Structure and Density of Cometary Nuclei

Models of comets with strongly variable nongravitational effects

International Astronomical Union Colloquium ◽

10.1017/s0252921100031705 ◽

1999 ◽

Vol 173 ◽

pp. 381-387

Author(s):

M. Królikowska ◽

G. Sitarski ◽

S. Szutowicz

Keyword(s):

Cometary Nucleus ◽

Spin Axis ◽

Reactive Force ◽

Orbital Elements ◽

Cometary Nuclei ◽

Short Period ◽

Basic Parameters ◽

Polar Radius ◽

Cometary Activity ◽

Nongravitational Effects

AbstractThe nongravitational motion of five “erratic” short-period comets is studied on the basis of published astrometric observations. We present the precession models which successfully link all the observed apparitions of the comets: 21P/Giacobini-Zinner, 31P/Schwassmann-Wachmann 2, 32P/Comas Solá, 37P/Forbes, and 43P/Wolf-Harrington. We used the Sekanina's forced precession model of the rotating cometary nucleus to include the nongravitational terms into equations of the comet's motion. Values of six basic parameters (four connected with the rotating comet nucleus and two describing the precession of spin-axis of the nucleus) have been determined along the orbital elements from positional observations of the comets. The solutions were derived with additional assumptions which introduce instantaneous changes of modulus of reactive force,Aand of maximum of cometary activity with respect to perihelion time. The present precession models impose some contraints on sizes and rotational periods of cometary nuclei. According to our solutions the nucleus of 21P/Giacobini-Zinner with oblateness along the spin-axis of about 0.32 (equatorial to polar radius of 1.46) is the most oblate among five investigated comets.

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Covering of cometary nucleus by refractory crust and its evolution into asteroid-like body

International Astronomical Union Colloquium ◽

10.1017/s0252921100031675 ◽

1999 ◽

Vol 173 ◽

pp. 365-370

Author(s):

Kh.I. Ibadinov

Keyword(s):

Laboratory Experiments ◽

Cometary Nucleus ◽

Sublimation Rate ◽

Cometary Nuclei ◽

Short Period Comet ◽

Short Period ◽

Brightness Decrease ◽

Crust Thickness ◽

Ice Sublimation ◽

Period Comet

AbstractFrom the established dependence of the brightness decrease of a short-period comet dependence on the perihelion distance of its orbit it follows that part of the surface of these cometary nuclei gradually covers by a refractory crust. The results of cometary nucleus simulation show that at constant insolation energy the crust thickness is proportional to the square root of the insolation time and the ice sublimation rate is inversely proportional to the crust thickness. From laboratory experiments resulted the thermal regime, the gas productivity of the nucleus, covering of the nucleus by the crust, and the tempo of evolution of a short-period comet into the asteroid-like body studied.

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The Chemical Composition of Cometary Nuclei

Symposium - International Astronomical Union ◽

10.1017/s0074180900006628 ◽

1972 ◽

Vol 45 ◽

pp. 265-270

Author(s):

L. M. Shul'man

Keyword(s):

Chemical Composition ◽

Cosmic Rays ◽

Organic Molecules ◽

Solid Phase ◽

Critical Concentration ◽

Energy Output ◽

Time Interval ◽

Nuclear Surface ◽

Solar Cosmic Rays ◽

Cometary Nuclei

The probable parent-molecules of radicals such as C3 and N2+ are discussed, and it is concluded that cometary nuclei may contain complicated organic molecules, such as C3H4, CH2N2, and C4H2. It is suggested that these molecules are formed by radiation synthesis in solid phase. In a time interval of order 107 to 109 yr bombardment from cosmic rays would be expected to transform the chemical composition to a depth of 1 m. Solar cosmic rays do not penetrate as far, and as a result the surface layer of the nucleus can be enriched with unsaturated hydrocarbons. After a critical concentration of this explosive material is reached a further burst of solar cosmic rays can initiate an explosion and thus an outburst in the comet's brightness. This mechanism is the only one advanced to date that can explain the synchronism of the energy output over the whole nuclear surface.

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Long-term simulations of the rotational state of small irregular cometary nuclei

Astronomy and Astrophysics ◽

10.1051/0004-6361:20030845 ◽

2003 ◽

Vol 406 (3) ◽

pp. 1123-1133 ◽

Cited By ~ 23

Author(s):

P. J. Gutiérrez ◽

L. Jorda ◽

J. L. Ortiz ◽

R. Rodrigo

Keyword(s):

Rotational State ◽

Cometary Nuclei

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Deep sub-surface exploration of cometary nuclei

Advances in Space Research ◽

10.1016/s0273-1177(99)80211-7 ◽

1999 ◽

Vol 24 (9) ◽

pp. 1167-1173 ◽

Cited By ~ 13

Author(s):

M.J.S. Belton ◽

M.F. A'Hearn

Keyword(s):

Cometary Nuclei ◽

Surface Exploration

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Mass Erosion and Transport on Cometary Nuclei, as Found on 67P/Churyumov-Gerasimenko

10.1093/acrefore/9780190647926.013.186 ◽

2021 ◽

Author(s):

Wing-Huen Ip

Keyword(s):

Southern Hemisphere ◽

Northern Hemisphere ◽

Ballistic Transport ◽

Dust Grains ◽

Cometary Nuclei ◽

Cometary Dust ◽

Physical Mechanisms ◽

Streaming Instability ◽

System P ◽

Nucleus Surface

The Rosetta spacecraft rendezvoused with comet 67P/Churyumov-Gerasimenko in 2014–2016 and observed its surface morphology and mass loss process. The large obliquity (52°) of the comet nucleus introduces many novel physical effects not known before. These include the ballistic transport of dust grains from the southern hemisphere to the northern hemisphere during the perihelion passage, thus shaping the dichotomy of two sides, with the northern hemisphere largely covered by dust layers from the recycled dusty materials (back fall) and the southern hemisphere consisting mostly of consolidated terrains. A significant amount of surface material up to 4–10 m in depth could be transferred across the nucleus surface in each orbit. New theories of the physical mechanisms driving the outgassing and dust ejection effects are being developed. There is a possible connection between the cometary dust grains and the fluffy aggregates and pebbles in the solar nebula in the framework of the streaming-instability scenario. The Rosetta mission thus succeeded in fulfilling one of its original scientific goals concerning the origin of comets and their relation to the formation of the solar system.

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