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Emily LakdawallaSeptember 28, 2009

Fifty-five hours from Mercury

Actually, at the time that I write this, MESSENGER is only about 32 hours and 400,000 kilometers from closest approach, but this photo was taken at 55 hours and 672,000 kilometers out:

55 hours from Mercury Flyby 3

NASA / JHUAPL / CIW

55 hours from Mercury Flyby 3
MESSENGER snapped this photo of Mercury from 672,000 kilometers away on September 27, 2009, on approach to its third flyby. A small strip of terrain near the limb has not before been seen by spacecraft.
Here's a cropped and enlarged version of the same, courtesy of Phil Stooke:
55 hours from Mercury Flyby 3

NASA / JHUAPL / CIW / Phil Stooke

55 hours from Mercury Flyby 3
MESSENGER snapped this photo of Mercury from 672,000 kilometers away on September 27, 2009, on approach to its third flyby. A small strip of terrain near the limb has not before been seen by spacecraft.
What I think is cool about this image is that we are seeing substantially farther around the limb than we did in our previous view:
MESSENGER approaches for its third Mercury flyby

NASA / JHUAPL / CIW

MESSENGER approaches for its third Mercury flyby
MESSENGER captured this photo of a crescent Mercury on September 25, 2009, on its way in to a September 29 flyby. This view of Mercury contains a small sliver of terrain never before observed by a spacecraft. MESSENGER will acquire much higher resolution views of this crescent as the distance between it and Mercury shrinks over the coming days. This version of the image has been enlarged by a factor of two.
Looking back up at the 55-hours-away image, the prominent bright crater in the north was imaged on approach to flyby 2. Then there's a cool dark-ring crater to the southwest of it. That dark-ring crater was only half-seen on the limb on approach to flyby 2; everything to the west (left) of it is brand-new territory, except possibly some terrain just at the edge of the disk that MESSENGER may have seen as it departed from flyby 2.

If this image is on Earth and squarely centered in the field of view, that would seem to indicate that all's well as MESSENGER approaches for its flyby, culminating tomorrow at 21:55 UTC (14:55 my time). Last night, I Tweeted about the latest mission update, which stated that by using solar sailing techniques they have targeted MESSENGER's flyby altitude to within 100 meters of the desired 228-kilometer-altitude aim point -- so they need no final trajectory correction maneuver.

Stay tuned for more!

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Emily Lakdawalla

Senior Editor and Planetary Evangelist for The Planetary Society
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