Voyager U.V. spectrometer observations of He 584 Å dayglow at Jupiter

The intensity of Jupiter's He 584 Å airglow has been measured by the Voyager U.V. spectrometers. The disc-averaged brightness is about 4 Rs and limb darkening is present. The intensity probably varies with longitude, the variation being out of phase with the H Lyman-α intensity bulge. Modelling of resonance scattering of the solar He 584 Å line by Jupiter's atmosphere has shown that the hydrogen and helium emissions can be explained about equally well by at least two self-consistent scenarios involving the structure (temperature and eddy diffusion coefficient) and excitation of the atmosphere. All our evidence points to a dramatic change of conditions in the Jovian atmosphere in the time between Pioneer and Voyager encounters.     

Strong interaction between the ring system and the ionosphere of saturn

An abnormally low electron density in the Saturnian ionosphere observed by the radio occultation experiment of the Pioneer 11 may be explained in terms of the contamination of water in the Saturnian upper atmosphere from its ring system.     

The origin and evolution of the atmospheres of the terrestrial planets

The chemical nature of the Earth's atmosphere is determined by its interaction with the biosphere, hydrosphere and lithosphere. Detailed balance is maintained over long time periods by a complex series of cyclical processes. The chemical differences between the atmosphere of the Earth, on the one hand, and the atmospheres of Venus and Mars, on the other, can be understood in terms of the greater complexity of the terrestrial interactions. When this has been taken into account, the origin of all three planetary atmospheres can be explained as resulting from degassing. Despite the similarity of the atmospheres of Venus and Mars, it seems necessary to invoke different mechanisms for the low amount of water vapour on each.     

Compton effect interpretation of solar red shift

The hypothesis that the solar red shift is due to Compton scattering of solar radiation through the electrons in the solar atmosphere predicts a variation in magnitude of the red shift with position in good agreement with observation. Quasar red shifts may be similarly explained.     

Jupiter's zone-belt structure at radio wavelengths: II. Comparison of observations with model atmosphere calculations

Model atmosphere calculations are presented which simulate high-resolution maps of Jupiter's radio emission. They are compared with observations recently obtained at the Very Large Array at 1.3, 2.0, 6.1, and 20.5 cm with resolutions ranging from 0.075 to 0.218 Jovian radii (I. de Pater and J. R. Dickel (1986). Jupiter's zone-belt structure at radio wavelengths. I. Observations. Astrophys. J., in press). The models indicate that ammonia gas is strongly depleted in the upper atmosphere with respect to the solar value both in zones and belts. At very high levels in the atmosphere (P < 0.3−0.5 bar) the gas is undersaturated and distributed uniformly over the planet. In the cloud formation region (0.5 < P < 2 bar), the ammonia depletion is largest in the belts, where it extends down to depths corresponding to 1.8–2 bar. In the zones, the lower ammonia abundances are found down to pressures of 1 bar. Deeper into the Jovian atmosphere, at pressures ≥2.2 bar, the gas is overabundant relative to the solar value by nearly a factor of 2 in both zones and belts. The altitude distribution of the ammonia gas is explained in terms of chemistry, cloud physics, and atmospheric dynamics. The undersaturation at high levels in the atmosphere is attributed to photodissociation of ammonia gas under influence of solar UV photons, coupled with Jupiter's meteorology (up- and downward drafts in the atmosphere). The general depletion of this gas throughout Jupiter's upper atmosphere may be caused by trapping of the gas in a layer of NH₄SH particles, and/or in an aqueous ammonia cloud. The cloud deck responsible for trapping ammonia gas is thicker above zones than belts. If the observed depletion of ammonia gas is entirely due to trapping in an NH₄SH cloud, the difference in thickness of this cloud between zones and belts gives rise to a temperature difference of 3–4°K between the two regions. This temperature difference may trigger the zonal wind motions in Jupiter's atmosphere near the cloud tops.     

Empirische Atmosphärenmodelle zur Erklärung des Lichtwechsels magnetischer Sterne

Empirical model atmospheres on the basis of MIHALAS models were investigated. If the temperature of the outer layers in a spot is higher than in the surrounding normal atmosphere and lower than in the deeper layers, many characteristics of the observed amplitude-wavelength relation of magnetic stars can be explained.     

