Weather on Mercury and Mars

Most recent answer: 10/22/2007

Is the temperature at Mercury’s north pole always the same? If so, why? Why are the seasons more extreme in Mars’s southern hemishere than in its northern hemisphere?
- Linda
Jarvis C.I., Toronto,ON,Canada
Overall, Mercury is a very hot planet; it gets ten times as much solar radiation as the Earth. At midday, the temperature can reach 430OC, hot enough to melt lead and zinc. The atmosphere is so thin that very little heat is captured, and the temperature can plummet to -170OC at night.

Some scientists think that Mercury has ice at its north pole. Not much sunlight reaches the north pole, and the radar photographs from 1975 show something that looks like ice covering an area of about 400 square kilometres. Again, the atmosphere is so thin that the little heat can be trapped at the north pole to melt this ice.

The seasons in Mars’s southern hemisphere include short, very hot summers, and longer, cold winters. The Martian orbit is less circular and more elliptical than Earth’s, which means for part of the year the planet is a lot closer to the sun. The southern hemisphere, tilted towards the sun when Mars is closest, has a hotter summer than the other hemisphere. The northern hemisphere is tilted towards the sun when Mars is farther away, and so its summers are not as hot.

Planets travel fastest when closest to the sun, so the hemisphere with the hotter summer will also have a shorter summer.

(published on 10/22/2007)