Venus

Venus is the second solar system planet from the Sun. Characteristics:

• 0.73 AU - orbital radius.
• 0.007 orbital eccentricity.
• 0.8 Earth masses.
• 0.95 Earth radii.
• 224 Earth days orbital period (Venusian Year).
• 116 Earth days solar day.

It has no moons. It is a rocky planet with an extremely dense atmosphere (92 atm) with more than 95% carbon dioxide, but with a minimal magnetic field. Its rotation is strikingly slow and retrograde, opposite of its orbit (and the orbit of all the solar system planets, and their rotation in general), which results in a shorter solar day (the time period required for the same spot on the surface to face the Sun again). Its surface temperature is 735K, far hotter than any other solar system planet including Mercury, apparently due to a runaway greenhouse effect, consistent with the striking amount of a greenhouse gas (carbon dioxide) in its atmosphere.

There is some thought that Venus formerly had liquid water on the surface, potentially for billions of years, presumably long enough for life to take hold and evolve, before the extreme greenhouse effect took hold. The current surface conditions of Venus make investigating this a challenge.