What's more important, water on the moon or on Mars?

The moon has no atmosphere to hold in moisture. However, that doesn't mean there isn't water there to harvest. By all accounts, the moon is a dry and desolate place, void of color and life. In 2009, though, a sensitive spectrometer on the Indian probe Chandrayaan-1 discovered the presence of water molecules embedded in the lunar soil. Scientists from Brown University have also been able to detect water molecules in regolith, or loose pebbles, retrieved during the Apollo missions. So what does this mean for humanity?

First of all, the water on the moon would need to be mined, then refined. The process of extracting the water is similar to cooking it out of the soil. Scientists have been able to extract two grams of water in the form of ice per minute using a one-kilowatt microwave. At that rate, astronauts would be able to extract about a ton of water per year [source: NASA]. It would take an estimated one ton of lunar dirt to extract one quart or liter of water. While that would make water a scarce commodity, if resourced responsibly, it could be used to grow plants and for drinking and maintaining a moon colony. Mining water would also eliminate the need to transport blocks of ice from Earth, a difficult and costly proposition.

At its closest possible point, the moon is 225,622 miles (384,104 kilometers) away from Earth, and at its furthest point the distance increases to 252,088 miles (405,986 kilometers). That's relatively close compared to Mars. The moon could serve as a hopping point to deeper space exploration. With the technology currently available, any colonization would have to be indoors. But greenhouses and other bio-dome technologies could someday make for a very habitable environment. As it stands, the moon is well within the habitable zone which lies between Venus and just on the inside edge of Mars. Unfortunately, the lack of gravity, which is one-sixth that of Earth's, severely inhibits the moon's ability to ever have an atmosphere. Without an atmosphere, you can forget about creating an outdoor environment capable of sustaining terrestrial life.

Mars, on the other hand, does have an atmosphere. As you'll learn about in the next section, the Red Planet is perhaps more livable than once thought. Does that mean there might actually be Martians gallivanting about? Turn the page to find out.

While water on the moon is a significant discovery, water on Mars may turn out to be the ticket for humans to leave Earth and live on another planet. But Mars suffers from the same problem as the moon in terms of atmospheric pressure limitations. While Mars does have an atmosphere, it's too thin and light to trap water vapor. Mars is essentially a dead planet, both geologically and with regard to terrestrial life. It's also too cold to contain liquid water on its surface. But that doesn't mean the prospect for future life is hopeless.

The Mars rover Spirit has discovered sulfate-rich soil beneath the ground, which suggests the past presence of liquid water. Similar samples of soil on Earth are found exclusively in wet dirt [source: Than]. Evidence has also led scientists to believe ice on Mars has and will continue to sublimate during a period of time when the planet tilts in just a way that its poles face the sun. In other words, the water vapor turns directly into a solid in the form of snow. When this snow accumulates, the lowest layer could be warm enough to melt into liquid water. In addition to the snow theory, NASA's Mars Reconnaissance Orbit probe revealed water ice in areas further away from the polar caps.

These discoveries provide hope that Mars could someday sustain life. At the very least, they set up nicely for a manned Martian mission. Humans could harvest this water much like they could on the moon. But they'll have to get there first, and traveling to Mars will be no easy feat. Let's crunch some numbers. At 36 million miles (57.9 million kilometers) away at its closest point, Mars is roughly 145 times as far away as the moon (using the average distance of 238,855 miles, or 384,400 kilometers) [sources: Dutch, NASA]. If NASA's Orion spacecraft were to travel similar speeds as the service module used in the Apollo missions to the moon (24,500 mph or 39,429 kilometers per hour), a trip to Mars would take 1,420 hours or roughly 59 days [source: Smithsonian]. The problem is, both Earth and Mars are in elliptical orbits around the sun. Because it takes Mars 687 days versus Earth's 365 days to complete a year, that "shortest" distance only works out once in every 25 months. So, in reality, it would take closer to 214 days [source: Cain].

Could this water lead to terrestrial life? To answer that, you have to think outside the box for a moment. Humans could attempt to transform Mars into a liveable planet. It's already been pointed out that Mars' atmosphere isn't suitable to sustain liquid water or water vapor. But what if we heated it up? Could we produce a thick layer similar to Earth's ozone layer?

Mars is on the edge of the habitable zone, so even if it was able to somehow obtain an atmosphere similar to Earth's, the temperatures would vary greatly at the poles and night and winter would borderline on inhabitable. Nevertheless, the discovery of water on Mars is a significant step in further space exploration. It also may be the key to whether scientists can ever determine if life in any form ever existed on the dead planet. But that's a discussion for another day.

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