Leonids peak earlier than expected
17 November 1998
This year's Leonids shower was a wonderful event for those who finally enjoyed clear skies and stayed up long after midnight on 16 November, or got up early on the 17th. All indications are now that the peak of the Leonids shower was well ahead of the predicted time for the maximum rates (predicted time 19:15 to 20:00 UTC 17 November). Preliminary results indicate that the Earth passed the maximum about 16 hours earlier.This is, however, well within the uncertainties. Besides the threat meteor storms pose to spacecraft, there is also a significant interest in their scientific study. Meteors provide us with information about the larger grains (size of a grain of sand to a few centimetres) emitted from the nucleus of comets and about their dynamics ie. orbits in space. The study of their trails when they burn up in the upper atmosphere gives us information on the composition of the grains.
Our poor understanding of how the dust grains are emitted from comets and of their density and shape - all factors that influence their dynamics - is responsible for the large uncertainties that exist when predicting the occurrence of storms.
But here Rosetta, ESA's mission to comet Wirtanen, will provide the crucial information. Besides studying in detail the composition of a cometary nucleus, the spacecraft will follow the comet along its path from its most distant point from the Sun through perihelion (about the Sun).
It will provide detailed information of the dust emission process - the emission speeds as a function of grain size - and study if the emission is continuous or in outburst, (so-called jets).
All this will contribute to a significantly better understanding of cometary processes and to a more accurate prediction of phenomena like meteor showers and storm.
G. Schwehm
Rosetta project scientist