Australasian Science: Australia's authority on science since 1938

Stars Can Be Late Parents

By David Reneke

Astronomers weigh a proto-planetary disk while miners set their sights on passing asteroids for gold and other valuable minerals.

David Reneke is an astronomy lecturer and teacher, a feature writer for major Australian newspapers and magazines, and a science correspondent for ABC and commercial radio. Subscribe to David’s free Astro-Space newsletter at

The full text of this article can be purchased from Informit.

This new decade has already heralded in a significant number of exciting cosmological discoveries, and the surprises continue in the relatively new field of extra-solar astronomy. Using the unique capabilities of the European Space Agency’s Herschel Space Observatory, astronomers have accurately “weighed” a star’s disc and found it still has enough mass to spawn 50 Jupiter-sized planets several million years after most other stars have already given birth.

Proto-planetary discs contain all the raw ingredients for building planets. They are composed mainly of cold molecular hydrogen gas, which is highly transparent and essentially invisible.

Usually it is much easier to measure the emissions from “contaminants” like the small fraction of dust mixed in the gas to estimate the total disc mass. In the past this technique has caused significant uncertainties, but thanks to the sensitivity of Herschel, astronomers have used a new, more accurate method involving a close relative of molecular hydrogen called hydrogen deuteride, or “heavy” molecular hydrogen.

Since the ratio of “normal” and “heavy” molecular hydrogen gas is well-known from measurements in our local solar neighbourhood, this approach provides a means to “weigh” a star’s total disc mass with ten times greater accuracy than ever before.

Using this technique, a substantial mass of gas...

The full text of this article can be purchased from Informit.