A transiting giant planet with a temperature between 250 K and 430 K

Of the over 400 known exoplanets, there are about 70 planets that
transit their central star, a situation that permits the derivation of
their basic parameters and facilitates investigations of their atmospheres.
Some short-period planets, including the first terrestrial
exoplanet (CoRoT-7b), have been discovered using a space mission
designed to find smaller and more distant planets than can be seen
from the ground. Here we report transit observations of CoRoT-9b,
which orbits with a period of 95.274 days on a low eccentricity of
0.11 +- 0.04 around a solar-like star. Its periastron distance of 0.36
astronomical units is by far the largest of all transiting planets, yielding
a ‘temperate’ photospheric temperature estimated to be between
250 and 430 K. Unlike previously known transiting planets, the
present size of CoRoT-9b should not have been affected by tidal heat
dissipation processes. Indeed, the planet is found to be well described
by standard evolutionmodels with an inferred interior composition
consistent with that of Jupiter and Saturn.