comets formed in the early phases of the solar system and may still contain unprocessed material. approching the sun, the cometary surface is heated up and a lot of material is released from the cometary surface into the coma. the cometary coma is composed of solid and semi-refractory particles which are, after their ejection from the surface, driven by the forces of radiation pressure and solar wind. the extend of the coma and the coma structure strongly depends on the processes on the cometary surface and its properties. the shape of the coma shows a lot of variations caused by fans and jets. since grains radiate most efficient close to their own size, particles of about the same properties can be traced by observing the coma at different wavelength. therefore, coma structures observed at wavelengths shortwards of the wavelength of maximum thermal emission will be caused mainly by .small.(hot) particles, because they are .overheated. in comparison to the black body equilibrium radiation. whereas coma structures visible at wavelengths longwards the wavelength of maximum thermal emission result from emission of .larger. particles. this would be the direct proof of the presence of large grains in the cometray coma. the observations of the temperature distribution in the coma could be compared directly with isochron-isodyn-models for cometary comae. due to the opaqueness of the earth.s atmosphere longwards of 20microns, no observations have been possible to test the grain distribution hypothesis raised by several models. the shape of the coma at different wavelengths would give a slight hint on the strength of radiation pressure and other forces and their influence on selceted kinds of particles. mapping the coma at different wavelengths would allow to determine precise absolute flux values and spacial resolved flux distributions. this would be the basis for modelling grain size distributions and multi-temperture evaluations within the cometary coma.
Instrument
PHT22
Temporal Coverage
1997-12-30T00:04:37Z/1997-12-30T00:58:33Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the worlds first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, PESCHKE et al., 1999, 'TOO: COMETARY COMAE IN THE IR DIMENSIONS comma STRUCTURES AND COMPOSITION', 1.0, European Space Agency, https://doi.org/10.5270/esa-fg1v6vf
