A new NASA video shows what Mars may have been like long ago when it had a denser atmosphere and liquid water.
The concept is based on evidence that Mars was once very different.
"There are characteristic dendritic structured channels that, like on Earth, are consistent with surface erosion by water flows,” said Joseph Grebowsky of NASA's Goddard Space Flight Center
in Greenbelt, Maryland. “The interiors of some impact craters have basins suggesting crater lakes, with many showing connecting channels consistent with water flows into and out of the crater.”
He added that small impact craters have been removed with time and larger craters show signs of erosion by water more than 3.7 billion years ago, and sedimentary layering is seen on valley walls. Minerals are present on the surface that can only be produced in the presence of liquid water, Grebowsky said.
Estimates about the amount of water needed to explain these features have equated to possibly as much as a planet-wide layer one-half a kilometer (1,640 feet) deep or more, according to Grebowsky.
It's unknown if the habitable climate lasted long enough for life to emerge on Mars.
"The only direct evidence for life early in the history of a planet's evolution is that on Earth," said Grebowsky. "The earliest evidence for terrestrial life is the organic chemical structure of a rock found on the surface in Greenland. The surface was thought to be from an ancient sea floor sediment. The age of the rock was estimated to be 3.8 billion years, 700 million years from the Earth's creation.”
The video ends with an illustration of NASA's MAVEN mission in orbit around present-day Mars. MAVEN will investigate how Mars lost its atmosphere. Scheduled to be launched in November, it will arrive at Mars in September 2014.
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 Grebowsky. "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.
Here's the video: