Claude Emerich

HST far-ultraviolet imaging of Jupiter during the impacts of comet Shoemaker-Levy 9

Hubble Space Telescope far-ultraviolet images of Jupiter during the Shoemaker-Levy 9 impacts show the impact regions darkening over the 2 to 3 hours after the impact, becoming darker and more extended than at longer wavelengths, which indicates that ultraviolet-absorbing gases or aerosols are more extended, more absorbing, and at higher altitudes than the absorbers of visible light. Transient auroral emissions were observed near the magnetic conjugate point of the K impact site just after that impact. The global auroral activity was fainter than average during the impacts, and a variable auroral emission feature was observed inside the southern auroral oval preceding the impacts of fragments Q1 and Q2.

On the analysis of the H Lyman-α dayglow of Jupiter, Saturn and Uranus

Abstract A new radiative transfer model, particularly well adapted to calculations in inhomogeneous atmospheres, has been applied, during the last 4 years, to analyse new and older Lyman-α airglow data from three giant planets. We review all the results obtained so far. Several features which were not accounted for by using the previous transfer codes have been satisfactorily simulated, using essentially the scattering of the solar and the interplanetary Lyman-α lines by hydrogen in the upper atmospheres. The search for a good fit both in intensity and in shape of the limb to limb data, and/or of the line profiles, provided constraints on the dynamics of the atmospheres, through the estimate of either the eddy diffusion coefficient, the total [H] column density, or of the possibility of some nonthermal turbulence processes at high altitude. Consequently, the need for an “electroglow” process for the Lyman-α emission was considerably reduced and may be dismissed in the majority of cases.

A model for the disc Lyman alpha emission of Uranus

A new efficient radiative transfer algorithm for inhomogeneous atmospheres has been used to simulate the limb to limb Lyman α reflectivities observed with the Voyager ultraviolet spectrometer during the flyby of Uranus. It was shown that complete frequency redistribution should be adequate to describe the disc emissions. The model atmosphere used was derived using a combination of Voyager measurements and modeling. Atomic H densities calculated had sources derivable directly from solar FUV and EUV fluxes. To fit the observations, four contributions are evaluated: (1) the resonance scattering of solar Lyman α radiation, (2) Rayleigh-Raman scattering of solar Lyman α radiation, (3) the resonance scattering of interplanetary Lyman α radiation, and (4) a possible internal source of unknown origin. From comparison with the observations, and provided that the published Voyager calibrations are correct, it is shown that only atmospheres with low eddy diffusion coefficients (KH ≤ 100 cm² s−1) and an internal source could simulate both the shape and the strength of the measured disc emission. The main results are then that the direct solar Lyman α scattering contribution (type 1 plus type 2) is of the order of 760 R, the scattering of interplanetary Lyman α contributes about 320 R, and a small additional internal source providing about 100–500 R is needed to match the measurements. Further, the analysis of the disc intensities suggests that there is no strong variation of K with latitude.

Far-UV emissions from the SL9 impacts with Jupiter

Observations with the International Ultraviolet Explorer (IUE) during the impacts of the fragments of comet D/Shoemaker-Levy 9 with Jupiter show far-UV emissions from the impact sites within a ∼10 min time scale. Positive detections of H2 Lyman and Werner band (1230–1620 A) and H-Lyα emissions are made for impacts K and S, and marginally for P2. No thermal continuum is observed. The radiated far-UV output was >1021 ergs. The H2 spectrum is consistent with electron collisional excitation if significant CH4 absorption is included. Such emissions could result from plasma processes generated by the impacts. Non-thermal excitation by the high altitude entry and explosion shocks may also be relevant. Emissions by Al+ (1671 A) and C (1657 A) of cometary origin are tentatively identified.

An Early Report on Iue Observations of the Impact of Comet Shoemaker-Levy With Jupiter

W. M. Harris, G. E. Ballester, J. Barker, J. Clarke, M. Combi, M. Vincent (U. Michigan, USA), R. Gladstone (SRI, USA), J. Kozyra (U. Michigan, USA), R. Prangi (IAS, France), L. Ben Jaffel (IAP, France), J.-P. Bibring, C. Emerich (IAS, France), W. Ip (Max Planck I., Germany), S. Miller (U.C.L., UK), D. Rego (IAS, France), D. Southwood, and M. Dougherty (I.C.L., UK), T. A. Livengood (NASA/GSFC, USA), S.A. Budzien (NRL, USA), F. Espenak (NASA/GSFC, USA), G.F.Fireman (CSC, USA), T. Kostiuk (NASA/GSFC, USA), M. A. McGrath (STScI, USA), P. D. Feldman, D.T. Hall, D.F. Strobel, H.W. Moos (Johns Hopkins U, USA), L.M. Woodney (U. Maryland, USA)