On Dec. 14, 2013, China’s Chang’e 3 spacecraft landed on the moon’s Mare Imbrium (Sea of Rains) just east of an impact crater approximately 1,500 feet (450 meters) in diameter. Soon after landing, a small rover named Yutu (Jade Rabbit in English) was deployed and took its first tentative drive onto the airless lunar surface. At the time of the landing, NASA’s Lunar Reconnaissance Orbiter (LRO) was far from the landing site, but on Dec. 24, the spacecraft approached the landing site and acquired six pairs of images. The highest resolution image was possible when LRO was nearly overhead, just before 11 p.m. EST that evening. At this time LRO was at an altitude of about 90 miles (150 km) above the site, and the pixel size was about 5 feet (150 cm).
View of the Chang’e 3 lander (large arrow) and Yutu rover (small arrow) just before sunset on their first day of lunar exploration. The image was taken by the Lunar Reconnaissance Orbiter Camera Narrow Angle Camera. The image width is approximately 1,900 feet (576 m). North is up. Image Credit: NASA/GSFC/Arizona State University
The rover is only about 5 feet (150 cm) wide, yet it shows up in the LRO’s Narrow Angle Camera (NAC) images for two reasons: the solar panels are very effective at reflecting light, so the rover appears as two bright pixels, and the setting sun allows the rover and lander to cast distinct shadows. Since the rover is close to the size of a pixel, how can scientists be sure they are seeing the rover and not a comparably sized boulder? Fortuitously, LRO acquired a “before” image of the landing site, with nearly identical lighting, on June 30, 2013. By comparing the before and after images of the site, the LRO camera team confirmed the position of the lander and rover and derived accurate map coordinates for the lander.
The lander set down about about 200 feet (60 meters) east of the rim of the impact crater on a thick deposit of volcanic materials. A large scale wrinkle ridge (about 60 miles long and 6 miles wide, or ~100 km long and 10 km wide) cuts across the area and was formed as tectonic stress caused the volcanic layers to buckle and break along faults. Wrinkle ridges are common on the moon, Mercury and Mars.
Panorma (top image) showing Yutu shortly after it drove down the ramp to the lunar surface. Yellow lines connect to craters seen in the panorama and the LROC image (lower image, taken after the rover had moved); red lines indicate approximate field of view of the panorama. Image Credit: Di Lorenzo and Kremer
Lunar mare basalts are divided into two main spectral (color) types: “red” and “blue”. (Blue is perhaps a misnomer; think “less red”.) Like basalts on Earth, lunar basalts are composed mainly of two minerals, pyroxene and plagioclase, though olivine and ilmenite can sometimes occur in significant amounts. The presence of ilmenite results in a “less red” color. Thus the blue basalts. The landing site is on a blue mare (indicating higher titanium) thought to be about 3 billion years old. The boundary (black arrows in WAC mosaic to the right) with an older (3.5 billion years) red mare is only about 6 miles (10 km) to the north.
Full discussion from the Lunar Reconnaissance Orbiter Camera team (850 Kb PDF)
LROC WAC context mosaic for the Chang’e 3 landing site (large white arrow). The small white arrows indicate wrinkle ridge terrain and the small black arrows indicate the boundary between “red” mare (northeast) and “blue” mare (southwest). The image is about 60 miles (100 km) wide. Image Credit: NASA/GSFC/Arizona State University
LROC WAC color overlain on WAC sunset BW image. Note the proximity of the landing site to a contact between red and blue maria. Image Credit: NASA/GSFC/Arizona State University
