WHAT ASTRONOMY HAS LEARNED FROM OBSERVATIONS OF H-3(+)

We review the uses to which H-3(+) astronomical observations have been put, in the five years since the first detection of this molecular io n in the aurorae of Jupiter. Spectroscopy of Jupiter shows that the io nospheric temperature is high (similar to 1000 K) compared with the lo wer atmosphere and that auroral column densities are between 10(12) an d 10(13) cm(-2). The molecule is also distributed widely across the pl anet in concentrations about 10% of peak auroral densities. Imaging in H-3(+)-sensitive wavelengths links the aurorae to open magnetic field lines, rather than those encompassing the Io plasma torus. Uranus sho ws H-3(+) emission intensities of a few percent olf the peak jovian au roral lines, with somewhat weaker emission from Saturn. On Uranus, H-3 (+) is distributed fairly evenly across the planet, with some indicati on that auroral enhancement is not more than a factor of two. Saturnin e H: appears to be concentrated more towards the magnetic poles. The i dentification of H; in the spectrum of the type II supernova SN1987a c onstrains models of the explosion to avoid microscopic mixing during m uch of the first year of the event. So far no reliable detection of H- 3(+) in the interstellar medium has been reported.