NASA's newest robotic explorer, Maven, has rocketed toward Mars on a quest to unravel the ancient mystery of the red planet's radical climate change, Belfast Telegraph said.

The Maven spacecraft is due at Mars next autumn after a journey of more than 700 million km.

Scientists want to know why Mars went from being warm and wet during its first billion years to cold and dry today. The early Martian atmosphere was thick enough to hold water and possibly support microbial life. But much of that atmosphere may have been lost to space, eroded by the sun.

Maven set off through a cloudy sky this afternoon in its effort to provide answers. An unmanned Atlas V rocket put the spacecraft on the proper course for Mars, and launch controllers applauded and shook hands over the success.

An estimated 10,000 NASA guests gathered for the launch, the most exciting one of the year from Cape Canaveral. The University of Colorado at Boulder, which is leading the Maven effort, was represented by a couple of thousand people.

"We're just excited right now and hoping for the best," said the university's Bruce Jakosky, principal scientist for Maven.

To help solve this environmental puzzle at the neighbouring planet, Maven will spend an entire Earth year measuring atmospheric gases once it reaches Mars on September 22, 2014.

This is NASA's 21st mission to Mars since the 1960s, but it is the first one devoted to studying the Martian upper atmosphere. The mission costs 671 million US dollars.

Maven - short for Mars Atmosphere and Volatile EvolutioN - bears eight science instruments. The spacecraft, at 2,450kg, weighs as much as an SUV. From solar wingtip to wingtip, it stretches 11.4m, about the length of a school bus.

A question underlying all of NASA's Mars missions to date is whether life could have started on what now seems to be a barren world.

"We don't have that answer yet, and that's all part of our quest for trying to answer, 'Are we alone in the universe?' in a much broader sense," said John Grunsfeld, NASA's science mission director. Unlike the 2011-launched Curiosity rover, Maven will conduct its experiments from orbit around Mars. Maven will dip as low as 125km above the Martian surface, sampling the atmosphere. The lopsided orbit will stretch as high as 6,218km.