The late great Arthur C Clarke was one of the first to point us toward Europa, a moon of Jupiter, as a place we might want to look for life in the solar system. Europa was part of the mission plan in his '2001' series of books. Turns out all these years later he may have been right. Europa is a strange place, with a frozen surface that almost certainly has an ocean beneath it.
NASA scientists lean toward the idea of a salt-water ocean, pointing to the red deposits thrown up on the surface from beneath the crust of ice. Because of geologic activity, the heavy tides from the pull of nearby Jupiter, and other factors, Europa is a dynamic, changing moon.
The picture on the right with the red spots and lines is evidence that Europa's icy shell churns away beneath the surface like a lava lamp, with warmer ice moving up and breaking through in places, where it re-freezes. Huge square-shaped blocks with lines all around are evidence of 'rafting', where ice breaks apart and also re-freezes, causing the border lines. Instead of normal tides like our own oceans, the gravitational forces can actually make the ice fluctuate. In any case, you have to wonder 'what lies beneath'.
In some places on Europa, the movement of ice throws up ridges and hills as high as 200 meters.
There is a proposal by NASA to send a probe to Europa that would land and attempt to melt or drill its way through the icy surface to reach the ocean underneath. However, no one is sure how thick the ice is, so they may just stay on the surface with any probe. It's still in the planning stages.
It is possible that life might exist under the icy crust, though. No one knows that either.
On Mars, the Viking 2 lander snapped pictures of mid-winter morning frost on the ground around the spacecraft. Scientists were undecided whether this was frozen CO-2 or actual water frost. Since then, we've mapped the ice caps and the recent findings by the Phoenix lander have confirmed the presence of water ice just a few inches under the surface near the south pole of Mars. If this is true, it makes it more feasible to consider a manned mission to the Red Planet, or perhaps even a permanent science station. Water is the one element you MUST have to sustain life beyond the supplies you could bring on such a mission. With water, you can create fuel, oxygen to breathe, and grow food. Without it, you cannot stay long.
NASA is now certain that water DOES occasionally upwell to the surface on Mars. They discovered this process by comparing high-resolution pictures from orbiters that were taken of the same spot - but years apart. On some of them, you can see where channels in the sand or along the surface have formed, go on for a short distance, and then fan out into smaller channels and end. They say this is caused when the water reaches the surface and moves along for a short distance. Then, it either freezes or evaporates into the thin atmosphere.
This could mean life exists on Mars, but underground. If it does, it would almost certainly be simple forms of life. Life on the surface of Mars would be nearly impossible due to the amount of ultraviolet radiation that reaches the ground. The atmosphere is so thin it cannot filter out most UV rays.
In 1994, the Clementine spacecraft went on a 70-day mission around our Moon. It discovered that near the north and south poles of the moon, radar waves sent into some of the bigger craters indicated the possible presence of water ice. (Radar waves reflect back differently when striking ice, as opposed to rocks and soil.) These findings have been in dispute for years. However, some of these craters are always shaded from the sun, and their surface temperatures are close to 300 degrees below zero.
Scientists believe that if there is water ice in deep craters near the south pole of the moon, it did not occur naturally, but was likely a comet strike. Comets are mostly ice. The theory is reasonably sound, but the final verdict will only come if we return to the moon and take a look for ourselves.
If you are seeking any other life in our Solar System, the odds are not good. But the two most likely places are either Mars (underground) or one of the Jovian moons, perhaps beneath those frozen oceans of Europa.
Europa was the guess of Arthur C Clarke. He's been right more than a few times, so I would put my money on Clarke.
This week the White House is being briefed for an 'announcement' by NASA hailing the possibility of life on Mars, since the Phoenix lander has now confirmed the presence of water ice. Of course, some NASA scientists are probably chuckling to themselves. Many of them have seen almost irrefutable evidence of water on Mars for years now, starting with Viking and right on up to the orbiters and the Rovers. When the Mars Rovers rolled across those empty Martian seas and found hematite in great quantities (small blue rocks that only form in the presence of water) they probably figured at least SOME of the water went underground. And it looks like they were right.
We can send all the probes we want, but there's nothing like an on-site exploration to answer some of the more difficult questions.
Now that we know water still exists on Mars, maybe it's time to re-think the idea of a manned mission.