ARE WE ALONE ? Since mankind discovered what stars really are, a new question began to be asked. If the stars are suns, many just like our Sun, then do they have planets and can those planets support life. We know for sure that there is life on at least one planet because we are part of that life but Patrick Moore always says he wonders if there is 'intelligent' life even on this planet. It will be one of the most important if not the most important discoveries in the history of mankind if life is found away from Earth because that will mean we are not alone. Even the discovery of the most simple forms of life will raise the possibility that there are higher forms of life on other planets.
The is question of life is really a two part question, question one is, 'is there life on any of the other planets in our Solar System?' and question two is, 'is there life on planets orbiting other stars ?'.
Of course this poses yet a third question, 'are there planets orbiting other stars ? Recently there has been much debate and even arguments over the microscopic 'fossils' found in a meteorite from Mars. The jury is still out on that question but it seems that the evidence is pointing to it not being the remains of life.
There has also been a lot of debate about photographic evidence from Mars which appears to show gullies where water may have flowed in the last million years and possibly in the much more recent past. It is generally considered that water is probably essential for life, as we know it, to exist. Other fluids have been considered as the possible mixing agent for the chemicals required for life. However water is so much more efficient then anything else, life is almost certain to use water if it is available. A number of orbiters and landers are planned to survey the most interesting sites in the next few years. It is even hoped that samples of the Martian soil can be brought back to Earth for study.
Scientists are searching the most inhospitable regions of Earth to find the extremes in which life can survive. This will give an indication of how extreme a climate can be on another planet and yet be able to allow life to survive. So far almost everywhere scientists have looked they have found life. From the cold barren valleys of Antarctica to the scorching, driest deserts. Even in the deepest ocean trenches and the upper atmosphere and deep underground, life is always there. Life also appears to have started almost as soon as Earth was able to support it. At this time, life as we know it today, could not survive but the earliest forms of life could survive in the early poisonous atmosphere. Simple bacterial life has even been found surviving inside rocks.
None of the other seven solar system planets can be expected to have or had life because they are either too hot or too cold. Life as we know it needs liquid water which can only exist at a small range of temperature and pressure. Life also needs some sort of energy source like the light and heat from the Sun. However, there is the possibility of life on one of Jupiter's moons called Europa. Space probe surveys have indicated that Europa has a deep liquid salty water ocean under a thick layer of ice. Europa is heated by the enormous gravitational forces of Jupiter which stretches and squashes the moon causing powerful tidal forces. We know from deep sea studies on Earth that life can exist with no sunlight but can be driven by the heat from volcanic vents called 'Black Smokers'. Some people even think that life on Earth may have begun around Black Smokers. It is possible that Europa may also have Black Smokers and therefore may also have life in the great oceans under the ice. NASA has plans to send a probe to Europa to drill through the ice and search for life using a miniature submarine.
But what about other Solar Systems which may exist around other stars and could there be life on those planets ? Astronomers have only recently had access to telescopes powerful enough to identify planets orbiting other stars and a few have been found. It is not yet possible to see these planets directly because the star is millions of times brighter than any planet. The light from the star completely drowns out the light from any planet that may be orbiting that star. However large planets have been detected through the wobbling of the star due to the orbiting planets. Nearly all the planets identified so far, are large gas planets like Jupiter only larger and orbiting very close to the star. One has been found recently orbiting much further out so there might be smaller rocky planets like earth further in.
Another method of finding planets is to measure the brightness of a star and see if it dims periodically. In some cases this dimming may be caused by a planet passing in front of the star. Within the last couple of months such a star has been found. The amount of dimming is incredibly small and extremely hard to detect but it has been done. The planet appears to be about the size of Jupiter but very close to the star. This method has a bonus compared to detecting wobbles. It may be possible to detect light from the star which has passed through any atmosphere that the planet may have. As light from the star passes through the atmosphere around the planet the gases of the atmosphere leave an imprint on the light. By separating the light into its separate colours the imprint of the gases can be detected. If this can be done it is possible to separate the spectrum of this atmosphere and work out its composition. One nearby extrasolar planet has had its atmosphere analysed and Sodium gas has been detected.
There may even be a way to see planets orbiting other stars, this is by using an interferometer. This instrument uses two beams of light from the star and delays the arrival of one beam by making it travel a tiny distance further. If that delay is exactly half a wavelength of the light, then the two beams will cancel each other out. Any light left over may be the light from a planet orbiting that star. Bigger and more sensitive telescopes are planned to look for smaller planets and even to detect Oxygen which can only be maintained on a planet as a by product of life. So the question is now 'LIFE WHERE ARE YOU ?'