Infrared spectrophotometry of Comet IRAS-Araki-Alcock (1983d): a bare nucleus revealed?

Hanner, M. S.; Aitken, D. K.; Knacke, R. F.; McCorkle, S.; Roche, P. F.; Tokunaga, A. T.

doi:10.1016/0019-1035(85)90174-5

Cited by 53 publications

(6 citation statements)

References 22 publications

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“…This diffuse comet was discovered by the IRAS spacecraft but was not reported to the Central Bureau for Astronomical Telegrams until a week later, when it was independently discovered by two ground‐based observers, only 8 days before closest approach! The nucleus of comet IRAS‐Araki‐Alcock was estimated to have a radius of ∼4 km [20] so it would have likely resulted in a major global catastrophe if it had struck the Earth.…”

Section: Discussionmentioning

confidence: 99%

Long‐period Comets and the Oort Cloud

Weissman

1997

Annals of the New York Academy of Sciences

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The long‐period comets pose a unique problem for the impact hazard problem. Because of their very long orbital periods and generally large distances from the Sun, they cannot be surveyed and catalogued in the same manner as the near‐Earth asteroids and short‐period comets. They appear at random, uniformly distributed on the celestial sphere. Current technologies can detect long‐period comets at distances of ∼5 AU, giving somewhat less than a one year warning time for potential Earth impactors. The mean impact probability for a long‐period comet crossing the Earth's orbit is 2.2 to 2.5 × 10−9 per perihelion passage. The mean impact velocity is ∼52 km sec−1, but the most probable impact energy is characterized by a velocity of 56 to 58 km sec−1. The estimated current impact rate for cometary nuclei large enough to create 10 km diameter (or larger) craters on the Earth is between 5 × 10−7 and 2.8 × 10−6 per year, with a best estimated value of 1.0 × 10−6 per year. Nuclei large enough to initiate global climatic disturbances strike the Earth, on average, every 16 Myr. The impact frequency may be increased substantially for brief periods of time during cometary showers, initiated by major perturbations of the Oort cloud. Improved technologies are needed to detect approaching long‐period comets at large heliocentric distances so as to increase the warning time for potential impactors.

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Section: Discussionmentioning

confidence: 99%

Long‐period Comets and the Oort Cloud

Weissman

1997

Annals of the New York Academy of Sciences

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“…This feature is apparently transient, since it was not present in spectra of comet Halley taken at the end of 1985 . Such a feature was not present in the spectrum of comet West 1976 VI (Oishi et al 1978) nor in comet IRAS-ArakiAlcock 1983 VI (Hanner et al 1985), but was recently detected in comet Wilson 19861 (Brooke et al 1987, Allen andWickramasinghe 1987).…”

Section: The 32-to 35-t~m Featurementioning

confidence: 92%

The 2.5–12 μm spectrum of comet halley from the IKS-VEGA experiment

Combes

Мороз

Crovisier

et al. 1988

Icarus

183

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The infrared instrument IKS flown on board the VEGA space probes was designed for the detection of emission bands of parent molecules, and for a measurement of the size and temperature of the thermal emitting nuclear region. The instrument had three channels with cooled detectors: an "imaging channel" designed to modulate the signal of the nucleus and two spectroscopic channels operating at 2.5-5 and 6-12 #m, respectively, equipped with circular variable filters of resolving power ~50. This paper presents and discusses the results from the spectral channels. On VEGA 1, usable spectra were obtained at distances D from the comet nucleus ranging from 250,000 to 40,000 km corresponding to fields of view 4000 and 700 km in diameter, respectively. The important internal background signal caused by the instrument itself, which could not be cooled, had to be eliminated. Since no sky chopping was performed, we obtain difference spectra between the current spectrum and a reference spectrum with little or no cometary signal taken at the beginning of the observing sequence (D ~ 200,000 km). Final discrimination between cometary signal and instrumental background is achieved using their different time evolution, since the instrumental background is proportional to the slow temperature drift of the instrument, and the cometary signal due to parent molecules or dust grains is expected to vary in first order as D -I.The 2.5-5 ~m IKS spectra definitely show strong narrow signals at 2.7 and 4.25 ~m, attributed to the ~; vibrational bands of H20 and CO2, respectively, and a broader signal in the region 3.2-3.5/tm, which may be attributed to CH-bearing molecules. All these signals present the expected D -1 intensity variation. Weaker emission features at 3.6 and 4.7 #m could correspond to the vl and l,s bands of H2CO and the (1 -0) band of CO, respectively. Molecular production rates are derived from the observed emissions, assuming that they are due to resonance fluorescence excited by the Sun's infrared radiation. For the strong bands of H20 and CO2, the rovibrational lines are optically thick, and radiative transfer is taken into account. We derive production rates, at the moment of the VEGA 1 flyby, of ~10 a° sec -1 for H20, ~2.7 x 1028 sec -1 for CO2, ~5 × 1028 sec -l for CO, and 4 xl02s sec -~ for H2CO, if attributions to CO and H2CO are correct. The production rate of carbon atoms in CH-bearing molecules is -9 x 10 29 sec -1 assuming fluorescence of molecules in the gas phase, but could be much less if the 3.2-3.5 pm emission is attributed to C-H stretch in polycyclic aromatic hydrocarbons or small organic grains. In addition, marginal features are present at 4.85 and 4.45 #m, tentatively attributed to OCS and molecules with the CN group, respectively. Broad absorption at 2.8-3.0 #m, as well as a narrow emission at 3.15/tm, which follow well the D -1 intensity variation, might be due to water ice. Emission at 2.8 /~m is also possibly present, and 404 0019-1035/88 $3.00 Copyright ,L~ 1988 by Academic Press, Inc. All rights o...

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“…Surface temperatures are also seen to exceed T eqBB in ground‐based observations of comets in which it is thought the majority of the infrared flux was due to the cometary nucleus rather than coma dust [ Hanner et al , 1985; Tokunaga and Hanner , 1985; Veeder et al , 1987]. Again, these higher temperatures are consistent with slow rotation of objects with dark surfaces.…”

Section: Aggregate Releasementioning

confidence: 93%

Release and fragmentation of aggregates to produce heterogeneous, lumpy coma streams

Clark

2004

J. Geophys. Res.

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[1] The unpredicted heterogeneity in particle number density in the coma of Wild 2 is consistent with delayed fragmentation to produce small particles from larger aggregates initially ejected from the cometary nucleus. The resultant heterogeneous inner coma results in stochastic variations in particle number and size distribution. Fragmentation can be accelerated after aggregate release by enhanced heating and one or more additional factors such as abrupt depressurization, phase transitions, exothermic chemical reactions, centrifugal forces, and electrostatic repulsion. Certain predicted characteristics of such in-flight disaggregation in coma particle streams correspond to known cometary phenomena.

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Infrared spectrophotometry of Comet IRAS-Araki-Alcock (1983d): a bare nucleus revealed?

Cited by 53 publications

References 22 publications

Long‐period Comets and the Oort Cloud

Long‐period Comets and the Oort Cloud

The 2.5–12 μm spectrum of comet halley from the IKS-VEGA experiment

Release and fragmentation of aggregates to produce heterogeneous, lumpy coma streams

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