Emily LakdawallaMar 04, 2014

Checking in on Chang'e 3 and Yutu from Lunar Reconnaissance Orbiter: Yep, still there!

Seeing hardware that was built by human hands sitting on the surface of another planet never, ever gets old. Today, the Lunar Reconnaissance Orbiter Camera (LROC) team released two new images of Chang'e 3 and Yutu on the Moon. In my favorite view of the landing site, you can clearly see Yutu's tracks on the Moon:

Here's an annotated version of the same photo:

The other images, assembled into an animation, confirm what we've been told already: Yutu didn't move much, if at all, between the last two images. The penultimate image was taken January 21, the last one February 17. The motor problem was reported on January 25.

It's cool how the appearance of the landing site shifts from photo to photo. Mars orbiters have "sun-synchronous" orbits, whose ground tracks shift westward at exactly the same rate that the Sun apparently does, so illumination angle is roughly constant with time (the seasons do cause changes in illumination angle). Lunar Reconnaissance Orbiter doesn't do that, so it sees spots on the Moon at all different solar incidence angles. High solar incidence angle means that topographic features throw long shadows, making it easy to see the landscape shape from shading. Low solar incidence angle suppresses topography, especially the more muted, longer-wavelength topograhy, and the lighter and darker areas are instead showing you different properties of the surface: fresh craters are surrounded by brighter splashes of material that hasn't been darkened by billions of years of space weathering. Here's the summary of the shifting light from the LROC website:

Chang'e 3 landed on Mare Imbrium (Sea of Rains) on 14 December 2013. LROC has now imaged the lander and rover three times: 25 December 2013 (M1142582775R), 21 January 2014 (M1144936321L), and 17 February 2014 (M1147290066R). From month-to-month the solar incidence angle decreased steadily from 77° to 45° (incidence angle at sunset is 90°); due to the latitude of the site (44.1214°N, 340.4884°E, -2630 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 0°, at dawn or dusk the incidence angle is 90°.

But, like her sisters at Mars, Lunar Reconnaissance Orbiter can perform some tricks to get unusual photos of interesting sites. Here is one more really awesome picture of the desolation of Chang'e 3's landing site, seen from an oblique, out-the-airplane-window type of perspective.

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