CHANCES OF LIFE BEYOND THE SOLAR SYSTEM - PART 3
DETECTING A POSSIBLE FUTURE
Now we know how planets are formed and how we can detect them in the night sky. But what have we detected so far in our search for life beyond our solar system?
Two Swiss astronomers using the Doppler technique in discovered the first extra-solar planet orbiting a sun like star in 1995. They found that the star 51 Pegasi moves forward and back every 4.2 days, which means that a planet orbits the star every 4.2 days. This orbit is the length of a year for anything that is living on that planet. Since we know that the smaller the orbit, the closer the planet is to the sun, this planet is very close to 51 Pegasi. This nearly discovered planet actually only orbits about one-eighth the distance from Mercury to the sun. At this close, the surface temperature of the planet would reach about 1,900 degrees. Since the planet is so close, we would expect it to be very small and rocky just like Mercury, but it is actually a huge gas giant, half the size of Jupiter.
Currently, we have found at least 15 planets around other stars. Most these are actually more massive than Jupiter and orbit closer than Mercury. The reason for these findings is that they are the easiest to find. The existence of these gas giants so close to their stars calls into the existence the question of whether our solar system is the template or just the exception when it comes down to solar systems. Scientists are struggling with how these giants could form so close to their stars.
Not all of the planets that we have discovered orbit close to their stars. We have also found Jupiter-sized planets farther away from their stars, at an orbital distance of about the same as Jupiter's, which suggests to many that Earthlike planets do indeed exist. This discovery makes the planets we see in the movies seem very reasonable.
Although we have a very limited means of tracking down the planets, we have found a planet at about one out of every twenty stars we've searched. Scientists are now estimating that ten percent of all stars have planets. This means that our galaxy alone is home to twenty billion solar systems. As far as Earthlike planets, scientists are estimating about two billion of these solar systems have the planets were looking for.
When I say Earthlike, I do not mean that when you look at it, you can see your country. This just means that the planet will have a rocky composition and a size similar to that of our own. Other than that, it may have very little in common with our own. Mercury, Venus and Mars are considered to be Earthlike, but that does not mean that alien life exists on the surface, or that human life can survive there.