scientific abstract: isocam images of cometary dust trails are proposed to determine trail structure at various positions along the trails of two periodic comets. primary targets are p/kopff and p/churyumov-gerasimenko for autumn 95 and p/kopff and p/gunn for a spring 96 launch. p/encke and p/pons-winnecke are considered as alternates depending on launch date. observations from iras (davies et al, nature 309 p315 1984) discovered an extended infrared tail (also referred to as a debris trail) associated with comet p/tempel-2. sykes et al (science 232 p115 1986) independently discovered the tempel-2 tail and subsequently identified a number of similar features in the iras skyflux plots.these trails may represent the main source of mass loss from comets yet they are too faint for ground based infrared observation. isocam images at various positions close to the nucleus will probe the fine structure of the trail and, by determining its width, place constraints on the ejection velocity of the particles and provide inputs to theoretical models of dust ejection. observation summary: we have modelled various trails at the time of the mission and find the trail of p/kopff to be about 1.5*10**-5 jy/arc sec**2 at 12um. in a few min/frame isocam would get s/n=10 in the lw10 filter (8-15 microns) using 6 arc sec pfov. since the comet moves these must be done as fixed time observations. the trails usually appear no more than 4 arc minutes wide so three frames at right angles to a trail taken with the 6 arcsec pfov should be enough to cover one trail at one position around the comet.s orbit and to get far enough away to reach the background. to obtain best sensitivity to these extended sources we will use the microscanning option in cam aot1 to scan across a trail at each position using the offsets to extend the coverage approx 2 iso fields along the trail. we require similar scans through the trail at positions 0.25 degrees in front of the nucleus, close to the nucleus itself and 1 and 2 degrees behind. observations are requested when the comet elongation is greater than 90 degrees in order to reduce the effects of the zodiacal background. jkd can supply positions on request. these observations should allow sampling of the large (leading) particles, the fresh trailing particles and a section of trail containing older particles. these images will also show if there are regions of enhanced density within the trails which would be prefered targets for spectrophotometric observations. if the trail is found to be very clumpy it would be desirable to make spectrophotometric observations of clumps and diffuse regions for comparison. (for example a clump might be the result of a large particle falling to pieces some time after ejection from the nucleus). spectrophotometric observations with isophot should take only a few seconds per filter, so these follow up studies would be short compared to the cam time required. the purpose of these filter/spectophotometic studies is to define the spectrum of the trail particles and compare the result to a black body since iras data indicates that the grains are warmer than expected for black bodies at the appropriate solar distance (sykes et al icarus 86 236 1990). this may be due to the presence of very small grains, as found in cometary comae, or to large grains able to support thermal gradients and which behave, thermally at least, like small asteroids. since the trail particles survive long after ejection from the nucleus they must represent refractory grains from which all the ices have evaporated. the grains are believed to be dark, consistent with the observations of the nucleus of halley, but modelling using the available iras data cannot be very precise. iso photometry will enable more detailed modeling to be done than is possible at present. this will lead to a more detailed understanding of the relationship between comets and the zodiacal dust complex, to better understanding of cometary dust production and cometary evolution. fixed time observations: (if any, otherwise drop this line) since the comets move these must be done as fixed time observations with precise details to be agreed between the pi and the sot near to the time of the observation.
Instrument
CAM01
Temporal Coverage
1996-03-25T01:44:34Z/1998-01-30T18:05:07Z
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, DAVIES et al., 1999, 'On the trail of tails. openParImaging the trails of comets P\/Kopff comma P\/Gunn and P\/Churyumov-Gerasimenko with CAMclosePar', 1.0, European Space Agency, https://doi.org/10.5270/esa-1f5pqd2
