Astronomy Picture of the Day - powered by LUNEXIT.IT

Today's image shows some changing Seasonal Frost Patterns on Louth Crater: an old Impact Crater that is located, as you should already know very well, at about 70° North Latitude, in the Martian Region of Vastitas Borealis. This Crater contains a Mound (---> terrapieno) covered by Water Frost that persists throughout the whole Martian Year (which is an unusual circumstance for this Latitude); however, even the frozen Seasonal Carbon Dioxide (CO2) Frost (that deposited during the Northern Winter) can reach such a Latitude and, therefore, there could well be, inside Louth Crater, a real "Mixture" of both kinds of Ice. Said that, you should also consider, anyway, that, at the time when this image was acquired (such as during the Northern Martian Spring), the Carbon Dioxide Frost was already in the process of sublimating back into the Atmosphere. Note, also, that the Sand Dunes which are near the edge of the Mound, always become completely clear of Frost during the Martian Summer.

Louth Crater (a name that, as far as we know, is still unofficial, but that it has been already submitted to the International Astronomical Union for consideration) has been identified to have a greater resemblance to the Polar Cap than previously expected [see the References n. 1 and 2]. Furthermore, this Crater seems to contain a central Water Ice Deposit that is suitable for testing models of Volatile (Materials') Stability in the Martian North Polar Regions.

An appropriate sensitive detector for Water Stability and Water Vapour Distribution, could clearly reveal the presence (better yet: the existence) of (certain kinds of) interactions between the Surface and the Atmosphere of Mars, by identifying some possible sources (of Water Vapour) and sinks. However, by adapting the Water Vapour analysis already developed and tested for the OMEGA/ESA - Mars Express Orbiter collected data [see the References n. 3 and 4], it has been possible to retrieve the total amount of Water Vapour from the CRISM/NASA - Mars Reconnaissance Orbiter data, and such a retrieval was performed on two independent High Spectral-Spatial Resolution Observations of Louth Crater. In the end, and for the first time, a Water Vapour Distribution (at the 1/1000 of a degree scale) has been presented, and such a remarkable result could be an opening to the possibility of studying the Atmospheric Water Dynamics of Mars at very High Spatial Resolutions (like, for instance, on the Boundary of the Ice Mound), thus providing Scientists with hints regarding the presence - and extent - of Water Ice even under the close and (very) "Dusty" Martian Regions.

References:
[1] A.J. Brown et al; ICARUS (in press) 2008
[2] A.J. Brown et al; LPCI 2008
[3] R. Melchiorri et al ; Plan and Space Sci. 55 (2007) 333–342
[4] T. Encrenaz et al A&A 441, L9–L12 (2005)

Geophysical Research Abstracts,
Vol. 10, EGU2008-A-10434, 2008
SRef-ID: 1607-7962/gra/EGU2008-A-10434
EGU General Assembly 2008

© Author(s) 2008
Louth crater: Water vapour distribution as seen by CRISM/MRO
R. Melchiorri (1); T.L. Roush (1); R.M. Haberle (1); A. J. Brown (2) ; T. Encrenaz
(3); CRISM team
1) NASA AMES Research Center, Moffet Field, CA, 94035, USA
2) SETI Institute, 515N. Whisman Rd, Mountain View, CA 94043, USA
3) LESIA Observatoire de Meudon 5, place Jules Janssen, 92195 Meudon, France

Mars Local Time: 14:32 (Early Afternoon)
Coord. (centered): 70,228° North Lat. and 103,397° East Long.
Spacecraft altitude: 316,2 Km (such as about 197,6 miles)
Original image scale range: 31,6 cm/pixel (with 1 x 1 binning) so objects ~ 95 cm across are resolved
Map projected scale: 25 cm/pixel
Map projection: POLAR STEREOGRAPHIC
Emission Angle: 1,7°
Phase Angle: 54,7°
Solar Incidence Angle: 56° (meaning that the Sun was about 34° above the Local Horizon at the time that the picture was taken)
Solar Longitude: 50,3° (Northern Spring/Southern Fall)
Credits: NASA/JPL/University of Arizona

This frame has been colorized in Absolute Natural Colors by (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.