ARES VALLIS, MARS—Earth-bound astronomers know the problem. You finally get your telescope time. You go up to the mountain. And it's socked-in by clouds—you can't get the data.

Now Mars Pathfinder knows the same problem. Pathfinder, also known as the Sagan Memorial Station, was attempting to observe the bright morning “star,” Earth. It was Pathfinder's sixteenth day on the planet, and Earth had risen several hours before the Sun. The IMP (Imager for Mars Pathfinder) team from the University of Arizona was eager to get this image of our home world—in part because it might inspire the public, and in part because Earth is one of a variety of astronomical targets that are used to help determine how much dust is suspended in the atmosphere.