March 5, 2014
Chang’e Lunar Rover Landing Site Viewed By NASA’s Lunar Reconnaissance Orbiter
Chang'e 3 landed on the moon's Mare Imbrium (Sea of Rains), on Dec. 14, 2013. The LROC instrument aboard NASA's Lunar Reconnaissance Orbiter has now imaged the Chinese lander and rover three times: Dec. 25, 2013 (M1142582775R), Jan. 21, 2014 (M1144936321L), and Feb. 17, 2014 (M1147290066R). From month-to-month the solar incidence angle decreased steadily from 77 degrees to 45 degrees (incidence angle at sunset is 90 degrees); due to the latitude of the site (44.1214 degrees north, 340.4884 degrees east, -2,630 meters elevation) the incidence angle cannot get much smaller. Solar incidence angle is a measure of the sun above the horizon; at noon on the equator the sun is overhead and the incidence angle is zero degrees, at dawn or dusk the incidence angle is 90 degrees.
As the sun gets higher above the horizon, topography appears subdued and reflectance differences become more apparent. In the case of the Chang'e 3 site, with the sun higher in the sky one can now see the rover Yutu's tracks. In the opening image you can see Yutu about 30 meters (about 100 feet) south of the Chang'e lander, then it moved to the northwest and parked 17 meters (about 56 feet) southwest of the lander. In the February image it is apparent that Yutu did not move appreciably from the January location.
Owing to the lower solar incidence angle the latest NAC image better shows Yutu's tracks and the lander engine blast zone (high reflectance) that runs north-to-south relative to the lander. Next month the solar incidence angle will again increase and subtle landforms will begin to dominate the landscape.