Sometimes it seems like Mars gets all the planetary love. There are currently nine active missions orbiting or trekking along the surface of the little red planet, and more than twenty have been launched internationally since the 1960’s. But why Mars in particular? Two traits make Mars an ideal target for exploration: the science it has to offer, and the relative ease of exploration.
Mars is like a giant history book, written in the language of geology and chemistry — when we can decode what it’s saying, we peer back into the past. Signatures of a long-gone magnetic field, arid riverbeds, and frozen fields of basaltic lava hint at a world that once was. What happened to this planet that seemed to once be teeming with dynamic flows of lava and liquids? Planetary scientists are hunting for evidence to put together a picture of how an active planet can become a desolate rock. Could Earth be headed towards the same cold, dry future? By studying other planets, we’re learning more about our origins, our selves, and possibly our futures. In addition, we get some inspiration as to “habitability” — potential conditions for life to arise and thrive. And then there’s the glamorous idea that we might one day send humans to visit and perhaps colonize the red planet. But that’s a discussion for another blog post.
This is an exaggerated color photo of the Martian surface from NASA’s Mars Reconnaissance Orbiter. Credit goes to NASA/JPL-Caltech/Univ. of Arizona.
The other reason we have such a persistent interest in Mars is that it’s accessible. Jupiter and Saturn both have interesting moons of ice which probably harbor lakes and oceans, but missions to the outer planets are quite a time investment, often taking a few years to reach their targets. Venus, Earth’s other neighbor, doesn’t like visitors too much — she’s extraordinarily hostile to any sort of landing spacecraft. With a heavy lower atmosphere of sulfuric acid clouds and winds up to 220 mph, we’d be basically trying to land a rover on a surface that’s hot enough to melt lead. Though Venus may have long ago had an environment much like Earth’s, a runaway greenhouse effect  has led the planet to often be nicknamed “Earth’s evil twin.” Probably not a very popular destination for cute little rovers. (But hopefully we’ll send a brave one there soon.)
With NASA’s budget, it seems that Mars is an attainable goal that produces solid science. But you don’t have to go there to do Martian science — I’ve got my very own mini-Mars in the basement of the Niels Bohr Institute!
 The runaway greenhouse effect occurs when a planet’s atmosphere absorbs heat that the planet emits, and then radiates it back towards the surface, heating it even more. This usually happens with atmospheres that contain lots of water, carbon dioxide, and other gases that absorb and emit in similar wavelengths.