[[Also: there’s a heat-shield on the spacecraft to keep the sunlight off of it. The unshielded side will still bake quite a bit when it’s facing Mercury’s day-side, however.]]

Good point! Thermal emission, and reflected sunlight, from a planet has to be taken into account in planning around a satellite’s environment. Mercury’s bolometric Bond albedo isn’t very high — I think 0.119 was what Bonnie Buratti’s team found in the ’90s — but the thermal radiation will pouring off that baby. Hang on, I feel compelled to do the math.

Solar constant at Mercury, assuming it’s exactly at the 0.387 AU midpoint of its orbit: 9,121.4 watts per square meter (I assume S at Earth’s orbit is 1,366.1 W m-2, which is the mean for Judith Lean’s data for 1951-2000). Mercury reflects back 1,085.4 W m-2 at shortwave wavelengths.

Subsolar temperature given the known semimajor axis and albedo: 558.0 K. Given perfect emissivity (e = 1.0), the thermal radiation given off should then be 5,497.3 W m-2 (I’ve got too many significant digits there, of course). So about five times as much thermal IR as shortwave. Thank God for the inverse square law. Presumably this baby won’t get closer than 100 km or so…?

My recollection is that MESSENGER will be a polar orbiter, so yes, the poles will feel the love.

Also: there’s a heat-shield on the spacecraft to keep the sunlight off of it. The unshielded side will still bake quite a bit when it’s facing Mercury’s day-side, however.

“Thirty hours before the closest approach point, we begin taking a 3 color movie of Mercury, which continues until about 2 hours before closest approach. We will be looking a crescent Mercury, and we will image some of the terrain that was observed by Mariner 10 back in the 1970’s. We then take a monochrome mosaic and an 11-filter color image of the same part of the surface.
During the closest part of the flyby, we are in shadow, so won’t be taking any images for about an hour. As we approach the terminator, we use the MDIS pivot to look ahead along the spacecraft ground track, and image a region that is in the sunlight part. Once we cross the terminator, we image this area another four times as we fly over it, in order to gather information about the texture of the surface as the viewing geometry changes. We also take our highest-resolution images of the surface at this time – from 100-200 m/pixel.

We are now taking images of the hemisphere of Mercury that has never before been seen by a spacecraft.
As we fly away from Mercury, we take a number of monochrome and color images of the same area, at a variety of resolutions down to ~1 km/pixel in monochrome, and ~5 km/pixel in color. Finally, about 2 hours after the closest approach point, we begin taking a monochrome departure movie, where we take 1 image every 5 minutes for another 18 hours.These images will be compared to the “known” hemisphere of Mercury, but they will be at generally higher resolution than Mariner 10, and some of them are in 11 filters instead of the 3 that Mariner 10 acquired.”