Astronomers have so far detected about 50 planets orbiting other stars. They are all giant, Jupiter-like planets, made mostly of gas, and their formation process is still unclear. ESA's Infrared Space Observatory, ISO, now sheds some light on this problem. These models will now have to be reviewed. They said, for instance, that Jupiter-like planets had to form in just a few million years, but the ISO result implies that the process can take up to 20 million years.
Planetary systems form very early in a star's life, actually during the star-birth itself.
While the whole process of star and planet formation is taking place the system remains covered by opaque dust and can therefore not be seen using an optical telescope. When, after the dispersion of the dust, the star becomes visible, much of the material in its protoplanetary disk is already 'locked' into the planets, and only left-over dust grains remain in the now very thin, feeble, circumstellar ring of debris. The gas, a key component of giant, Jupiter-like planets, has all gone. Or so it seemed. Contrary to what the scenario described above says, Thi, Blake et al.