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Emily LakdawallaJanuary 20, 2013

More Chang'E 2 Toutatis flyby images

Last week at a meeting of NASA's Small Bodies Assessment Group (SBAG), Han Li of the Chinese Academy of Sciences gave a lengthy presentation on Chang'E 2. Much of the presentation focused on the mission's work at the Moon, but at the end she spent several slides discussing the Toutatis flyby. Her slides are posted here, and they include, on slide 76, eleven images from the flyby. The closest three are truncated, but not for the usual reason (the usual reason being that the target was out of the frame). They're truncated because they're occulted by the solar panel, which makes sense, because this was a solar-panel-monitoring engineering camera.

Chang'E 2 images of Toutatis

Chinese Academy of Sciences

Chang'E 2 images of Toutatis
A set of Chang'E 2 Toutatis flyby images taken from Han Li's January 15, 2013 presentation to the Small Bodies Assessment Group.

Compared to the previously published set of images (which I'm including below for comparison), this set is of lower quality, I presume because it was embedded within a PDF file and the image quality was reduced during saving.

Chang'E 2 images of Toutatis

Chang'E 2 images of Toutatis
The closest fly-by was at 08:30:09 UTC on December 13 at an altitude of just 3.2 km and at a relative velocity of 10.73 km/s. Quite a few photos were snapped by the CCD camera - including this series of photos taken 93 - 240 km away from Toutatis:

It didn't take long for Daniel Macháček to combine the truncated images with the best full-disk (if you can call it a disk) image from the previous set, making the best-yet composite view of the asteroid:

Composite image of Toutatis from Chang'E 2 photos

Chinese Academy of Sciences / Daniel Macháček

Composite image of Toutatis from Chang'E 2 photos
A mosaic of four Chang'E 2 photos.

Another notable difference in the new set of images is the metadata -- there's been a revision of the ranges and times reported for each image. The range, Li reported, is based upon inspection of the images rather than tracking data, so revision of the range is not surprising. But I'm a little befuddled by why the times would need to be changed by several seconds. I thought that maybe these were spacecraft time and the previous ones Earth-received time, but the difference is not large enough for that; Chang'E 2 was 7 million kilometers from Earth during the encounter, about 25 light-seconds one-way.

Read more: near-Earth asteroids, pretty pictures, amateur image processing, asteroids, asteroid 4179 Toutatis, Chang'E program

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Emily Lakdawalla

Senior Editor and Planetary Evangelist for The Planetary Society
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