Both Mercury and the Moon had active volcanic eruptions early in their history, but they are small. They cooled quickly and are now solid throughout. Their atmospheric gases either escaped quickly to space from their weak gravitational fields or were blown off by major impacts. Today Mercury and the Moon are airless and lifeless. Venus is larger than the Moon or Mercury, almost the same size as Earth.
Volcanic rocks cover most of the planetary surface.
Like Earth, Venus has had a long and active geological history, with a continuing supply of volcanic gases for its atmosphere, and it has a strong gravitational field that can hold most gases. But Venus is closer to the Sun than Earth is, and the larger amount of solar radiation hitting the planet was trapped so effectively by water vapor and CO 2 that water molecules may never have condensed out as liquid water. Today the dense, massive atmosphere of Venus consists largely of CO 2 . Atmospheric pressure at the surface is 100 times that of Earth's. We can be sure that there is no life on the grim surface of Venus.