Volcanic features have been observed on our fellow rocky planets, Venus and Mars, but they largely appear to be inactive ...

Distance from the sun can only partly explain why the atmospheres of these two planets are so different. If life had not appeared on the earth, its atmosphere might resemble that of one or the other ...

The crescent moon and Venus and Mars just after sunset on Feb. 8, 2015 in Sanya, China. Credit: Volvo Ocean Race via Getty Images The moon, Venus and Mars are getting close in the night sky this week.