If you think this star system looks a little crowded, that's because it contains all of the possible alien worlds found by the Kepler planet-hunting mission so far.

This animation made by Alex Parker, a postdoctoral researcher in planetary science at the Harvard-Smithsonian Centre for Astrophysics, shows all 2299 of the most likely planetary candidates found by Kepler up until 27th February 2012 as if they orbited just one star. Each planet is drawn to scale with the host star, and its colour represents an estimate of the planet's temperature.

Astronomers detect exoplanets by watching as they pass in front of the star they orbit. From the dip in light as the planet obscures the star during this transit, they can work out a planet's distance from its star and its size.

Parker explains how he made the animation:

I have illustrated the planet candidates as if they orbit a single star. Using a transit lightcurve, a planet's distance from a star and its radius are both measured in terms of the host stars' radius, and those relationships are preserved here. This means that for two planets of equal size, if one orbits a larger star it will be drawn smaller here. Similarly, because the orbital distances scale with the host stars' sizes, some planets orbit faster than others at a given distance from the star in the animation (when in reality, planets on circular orbits around a given star always orbit at the same speed at a given distance). These faster-moving planets are orbiting denser stars.

If you prefer your candidate exoplanets in a list, you can also take a look at the full database - complete with details for each one. The full list actually includes several planets not in the animation above, because Parker didn't include some of the candiate planets that have already been flagged as likely false-positives. (NASA's Kepler mission site has a list of confirmed planet discoveries if you'd like something a little more certain.)

Some of the planet candidates in this animation will probably be ruled out as false positives in time, but the sheer number of them shows just how succesful Kepler has been since it started its search for alien worlds.