Southern solstice on Mars

Astronomy blog for the week ending April 2, 2011

Mars is about to go through its southern solstice. If the red planet’s seasons were more like Earth’s, we’d say it’s winter in the northern hemisphere and summer in the southern hemisphere. Solstice time is April 8, 2011 at 09:41 UT.

The atmosphere on Mars is thinner than Earth’s. The sun’s farther away. The days aren’t as long. There’s no vegetation. And the surface of Mars is mostly rock instead of water. For all those reasons, weather and climate on Mars are different than on Earth so we can’t make all of the same expectations of the seasons there.

On a really warm day on Mars the high might be 20°C (68°F). But you wouldn’t be out in short sleeves. There aren’t many air molecules to protect you from radiation from space. And even if you could breathe such thin air, you couldn’t tolerate the 95% carbon dioxide content. Any people heading to Mars for exploration, recreation, or whatever in the decades ahead will need space suits.

Dust storms are rather common on Mars. They happen more often when the planet is near perihelion (closest to the sun) as Mars was in March. The closer sun is able to heat the thin Martian air a little more at this time and cause more of a heat differential to drive the winds.

The dust storms there are no mere dust devils. They’re often bigger than the 1930s dust bowl storms. The entire planet can be obscured by dust as happened when Mariner 9 took pictures in 1971. You can see surface details on Mars with a telescope when there’s not a dust storm happening. But you’ll see haze when there is.

Even without dust storms, the appearance of Mars changes. The polar ice caps grow and shrink depending on the season. Other parts look darker or lighter. It’s not hard to understand why people who pointed scopes at Mars in the 1800s thought it must be vegetation growing and dying off as happens in the temperate zones of Earth.

Today, evidence that is more directly obtained and more critically examined hasn’t convinced scientists that there’s life of any sort on Mars. But that’s not stopping some of them from trying to prove that there used to be life there. There are some who wonder if the red planet can be terraformed, that is, made to be like Earth so we can have another planet to call home when Earth isn’t suitable anymore or when Earth is overpopulated.

If you want to take a look at what’s happening on Mars these days, it’s a little bit of a challenge. It rises just a little before the sun. Surface details will be easier to see in July when the planet is surrounded by night darkness. Earth’s seasons will change by then from northern spring and southern fall to northern summer and southern winter. But Mars, taking twice as long to orbit the sun, will still be in northern winter and southern summer.