In an amazing announcement today, NASA's Kepler mission has now more than tripled the number of exoplanets they have discovered, and nearly doubled the total number of known planets. Twenty years ago, no planets were known to exist outside of our own solar system, while this latest result brings the total up past 1700 exoplanets, with over 900 coming from this one space telescope (A complete list of the Kepler planets can be viewed here).

As most people know by now, the first such planets were discovered in the 1990s using ordinary ground based telescopes which measured tiny variations in the intensity of light from distant stars. Each time a planet would cross in front of the star, its light would dim slightly. By studying the variations of large numbers of stars, astronomers were able to find several more planets using this same method to study one planet at a time.

Kepler was launched in March 2009 with the primary goal of seeking out new worlds, and continued to use these methods to add about 200 more exoplanets to the list. This latest result is interesting and different not only because of the sheer number of new worlds, but because of the techniques used. Instead of measuring the effect of individual planets, the team tried new statistical analysis methods to look for several planets simultaneously in more complex solar systems. These new planets orbit close to their host stars in groups of three or four (or more), and it is essentially their combined effect on the star's intensity that is measured.

Also interesting in these new results are four planets that are only slightly larger than the Earth, and which orbit in the habitable zone around their host stars. This could indicate that they are worlds containing liquid water, which is an indicator of the possibility of life. Of course there is no way yet to confirm if these are habitable worlds, as they could also be rocky worlds or gaseous worlds which have the right temperatures but not the right chemicals for life. However it is still a step forward to discover that there are worlds which are at the least viable candidates for life.

So congratulations to the Kepler team on an interesting set of new worlds for scientists to study in the decades to come. To go from zero worlds to 1700 in only twenty years, and half of those discovered in under five years, shows the sudden and rapid progress that can be made in human knowledge, and leaves us to wonder what the next five years will reveal...