Mapping methane in Martian atmosphere with PFS-MEX data

In this study we map the methane gas in the Martian atmosphere. The main goal of this work is to show the methane behaviour across the planet seasonally. To this aim, we analyze the strongest methane band in the short wavelength channel of the Planetary Fourier Spectrometer (PFS) on board ESA Mars Express (MeX) spacecraft. The optical line depth is used to derive the column density of methane. The maps thus obtained show the spatial variability of this non-condensable gas and how the gas is transported in the atmosphere due to the cycle of carbon dioxide. Moreover, the increase of methane over the north polar cap during local summer, which cannot be explained by global circulation, strongly suggests that there could be methane reservoir associated with the polar cap.     

On the relationship of 6300 Å airglow to parameters of the F-region of the ionosphere

It is shown that variations in 6300 Å airglow intensities can, under certain assumptions, be simply related to $\text{?}{}_0\text{F2}$ and its time derivative. In deriving the relationship it is not necessary to assume that the concentration of the neutral atmosphere remains constant and so the relationship is useful on occasions when changes in the neutral atmosphere do occur making it difficult to obtain agreement between observed and calculated 6300 Å intensities; An example is given of a night in which a post-midnight enhancement occurred in the airglow and for which the observations could not be reproduced using a neutral atmosphere constant with time. It is shown that the airglow variations can be explained in terms of the variations of f₀F2, implying that the airglow is due to recombination and that, during the night, changes occurred in the concentrations of the constituents of the neutral atmosphere.     

Reflectionless propagation of acoustic waves in the solar atmosphere

The possibility that vertical acoustic waves with frequencies lower than the cutoff frequency corresponding to the temperature minimum pass this minimum is investigated. It is shown that the averaged temperature profile in the solar atmosphere can be approximated by several so-called reflectionless profiles on which the acoustic waves propagate without internal reflection. The possibility of the penetration of vertical acoustic waves, including low-frequency ones, into the solar corona is explained in this way.     

Origin of tektites: Constraints from heavy noble gas concentrations

Abstract— Heavy noble gas concentrations in tektites (splash-form type) are considerably lower than those in impact glasses. This can not be explained only by high formation temperatures for tektites, as might be expected from low concentrations of water and most volatile elements in tektites, and indicates that tektites solidified in an atmosphere with an ambient pressure of much less than 1 atm. The heavy noble gas concentrations may be an indicator of the height to which tektites were carried by the impact before they solidified.     

Presence of a primary solar-type atmosphere around the earth: evidence of dissolved noble gas

Recent noble gas data of mantle-derived samples show that there are two end members: PLUME-type and MORB-type. The estimated high ³He and ²²Ne abundances of the PLUME source, possibly representing the lower mantle, should reflect the remnant of dissolved solar-type atmosphere. Calculations of the structure of the primary atmosphere and the noble gas dissolution into the magma ocean of the accreting planet suggest that the high ³He and ²²Ne abundances can be explained if the primary atmosphere persisted until M0.4–0.6 M_E (M_E being the present Earth mass). The PLUME source has higher ³He/⁴He and lower ²¹Ne/²²Ne than the MORB source. This is explained by assuming that the lower mantle was less degassed during magma ocean cooling. The carbon abundance in the mantle can be constrained from the estimated abundance of mantle ³He and C/³He data of the present mantle-derived samples. Dissolved solar-type noble gas might explain high noble gas abundance in the present Venus, if the primary atmosphere persisted until the final stage of accretion under lower dust opacity of the atmosphere.     

Tunnel-effect and propagation of 5-min oscillations in the solar atmosphere

Summary Tunneling of surface waves (which are also called non-propagating or evanescent mode) in isothermal atmosphere is considered. Tunneling of 5-min oscillations in solar atmosphere is discussed. Phase lead of chromospheric oscillations with respect to photospheric oscillations (Tanenbaum et al., 1971) can be explained by tunneling only.     

Parameters of irradiated accretion disks from optical and X-ray observations of GS 1826-238

We show that the set of observational characteristics for low-mass X-ray binaries in the optical and X-ray bands can be explained in terms of the model of an optically thick accretion disk with an atmosphere irradiated by a central X-ray source. We show that this set of observational data can be successfully used to measure the orbital inclination of a binary, the geometric parameters of its accretion disk, and the reprocessing time of X-emission to optical one. For the burster GS 1826-238, a low-mass X-ray binary with a neutron star, we have estimated the binary inclination and the thickness of the disk atmosphere at the outer edge from the mean optical flux and the amplitude of periodic modulations in the optical light curve: i = 62.5° ± 5.5° and H _d/R _d = 0.145 ± 0.009. The optical response time of the binary to an X-ray burst disagrees with the geometric delay in the propagation of X-ray photons in the binary. We believe that this points to a finite X-ray reprocessing/reradiation time, 1.0 s ≲ τ _repr ≲ 2.2 s, in the hot atmosphere above the accretion disk.     

