(CRISM Science Operations Center, February 1, 2007) - CRISM is now approaching 100 days of operation in Mars orbit. In that time, the "ops" team has taken over 700 images of specific targets including over 250 at high resolution (typically 20 meters, or 66 feet per pixel in 544 colors). On top of that, nearly 25% of the planet has been mapped at reduced resolution (200 meters, or 660 feet per pixel in 72 colors).

The data volume is enormous. MRO is already nearly surpassing the data return of Mars Odyssey, which has been operating for 5 years. CRISM has had a 30% share of this. Once on the ground and converted from raw data to brightness measurements, the largest individual images are about 720 megabytes in size! The large size comes from the fact that each image has 544 colors.

In some images, CRISM has revealed new details never expected on Mars: intricate compositional layering of the polar caps, vast fields of gypsum-rich sand dunes, and ancient rocks from Mars' earliest history that record a time when liquid water was pervasive and long-lasting.

With other images, the ops team is using CRISM as a surveyor's tool, to help find a suitable landing site for the next landed mission to Mars, called Phoenix. That mission will land somewhere in the high latitude northern plains of Mars in May of 2008, and begin to characterize the cold, dry landscape. One main goal of the Phoenix mission is to determine the composition of both dry surface soil and ice-rich subsurface soil. So a suitable landing site will have plenty of dry soil to measure, but also water ice at a shallow enough depth that Phoenix's robotic arm will be able to reach it. Conversely, patches of ice shouldn't be exposed at the surface - even ice-cemented soil - because if Phoenix happens to land there the robotic arm might not be able to reach a sample of dry soil. At the same time, the site should be level and free of large boulders to ensure a safe landing.

Phoenix's science team has identified four large regions, named A, B, C, and D, that may meet these criteria. All are at high northern latitudes from 65 to 72 degrees, where Mars Odyssey's gamma-ray spectrometer sees subsurface ice, and where images from THEMIS and MOC seem to show a flat surface with few boulders. All four regions have now been imaged by MRO's high-resolution instruments, CRISM, HiRISE, and CTX, to verify that the sites really are flat, safe, and free of exposed patches of ice. The higher resolution of the MRO instruments has allowed the Phoenix team to look for features not discernible to the earlier instruments.

CRISM has several roles in surveying candidate Phoenix landing sites. One is to determine how much ice is exposed at the surface, even ice mixed with the soil that THEMIS or MOC might not recognize. Another is to determine if the surface has too high a concentration of salts. CRISM's infrared wavelengths are crucial to both measurements, because of their sensitivity to ice and to many salts like sulfates, which are very common in some parts Mars. The operations team uses both major instrument modes; a lower-resolution mapping mode covers as much of the four regions as possible while the high-resolution targeted mode captures images of representative terrains at about 10 kilometers (6 miles) across. The high-resolution images below show regions A, B, C, and D in a combination of blue, green, and red colors, enhanced to bring out subtle shades of variation. All four regions are compositionally "bland" compared to some other martian landscapes CRISM has seen - and that's good, for Phoenix. Ice has only been seen as small patches on the cold, north-facing sides of steep craters where seasonal frost resides well into late summer (for example in region A, below), and not poking out of the subsurface.

The period of time for CRISM to observe the Phoenix landing sites is now ending, as the autumnal equinox looms, polar night begins to approach, and an autumn cover of ice clouds spread over Mars' northern regions (some clouds are even visible in the image of region C below). We'll be back in 2008 a few months before landing, in the local springtime, to image the location that the Phoenix team chooses to be the final landing site. We'll also monitor any changes in the landing site (such as frost accumulation) as the Phoenix mission swings into full action.

Image IDs by region: (A) FRT0000332C, acquired 28 Nov 2006). (B) FRT00002903, acquired on 5 October 2006. (C) FRT00003130, acquired 20 November 2006. (D) FRT000032DA, acquired 27 November 2006.