Mars
Scientists, too, have speculated about the possibility of life on Mars. During the 1800s, some leading astronomers thought that an […]
Earth
But it was only in the sixteenth century, around the time of Copernicus, that people began to see Earth as
Venus
The Venusian clouds kept astronomers from seeing the planet's surface. Without visible landmarks, they could not measure how fast Venus
Mercury
Mercury's surface closely resembles the Moon's. It is covered by impact craters, ancient lava flows, and quake fault lines. Mile-high