NASA, citing "increased confidence" in the ability of its Mars Science Laboratory rover to make a precision landing, has decided to retarget the craft's landing zone to a much smaller area, closer to both its science objective and some dangerous obstacles.
The above pic shows how the landing target for the rover, also known as Curiosity, has been changed: from an ellipse 20 kilometers by 25 kilometers, the new target is just 7 kilometers by 20 kilometers. Here's another view:
These ellipses represent the target areas in which Curiosity, using a "jet pack" and rappelling down cables in what NASA calls the "sky crane" maneuver, will attempt to land. The center of each ellipse is where the rover will touch down if everything goes perfectly, but the perimeters designate the possible landing zone if everything goes not perfectly but normally, and accounts for atmospheric randomness and things like that. The larger ellipse in this picture, the original landing zone, is already smaller than any previous landing zone used for any other mission, but NASA believes that it can safely shrink it down.
The benefit of the smaller target zone is that, if everything goes well, MSL will land significantly closer to that big mountain in the pics (technically an uplift structure at the center of Gale Crater) called Mount Sharp. This could cut months off of the rover's trip to the mountain, where it'll be searching for evidence of environments favorable for microbial life.
With benefit comes risk, however, and the risk is that this new landing zone is close enough to the steep slopes of Mount Sharp that a miscalculation could lead to Curiosity being dropped into a hazardous area and not surviving the landing process. Remember, this is the "sky crane" landing process:
Yep, not especially friendly to mountainous slopes. We'll be holding our breath, keeping our fingers crossed, munching on peanuts, and praying to Ares all at the same time come August 5th.
Via [ NASA ]