1. 23.2 The Terrestrial Planets

2. Key Concept Mercury has the greatest temperature extremes of any planet.

3. Key Concept These data have confirmed that basaltic volcanism and tectonic activity shape Venus’ surface. Based on the low density of impact craters, these forces must have been very active during the recent geologic past.

4. Key Concept Although the atmosphere of Mars is very thin, extensive dust storms occur and may cause the color changes observed from Earth. Hurricane-force winds up to 270 kilometers per hour can persist for weeks.