Cometary Outbursts, A Brief Survey
Abstract
The general characteristics of cometary outbursts (sudden increases in the brightness of a comet, usually of between 2 and 5 magnitudes) are reviewed, and mechanisms that have been suggested to explain their occurrence are discussed. The sudden increment in brightness is followed by the expansion of a shell of nebulous matter, which fades about 4 weeks after onset. Spectral observations of the outburst consistently show reflected solar continuum without superimposed molecular bands. Of the 79 comets known to have passed their perihelion during the past 40 years, 59 apparitions were accompanied by outbursts. The probability of occurrence is probably independent of the comet's heliocentric distance at least when this distance does not exceed 7.5 AU. Outbursts are frequently associated with nuclear splitting. Possible mechanisms include pressure release from gas pockets, explosive chemical reactions involving free radicals, collisions between comets and interplanetary boulders, and minor breakup of the nucleus. Patashnick et al. (1974) have suggested that cometary outbursts occur when amorphous ice formed by the deposition of water vapor at temperatures less than 95 K and pressures below 1 N/sq m undergoes a transition to cubic ice at temperatures near 140 K.
- Publication:
-
Quarterly Journal of the Royal Astronomical Society
- Pub Date:
- December 1975
- Bibcode:
- 1975QJRAS..16..410H
- Keywords:
-
- Comet Heads;
- Comets;
- Luminous Intensity;
- Periodic Variations;
- Astronomical Spectroscopy;
- Astrophysics;
- Comet Nuclei;
- Cratering;
- Graphs (Charts);
- Probability Theory;
- Solar System;
- Spatial Distribution;
- Astronomy