Constraints on the composition of Jupiter's stratospheric aerosols from ultraviolet photometry

The absolute reflectivity of Jupiter has been obtained in 50 A-wide regions centering on 0.221, 0.233, 0.252, and 0.330 microns from three series of IUE satellite spectra taken in November 1979. The data indicate a strong decrease in reflectivity for latitudes greater than about 30 deg, in keeping with Voyager measurements. An additional 24 spectra were also obtained in a west-east series along the equator, as well as near 40 deg N latitude. These data favor models in which the haze particles have effective radii within a factor of 2 of 0.2 microns. Near the equator, the haze aerosols produce much less absorption than near 40 deg N; the aerosol distributions and optical properties derived are noted to be more dependent on the assumed location and reflectivity of the top of the tropospheric cloud

Absorption of sunlight in the atmosphere of Venus

The profiles of upward, downward and net solar flux on Venus were measured at altitudes from about 62 km to the surface in three spectral bands at a vertical resolution of a few hundred meters. These data measured the penetration and absorption of solar energy in Venus' lower atmosphere quantities that are essential in evaluating the role of the greenhouse mechanism in supporting Venus' remarkably high surface temperature. In addition, the data constrained the vertical structure and optical properties of the Venus clouds

The single scattering phase functions of Jupiter's clouds

The determination of the single scattering phase functions of Jupiter's clouds and a thin upper haze by Tomasko et al. was refined and extended to seven latitudes in blue and red light. The phase function is well-constrained by the Pioneer 10 and 11 photometric data sets. Multiple scattering models were computed to match the limb darkening at each latitude at up to 15 phase angles from 12 deg to 151 deg. Ground-based observations were used for absolute calibration and to extend the data to lower phase angles. The phase functions were parameterized using the double Henyey-Greenstein function. The three Henyey-Greenstein parameters and the single scattering albedo were determined using a non-linear least squares method for the haze and the clouds below. The phase functions derived for the northen zone and belt are remarkably similar to the phase functions of the corresponding regions in the south, with most of the differences in brightness of the northern and southern features resulting from minor differences in single scattering albedo. Analysis of the Equatorial Region is complicated by the presence of numerous small features, but the phase function required is generally similar to that seen in the more homogeneous regions. Details of the phase functions of the haze and clouds are presented, and the differences between the cloud phase functions at low and high latitudes in red and blue light are discussed

Spectrophotometry of planets, asteroids and satellites from the international ultraviolet explorer satellite

A total of 14 8 hour I.U.E. observing sessions resulted in 39 spectra of 11 asteroids and 9 solar type stars as well as 57 spectra at various locations on the disk of Jupiter. The Jupiter observations include a total of 5 center to limb series of spectra at various latitudes and a North South series along the central meridian. In the range from 2000-3000 A, the planet shows a striking decrease in brightness at latitudes greater than about 30 degrees, and exhibits limb brightening at low latitudes and limb darkening at high latitudes. Preliminary results indicate that about 6 km-amagats of clean hydrogen are required above a haze of absorbing aerosols to reproduce the limb brightening observed at 2500 A in the equatorial regions. At higher latitudes, the aerosols extend to even higher levels of the atmosphere. Comparison of the Jovian data with detailed model calculations and the analyses of the asteroid spectra are still in progress with other support

A grid of polarization models for Rayleigh scattering planetary atmospheres

We investigate the intensity and polarization of reflected light from planetary atmospheres. We present a large grid of Monte Carlo simulations for planets with Rayleigh scattering atmospheres. We discuss the disk-integrated polarization for phase angles typical of extrasolar planet observations and for the limb polarization effect observable for solar system objects near opposition. The main parameters investigated are single scattering albedo, optical depth of the scattering layer, and albedo of an underlying Lambert surface for a homogeneous Rayleigh scattering atmosphere. We also investigate atmospheres with isotropic scattering and forward scattering aerosol particles, as well as models with two scattering layers. The model grid provides a tool for extracting quantitative results from polarimetric measurements of planetary atmospheres from solar system planets and extrasolar planets, in particular on the scattering properties and stratification of particles in the highest atmosphere layers. Spectropolarimetry of solar system planets offers complementary information to spectroscopy and polarization flux colors can be used for a first characterization of exoplanet atmospheres. From limb polarization measurements, one can set constraints on the polarization at large phase angles.Comment: 19 pages, 21 figures. Minor changes. Published in Astronomy and Astrophysic

Study of spin-scan imaging for outer planets missions: Executive summary

The development and characteristics of spin-scan imagers for interplanetary exploration are discussed. The spin-scan imaging photopolarimeter instruments of Pioneer 10 and 11 are described. In addition to the imaging function, the instruments are also used in a faint-light mode to take sky maps in both radiance and polarization. The performance of a visible-infrared spin-scan radiometer (VISSR), which operates in both visible and infrared wavelengths, is reported

