NASA Mars probe Maven set to lift off

A US spacecraft set to launch Monday is intended to help scientists explain how Mars went from a warm, wet world to a place that's cold and dry, NASA says. The robotic space probe known as Maven -- short for Mars Atmosphere and Volatile Evolution, with a capital N in "EvolutioN" -- will measure how the martian atmosphere and water, presumed to be substantial long ago, were lost over time. The explorer is scheduled to lift off atop an Atlas V 401 rocket from Florida's Cape Canaveral Air Force Station at 1:28 p.m. EST. The weather at the time is to be partly cloudy, 81 degrees Fahrenheit, with a southwest breeze about 4 mph, AccuWeather forecast. The first spacecraft devoted entirely to studying Mars' upper atmosphere is to arrive above the Red Planet Sept. 22, NASA says. The solar-powered craft will slip into an elliptical orbit ranging from a low of 93 miles above the surface -- whose features are reminiscent of the impact craters of the moon and the volcanoes, valleys, deserts and polar ice caps of Earth -- to a high of 3,728 miles, the National Aeronautics and Space Administration says. The craft also will take five "deep dips" during the course of the mission, flying as low as 77 miles in altitude and providing a cross-section of the top of the atmosphere. "Maven will begin to look at those processes that tell us what happened to Mars' atmosphere, and why Mars perhaps underwent a major climate change in its past," NASA Director of Planetary Science Jim Green told reporters in a prelaunch briefing. "We expect to learn how the modern Mars works, really in detail," NASA investigator James Garvin told CNN. "To see its climate state, to understand how the atmosphere is lost to space -- how Mars may have lost a magnetic field -- to take that information and map it back in time." Maven is an 8-foot cube weighing about 5,400 pounds at launch -- as much as a fully loaded sport utility vehicle. When its twin pairs of gull-wing-shaped solar panels are extended, it will stretch 37 feet from wingtip to wingtip, about as long as a school bus, NASA says. The $671 million mission follows the Curiosity rover mission, which is exploring a martian crater after landing on the planet in August 2012. By the time Maven reaches Mars, Curiosity will have made surface measurements that will help guide the interpretation of Maven's upper-atmosphere measurements, NASA says.