New planet GJ 1214 b

A new planet, GJ 1214 b, has been found some 40 l.y. away
with 2.678 Earth radius and 6.55 Earth mass.
[It was found using a 16-in telescope and a commercially
available camera, kind of something someone could have
done in his backyard, that's cool even if the planet is
hot].

What surprises me is its density, about 1870 kg/m^3, which
is consistent with 75% water and 25% rock. I'm no expert
in this area, but so much water (or other low density
liquid or solid) seems improbable to me. Does anyone
know about how the radius was measured? Is it possible
that it would be a much denser planet with a very large
atmosphere. The atmosphere giving it nearly half its
radius?

Does anyone think that 75% water for such a large planet
is a likely scenario.



Alain Fournier