The discovery of a massive planet (51 Peg B) at only 0.05 AU from its star
(51 Peg) was a surprising discovery last year. Planets so close to their star
had not been predicted by theory and raise new questions on the scenario
for the formation of planetary systems.
Although simulations have shown that a large gas giant can be stable so close
to 51 Peg, we expect a significant evaporation of its atmosphere due to
thermal/non-thermal escape and/or gravitational mass loss. The escaping
molecules and their dissociation and ionization products can form a large
enveloppe around the planet which partially occults the star, since the orbit
inclination of 51 Peg B is close to 90 degrees. We propose to search for
absorption features of such an enveloppe in the IR spectrum of 51 Peg during
the eclipse. We plan to search in the range from 2.38 mu to 3.52 mu and from
4.55 mu to 4.74 mu. These ranges include absorption lines of many potentially
present molecules and their daughter products (e.g. H2, He+, CO, CO+, N2+, NH3,
CH4,..).
The discovery of extra-solar planets is one of the most exciting discoveries in
astronomy in this century. At the present stage very little is known about
their nature and predictions are rather insecure. We feel that it is strongly
required to obtain all information possible about these objects at the
available wavelength ranges. ISO can extend these investigations to
wavelength ranges not accessible from the ground.