And how exacly do they manage to work out what gasses make up the atmosphere of a planet when it is 50 light years away?

To quote from the paper :"The habitability of Super-Earths in Gliese 581" (arXiv:0705.3758v2 [astro-ph] 6 Jul 2007), "Very recently, Udry et al. (2007) announced the detection of two super-Earth planets in this system, Gl 581c with a mass of 5.06 Mearth with a semi-major axis of 0.073 AU, and Gl 581d with 8.3 Mearth and 0.25 AU."

While I do not have error bars on this estimate, Gl581c would seem to be as small as the reported planet in your article. Also, from the paper "Discovery of a cool planet of 5.5 Earth masses through gravitational microlensing"
(J.-P. Beaulieu1,4 et. al.: 26 Jan 2006 issue of Nature) "Here we report the discovery of a 5.5 (-2.7,+5.5) Mearth planetary companion at a separation of 2.6(-0.6,+1.5) AU from a
0.22 (-0.11,+0.21) solar mass M-dwarf star."

At the lower limit of the error bar on this estimate (5.5 – 2.7 = 2.8 Mearth) this planet could be smaller than the one reported here!

Thanks!

Current astronomical practice is to label exoplanets with the star designation (GJ 436 in this case) followed by a lower-case letter from the alphabetic sequence starting with 'b', in order of discovery. Since this is the second planet discovered around GJ 436, it becomes 'c'.

Why not start the sequence with 'a'? Because there's at least one star catalogue where stars inserted into an existing number sequence have been distinguished by adding 'a' to the number. For example; LHS 1095 and LHS 1095a are two different stars.

Why lower-case letters? Because upper-case letters (A, B, C etc.) are used to label individual stars which are components of a multiple system (binary or larger). Once again, the letters are assigned in order of discovery, which usually means descending order of brightness.

To give a completely hypothetical example; suppose LHS 1095, which I mentioned above, was discovered to have a planet orbiting it. that would then be LHS 1095b. A second planet would be LHS 1095c, and so on. If LHS 1095 was discovered to be a binary system, the two stars would be labeled LHS 1095A and LHS 1095B. If planets were then discovered around the A component, these would be LHS 1095Ab, LHS 1095Ac and so on.

about the names.. everyday i'm more sure they use Stargate SG1 names..

The greater pressure in the center of the planet would likely increase the overall density given similar composition, but the the planet could be made of lighter elements on average than earth (less iron), so a gravity in the range of 1x to 3x earth's seems likely.

Lot's of people can walk (rather haltingly) while carrying extra weights equal to their own body weight, so I think animals evolved in the higher gravity would be about as complex as earth animals but of a more squat design.

If a planet five time the size of Earth was at an acceptable distance from its star, what are the consequences for life in that sort of gravity?