From 1989 to 1995, astronomers discovered the first exoplanets. 1056 exoplanets later, they probably discovered the first exomoon, located at 1800 light-years from the Sun. Pandora could have finally a cousin ...

To see exommons (in the fiction), you just have to search "space wallpaper" or "planets wallpaper" on Google. Or, re-watch the films Avatar (Pandora) and Return of the Jedi (Endor).

But here, we are approaching reality. David Bennett (of the University of Notre Dame, Indiana) and his colleagues report on 13 December that they spotted a microlensing event in 2011, named  MOA-2011-BLG-262, using several telescopes in the world. First, they saw the star's light amplified to 70 times its normal brightness. And an hour later, a second came, smaller increase in brightness. So that would mean that a great object passed in front of the star, followed by a smaller object.

The first scenario that fits in the microlensing data is the following : it's an exoplanet followed by its moon, and both are at a distance of 1800 light-years from the Sun. The exoplanet's mass is about 4 times the mass of Jupiter, while the mass of its moon is half Earth's mass, that is to say 3 x 10^24 kg, so 20 times the mass of Ganymede (which is the heaviest moon of the solar system).
Even weirder : according to this model, the exomoon would be orbiting at about 20 million km from its host planet, while Ganymede orbits at 1,070,000 km from Jupiter. If the scenario is correct, we would have to explain why it is possible that there's a great distance between the planet and its moon.

The second scenario which could work is that the two detected objects are much further away and consists of a very small star or a failed star known as a brown dwarf, orbited by a Neptune-mass planet.

Today we can't confirm any of the 2 scenarios. However, exomoon research interest astronomers because exomoons in more normal planetary systems might even support life. If it is true, we could find then "cousins" of Pandora (whose Jake Sully could explore the oceans in Avatar 2).

Sources : NewScientist and International Science Times

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