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Emily Lakdawalla • Oct 02, 2009

MESSENGER gets two planets for the price of one

Here's a pretty shot of Mercury taken by MESSENGER on approach. I've posted such approach images already, though, making this one relatively non-newsworthy...but wait, what's that tiny little speck in the lower left corner of the photo?

Mercury and Venus from MESSENGER
Mercury and Venus from MESSENGER On approach to its third flyby of Mercury on September 29, 2009, MESSENGER captured this view of Mercury, with Venus visible as a tiny speck near the lower left of the image.Image: NASA / JHUAPL / CIW

Why, it's Venus! The solar system is really a very empty place, so it's quite remarkable that MESSENGER just happened to catch two planets in one camera frame. But it really is Venus; you can tell from this simulated view from JPL's Solar System Simulator. Yeah, Venus is only a tiny speck. I still think the photo is awfully cool.

That image is cropped from this one that they released today, which nicely demonstrates the difference in the views you get through MESSENGER's wide- and narrow-angle cameras. It's the norm for spacecraft to carry at least two different camera instruments. Typically there's one wide-angle camera, which can take in a large amount of the sky (or a planet) in one view at relatively low resolution, and one narrow-angle camera, which can capture much higher-resolution pictures but at a cost of seeing much less in each field of view. MESSENGER's wide-angle camera has a 10.5-degree field of view, while its narrow-angle camera has a 1.5-degree field of view. So the narrow-angle camera has seven times higher resolution, but it would take 49 narrow-angle camera images to cover the area that you can see in one wide-angle camera shot.

MESSENGER's wide- and narrow-angle camera views
MESSENGER's wide- and narrow-angle camera views On approach to its third flyby of Mercury, MESSENGER snapped these views of the planet with its wide-angle camera (top) and narrow-angle camera (bottom) at nearly the same time. The wide-angle camera has a field of view seven times the width of the narrow-angle camera, at seven times lower resolution.Image: NASA / JHUAPL / CIW

The MESSENGER team has released several images per day from the flyby; check out their gallery to see them all. Here's my favorite among the recent ones. There's something about those double-ring basins that I find visually compelling. This one still needs a name.

Caravaggio double-ring basin on Mercury
Caravaggio double-ring basin on Mercury Dramatic lighting at local dawn brings the double rim of a double-ringed impact basin into high relief in this image taken by MESSENGER as it approached for its third flyby. The 160-kilometer basin was later named Caravaggio.Image: NASA / JHUAPL / CIW

This map shows you that despite the safing event, MESSENGER completed one very important goal for this flyby: it filled the last big gap in imaging coverage, a north-to-south stripe of the planet around 50 degrees longitude. Having that gap filled will be very helpful to the team as they plan for the orbital phase of their mission.

Map of Mercury after MESSENGER’s third flyby
Map of Mercury after MESSENGER’s third flyby Following MESSENGER's final Mercury flyby before entering orbit, the map coverage of Mercury is nearly complete. Mariner 10 mapped about 45% of the planet (green outline). MESSENGER covered another 20% on its first flyby (blue outline). The second flyby nailed 25% more (red outline). The most recent flyby filled in another 5%, including the last missing piece of the equator and mid-latitudes. Now only 5% of the planet remains unmapped, most of it poleward of 60° north and south latitude.Image: NASA / JHUAPL / CIW

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