The Ingredients For Life And Earth-like Planets
Chris - Why are you interested in looking at planetary configurations?
Simon - There is only one planet we know that supports life, and this planet has certain things that are special to it. Firstly, Earth is the right distance away from the sun to have liquid water. Secondly, Earth has a very large moon. The fact it gives us tides might be quite important, but more important is that the moon stabilises the Earth's axis. Without the moon, the planet would flip every so often by twenty or thirty degrees. This can be caused by the gravitational effects of other planets. It wouldn't necessarily kill life off, but it certainly wouldn't be good for it! A flipping Earth could have serious problems, so having a large moon is a very fortunate arrangement.
Our solar system also has a massive comet hoover. As comets fly through the solar system, most are caught by Jupiter's gravitational field and stops them crashing into Earth. The last comet to hit Earth killed the dinosaurs, so without a huge planet like Jupiter nearby, life might not get going.
Chris - How many other solar systems are there?
Simon - Billions! The planets we have found so far are all similar to Jupiter, but hopefully we will find an Earth-like planet soon. Jupiter-like planets are easiest to find because they are big, but we have a suspicion that there must be more planets like Earth. Life is probably very common, but the big question is whether any of it is intelligent.
Chris - Are we far from being able to spot Earth-like planets?
Simon - We are close. At the moment, we can look for a slight eclipse in front of stars similar to the recent transit of Venus. We are building satellites to look for these dips. This means that so far, we have only seen the effect of planets on stars: an indirect way of seeing. Other ideas include looking directly at the light from Earth-like planets by blocking out the light from stars. Once can see light from a planet, we can look at its spectrum. The best possible outcome would be seeing ozone in this spectrum. This would indicate a large amount of oxygen, and for this much oxygen, we need life!