Astronomy Picture of the Day
October 19, 2014

Perennial Water Ice within an Unnamed Northern Crater (EDM)
Perennial Water Ice within an Unnamed Northern Crater (EDM)

As you know, most of the Surface Ice on Mars is only temporary. The (North and South) Polar Layered Deposits are, in fact, thick stacks of Permanent Water Ice located at each Pole, but the South Polar Residual Cap may be a Permanent (although dynamic) Layer of Carbon Dioxide Ice. However, at lower Latitudes, the Seasonal Frost (mostly Carbon Dioxide Frost, but with some Water Ice mixed with it) comes and goes each year.

Some Outliers of Water Ice are found near the North Polar Layered Deposits and, in many cases, they have accumulated a significant thickness, as it occrred in the "famous" Louth Crater. In this case, instead, a thin Layer of bright Frost was visible in a HiRISE image during the early North Polar Summer, covering part of the Inner Northern Wall and a very small part of the Southern Outer Wall of an Unnamed Impact Crater. In any case, the thickness, here, was small — and there is little visible effect of such a little thickness on the Topography of the Crater itself.

The HiRISE monitored this location through the rest of the Season and found out that the Frost remained all Summer long, and therefore this is (should be) a a case of so-called "Perennial Ice Patch", although the Edges of the Patch shrank slightly over the Summer. Anyway, since the Carbon Dioxide (CO2) Frost and Ice are not stable under the Summer Martian conditions, in this situation is (very likely) that we are in front of a Patch of Perennial Water Ice Frost. It may be that it is in its early stages of accumulation, or that the equilibrium amount of Ice in a small Impact Crater that is relatively far from the Pole, is just thin.

Last, but not least, a still-unexplained Feature of this Unnamed Impact Crater is in the diffuse Dark Smudges visible on its Floor. These smudges, in fact, resemble “defrosting spots” which are only visible on Carbon Dioxide Ice in the early Spring but, on the other hand, they occur on Frost-free Areas and (usually) survive throughout the whole Summer.

Mars Local Time: 15:06 (Early Afternoon)
Coord. (centered): 73,860° North Lat. and 152,252° East Long.
Spacecraft altitude: 319,0 Km (such as about 198,099 miles)
Original image scale range: 31,9 cm/pixel (with 1 x 1 binningso objects ~ 96 cm across are resolved
Map projected scale: 25 cm/pixel
Emission Angle: 1,8°
Phase Angle: 76,7°
Solar Incidence Angle: 75° (meaning that the Sun was about 15° above the Local Horizon at the time the picture was taken)
Solar Longitude: 170,5° (Northern Summer - Southern Winter)
Credits: NASA/JPL/University of Arizona
Additional process. and coloring: Lunar Explorer Italia

This picture (which is a crop taken from a NASA - Original Mars Reconnaissance Orbiter b/w and NON Map-Projected frame identified by the serial n. ESP_037551_2540) has been additionally processed, magnified to aid the visibility of the details, contrast enhanced, Gamma corrected, and then 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 down, towards the Surface of Mars), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team.

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