• There is the whole historical notion of little green men, or big scary aliens, coming to Earth from Mars.
• There is the fact that Mars is the only other planet in the solar system that is even vaguely Earth-like, and therefore the only other planet where life might have evolved (another possibility is the ice moon Europa orbiting Jupiter, but that is not a planet).

  Photo courtesy NASA Mars, as seen from the Mars Exploration Rover Spirit: The two rovers' pictures are the most detailed images of the Mars surface ever seen.

• Mars is the only planet in the solar system that human beings have any hope of landing on, walking on and exploring in a traditional sense any time soon.
• Mars is the only planet that might be terraformed and turned into an Earth-like planet.

For these reasons and more, humans have sent over 30 different spacecraft to explore Mars. NASA's two Mars Exploration Rovers Spirit and Opportunity are the planet's most recent visitors.

In this article, you will have the chance to learn about these rovers and understand what they will be able to discover as they explore the planet Mars!