New evidence shows that Mars once had immense quantities of water, the vital and indispensable substance of life requisite for any sustained human settlement of the red planet.

Water is enormously important to any colonization of Mars, because it can meet so many requirements for human life:

Humans, of course, must have water to drink.

As well, humans must have food, and water would be required for astronauts to grow plants for food in the Martian soil.

Water contains one oxygen molecule and two hydrogen molecules. By using electricity, water can be split into hydrogen and oxygen. That would provide a source of oxygen to breathe, meeting another vital human need.

Also, Mars can be cold, especially at night, and hydrogen could be a fuel to generate electricity that would heat and light homes and offices on the red planet.

That electricity also would power computers and communications equipment, along with electric cars that would drive on Martian roads.

These indications of vast prior amounts of water on Mars are hugely significant.

The new studies add to major discoveries concerning water on Mars announced earlier this year.

The Phoenix Mars Lander that arrived at the planet recently dug into soil in a northern polar area and discovered a whitish material. Days later, some of the whitish material had disappeared. Researchers deduced that the material was ice — frozen water — and some of it evaporated. (To view pictures, please see Space & Missile Defense Report, Monday, June 23, 2008.)

Since then, some of the latest evidence was gathered by the Mars Reconnaissance Orbiter, a NASA vehicle.

According to a study in the July 17 issue of Nature, there once were rivers and huge lakes on Mars.

The orbiter discovered this by checking Martian soils and finding clay minerals that only can form in the presence of lava.

This evidence, however, might well have gone unseen by the orbiter, because the clay minerals were buried across the planet.

But, happily, excavations of the Martian surface brought them to light again, visible to the orbiter. Those excavations were performed by incoming asteroids.

So the orbiter was able to provide evidence that vast regions of the ancient highlands of Mars, which cover about half the planet, contain those clay minerals.

Volcanic lavas buried the clay-rich regions during subsequent, drier periods of the planet’s history, but impact craters later exposed them at thousands of locations across Mars.

Data for this study derives from images taken by the Compact Reconnaissance Imaging Spectrometer for Mars, or CRISM, and other instruments on the orbiter.

"The big surprise from these new results is how pervasive and long-lasting Mars’ water was, and how diverse the wet environments were," said Scott Murchie, CRISM principal investigator at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

The clay-like minerals, called phyllosilicates, preserve a record of the interaction of water with rocks dating back to what is called the Noachian period of Mars’ history, approximately 4.6 billion to 3.8 billion years ago.

This period corresponds to the earliest years of the solar system, when Earth, the moon and Mars sustained a cosmic bombardment by comets and asteroids. Rocks of this age have largely been destroyed on Earth by plate tectonics. They are preserved on the moon, but were never exposed to liquid water. The phyllosilicate-containing rocks on Mars preserve a unique record of liquid water environments possibly suitable for life in the early solar system.

"The minerals present in Mars’ ancient crust show a variety of wet environments," said John Mustard, a member of the CRISM team from Brown University, and lead author of the Nature study. "In most locations the rocks are lightly altered by liquid water, but in a few locations they have been so altered that a great deal of water must have flushed though the rocks and soil. This is really exciting because we’re finding dozens of sites where future missions can land to understand if Mars was ever habitable and if so, to look for signs of past life."

And now for yet more evidence of an aqueous presence on the red planet.

Another study, published in the June 2 issue of Nature Geosciences, finds that the wet conditions on Mars persisted for a long time.

Thousands to millions of years after the clays formed, a system of river channels eroded them out of the highlands and concentrated them in a delta where the river emptied into a crater lake slightly larger than California’s Lake Tahoe, approximately 25 miles in diameter.

"The distribution of clays inside the ancient lakebed shows that standing water must have persisted for thousands of years," says Bethany Ehlmann, another member of the CRISM team from Brown. Ehlmann is lead author of the study of an ancient lake within a northern-Mars impact basin called Jezero Crater. "Clays are wonderful at trapping and preserving organic matter, so if life ever existed in this region, there’s a chance of its chemistry being preserved in the delta."

CRISM’s high spatial and spectral resolutions are better than any previous spectrometer sent to Mars and reveal variations in the types and composition of the phyllosilicate minerals.

By combining data from CRISM and the orbiter’s Context Imager and High Resolution Imaging Science Experiment, the team identified three principal classes of water-related minerals dating to the early Noachian period. The classes are aluminum-phyllosilicates, hydrated silica or opal, and the more common and widespread iron/magnesium-phyllosilicates. The variations in the minerals suggest that different processes, or different types of watery environments, created them.

While all of this doesn’t answer the truly huge question of whether life ever existed on Mars, the findings do point to places on the planet where an answer may be found.

"Our whole team is turning our findings into a list of sites where future missions could land to look for organic chemistry and perhaps determine whether life ever existed on Mars," Murchie said.

The Jet Propulsion Laboratory in Pasadena, Calif., part of NASA, manages the Mars Reconnaissance Orbiter mission for the NASA Science Mission Directorate in Washington. The Applied Physics Laboratory operates the CRISM instrument in coordination with an international team of researchers from universities, government and the private sector.