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  A tale of two very different comets: ISO and MSX measurements of dust emission from 126P/IRAS (1996) and 2P/Encke (1997)

Lisse, C. M., Fernández, Y. R., A'Hearn, M. F., Grün, E., Käufl, H. U., Osip, D. J., et al. (2004). A tale of two very different comets: ISO and MSX measurements of dust emission from 126P/IRAS (1996) and 2P/Encke (1997). Icarus, 171(2), 444-462.

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Item Permalink: http://hdl.handle.net/11858/00-001M-0000-0011-8B35-E Version Permalink: http://hdl.handle.net/11858/00-001M-0000-0011-8B36-C
Genre: Journal Article


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Lisse, C. M.1, Author
Fernández, Y. R.1, Author
A'Hearn, M. F.1, Author
Grün, Eberhard2, Author              
Käufl, H. U.1, Author
Osip, D. J.1, Author
Lien, D. J.1, Author
Kostiuk, T.1, Author
Peschke, S. B.2, Author              
Walker, R. G.1, Author
1University of Maryland, Department of Astronomy, College Park, MD 20742, USA Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA University of Maryland, Department of Astronomy, College Park, MD 20742, USA Karl-Schwarzschildstrasse 2, D-85748 Garching, Germany Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena, Chile Oklahoma State University, Department of Physics, Stillwater, OK 74078, USA NASA Goddard Spaceflight Center, Code 693.1, Greenbelt, MD 20771, USA ISO Data Centre, Villafranca Del Castillo, ESA Satellite Tracking Station, Apdo. 50727, E-28080 Madrid, Spain Monterey Institute for Research in Astronomy, 200 Eight Street, Marina, CA 93933, USA, ou_persistent22              
2Ralf Srama - Heidelberg Dust Group, Research Groups, MPI for Nuclear Physics, Max Planck Society, ou_907558              


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 Abstract: We present the characteristics of the dust comae of two comets, 126P/IRAS, a member of the Halley family (a near-isotropic comet), and 2P/Encke, an ecliptic comet. We have primarily used mid- and far-infrared data obtained by the ISOPHOT instrument aboard the Infrared Space Observatory (ISO) in 1996 and 1997, and mid-infrared data obtained by the SPIRIT III instrument aboard the Midcourse Space Experiment (MSX) in 1996. We find that the dust grains emitted by the two comets have markedly different thermal and physical properties. P/IRAS's dust grain size distribution appears to be similar to that of fellow family member 1P/Halley, with grains smaller than 5 microns dominating by surface area, whereas P/Encke emits a much higher fraction of big (20 μm and higher) grains, with the grain mass distribution being similar to that which is inferred for the interplanetary dust population. P/Encke's dearth of micron-scale grains accounts for its visible-wavelength classification as a ``gassy'' comet. These conclusions are based on analyses of both imaging and spectrophotometry of the two comets; this combination provides a powerful way to constrain cometary dust properties. Specifically, P/IRAS was observed preperihelion while 1.71 AU from the Sun, and seen to have a 15-arcmin long mid-infrared dust tail pointing in the antisolar direction. No sunward spike was seen despite the vantage point being nearly in the comet's orbital plane. The tail's total mass at the time was about 8×109 kg. The spectral energy distribution (SED) is best fit by a modified greybody with temperature T=265+/-15 K and emissivity ϵ proportional to a steep power law in wavelength λ: ϵ~λ-α, where α=0.50+/-0.20(2σ). This temperature is elevated with respect to the expected equilibrium temperature for this heliocentric distance. The dust mass loss rate was between 150-600 kg/s (95% confidence), the dust-to-gas mass loss ratio was about 3.3, and the albedo of the dust was 0.15+/-0.03. Carbonaceous material is depleted in the comet's dust by a factor of 2-3, paralleling the C2 depletion in P/IRAS's gas coma. P/Encke, on the other hand, observed while 1.17 AU from the Sun, had an SED that is best fit by a Planck function with T=270+/-15 K and no emissivity falloff. The dust mass loss rate was 70-280 kg/s (95% confidence), the dust-to-gas mass loss ratio was about 2.3, and the albedo of the dust was about 0.06+/-0.02. These conclusions are consistent with the strongly curved dust tail and bright dust trail seen by Reach et al. (2000; Icarus 148, 80) in their ISO 12-μm imaging of P/Encke. The observed differences in the P/IRAS and P/Encke dust are most likely due to the less evolved and insolated state of the P/IRAS nuclear surface. If the dust emission behavior of P/Encke is typical of other ecliptic comets, then comets are the major supplier of the interplanetary dust cloud.


Language(s): eng - English
 Dates: 2004-10
 Publication Status: Published in print
 Pages: -
 Publishing info: -
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 Rev. Type: -
 Identifiers: eDoc: 207044
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Title: Icarus
Source Genre: Journal
Publ. Info: -
Pages: - Volume / Issue: 171 (2) Sequence Number: - Start / End Page: 444 - 462 Identifier: -