David Bowie's "Life On Mars" asked the question in 1971: is there life on Mars? Now, thanks to the Mars Curiosity rover, which is celebrating its second year on the red planet, we may sort of have an answer.

Of course, the question we should ask is if Mars is or ever was a habitable planet, capable of sustaining life. The answer is "maybe." Curiosity drilled into samples of rocks and found those ingredients believed key in supporting life, such as carbon and oxygen. This suggest that Mars once sustained life in some form.

Curiosity also found evidence that water once flowed on the red planet. Smooth rocks and layers of bedrock suggest the presence of rivers on ancient Mars. Curiosity also uncovered the most evidence of water on Mars when it found sedimentary rocks with clay in a crater on Mars called Yellowknife Bay.

Scientists believe that water is also important for habitability, and is believed to be one of the main factors needed for a planet to sustain life.

"It is surprising how much water persists under the surface of Mars and how much water must have been there," says Lisa May, NASA's lead program executive for Mars missions. "What happened? It either went into the rocks or out through the atmosphere."

After its first year, Curiosity began its journey towards Mount Sharp, where its long-term science mission awaits. It is currently about two miles away from its final destination. Scientists are hoping to get a good look at Mount Sharp's geology, as well as observe its layers. By doing that, we may get some insight into Mars' ancient history.

Curiosity's mission was only intended to last two years, but it was extended a few years ago due to its success. However, the rover experienced several challenges in its journey.

"The wheels took some damage getting across Zabriskie Plateau, but it's less than I expected from the amount of hard, sharp rocks embedded there," says Jim Erickson, Curiosity's project manager.

However, NASA feels confident that Curiosity can traverse the rocky terrain, although there are still rough patches along its intended path. The agency is doing its best to guide the vehicle around the most treacherous areas.

Curiosity fans can keep track of the rover's progress through NASA's website, which also contains the latest updates about the mission and photos taken by the rover.

NASA plans to continue Mars exploration in 2020 with a new rover mission that will act as a preliminary step for placing humans on the surface of the red planet.