D. G. W. Smith

The upper Jovian atmosphere aerosol content determined from a satellite eclipse observation

The Galilean satellite eclipse technique for measuring the aerosol distribution in the upper Jovian atmosphere is described and applied using 30 color observations of the 13 May 1972 eclipse of Ganymede obtained with the 5-m Hale telescope. This event probes the South Temperate Zone. The observed aerosol lies above the visible cloud tops, is very tenuous and varies with altitude, increasing rapidly with downward passage through the tropopause. The aerosol extinction coefficient, κa (λ1.05 μm), is ∼1.1 × 10−9 cm−1 in the lower stratosphere and ∼1.1 × 10−8 cm−1 at the tropopause. The 1σ uncertainty in these values does not exceed 50% The observations require some aerosol above the tropopause but do not clearly determine its structure. The present analysis emphasizes an extended haze distribution, but the alternate possibility is not excluded that the stratospheric aerosol resides in a thin layer. The aerosol extinction increases with decreasing wavelength and indicates the particle radius to be ⩽0.2 μm. Larger radii are impossible. These overall results confirm Axels (1972) suggestion of a small quantity of dust above the Jovian cloud tops and the optical depths are consistent with those required to explain the low uv albedo.

Spectrophotometry of J8, J9, and four Trojan asteroids from 0.32 to 1.05 μm

Abstract New 30-channel narrowband photometry from 0.32 to 1.05 μm of the retrograde Jovian satellites J9 (to 0.7 μm) and J8 and the trailing Trojan asteroids 617, 884, 1172, and 1173 is presented. The data confirm previous measurements of J8, 617, 884, and 1172 at λ μ m, but the extension into the infrared shows that the normalized spectral reflectance of these objects rises steadily from ∼0.8 at 0.4 μ m to ∼ 1.4 at 1.05 μ m, suggesting they are too bright in the near infrared to be C-type asteroids. The C classification of 1173 is confirmed. J9 is markedly redder than J8 at visible wavelengths. The results indicate a greater taxonomic contrast between these distant objects and main-belt asteroids than previously thought.

Galilean satellite eclipse studies II. Jovian stratospheric and tropospheric aerosol content

Abstract The Galilean satellite eclipse technique for measuring the aerosol distribution in the Jovian lower stratosphere and upper troposphere is described and applied using 30 color observations of 12 natural satellite eclipses obtained with the 200-in Hale telescope. These events probe the North and South Polar Regions, the North Temperate Belt, the South Equatorial Belt, the South Tropical Zone, the South Temperate Zone, and the Great Red Spot. Aerosol is found above the visible cloud tops in all locations. It is very tenuous and varies with altitude, increasing rapidly with downward passage through the tropopause. The aerosol extinction coefficient at 1.05 μm is 1.0 ± 0.05 × 10 −8 cm −1 at the tropopause and the mass density is a few times 10 −13 g cm −3 . The observations require some aerosol above the tropopause but do not clearly determine its structure. The present analysis emphasizes an extended haze distribution, but the alternate possibility that the stratospheric aerosol resides in a thin layer is not excluded. The vertical aerosol optical depth above the tropopause at 1.05 μm exceeds 0.04 in the NPR, SPR, NTB, SEB, and StrZ, is ∼0.006 ± 0.003 in the STZ, and is ∼ 0.003 ± 0.001 above the GRS. The aerosol extinction increases with decreasing wavelength in the STZ and NTB and indicates a particle radius of 0.2–0.5 μm; a radius of ∼0.9 μ m is indicated in the STrZ.

Measurement of stratospheric aerosol on Saturn using an eclipse of Titan

Abstract An eclipse of Titan by Saturn was observed on December 20, 1979, to measure the aerosol content in the atmosphere of Saturn. The measurements were made with the 74-in. telescope of the Helwan Observatory, Egypt, in the bandpass 6300–7300 A and extend to ∼5 magnitudes of eclipse darkening. The faint portion of the lightcurve unambiguously requires the presence of aerosol in the lower stratosphere of Saturn. The aerosol extends to at least 20 km above the tropopause and has a one-way stratospheric vertical optical depth of 0.4−0.02+0.04 at 6700 A. The results apply to the sunset terminator at a cronographic latitude of 23°S.

Galilean satellite eclipse studies I. Observations and satellite characteristics

Abstract Spectrophotometric light curves of 12 Galilean satellite eclipses are reported. The observations were made in 20 to 30 channels over the wavelength range 3240 to 10,500 A using the 200-in. telescope. The initial data processing is described. These data measure the Jovian aerosol content in the lower stratosphere and uppermost troposhere and the methane abundance in the lower stratosphere. The data are consistent with a lack of limb darkening on the Galilean satellites. The orbit of Callisto is shown to be inclined 0.08 ± 0.02° to the equatorial plane of Jupiter.

Galilean satellite eclipse studies: III. Jovian methane abundance

Abstract The methane abundance in the lower Jovian stratosphere is measured using Galilean satellite eclipse light curves. Spectrally selective observations in and between absorption bands are compared. An average mixing ratio at the locations measured is [CH 4 ]/[H 2 ] ∼ 1.3 × 10 −3 , larger than the value 0.9 × 10 −3 expected for a solar abundance of carbon. Some zenographic variation of the mixing ratio may occur. Observationally compatible values are 1.3–2.0 × 10 −3 in the STZ, 1.3– 2.6 × 10 −3 on the GRS/STrZ edge, and 0.7–1.3 × 10 −3 in the GRS.

Eclipse spectrophotometry of the Galilean satellites

Abstract Narrowband spectrophotometry of satellite eclipses is presented for each of the Galilean satellites. Comparing the partially eclipsed full-phase satellite disk to the uneclopsed disk can reveal colorimetric inhomogeneities on the surface. The trailing half-disk of Ganymede is slightly blue compared to the leading half-disk. The trailing and leading half-disks of Callisto are similar to each other, as are the northern and southern half-disks. The northern half-disk shows evidence of blue and red portions. The trailing half-disk of Europa is redder than the leading half-disk.

Mid-eclipse brightening of the Galilean satellites

Brinkmann (1973) has suggested that the Galilean satellites might briefly manifest a brightening at mid-eclipse due to a concentration of light refracted into the geometric umbra of Jupiter by the atmosphere around the terminator. Results obtained using two different models of the Jovian atmosphere indicate that such a brightening is unlikely even for Callisto due to the probable aerosol concentration in the Jovian atmosphere at the relevant altitudes.

Atmospheric Properties of Jupiter Determined from Galilean Satellite Eclipse Light Curves

Twelve eclipse light curves for the Galilean satellites have been observed at 30 colors. The shape of the curves depend upon Jovian atmospheric properties such as Rayleigh scattering, aerosol distribution, molecular absorption, scale height and cloud top altitude, as well as the satellite diameter. Different zenographic latitudes and longitudes along the sunrise and sunset terminator have been observed. Very long absorption path lengths are obtained compared to normal incidence because of the tangential passage of the Sun’s rays. Refractive tails are observed in most cases which allow aerosol distributions to be determined. The other atmospheric properties may also be derived.