If we saw an extra-terrestrial life form what would it look like? How different would they be from us? What if we couldn't even perceive them? Or they, us? Or another question to ponder is this: Are humans the next extra-terrestrial life forms? Who says that alien life forms have to be non-human? They could still be radically different from us in some ways and still be human? Something to think about. I bring this up because while scientists often look for evidence of past or present life on other planets it is likely that we ourselves will be the life we find on other planets. What we gather about other places in the solar system may help our own expansion into space, colonization and space exploration!
For now, the best guess we have is that any alien life that exists in our solar system is most likely bacterial in form -extremely elemental, non-intelligent life. This is what many scientists are on the search for now. The first question about alien life is why would they look like us? Life as we understand it at this point requires carbon, water and amino acids. But all we know and understand is earth based life forms. In examining alien planets how would life survive there? Take Jupiter. You would have to have a life form that could float indefinitely since Jupiter has no surface. Since Jupiter has no internal heat source this life form would also have to gather heat from sunlight and it would have to be extremely efficient at doing so because A). Jupiter is very far from the sun and B). It is a gas giant; a vast mass of thick clouds that would blot out much of the sunlight coming in.
Looking at the outer planets right now, let us turn to the moons. What about Europa? Europa might have a heated iron core and it might have a deeply hidden liquid ocean. But no one knows for sure. We need liquid water for life as we know it. Most of the water on Europa is frozen. Europa is also, like Jupiter, very far from the sun so any liquid that comes to the surface of this moon would freeze. But perhaps there's hope. The top of its ice layer has oxygen and the planet is active; there are cracks all along the entire face of the planet as if it is still going through a growing stage.
Titan - Titan would be a planet in its own right. It's 50 percent larger than our moon and it is active geologically. But Titan is so very cold (at 300 degrees below zero) that frozen water on the planet behaves like rock. The methane and ethane on the planet is in liquid form - that's how cold it is there! Giant stretches of methane and ethane lakes crisscross the planet. Many scientists think that harsh, extreme places on earth might help up us understand how life might arise on other planets far more hostile to life. Such as Titan. But harsh enviroments on earth and harsh environments on other planets like Mars or Titan are something altogether different. The environments on Titan and Europa make the harsh environments on Earth look like a picnic.
How life might arise in such environments is anyone's guess, but what is truly important is space exploration for humans; looking into the last, great frontier and figuring out how to explore and live in space. We are building powerful instruments that are helping us better understand our solar system and each decade we get closer and closer to putting humans into space, reaching out for new planetary homes.
One of those fantastic things that is helping us learn more about the environments in the solar system is MRO - Mars Reconnaissance Orbiter. It will travel 100 million miles to reach Mars and it will collect highly detailed images of the surface and subsurface area of Mars. It will be able to beam back vast quantities of information, more than any orbiter before it.
MRO has a cost of $450 million. It required over 1000 people over 5 years to create and it about 400 people to maintain and operate it for the mission to succeed. Half of all space craft sent to Mars have failed. They either spun out, crashed or burned up in the atmosphere of the planet. MRO succeeded in getting to Mars safely. The purpose is to better study geology and atmosphere; how these features intersect with the climate and other planetary elements and will give clues as to whether there may have been life on Mars in the past and whether it can be inhabited in the future.
In 2004 the probes named Spirit and Opportunity both sent back beautiful photos that revealed land formations that suggested that Mars may have had flowing water in the past. Where there's liquid water, there may be life. Either previous life or possible colonization. In the past the resolution from the photos orbiters took were not sharp enough to render highly detailed images for scientists to really see Mars. MRO changes that. Mars has vast amounts of craters, crevices, rocks and it has extensive mountain ranges. They found rocks that looked like water beds. Before, scientists could only get small parts of Mars' geological features but now with MRO they can take high res images of the entire planet and examine them in detail.
MRO was launched in August of 2005 and will give scientists a detailed look at how color variations in Mars rock are distributed on the ground, detailed weather patterns, water vapor behavior, and MRO has the ability to probe the depth and mineral composition of underground rock on Mars. This will all give clues as to water flow, possible past life and even possible terra-forming in the future. MRO is probably one of the many modern baby steps we take to reaching other planets and reaching the stars.