http://youtu.be/MIpFgump7so What's the News: On Friday, after five years of deliberation over 100 candidates, NASA announced its choice of landing site for Curiosity, the next Mars rover: Gale crater, a massive pit with a three-mile-high mound in its center. The mission's primary goal is to assess whether conditions suitable for microbial life ever existed on the Red Planet; Gale was selected over the three other finalists in part because its mountain promises access to layered sediments extending deep into the Martian past. Why Gale Crater:
In choosing the landing site, scientists had to balance many factors. As ancient water bodies seem to be Mars' best bet of having harbored life, one of their primary criteria for a site was evidence of water, like deltas, possible lakeshores, and other structures, glimpsed in satellite images.
Gale has some promising features, though the evidence for water isn't quite as clear as at Eberswalde crater, a competing site. With Eberswalde, there was the additional benefit that scientists understand better how the crater formed, which would make interpreting the chemical clues the rover will pick up easier. But Gale also has the mountain, whose origins are still unclear and whose layers scientists are eager to explore with the specialized instrumentation in the rover.
In the end, they traded ease of interpretation for the varied terrain and look into Mars' geological history Gale offers.
What Will the Rover See:
The Mars Science Laboratory, as Curiosity is formally known, has several jumps on the earlier rovers in the program, Spirit and Opportunity, which were small and solar powered. It's the size of a Mini Cooper and powered by 10 pounds of plutonium, which means it can continue its work even during Martian dust storms and has power for a laser that can vaporize rock samples for analysis from a distance of 30 feet. It's also being dropped on the planet with much greater precision than the airbag-encircled earlier rovers: check out the video above.
It will be looking for what astrobiologists call signs of habitability, clues to whether life as we know it---carbon-based, roughly Earth-like life---could have survived on Mars in the past. That means it will be looking closely at the clay and sulfates that scientists believe lace the base of the mountain---both are known to form in the presence of water.
Not So Fast:
Habitability is a slippery thing, and there is no set definition of what chemical readouts mean that a site was livable, just as there is no absolute definition of life (just look at the Viking mission, which appeared to have reported the existence of life on Mars).
While scientists hope they'll turn up some sign of organic, or carbon-based, compounds, even organics don't necessarily mean life ever existed. Using their sense of what the planet used to be like based on such data, astrobiologists will continue to develop their ideas about what such hypothetical life might have looked like and where life might exist elsewhere in the universe, such as on exoplanets.
The Future Holds: In two years, Curiosity will blast off from Florida and make its way to Mars over the next 9 months. Once ensconced in Gale crater, it will spend two years motoring around performing experiments---and sending images and data back to Earth.
