Three studies map out the shores of ancient seas that scientists say once existed on Mars.
One study, appearing in Sunday's issue of Nature Geoscience, contends that a vast ocean probably covered a third of the Red Planet's surface 3.5 billion years ago. The University of Colorado's Gaetano Di Achille and Brian Hynek came to that conclusion after looking at 52 delta deposits and thousands of dry river valleys on the Martian surface.
Elevation readings from a variety of NASA probes as well as Europe's Mars Express orbiter were fed into a geographic information system, or GIS, for an analysis of the valley and delta patterns. What emerged was a map indicating that much of Mars' northern hemisphere was underwater early in the planet's history. The ancient sea would have contained about 30 million cubic miles (124 million cubic kilometers) of water. That's about a tenth of the total volume of Earth's oceans today, on a planet that's slightly more than half of Earth's size.
This study was funded by NASA's Mars Data Analysis Program.
Another research report, in the Journal of Geophysical Research-Planets, detected roughly 40,000 river valleys on Mars. That number is about four times as high as previously thought, said Hynek, who conducted this study with University of Colorado colleagues Michael Beach and Monica Hoke.
It would take a sustained level of precipitation to create so many valleys, Hynek said in a university news release. "This effectively puts a nail in the coffin regarding the presence of past rainfall on Mars," he said.
Some researchers have suggested that the water-carved features seen on Mars today were created by massive flash floods early in its history, while others say ancient Mars had a longer-lasting hydrologic cycle like Earth's, complete with rainfall, running rivers, seas and evaporation. Clearly the latter scenario is more favorable for the development of life. "If life ever arose on Mars, deltas may be the key to unlocking Mars' biological past," Hynek said.
Yet another survey, by a different group of researchers, came up with a similar map: This survey was based on an analysis of topographic and geological data from NASA's Mars Global Surveyor, Mars Odyssey and Viking orbiters, and concentrated on the lakes that appear to have existed in Mars' southern hemisphere. Leslie Bleamaster, a research scientist at the Arizona-based Planetary Science Institute, said the mapping project supports the idea that lakes once existed within the Hellas impact basin and elsewhere in the Martian south.
"This mapping makes geologic interpretations consistent with previous studies, and constrains the timing of these putative lakes to the early-middle Noachian period on Mars, between 4.5 and 3.5 billion years ago," he said in a news release.
A map of Mars' Hellas Planitia shows how river valleys and shorelines might have looked billions of years ago.
You can get a closer look at the map and an accompanying pamphlet on the U.S. Geological Survey's website. (USGS serves as a repository for geographical data about other worlds as well as our own.) The project was supported through NASA's Planetary Geology and Geophysics program.
So where did all the water go?
Because Mars is so much smaller than Earth, scientists suspect that its molten core cooled down relatively quickly, which caused the planet to lose its global magnetic field. Without a magnetosphere like Earth's, Mars was less able to fend off electrically charged particles from the solar wind. In time, those particles might have blasted away much of the Martian atmosphere, disrupting the hydrologic cycle.
An alternate explanation would be that Mars was less able to hang onto its atmosphere simply because of its weaker gravitational pull. In either case, the Martian atmosphere was reduced to a stripped-down layer of carbon dioxide. And without an airy blanket to keep it warm, the planet went into a deep freeze. Today, Martian H2O exists mostly as ice, at the poles or mixed in with the chilly soil. Some of the water appears to have reacted with minerals to form carbonate rocks, and scientists recently reported signs that water trickled out to the surface 1.25 million years ago.
Hynek said figuring out where all the water on Mars went is "one of the main questions we would like to answer." Future Mars missions could provide better answers to the question. The University of Colorado at Boulder happens to be managing one of those missions for NASA: the $485 million Mars Atmosphere and Volatile Evolution mission, or MAVEN, which is due for launch in 2013.
More about Mars:
- Special report: Return to the Red Planet
- Gallery: Greatest hits from Mars
- Water found (and lost) on Mars
- Mystery solved: Mars had large oceans