NARROW DUST JETS IN A DIFFUSE GAS COMA: A NATURAL PRODUCT OF SMALL ACTIVE REGIONS ON COMETS

Comets often display narrow dust jets but more diffuse gas comae when their eccentric orbits bring them into the inner solar system and sunlight sublimates the ice on the nucleus. Comets are also understood to have one or more active areas covering only a fraction of the total surface active with sublimating volatile ices. Calculations of the gas and dust distribution from a small active area on a comet's nucleus show that as the gas moves out radially into the vacuum of space it expands tangentially, filling much of the hemisphere centered on the active region. The dust dragged by the gas remains more concentrated over the active area. This explains some puzzling appearances of comets having collimated dust jets but more diffuse gaseous atmospheres. Our test case is 67P/Churyumov–Gerasimenko, the Rosetta mission target comet, whose activity is dominated by a single area covering only 4% of its surface.

[1]  W. Huebner.  Physics and Chemistry of Comets , 2011 .

[2]  H. Melosh,et al.  EPOXI at Comet Hartley 2 , 2011, Science.

[3]  R. Schulz,et al.  Evolution of the dust coma in comet 67P/Churyumov-Gerasimenko before the 2009 perihelion , 2011, 1105.0329.

[4]  J. Bertaux,et al.  WATER PRODUCTION BY COMET 103P/HARTLEY 2 OBSERVED WITH THE SWAN INSTRUMENT ON THE SOHO SPACECRAFT , 2011, 1104.4906.

[5]  V. Tenishev,et al.  NUMERICAL SIMULATION OF DUST IN A COMETARY COMA: APPLICATION TO COMET 67P/CHURYUMOV-GERASIMENKO , 2011 .

[6]  M. Belton.  Cometary activity, active areas, and a mechanism for collimated outflows on 1P, 9P, 19P, and 81P , 2010 .

[7]  Johan Warell,et al.  Gas kinetics and dust dynamics in low-density comet comae , 2010 .

[8]  E. Grün,et al.  Comet 67P/Churyumov-Gerasimenko: the GIADA dust environment model of the Rosetta mission target , 2010 .

[9]  J. Waite,et al.  An approach to numerical simulation of the gas distribution in the atmosphere of Enceladus , 2010 .

[10]  A. Nagy,et al.  Three-dimensional study of Mars upper thermosphere/ionosphere and hot oxygen corona: 1. General description and results at equinox for solar low conditions , 2009 .

[11]  D. Schleicher.  THE LONG-TERM DECAY IN PRODUCTION RATES FOLLOWING THE EXTREME OUTBURST OF COMET 17P/HOLMES , 2009 .

[12]  R. Schulz,et al.  Rosetta—one comet rendezvous and two asteroid fly-bys , 2009 .

[13]  U. Fink.  A taxonomic survey of comet composition 1985-2004 using CCD spectroscopy , 2009 .

[14]  V. Zakharov,et al.  Monte-Carlo and multifluid modelling of the circumnuclear dust coma II. Aspherical-homogeneous, and spherical-inhomogeneous nuclei , 2009 .

[15]  V. Tenishev,et al.  A Global Kinetic Model for Cometary Comae: The Evolution of the Coma of the Rosetta Target Comet Churyumov-Gerasimenko throughout the Mission , 2008 .

[16]  J. Sunshine,et al.  Asymmetries in the distribution of H2O and CO2 in the inner coma of Comet 9P/Tempel 1 as observed by Deep Impact , 2007 .

[17]  M. Belton,et al.  Dust coma morphology in the Deep Impact images of Comet 9P/Tempel 1 , 2007 .

[18]  E. Grün,et al.  Dust Environment Modelling of Comet 67P/Churyumov-Gerasimenko , 2007, 1001.3010.

[19]  M. Kaasalainen,et al.  A Portrait of the Nucleus of Comet 67P/Churyumov-Gerasimenko , 2007 .

[20]  D. Schleicher.  Compositional and physical results for Rosetta's new target Comet 67P/Churyumov–Gerasimenko from narrowband photometry and imaging , 2006 .

