Here's an experiment.  Prepare for 3 days of hiking.  Pack light-- sleeping bag, tarp, knife, matches.  Bring protein bars and rice for food.  And then pick up 3 gallons (11 liters) of water and start walking.  What's the heaviest part of your gear?  Of course it's the water.

If we're going to get anywhere in this solar system, we need to go where there is water.  Everything else can be dehydrated, miniaturized, made more portable.  You can even make oxygen from water, just by adding some electricity (such as from solar power).  But water-- which also makes up most of our body-- is the one item we so desperately need, but can't mimic.

Enter this game changing bit of Mars research-- there is water on Mars, not just speculative 'might be water', not just locked up at the frozen poles.  Ice water, not methane or some other non-drinkable.  And it's near the surface even at lower latitudes.

The patch of ice exposed at this late-2008 crater was large enough for the orbiter's spectrometers to take readings and confirm that it is H2O.  Courtesy of Science@NASA.

NASA's Mars Reconnaissance Orbiter (MRO) found surface water on Mars in five recent meteor impact sites.  "This ice is a relic of a more humid climate from perhaps just several thousand years ago," says Shane Byrne of the University of Arizona, Tucson.

People sometimes wonder why we want to go back to the Moon or to planets we've visited before.  This sort of story tells us why-- because we need to keep finding new stuff, to keep digging.  The NASA report notes the ice exposed by fresh impacts suggests that NASA's Viking Lander 2, digging into mid-latitude Mars in 1976, might have struck ice if it had dug only 10 centimeters (4 inches) deeper.

This map shows five locations where fresh impact cratering has excavated water ice from just beneath the surface of Mars (sites 1 through 5) and the Viking Lander 2 landing site (VL2),  in the context of color coding to indicate estimated depth to ice. Map and caption from Science@NASA.

And just for fun, that same day, NASA also announced the definitive discovery of water on the Moon.  Small amounts, yes, barely a trace, but then again, the Moon doesn't have any real atmosphere.  Surface water just boils away into vacuum.  But in the lunar soil was clear evidence of water molecules, in small but real amounts.  The Moon Mineralogy Mapper (M3) on Indian's Chandrayaan-1 mooncraft saw it, and Cassini and Expoi confirmed the results.

A very young lunar crater as viewed by NASA's Moon Mineralogy Mapper. On the right, the distribution of water-rich minerals is shown in false-color blue. Courtesy of Science@NASA

It's not a flowing spring waiting for settlers to arrive, but it is water, and it suggests there might be more.  One theory says the dark, unlit portions of ordinary lunar craters might have water.

Humorously, some use these sorts of discoveries to argue against funding space exploration.  The argument starts with "since we've already explored these places, why go back?", then concludes with "and look, those scientists keep changing their minds!"  In science, change is good.

The purpose of science is to progressively increase our body of knowledge in order to make better predictions that ultimately lead to a better world.  In this case, that better world may be the Moon, or Mars.

Alex, The Daytime Astronomer, Tues&Fri here, via RSS feed, and twitter @skyday

Read about my own private space venture in The Satellite Diaries!