In books and movies, invading Martians always seem to come equipped with "death rays" -- weapons that are a lot like laser beams. Now, Earth is about to strike back. The next Mars rover will carry its own laser. It's not out to get the Martians, though. Instead, it'll use the laser to vaporize Martian rocks, allowing scientists to analyze their chemical composition.

Actually, this won't be the first time that a laser has taken aim at Mars. An orbiter used a laser to measure its precise altitude above the surface, producing highly accurate maps of Martian topography.

Those maps will help scientists pick the landing site for the next Mars rover, Curiosity. And when it arrives at Mars in about two years, it'll put its own laser to work.

The laser will fire at rocks, vaporizing a thin layer of material on the surface. An instrument aboard the rover will measure the composition of the vaporized material. The laser will fire several shots to clear away layers of dust, allowing it to probe deeper into the rocks. Each analysis will take just a few minutes, so Curiosity will have plenty of time to zap lots of Martian rocks.

Mars is in good view tonight. It's above the Moon as night falls this evening, and follows the Moon down the sky. Mars looks like a bright orange star.

We'll talk about what lasers are telling us about the Moon tomorrow.

Script by Damond Benningfield, Copyright 2010