Mars Reconnaissance Orbiter and then looked outside, towards the Martian moon Phobos), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team.

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