Gaussian quadrature exponential sum modeling of near infrared methane laboratory spectra obtained at temperatures from 106 to 297 K

Transmission measurements made on near-infrared laboratory methane spectra have previously been fit using a Malkmus band model. The laboratory spectra were obtained in three groups at temperatures averaging 112, 188, and 295 K; band model fitting was done separately for each temperature group. These band model parameters cannot be used directly in scattering atmosphere model computations, so an exponential sum model is being developed which includes pressure and temperature fitting parameters. The goal is to obtain model parameters by least square fits at 10/cm intervals from 3800 to 9100/cm. These results will be useful in the interpretation of current planetary spectra and also NIMS spectra of Jupiter anticipated from the Galileo mission

Study of spin-scan imaging for outer planets missions

The constraints that are imposed on the Outer Planet Missions (OPM) imager design are of critical importance. Imager system modeling analyses define important parameters and systematic means for trade-offs applied to specific Jupiter orbiter missions. Possible image sequence plans for Jupiter missions are discussed in detail. Considered is a series of orbits that allow repeated near encounters with three of the Jovian satellites. The data handling involved in the image processing is discussed, and it is shown that only minimal processing is required for the majority of images for a Jupiter orbiter mission

New laboratory measurements of CH4 in Titan's conditions and a reanalysis of the DISR near-surface spectra at the Huygens landing site

International audienceLaboratory spectra of methane-nitrogen mixtures have been recorded in the near-infrared range (1.0 - 1.65 µm) in conditions similar to Titan's near surface, to facilitate the interpretation of the DISR/DLIS spectra taken during the last phase of the descent of the Huygens Probe, when the surface was illuminated by a surface science lamp. We used a 0.03 cm-1 spectral resolution, adequate to resolve the lines at high pressure (pN2 ~ 1.5 bar). By comparing the laboratory spectra with synthetic calculations in the well-studied ν2 + 2ν3 band (7515-7620 cm-1), we determine a methane absorption column density of 178±20 cm-am and a temperature of 118±10 K in our experiment. From this, we derive the methane absorption coefficients over 1.0-1.65 µm with a 0.03 cm-1 sampling, allowing for the extrapolation of the results to any other methane column density under the relevant pressure and temperature conditions. We then revisit the calibration and analysis of the Titan "lamp-on" DLIS spectra. We infer a 5.1±0.8 % methane mixing ratio in the first 25 m of Titan's atmosphere. The CH4 mixing ratio measured 90 sec after landing from a distance of 45 cm is found to be 0.92±0.25 times this value, thus showing no post-landing outgassing of methane in excess of ̴ 20 %. Finally, we determine the surface reflectivity as seen from 25 m and 45 cm and find that the 1500 nm absorption band is deeper in the post-landing spectrum as compared to pre-landing

Albedo and Reflection Spectra of Extrasolar Giant Planets

We generate theoretical albedo and reflection spectra for a full range of extrasolar giant planet (EGP) models, from Jovian to 51-Pegasi class objects. Our albedo modeling utilizes the latest atomic and molecular cross sections, a Mie theory treatment of extinction by condensates, a variety of particle size distributions, and an extension of the Feautrier radiative transfer method which allows for a general treatment of the scattering phase function. We find that due to qualitative similarities in the compositions and spectra of objects within each of five broad effective temperature ranges, it is natural to establish five representative EGP albedo classes: a ``Jovian'' class (T$_{\rm eff} \lesssim 150$ K; Class I) with tropospheric ammonia clouds, a ``water cloud'' class (T$_{\rm eff} \sim 250$ K; Class II) primarily affected by condensed H$_2$O, a ``clear'' class (T$_{\rm eff} \gtrsim 350$ K; Class III) which lacks clouds, and two high-temperature classes: Class IV (900 K $\lesssim$ T$_{\rm{eff}}$ $\lesssim$ 1500 K) for which alkali metal absorption predominates, and Class V (T$_{\rm{eff}}$ $\gtrsim$ 1500 K and/or low surface gravity ($\lesssim$ 10$^3$ cm s$^{-2}$)) for which a high silicate layer shields a significant fraction of the incident radiation from alkali metal and molecular absorption. The resonance lines of sodium and potassium are expected to be salient features in the reflection spectra of Class III, IV, and V objects. We derive Bond albedos and effective temperatures for the full set of known EGPs and explore the possible effects of non-equilibrium condensed products of photolysis above or within principal cloud decks. As in Jupiter, such species can lower the UV/blue albedo substantially, even if present in relatively small mixing ratios.Comment: revised LaTeX manuscript accepted to Ap.J.; also available at http://jupiter.as.arizona.edu/~burrows/paper