There are trillions of stars in our galaxy alone and probably as many galaxies as there are stars in our galaxy. The distances between the stars are a major hurdle for us to visit and them to visit. The nearest star to our own planet is 4 light years away. In other words, it would take 4 years travelling the speed of light non-stop all the way. When we get there, we'd probably only be disappointed as there has not been any evidence yet that the star has an orbiting planet. Planets that have been discovered outside our solar system have been large gas planets that orbit too close to their star for life to exist. Scientists have apparently identified a star that is not too far away and not too cold, just about right to support an Earth-like planet. For more details you will need to check out the BBC Report on the matter.
One of Einstein's theories is that nothing can travel faster than the speed of light. In order for us to get there and back from any other solar system in a reasonable amount of time, this theory will have to be broken. If this was not possible, the only other way would be to send a spaceship with an infinite amount of fuel containing people on an one way journey to the new world to colonize.
This would cause a number of problems, who would volunteer for such a journey, being coupled up on a space ship for so long a time. Would we do what the British did in the early part of the 18/19th century who sent convicts to Australia but this time into space. They would need to be able to sustain themselves both in terms of food and human population. One idea would be to put them into sleep until they reached the new world. Once there, would they welcome by any alien life forces we discover at the end of the journey.
There has been a great deal of speculation as to whether there is or ever has been life on Mars. The current thinking is that if any life does exist on Mars now then it's a very basic viral life form. The British Space Community launched Beagle 2 as part of a European exploration of Mars to discover if there is any primitive life or not. Beagle 2 would land on the planet to carry out the experiments on the planets surface and beam them up to the Mars Explorer. America is sending two rover vehicles to the planets and the Japanese are sending ones too. The Beagle 2 is due to land on the planet on 25th December 2003. The reason for the intense interest in Mars at the moment is because Earth and Mars are at their closest. There is a theory that has been expressed that Martians live underground, unfortunately we will not find out this unless they live near the surface. The Beagle 2 will not bring back any samples, all experiments will be carried out on the red planet.
Another mission to the planet is planned in a couple of years time to bring samples back to Earth. There was a recent report in the news that said Nasa had found the fossilised remains of a virus on a rock from Mars. The rock had landed on Antarctica, it had ended up on the planet after being thrown into space as debris from a meteor hit on the planet. The Mars rock viral remains has since been discounted. It is in my view that life once did exist but not now. Scientists recently said that methane, a gas more commonly produced by living creatures was discovered on Earth. This raises the prospect of life on Mars. For millions of years before the dinosaurs, the only life that existed on Earth was viruses. Humans were only able to evolve once the conditions were right which Mars has not yet got to that position yet and more than likely never will. When the planets were created, Earth included, both planets had very basic life on them. However, life on Earth was able to survive but it wasn't successful on Mars. The BBC website has documented stories relating to the meteorite from Mars, to discover more, starting reading from this weblink.
The only other celestial body that people believe could support life in our solar system is the Jupiter moon Europa. Space probes that have flown past have indicated a large area of frozen water on the moon. Scientist believe that below the surface could be unfrozen liquid which could contain life. An exploration satellite to the moon is not set to blast off for years yet, five maybe ten years.