Kepler 11

Kepler 11 is a Sun-like star 2,000 light-years away from Earth. It has a mass equal to 95% of that of the Sun and a radius approximately equal to that of our star. However, the similarities with the Sun do not stop there: even Kepler 11 is in fact surrounded by a system of planets. Six of them have been discovered to date.

In the Solar System, the outermost planet (which is Neptune) is located 30 AU away from the Sun. In the Kepler 11 system, all six planets are located within a distance of only 0.47 AU from their star (slightly greater than distance that separates Venus from the Sun).

The differences between the planets of Kepler 11 and those of the Solar System do not stop there.

In fact, one might expect that all being located so close to their star, Kepler 11's exoplanets are all similar in size to Mercury or Earth. However, observations conducted by the Kepler Telescope revealed that these are actually all Super Earths or Neptune-like gas giants. The masses of the six exoplanets vary in fact between 3 and 10 Earth masses, while their diameter is between 1.8 and 4.2 times larger than that of our planet.

Even today it is not clear how such a compact system can be formed. Two different scenarios have been formulated so far. The first assumes that the six planets formed in their current positions. The second, more probable but also more complex, assumes that the planets formed much further from their star and that they migrated to their current positions as a result of gravitational interactions with the protoplanetary disk.

Credit: NASA, Tim Pyle. 

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