Astronomers at the universities of Amsterdam, Louvain, Groningen and Utrecht have found proof that planets can form around old, dying stars. In the vicinity of the Red Rectangle, an old binary star in the Monoceros constellation, they have detected a ring of matter constituting the first stage of planet formation. Their results were published in Nature on 26 February 1998. It had previously been assumed that planets can form only round new-born stars.

Many young stars are ready to build planets

A dust disk where ISO found olivine signature. Red Rectangle imaged by ISO/MPG 2.2 microns (visible light)

Is the Solar System a unique pearl in the Universe, the only example of planets orbiting a star? Definitely not. While other astronomers detect unseen planets by their effect on the motion of their parent stars, ISO teams see favourable circumstances for planet-making. The left-over gas and dust that swirls around many new-born stars evolves into a so-called protoplanetary disk which glows with infrared light.

Planets can form from the dust grains. When the process is over, only a thin ring of debris remains. Although no telescope has been able so far to image any alien planet, ISO has detected many of these thin debris disks, which astronomers believe are made of small bodies like comets.

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