The decision was based on continued evaluation of all available data and consultation/input from members of the LCROSS Science Team and the scientific community, including impact experts, ground and space based observers, and observations from Lunar Reconnaissance Orbiter (LRO), Lunar Prospector (LP), Chandrayaan-1 and JAXA's Kaguya spacecraft. This decision was prompted by the current best understanding of hydrogen concentrations in the Cabeus region, including cross-correlation between the latest LRO results and LP data sets.
The general consensus of lunar experts led by the LCROSS science team is that Cabeus shows, with the greatest level of certainty, the highest hydrogen concentrations at the south pole. Further consideration of the most current terrain models provided by JAXA's Kaguya spacecraft and the LRO Lunar Orbiter Laser Altimeter (LOLA) was important in the decision process.The models show a small valley in an otherwise tall Cabeus perimeter ridge, which will allow for sunlight to illuminate the ejecta cloud on Oct. 9, and much sooner than previously estimated for Cabeus. While the ejecta does have to fly to higher elevations to be observed by Earth assets, a shadow cast by a large hill along the Cabeus ridge, provides an excellent, high-contrast, back drop for ejecta and vapor measurements.
The LCROSS team concluded that Cabeus provided the best chance for meeting its mission goals. The team critically assessed and successfully advocated for the change with the Lunar Precursor Robotic Program (LPRP) office. The change in impact crater was factored into LCROSS' most recent Trajectory Correction Maneuver, TCM7.
During the last days of the mission, the LCROSS team will continue to refine the exact point of impact within Cabeus crater to avoid rough spots, and to maximize solar illumination of the debris plume and Earth observations.
Weather as seen in the LCROSS NIR Camera
The Near Infrared (0.9-1.7 mm) Camera #2 image of Earth as part of a LCROSS payload calibration activity on Sept. 18, 2009. At the time of this image, the LCROSS spacecraft was nominally 348,000 miles (559,400 km) from Earth. The inset shows the Earth face as seen by the LCROSS spacecraft. The Earth’s north pole is indicated by the arrow. The image on right shows water vapor as seen by GOES at a similar time as the LCROSS observation. The red letters indicate potential weather features common in both images. Click image for full resolution.
Shown here is the slightly greater than quarter-Earth, sized ~1.5 deg along its diameter, in four colors. The false color (where red is warm, blue is cold) mid-infrared images reveal warmer summer mid-Atlantic temperatures about the equator and Northern Hemisphere. The images also reveal the whole Earth’s disk. South America is to the left. Africa is to the right. Antarctica is at the bottom. All instruments performed well during the calibration. Click image for full resolution.
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