Three years ago this week, the Mars rover Opportunity landed in a tiny crater in a largely featureless plain known as Meridiani Planum. It had already been preceded 3 weeks earlier by its twin, Spirit, which bounced to a stop in Gusev Crater. NASA designed the rovers to survive 3 Earth months. So, surviving — and thriving — for 3 years seems an anniversary worth celebrating.
And the rovers are just getting stronger (or, at the very least, smarter). Recent software upgrades allow the probes to identify interesting atmospheric features, so the rovers don't have to transmit to Earth any featureless images of the atmosphere. Other upgrades let the rovers navigate on their own toward a target and better avoid potential hazards. If year number four turns out anything like the previous three, we'll have plenty of ground-breaking discoveries to report.
Yet Mars exploration doesn't end on the surface. Although NASA lost contact with the Mars Global Surveyor spacecraft last November, three other orbiters continue their explorations. NASA's Mars Odyssey reached the Red Planet in October 2001, and the European Space Agency's Mars Express went into orbit in December 2003. Both continue doing yeoman's work, examining the martian air, surface, and subsurface to learn as much as possible about the planet and the role of water in its history.
The new kid on the block is NASA's Mars Reconnaissance Orbiter (MRO). This advanced spacecraft, which carries the most powerful camera ever sent to another world, began its science mission in November. Details only a foot or two across (less than 1 meter) show up in most of the images. During its scheduled 2-year mission — we can only hope its lifetime balloons as nicely as Spirit's and Opportunity's — MRO will return more data to Earth than all previous Mars missions combined.
You'd think planetary scientists would be happy with five spacecraft exploring Mars. You'd be wrong. There are more on the way, starting with NASA's Phoenix mission. It will launch in August and touch down in Mars' north polar region in May 2008. Phoenix will study the history of water in the martian arctic and assess whether the ice-rich soil can support life. The lander's robotic arm will dig into the soil and deliver soil and ice samples to be analyzed onboard. Sophisticated cameras and an advanced weather station round out the experimental package.
With all the Mars exploration that's taken place over the past few years (and decades), it would be easy to think we've about exhausted the potential for excitement. I'm willing to bet that's not true. And you can count on me (and Astronomy) to keep you abreast of the latest discoveries.