Mars wasn’t always the cold, dry world that it is today — billions of years ago it likely looked a lot more like Earth, with seas and rivers of liquid water on its surface and a thick atmosphere with air and clouds. But something happened over the course of Mars’ history to transform it from a warm, wet world to a cold, desiccated desert planet, and while there are many viable suggestions as to what process is responsible, no verdict has yet been delivered.

This video, just released by NASA’s Goddard Space Flight Center, shows what Mars might have looked like four billion years ago. As the camera tracks back the clouds gradually disappear, the lakes and rivers turn to rubble-strewn plains and the skies change from blue to pale orange. As we rise above the dust clouds that roll across the planet, we see the first evidence of modern times: NASA’s MAVEN spacecraft, flying high overhead to investigate the mystery of a lost Mars.

Liquid water cannot exist pervasively on the Martian surface today due to the low atmospheric pressure and surface temperature (although there is evidence for spurts of liquid flow that perhaps consist of a briny solution with reduced freezing temperature.) So where did Mars’ atmosphere go? Read more from a NASA Goddard article:

There are several theories of how Mars was stripped of its thick atmosphere. “Hydrodynamic outflow and ejection from massive asteroid impacts during the later heavy bombardment period (ending 4.1 billion to 3.8 billion years ago) were early processes removing part of the atmosphere, but these were not prominent loss processes afterwards,” said Joseph Grebowsky of NASA’s Goddard Space Flight Center. “The leading theory is that Mars lost its intrinsic magnetic field that was protecting the atmosphere from direct erosion by the impact of the solar wind.”

The solar wind is a thin stream of electrically charged particles (plasma) blowing continuously from the sun into space at about a million miles per hour. “The interaction of the atmosphere with the solar wind leads to escape by sputtering of atoms and molecules out of the atmosphere, electromagnetic loss process of the planet’s ionospheric particles, direct escape of hot plasma particles or by chemical processes that produce atoms with escape speeds,” said Grebowsky.

“Studies of the remnant magnetic field distributions measured by NASA’s Mars Global Surveyor mission set the disappearance of the planet’s convection-produced global magnetic field at about 3.7 billion years ago, leaving the Red Planet vulnerable to the solar wind,” said Grebowsky.

“MAVEN has been designed to measure the escape rates for all the applicable processes and will be able to single out the most prominent,” said Grebowsky. It will also work with other missions to examine the past habitability of Mars. “Previous remote Mars observations from orbiting spacecraft have observed the geological features that have been used to estimate the amount of water that did exist and have analyzed the global distribution of water ice and surface chemistry to infer that water was lost through time. Mars Curiosity rover has the ability to analyze the chemical composition of the solid surface, which contains information of the atmospheric composition during the formation of the planet, in particular the isotope ratios, the lower atmosphere composition, and the current gas exchange with surface reservoirs. MAVEN is going to measure the current rates of loss to space and the controlling processes. Given the lower-atmosphere information and the nature of the escaping processes, one can extrapolate from current conditions into the climate of the past,” said Grebowsky.

For more information regarding MAVEN’s investigation of Mars’ atmospheric past, here’s a video featuring Dr. Jim Garvin, Chief Scientist for the MAVEN mission:

MAVEN is slated to launch from Cape Canaveral on Nov. 18, 2013, at 1:28 p.m. It will arrive at Mars in September 2014.

Video credit: Michael Lentz/NASA Goddard Conceptual Image Lab