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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.11.004 Byline: Sergey L. Gratiy (a), Andrew C. Walker (b), Deborah A. Levin (a), David B. Goldstein (b), Philip L. Varghese (b), Laurence M. Trafton (b), Chris H. Moore (b) Keywords: Radiative transfer; Io; Atmospheres, Dynamics; Atmospheres, Structure; Satellites, Atmospheres Abstract: Conflicting observations regarding the dominance of either sublimation or volcanism as the source of the atmosphere on Io and disparate reports on the extent of its spatial distribution and the absolute column abundance invite the development of detailed computational models capable of improving our understanding of Io's unique atmospheric structure and origin. Improving upon previous models, Walker et al. (Walker, A.C., Gratiy, S.L., Levin, D.A., Goldstein, D.B., Varghese, P.L., Trafton, L.M., Moore, C.H., Stewart, B. [2009]. Icarus) developed a fully 3-D global rarefied gas dynamics model of Io's atmosphere including both sublimation and volcanic sources of SO.sub.2 gas. The fidelity of the model is tested by simulating remote observations at selected wavelength bands and comparing them to the corresponding astronomical observations of Io's atmosphere. The simulations are performed with a new 3-D spherical-shell radiative transfer code utilizing a backward Monte Carlo method. We present: (1) simulations of the mid-infrared disk-integrated spectra of Io's sunlit hemisphere at 19[mu]m, obtained with TEXES during 2001-2004; (2) simulations of disk-resolved images at Lyman-[alpha] obtained with the Hubble Space Telescope (HST), Space Telescope Imaging Spectrograph (STIS) during 1997-2001; and (3) disk-integrated simulations of emission line profiles in the millimeter wavelength range obtained with the IRAM-30m telescope in October-November 1999. We found that the atmospheric model generally reproduces the longitudinal variation in band depth from the mid-infrared data; however, the best match is obtained when our simulation results are shifted [approximately equal to]30[degrees] toward lower orbital longitudes. The simulations of Lyman-[alpha] images do not reproduce the mid-to-high latitude bright patches seen in the observations, suggesting that the model atmosphere sustains columns that are too high at those latitudes. The simulations of emission line profiles in the millimeter spectral region support the hypothesis that the atmospheric dynamics favorably explains the observed line widths, which are too wide to be formed by thermal Doppler broadening alone. Author Affiliation: (a) Department of Aerospace Engineering, Pennsylvania State University, University Park, PA 16802, USA (b) Department of Aerospace Engineering, University of Texas at Austin, Austin, TX 78712, USA Article History: Received 19 June 2009; Revised 29 October 2009; Accepted 4 November 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.01.002 Byline: Hiroshi Kobayashi (a)(b), Sei-ichiro Watanabe (b), Hiroshi Kimura (c)(a), Tetsuo Yamamoto (a) Keywords: Celestial mechanics; Interplanetary dust; Debris disk Abstract: Dust particles exposed to the stellar radiation and wind drift radially inward by the Poynting-Robertson (P-R) drag and pile up at the zone where they begin to sublime substantially. The reason they pile up or form a ring is that their inward drifts due to the P-R drag are suppressed by stellar radiation pressure when the ratio of radiation pressure to stellar gravity on them increases during their sublimation phases. We present analytic solutions to the orbital and mass evolution of such subliming dust particles, and find their drift velocities at the pileup zone are almost independent of their initial semimajor axes and masses. We derive analytically an enhancement factor of the number density of the particles at the outer edge of the sublimation zone from the solutions. We show that the formula of the enhancement factor reproduces well numerical simulations in the previous studies. The enhancement factor for spherical dust particles of silicate and carbon extends from 3 to more than 20 at stellar luminosities L.sub.a=0.8-500L.sub.a, where L.sub.a is solar luminosity. Although the enhancement factor for fluffy dust particles is smaller than that for spherical particles, sublimating particles inevitably form a dust ring as long as their masses decrease faster than their surface areas during sublimation. The formulation is applicable to dust ring formation for arbitrary shape and material of dust in dust-debris disks as well as in the Solar System. Author Affiliation: (a) Institute of Low Temperature Science, Hokkaido University, Kita-Ku Kita 19 Nishi 8, Sapporo 060-0819, Japan (b) Department of Earth and Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan (c) Center for Planetary Science, Graduate School of Science, Kobe University, Nada-ku Rokkodai-cho 1-1, Kobe 657-8501, Japan Article History: Received 7 March 2008; Revised 16 October 2008; Accepted 8 January 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.12.022 Byline: V.V. Zakharov (a)(b), A.V. Rodionov (c), G.A. Lukianov (b), J.F. Crifo (d) Keywords: Atmospheres; structure; Comets; Comets; dust Abstract: We use our newly developed Dust Monte-Carlo (DMC) simulation technique [Crifo, J.F., Lukianov, G.A., Rodionov, A.V., Zakharov, V.V., 2005. Icarus 176, 192-219] to study the dynamics of dust grains in the vicinity of some of the benchmark aspherical, homogeneous cometary nuclei and of the benchmark spherical, inhomogeneous nuclei studied by us precedingly. We use the interim unrealistic simplifying assumptions of grain sphericity, negligible nucleus rotation rate, and negligible tidal force, but take accurately into account the nucleus gravitational force, gas coma aerodynamic force, and solar radiation pressure force, and consider the full mass range of ejectable spherical grains. The resulting complicated grain motions are described in detail, as well as the resulting complicated and often counter-intuitive dust coma structure. The results are used to answer several important questions: (1) When computing coma dust distributions, (a) is it acceptable to take into consideration only one or two of the above mentioned forces (as currently done)? (b) to which accuracy must these forces be known, in particular is it acceptable to represent the gravity of an aspherical nucleus by a spherically symmetric gravity? (c) how do the more efficient but less general Dust Multi-Fluid (DMF) computations compare with the DMC results? (2) Are there simple structural relationships between the dust coma of a nucleus at small heliocentric distance r.sub.h, and that of the same nucleus at large r.sub.h? (3) Are there similarities between the gas coma structures and the associated dust coma structures? (4) Are there dust coma signatures revealing non-ambiguously a spherical nucleus inhomogeneity or an homogeneous nucleus asphericity? (5) What are the implications of the apparently quite general process of grain fall-backs for the evolution of the nucleus surface, and for the survival of a landed probe? Author Affiliation: (a) LESIA, Observatoire de Paris, F 92195 Meudon Cedex, France (b) Center for Advanced Studies, St.-Petersburg State Technical University, Polytechnicheskaya str., 29, 195251 St.-Petersburg, Russia (c) Central Research Institute on Machine Building (TsNIIMASH), Pionyerskaya st., 4, Korolev, Moscow Region 141070, Russia (d) Service d'Aeronomie du CNRS, BP 3, F 91371 Verrieres le Buisson Cedex, France Article History: Received 7 May 2008; Revised 19 November 2008; Accepted 12 December 2008

This paper traces the evolution of James Jeans' views on radiation theory. The first recounts the sources and details of his initial staunch opposition to the validity of Planck's law in describing the spectral distribution of radiant energy in a black body. In particular I take issue with how some commentators (Poincare in 1913, Kuhn in 1978) have understood Jeans' position. During 1910, Jeans repositioned himself on the side of quantum theory. The second part exhibits how this shift of allegiance had both empirical reasons (the inability of classical theory to account for the observed laws of radiation) and theoretical reasons (arguments showing the necessity and sufficiency of the quantum hypothesis for Planck's law).