Mars today is a frozen desert,but the photos sent back by the Mariner and Viking probes in the 1970s indicate its past was less bleak and more Earth-like. The images showed sinuous channels and valleys that were al-
At a current distance of 4. 5 billion kilometers from the sun, Pluto isthe only planet in our solar system not yet visited by a spacecraft. Mostmission plans call for a long and expensive journey to the faraway planet...
The fiery planet Mercury, where the temperature at high noon can exceed 750°F, is not a place that you would expect to find ice. The closestplanet to the sun, this airless, cratered world appears devoid of any wa-ter...