X-ray emission from comets and planets

Abstract

X-ray emission has been observed from many objects throughout the solar system including the Sun, the Moon, the Earth, Jupiter, and comets. A brief review of these observations and some of the emission mechanisms suggested to explain the observed X-rays are given in this paper. Cometary X-ray emission and Jovian X-ray emission will be emphasized. The initial discovery of X-rays from comet Hyakutake (Lisse et al., 1996) was surprising and a number of explanations were put forth, including bremsstrahlung associated with hot electron collisions with cometary neutrals or ions, scattering or fluorescence of solar X-rays from cometary neutrals or from dust particles, and charge transfer of heavy solar wind ions with neutrals. X-rays have also been observed both from Jupiter's auroral region as well as from low latitudes (Waite et al., 1997). Again, a number of emission mechanisms have been proposed, including precipitation of energetic heavy ions from the magnetosphere. Predictions of X-ray emission from Venus, Mars, and from interstellar neutrals in the heliosphere are made.