[meteorite-list] LRO Images Chang'e 3 Lander and Rover From Above

[Ron Baalke]

http://lroc.sese.asu.edu/news/index.php?/archives/849-Change-3-Lander-and-Rover-From-Above.html

Chang'e 3 Lander and Rover From Above
December 30, 2013

[Image]
LROC NAC view of the Chang'e 3 lander (large arrow) and rover (small arrow) 
just before sunset on their first day of lunar exploration. LROC NAC M1142582775R, 
image width 576 m, north is up [NASA/GSFC/Arizona State University].

Chang'e 3 landed on Mare Imbrium (Sea of Rains) just east of a 450 m diameter 
impact crater on 14 December 2013. Soon after landing, a small rover named 
Yutu (or Jade Rabbit in English) was deployed and took its first tentative 
drive onto the airless regolith. At the time of the landing LRO's orbit 
was far from the landing site so images of the landing were not possible. 
Ten days later on 24 December, LRO approached the landing site, and LROC 
was able to acquire a series of six LROC Narrow Angle Camera (NAC) image 
pairs during the next 36 hours (19 orbits). The highest resolution image 
was possible when LRO was nearly overhead on 25 December 03:52:49 UT (24 
December 22:52:49 EST). At this time LRO was at an altitude of ~150 km 
above the site, and the pixel size was 150 cm. 


[Images]
LROC NAC before and after images of the Chang'e 3 landing site [NASA/GSFC/Arizona 
State University].

The rover is only about 150 cm wide, yet it shows up in the NAC images 
for two reasons: the solar panels are very effective at reflecting light 
so the rover shows up as two bright pixels, and the Sun is setting thus 
the rover casts a distinct shadow (as does the lander). Since the rover 
is close to the size of a pixel, how can we be sure we are seeing the 
rover and not a comparably sized boulder? Fortuitously, the NAC acquired 
a "before" image (M1127248516R) of the landing site, with nearly identical 
lighting, on 30 June 2013. By comparing the before  and after landing 
site images, the LROC team confirmed the position of the lander and rover, 
and derived accurate map coordinates for the lander (44.1214°N, 340.4884°E, 
-2640 meters elevation).


[Image]
Chang'e 3 lander panorama [Images from CNSA; compiled by Di Lorenzo and 
Kremer] showing Yutu shortly after it drove down the ramp to the surface. 
Yellow lines connect craters seen in the panorama and the LROC image (taken 
at a later date after the rover had moved), red lines indicate approximate 
field of view of the panorama.

The lander set down about 60 meters east of the rim of a 450 meter diameter 
impact crater (40 meters deep) on a thick deposit of volcanic materials. 
A large scale wrinkle ridge (~100 km long, 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.


[Image]
LROC WAC context mosaic for the Chang'e 3 landing site (large white arrow); 
small white arrows indicate wrinkle ridge and small black arrows delimit 
boundary between "red" mare (northeast) and "blue" mare (southwest), image 
is 100 km wide [NASA/GSFC/Arizona State University].

Lunar mare basalts are divided into two main spectral (color) types: "red" 
and "blue" (blue is perhaps a misnomer, think "less red"). Basalts on 
the Moon (same on Earth) are composed mainly of two minerals, pyroxene 
and plagioclase, though olivine and ilmenite can sometimes occur in significant 
amounts. The presence of ilmenite (FeTiO3) results in lower reflectance 
and a "less-red" color - thus the blue basalts. The landing site is on 
a blue mare (higher titanium) thought to be about 3.0 billion years old. 
The boundary (black arrows in above WAC mosaic) with an older (3.5 billion 
years) red mare is only 10 km to the north.

[Image]
LROC WAC color (689 nm, 415 nm, 321 nm) overlain on WAC sunset BW image. 
Note the proximity of the landing site to a contact between red and blue 
maria [NASA/GSFC/Arizona State University].


A large area LROC WAC topography map of the Imbrium basin and surrounds 
is available here. 


[Image]
LROC NAC before and after shown in the animation at the top of this Featured 
Image [NASA/GSFC/Arizona State University].