To reach colonists on Mars, you might attach “mars.sol” to the e-mail address. For retrieving images from one of Jupiter’s moons, a file transfer from a “europa.sol” site might be in order. The space missions making that possible may be years or lifetimes away, but initial steps toward extending the Internet’s reach are already in the works. The first component, a short-range transceiver, hitched a ride on the Mars Odyssey, which was launched in April and is due to reach the Red Planet in October.