There are just two landing sites left competing for exploration by Mars Science Laboratory's Curiosity Rover that is due to blast off from Cape Canaveral later this year: Gale Crater and the Eberswalde crater delta.

John Grotzinger, MSL project scientist, told members of the press during a science missions news conference at Kennedy Space Center yesterday that a final decision will be made by the end of the July.

Both sites present high science potential. Eberswalde is a former river delta bearing clay minerals formed as a river flowed into a lake. Studying regions once dominated by water could help determine whether life once existed on the red planet.

Competing is the central peak region inside Gale Crater. Layers of material that make up the mountain stack offer a look back in time, allowing scientists to study the transition between environments that reflect a wetter past to today's drier climate.

Curiosity will arrive at Mars in August 2012 and will use a novel entry, descent and landing system that will place it within a 20 kilometer landing ellipse.

"Curiosity rover is the latest installment in Mars exploration," said Grotzinger who described the rover as being as big as a car and literally weighing a ton. It is optimized to drive at least 20 kilometers in two Earth years. "But if you scale it to the Mars Exploration Rovers which are still going seven years into their proposed 90 day mission, we've probably got a pretty good mission ahead of us!"