NASA's newest Martian explorer on its launch pad in Florida, is all set to soar almost a fortnight after India's Mangalayan.
An unmanned Atlas V rocket would power the space craft into space this afternoon.
The Maven would study the red planet's upper atmosphere. Scientists want to know the reason(s) why the planet went from being warm and wet during its first billion years, to the cold and dry place it is today.
Though the early Martian atmosphere was thick enough to hold water and possibly support microbial life, according to scientists much of that atmosphere may have been lost to space, eroded by the sun.
University of Colorado's Bruce Jakosky, the principal Maven scientist said on the eve of Maven's flight that something clearly happened, according to Associated Press.
The agency further quoted him as saying that what scientists wanted to understand the reasons for that change in the climate.
Maven, which will carry eight science instruments would take 10 months to reach Mars, and enter into the orbit around the red planet in September 2014.
A question that all 21 NASA Mars missions to date have sought to answer was whether life could have started on what now seemed to be a barren world.
Associated Press quoted John Grunsfeld, NASA's science mission director, as saying that NASA did not have the answer to the question yet and that was all part of its quest to answer whether we were alone in the universe in a much broader sense.
Maven is the acronym of Mars Atmosphere and Volatile Evolution, with a capital "N" in EvolutioN.
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.
The Solar Wind Electron Analyser or SWEA, one of the eight instruments aboard MAVEN would try to solve the mystery of Mars' dwindling atmosphere, a process that has turned the planet into a frozen desert.
The product of a collaboration between the Space Sciences Laboratory (SSL) at the University of California, Berkeley, the Institut de Recherche en Astrophysique et Planétologie (IRAP) in France, SWEA's task is to analyse electrons in two distinct regions around Mars: the solar wind passing by and a layer of Mars' upper atmosphere - the ionosphere.
TG Daily quoted, instrument lead David L Mitchell of SSL as saying that SWEA would use the information on electrons to track how other charged particles, such as planetary oxygen ions, were escaping the planet's atmosphere.