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Journal ArticleDOI

Radioactive Heating and Layered Structure of Cometary Nuclei

01 Mar 1988-Earth Moon and Planets (Kluwer Academic Publishers)-Vol. 40, Iss: 3, pp 303-313
TL;DR: In this paper, it was argued that the unusual activity of comet Bowell could be explained by sublimation mainly of N2 and CO in its first several approaches to the sun.
Abstract: Following the work of Whipple and Stefanik, radioactive heating by uranium, thorium and pottasium of a cometary nucleus is discussed The assumed composition is that of interstellar medium If thermal diffusivity is 10−4 cm2s−1, the central temperature of a nucleus with radius 10 km can be above 50 K, while if the thermal diffusivity is 5 × 10−3, the central temperature can be only 25 K or so Volatile gases such as N2 and CO will flow toward the outer part of the nucleus and are lost in their first several approaches to the sun This mechanism appears capable of explaining the depletion of N2 and CO relative to the interstellar abundance It is argued that unfamiliar activity of comet Bowell could be explained by sublimation mainly of N2 and CO
Citations
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Journal ArticleDOI
15 Nov 2005-Icarus
TL;DR: In this article, the authors used the H10 photometric system and a new set of photometric rules and functions to analyze the visible light curves of eight comets listed in the title.

36 citations

Journal ArticleDOI
TL;DR: In this article, the authors presented a collection of 27 periodic and non-periodic comets to create the secular light curves (SLCs), using two plots per comet.

34 citations

01 Dec 2007
TL;DR: In this paper, the authors presented a collection of 27 periodic and non-periodic comets to create the secular light curves (SLCs), using two plots per comet.
Abstract: In this work we have compiled 37,692 observations of 27 periodic and non-periodic comets to create the secular light curves (SLCs), using two plots per comet. The data have been reduced homogeneously. Our overriding goal is to learn the properties of the ensemble of comets. More than 30 parameters are listed, of which over ∼20 are new and measured from the plots. We define two ages for a comet using activity as a proxy, the photometric age P-AGE, and the time-age, T-AGE. It is shown that these parameters are robust, implying that the input data can have significant errors but P-AGE and T-AGE come out with small errors. This is due to their mathematical definition. It is shown that P-AGE classifies comets by shape of their light curve. The value of this Atlas is twofold: The SLCs not only show what we know, but also show what we do not know, thus pointing the way to meaningful observations. Besides their scientific value, these plots are useful for planning observations. The SLCs have not been modeled, and there is no cometary light curve standard model as there is for some variable stars (i.e. eclipsing binaries). Comets are classified by age and size. In this way it is found that 29P/Schwassmann-Wachmann 1 is a baby goliath comet, while C/1983 J1 Sugano-Saigusa-Fujikawa is a middle age dwarf. There are new classes of comets based on their photometric properties. The secular light curves presented in this Atlas exhibit complexity beyond current understanding.

31 citations

Book ChapterDOI
01 Jan 1989
TL;DR: In this paper, observational data available at present to infer physical conditions of the formation environment of cometary matter are briefly surveyed, including the chemical and isotopic composition of comets, and the nuclear spin temperature derived from the ortho/para abundance ratio of H2O molecules.
Abstract: Firstly, observational data available at present to infer physical conditions of the formation environment of cometary matter are briefly surveyed These include the chemical and isotopic composition of cometary matter, and the nuclear spin temperature derived from the ortho/para abundance ratio of H2O molecules Secondly, theories on the origin of comets—theories based upon the chemical composition of the volatile component of cometary matter—are reviewed The theories are classified into two types, distinguished by whether cometary volatiles originate as solar nebula condensates or as the sublimation residue of interstellar ices Observational items helpful to test the theories are pointed out Thirdly, discussion is given on the physical properties of ices relevant to the chemical theory of the origin of comets

29 citations

References
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Book
01 Jan 1978
TL;DR: This encyclopedic work includes authoritative coverage of atomic and molecular structure, organic chemistry (revised), inorganic, analytical, and electro- chemistry, mathematics as applied to chemistry, and more.
Abstract: Lange's Handbook has served as a leading source of reliable chemical information and data for chemists, engineers, and other technical specialists since l934. This encyclopedic work includes authoritative coverage of atomic and molecular structure, organic chemistry (revised), inorganic, analytical, and electro- chemistry, mathematics as applied to chemistry, and more. It also includes nomenclature consistent with recommendations of the IUPAC Commission rules.

7,848 citations

Journal ArticleDOI
TL;DR: The opponent-process theory of such new or experiential motives as drug addiction, love, affection and social attachment, and cravings for sensory and aesthetic ex- periences are described and the empirical laws governing the establishment of these new motives are described.
Abstract: When an unconditioned stimulus, a reinforcer, or an innate releaser is repeatedly presented to human or animal subjects, three major affective phenomena are often observed. First, one often sees affective or hedonic contrast. Second, frequent repeti- tion of the unconditioned stimulus, reinforcer, or innate releaser often gives rise to affective or hedonic habitu- ation (tolerance). Finally, after frequent repetition of these stimuli, a withdrawal or abstinence syndrome often emerges directly following stimulus termination. These affective dynamics of organismicall y important stimuli generate new motives, new opportunities for reinforcing and energizing operant behaviors, based on the hedonic attributes of withdrawal or abstinence syndromes. This article describes the opponent-process theory of such new or experientiall y produced motives and discusses recent research testing the theory. The theory attempts to account for such diverse acquired motives as drug addiction, love, affection and social attachment, and cravings for sensory and aesthetic ex- periences (cases in which the initial reinforcers are posi- tive) and for such acquired motives as parachuting, jog- ging and "marathoning," sauna bathing, and a variety of self-administered, aversive stimuli like electric shocks (cases in which the initial reinforcers are negative). The empirical laws governing the establishment of these new motives are described. Crucial variables include the quality, intensity, and duration of each stimulus presentation and the time intervals between presenta-

1,077 citations

Book
01 Jan 1965

928 citations