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Last year, two astronomers in California claimed they had found evidence of
planets orbiting three young stars in the constellation of Taurus. But it
seems their claim may have been premature. The evidence – ‘dips’ in the
infrared spectra of discs of dust surrounding the stars – could have an
entirely different explanation.

When Kenneth Marsh and Michael Mahoney of the Jet Propulsion Laboratory in
Pasadena, California, discovered the dips, they interpreted them as arising
from gaps in the stars’ discs. They went on to suggest that each gap was
created by a planet orbiting each star (New Å®ÉúСÊÓƵ, Science, 6 June
1992).

Now Alan Boss of the Carnegie Institution of Washington and Harold Yorke of
the University of Wurzburg in Germany have calculated the expected infrared
spectrum of a young star’s disc. They have discovered that a dip occurs in
the spectrum even if the disc has no gap. The reason is that dust grains
evaporate at a temperature of around 30 oC, removing infrared radiation at a
wavelength corresponding to this temperature.

Marsh refereed Boss and Yorke’s paper, but is unconvinced by their findings.
‘Their result may or may not be right,’ says Marsh. ‘Their conclusions
involved quite an extrapolation from the calculations that they did, so I
don’t believe that they’ve provided a viable alternative to the gap model.’

Boss and Yorke will publish their work in the 10 July issue of Astrophysical
Journal Letters.