[21]  W. Ip,et al.  Cassini Ion and Neutral Mass Spectrometer: Enceladus Plume Composition and Structure , 2006, Science.

[22]  P. Lamy,et al.  Hubble Space Telescope observations of the nucleus fragment 73P/Schwassmann–Wachmann 3-C , 2005 .

[23]  V. Zakharov,et al.  Direct Monte Carlo and multifluid modeling of the circumnuclear dust coma , 2005 .

[24]  H. Keller,et al.  Direct statistical simulation of the near-surface layers of the cometary atmosphere. I. A spherical nucleus , 2006 .

[25]  J. Bertaux,et al.  Pre- and Post-Perihelion Activity of Comet Hyakutake (1996 B2) , 2005 .

[26]  J. T. Mäkinen.  Water production rate of comet 67P/Churyumov-Gerasimenko , 2004 .

[27]  P. Feldman,et al.  Observations of Comet 67P/Churyumov-Gerasimenko with the International Ultraviolet Explorer at Perihelion in 1982 , 2004 .

[28]  Rita Schulz,et al.  Rosetta target comet 67P/Churyumov-Gerasimenko: Postperihelion gas and dust production rates , 2004 .

[29]  D. Brownlee,et al.  Modeling the Nucleus and Jets of Comet 81P/Wild 2 Based on the Stardust Encounter Data , 2004, Science.

[30]  H. Rauer,et al.  Optical observations of Comet 67P/Churyumov-Gerasimenko , 2004 .

[31]  M. Kidger.  Dust production and coma morphology of 67P/Churyumov-Gerasimenko during the 2002–2003 apparition , 2003 .

[32]  G. Bourgois,et al.  Observations at Nançay of the OH 18-cm lines in comets - The data base. Observations made from 1982 to 1999 , 2002 .

[33]  J. Crifo,et al.  The Dependence of the Circumnuclear Coma Structure on the Properties of the Nucleus: IV. Structure of the Night-Side Gas Coma of a Strongly Sublimating Nucleus , 2000 .

[34]  G. Fazio,et al.  The Nucleus of Comet Hyakutake (C/1996 B2) , 1999 .

[35]  L. Jorda,et al.  Comet 46P/Wirtanen, the target of the Rosetta mission , 1998 .

[36]  J. Crifo,et al.  The Dependence of the Circumnuclear Coma Structure on the Properties of the Nucleus , 1997 .

[37]  K. Powell,et al.  Dust-Gas Interrelations In Comets: Observations And Theory , 1997 .

[38]  R. Honeycutt,et al.  Evidence for interacting gas flows and an extended volatile source distribution in the coma of comet C/1996 B2 (Hyakutake). , 1997, Science.

[39]  M. Combi.  Time-Dependent Gas Kinetics in Tenuous Planetary Atmospheres: The Cometary Coma , 1996 .

[40]  M. Combi.  The fragmentation of dust in the innermost comae of comets: Possible evidence from ground-based images , 1994 .

[41]  G. Bird.  Molecular Gas Dynamics and the Direct Simulation of Gas Flows , 1994 .

[42]  A. Cochran,et al.  Spectrophotometry of the continuum in 18 comets , 1992 .

[43]  D. Osip,et al.  Comets: Groundbased observations of spacecraft mission candidates , 1992 .

[44]  T. Gombosi,et al.  A time-dependent dusty gas dynamic model of axisymmetric cometary jets , 1990 .

[45]  M. Combi.  The outflow speed of the coma of Halley's comet , 1989 .

[46]  A. Nagy,et al.  Dust and neutral gas modeling of the inner atmospheres of comets , 1986 .

[47]  M. Hanner,et al.  The dust coma of periodic comet Churyumov-Gerasimenko (1982 VIII) , 1985 .

[48]  Robert L. Millis,et al.  The ensemble properties of comets: Results from narrowband photometry of 85 comets , 1995 .

[49]  R. Probstein,et al.  A theory of dust comets. I. Model and equations , 1968 .