Evolution of mobile phases in cometary interiors

Abstract Beginning with loose aggregations of dust particles coated with heterogeneous ices under vacuum at Kuiper Belt temperatures, moving to Jupiter/Saturn distances and eventually to low-perihelion orbit, we consider the likely development of the gaseous phase within a cometary nucleus over the course of its lifetime. From the perspective of physical chemistry, we consider limits on the spatial and temporal distribution and composition of this gaseous phase. The implications of the gaseous phase for heat transfer and for the possible spatial and temporal development of liquid phases are calculated. We conclude that the likely temperatures, pressures, and compositions beneath the outer crust of typical cometary nuclei are such that fluidised phases can exist at significant depths and that these reservoirs give a coherent explanation for the high-intensity outbursts observed from cometary nuclei at large distances from perihelion.

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The Evolution of Cometary Nuclei

Symposium - International Astronomical Union ◽

10.1017/s007418090000663x ◽

1972 ◽

Vol 45 ◽

pp. 271-276 ◽

Cited By ~ 3

Author(s):

L. M. Shul'Man

Keyword(s):

Size Distribution ◽

Cometary Nucleus ◽

Dust Content ◽

The Other ◽

Dust Particles ◽

Nuclear Radius ◽

Cometary Nuclei ◽

Other Hand ◽

Brightness Decrease

The evolution of a cometary nucleus depends on the size distribution of the dust content. If all the dust particles are small enough, they will all be thrown off into the coma; the secular decrease in the comet's brightness is due simply to the decrease in the nuclear radius, and the comet eventually disintegrates. On the other hand, if larger grains are present, they will start to form spots of a low-emissivity mineral envelope on the surface of the nucleus; in this case, the decrease in brightness is due to the increase in the area of the screened part of the surface, and the reduction in the nuclear radius is comparatively small. It is shown that after about 90% of the surface has been screened, the rate of screening increases considerably, as smaller particles become trapped between the larger ones; and there will be a corresponding acceleration in the brightness decrease. These nuclei are eventually covered with a solid mineral envelope, and they are transformed into asteroids.

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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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