Showing papers by "N. C. Wickramasinghe published in 1996"
TL;DR: In this article, a few tenths of a megatonne of carbonaceous particles with radii of several tens of Angstroms were observed in the cometary coma on March 26-28, 1996.
Abstract: X-ray fluxes observed from comet C/1996 B2 (Hyakutake) are readily explained in terms of scattering by carbonaceous particles with radii of several tens of Angstroms. A few tenths of a megatonne of such particles appear to have been present in the cometary coma on March 26-28, 1996.
30 citations
TL;DR: A mass contribution of graphite whiskers as small as 0.1% to the population of interstellar grains could dramatically change their far-infrared extinction properties as mentioned in this paper, with varying mass fractions and for different size parameters, the infrared extinction could vary from a λ-2 dependence to λ 0.
Abstract: A mass contribution of graphite whiskers as small as 0.1% to the population of interstellar grains could dramatically change their far-infrared extinction properties. With varying mass fractions of graphite whiskers, and for different size parameters, the infrared extinction could vary from a λ-2 dependence to λ0, consistent with the requirements of some astronomical observations.
23 citations
TL;DR: Giant comets are a major source of mass flux into the inner planetary system and their disintegration products may give rise to climatic cycles, ice epochs, periodic mass extinctions and other global disturbances.
Abstract: Giant comets thrown into short-period, Earth-crossing orbits are a major source of mass flux into the inner planetary system. Their disintegration products may give rise to climatic cycles, ice epochs, periodic mass extinctions and other global disturbances. Comets ≳100 kilometres in diameter, in chaotic orbits beyond Jupiter, probably constitute a more substantial current hazard than stray asteroids.
15 citations
TL;DR: A broad emission band over the wavelength range ∼ 6000-7500 A in submicron dust in the galaxy and in M82 can be explained by fluorescence phenomena in low-temperature chloroplasts and bacterial pigments.
Abstract: A broad emission band over the wavelength range ∼ 6000–7500 A in submicron dust in the galaxy and in M82 can be explained by fluorescence phenomena in low-temperature chloroplasts and bacterial pigments. Alternative explanations do not appear to be promising.
12 citations
TL;DR: The prodigious output of dust and CO observed in comet Hale-Bopp at a heliocentric distance of 6.5 AU is strongly suggestive of high-pressure release of material from liquified subsurface domains rather than thermal evaporation from a sunlit patch of frozen CO as discussed by the authors.
Abstract: The prodigious output of dust and CO observed in comet Hale-Bopp at a heliocentric distance of 6.5 AU is strongly suggestive of high-pressure release of material from liquified subsurface domains rather than thermal evaporation from a sunlit patch of frozen CO.
10 citations
TL;DR: In this article, the optical constants of a carbon polymorph, calculated using the Drude dispersion theory, are shown to lead to close agreements with the mean interstellar extinction curve over the waveband 0.3 ≤ λ-1 ≤ 5.5 μm-1 for particles of Rayleigh scattering sizes.
Abstract: The optical constants of a carbon polymorph, calculated using the Drude dispersion theory, are shown to lead to close agreements with the mean interstellar extinction curve over the waveband 0.3 ≤ λ-1 ≤ 5.5 μm-1 for particles of Rayleigh scattering sizes. Astrophysical microsoot grains of radii ≤50A may be related to microdiamond grains of similar sizes that have recently been discovered in carbonaceous chondrites. It is postulated that such microsoot particles could contribute to the nearly invariable interstellar extinction law observed over the near IR, visible and near to mid UV spectral regions. Admixtures of microsoot with micron-sized microsoot clumps, microdiamond and hollow organic / biologic grains provide an explanation for the full range of extinction and polarization data.
2 citations
TL;DR: In this paper, the authors present evidence for a giant comet, fragmented into subcomets on close encounter with Jupiter, and subsequently perturbed into Earth-crossing orbits, and the dynamics of dust from the disintegrating comet fragments favours retention in Earth crossing orbits of the sub-micron fraction of organic composition.
Abstract: The extended period of mass extinctions around the K/T boundary correlating with extraterrestrial amino acids in the sediment record constitutes strong evidence of a cometary cause. The input of extraterrestrial matter over 105 yr supports the hypothesis of a giant comet, fragmented into subcomets on close encounter with Jupiter, and subsequently perturbed into Earth-crossing orbits. Copious amounts of dust were emitted via this and possibly successive fragmenting encounters, and via normal cometary evaporation. The dynamics of dust from the disintegrating comet fragments favours retention in Earth-crossing orbits of the sub-micron fraction of organic composition. The shroud of dust accreted in the Earth’s upper atmosphere varied with time and imposed climatic stresses that caused species extinctions over 105 yr. While the iridium peak in the sediments coincides with the Chicxulub crater impactor, other iridium detail suggests that some of the impactor material was reinjected into space and in part re-accreted by Earth from the interplanetary orbits.
1 citations