The winter solstice on Mars happened today. It occurred on the Mars explorer rover Spirit's 923rd sol of exploration. Since April, the rover has been parked on an outcrop known as "Low Ridge Haven," tilted 11 degrees to the north. On the opposite side of the planet, Spirit's twin, Opportunity, continues to advance toward Victoria Crater, the largest crater yet visited on the surface of Mars. While exploring Martian plains north of the equator, Opportunity, too, has experienced lower power levels during the southern hemisphere winter, though not to the same degree as Spirit.