But in this case, they have a pretty densely sampled and well-calibrated spectrum from one of the instruments (http://dawn.jpl.nasa.gov/multimedia/vir_gallery.asp -- there appear to be ~100 spectral samples), so they would be able to make a black-body assumption, derive a temperature, and then validate the extent to which that is correct. In other words, it's not just a plain IR image, it's a whole spectrum.
But in this case, they have a pretty densely sampled and well-calibrated spectrum from one of the instruments (http://dawn.jpl.nasa.gov/multimedia/vir_gallery.asp -- there appear to be ~100 spectral samples), so they would be able to make a black-body assumption, derive a temperature, and then validate the extent to which that is correct. In other words, it's not just a plain IR image, it's a whole spectrum.