Life on other planets: an interview with the experts
When we think of the possibility of life outside our solar system, our mind tends to drift towards little green life forms with flying saucers. However for the astrologists and astrophysicists studying the possibility of life, their minds concentrate on even the simplest forms of life, like bacteria. And their first step towards finding life, is finding a planet that will support it; a planet whose conditions are similar to earth so that life can flourish.
Professor Debra Fischer who teaches Astronomy at Yale University states that finding a planet with the right mass (i.e. like Earth’s) is extremely important when determining if life could form on a certain planet. “Gas giant planets like Jupiter have temperature and pressure that change strongly with depth in the atmosphere while very small planets (like Mars) do not have sufficient gravity to hold on to their atmospheres and they cool quickly,” says Professor Fischer. “This means that small planets lose liquid interior cores and therefore lose global magnetic fields. The exact range of ‘right mass’ is not known precisely, but I expect that it's something like 0.5 to 10 times the mass of the Earth.”
Professor Geoff Marcy from the University of California, Berkley is one of the astrologists on the Kepler Mission, a research team that uses the Kepler Satellite to locate planets across the universe. Recently they discovered two planets’ whose size is extremely close to Earth’s. However Professor Marcy tries to look for planets that have a hard, rocky surface that would allow water to puddle on its surface in ponds, lakes, and oceans. “Habitable planets must also have lukewarm temperatures between 0 – 100 C, so that any water would be in liquid form, not steam (if too hot) or ice (if too cold),” says Professor Marcy.
Professor Fisher agrees though notes that a having a precise distance between the planet and sun is important when discussing water on planets. “It seems ideal to have water as a solvent for carbon based life (the type of life that will be easiest for us to recognize),” says Professor Fischer. “Yet if the planet is too close to the host star then the water will be lost, but if it is too far the water will freeze.”
The real question that remains is the likelihood of finding earth-like planets in the universe. Professor Marcy is optimistic as he believes the probability of finding such a planet is 99.999…%. “The reason for this high probability,” says Professor Marcy, “is that our Milky Way Galaxy contains 200 billion stars, many of which probably contain Earth-size, rocky planets that may have lukewarm temperatures. In addition, our Milky Way is only one of hundreds of billions of galaxies in the universe. So the number of host stars is roughly 200 billion x 100 billion = 2 x 10^22 stars with possibly even more planets that are surrounding them.”
Professor Fisher also expects that Earth-like planets are quite common. Yet based on Kepler data and Doppler detections statistical estimate put the chance of finding such a planet “at around 50%: plus or minus 25%, so it's not known very precisely,” states Professor Fischer. Yet as time continues and our data grows and our technologies improve we may very well discover a planet with extraterrestrial life.