UBV photoelectric photometry of the 1976–1978 eclipse of VV Cephei

This paper presents the result of UBV photoelectric photometry of VV Cephei. The contact times are determined from the B-V and U-B curves. The epoch of mideclipse is JD 2443361 in agreement with prediction. The unequal depths of the falling and rising branches of the colour curves can be explained by gas streaming from the M-type supergiant component. The radius of the M-type supergiant is about 1860 R and its atmosphere has a thickness of 450 R.     

Jupiter: An inhomogeneous atmospheric model analysis of spatial variations of the H2 4-0 S(1) line

An analysis of the structure of the Jovian atmosphere, primarily based on center-to-limb variations (CTLV) of the equivalent width of the hydrogen quadrupole 4-0 S(1) line, is presented. These data require that the atmosphere have regions of both long- and short- scattering mean free paths. Two alternative cloud structures which fit the data are developed. The first is a two-cloud model (TCM) consisting of a thin upper cloud and a lower semi-infinite cloud, with absorbing gas between the clouds and above the upper cloud. The second model is a reflecting-scattering model (RSM), in which a gas layer lies above a haze consisting of scattering particles and absorbing gas. The cloud-scattering phase function in both models must have a strong forward peak. The CTLV data require, however, the presence of a backscattering lobe on the phase function, with the backscattering intensity about 4% of the forward scattering. The decrease in reflectivity of all regions from the visible to the ultraviolet is explained by the presence of dust particles mixed with the gas. Most of the ultraviolet absorption in the atmosphere must occur above the upper cloud layer. Particles with a uniform distribution of radii from 0.0 to 0.1 μm with a complex index of refraction varying as λ^?2.5 are used. The contrast in reflectivity between belts and zones may be explained by the larger concentration of dust in the belts than in the zones. Spatially resolved ultraviolet limb-darkening curves will help to determine the dust distribution of the Jovian atmosphere. The visible methane bands at λλ 6190, 5430, and 4860 Å are analyzed in terms of these models. We derive a methane-to-hydrogen mixing ratio of 2.8 × 10^?3, which is about 4.5 times the value for solar composition.     

Seasonal changes on Jupiter: 2. Influence of the planet exposure to the Sun

From our investigation of the behavior of changes in the visible brightness of Jupiter observed since 1850, it follows that the 22.3-year Hale magnetic cycle of solar activity produces the dominating influence on the processes taking place in the troposphere at a level of forming the upper boundary of clouds. The maximum values of the integral brightness of Jupiter fall on the solar cycle with the highest value of the Wolf number for the last 165 years (around 1957). The lowest estimates of brightness were obtained in 1855, when the Wolf number in the 12th solar-activity cycle was smallest. The analysis of the reflectance of Jupiter’s hemispheres in the visible spectral range for 1962–2015 revealed the alternating increase in the brightness of southern and northern tropical and middle regions for one rotation period of Jupiter about the Sun. Such a change in brightness and the increase in the activity of different hemispheres of the planet may indicate the periodic global alteration in the circulation system, the structure of cloud layers, and the overcloud haze. This suggests the interrelation between the observed variations in the reflectance of the considered latitudinal belts of Jupiter and the change in the axial tilts of the planet itself and its magnetic field to the orbital plane, i.e., the seasonal alteration in the atmosphere. The comparison of the temporal dependence of the activity factor A _j of the Jovian hemispheres in the visible spectral range with the change in the solar-activity index R shows that, from 1962 to 1995, these parameters almost synchronously changed, though the response of the visible cloud layer somewhat lagged behind the regime of exposure of the atmosphere to the Sun. The analysis shows that, when the planet is moving along the orbit, the reflectance of Jupiter’s hemispheres varies in response to the 21-percent change in the exposure of different hemispheres with a lag of 6 years. Such a lag coincides with the radiation- relaxation time of the hydrogen–helium atmosphere under the Jovian conditions. Desynchronization in their behavior that occurred after 1997 may be explained by the unbalanced influence of the three mentioned causes on the atmosphere of the planet.     

Dense Spot Coverage and Polar Caps on SV Cam

We have used spectrophotometric data from nine Hubble Space Telescope orbits to eclipse-map the primary component of the RS CVn binary SV Cam. From these observations and its HIPPARCOS parallax we find that the surface flux in the eclipsed low-latitude region is about 30 % lower than computed from the best fitting PHOENIX model atmosphere. This flux deficit can only be accounted for if about a third of the primary's surface is covered with unresolved spots. Even when we extend the spottedness from the eclipsed region to the entire surface, there still remains an unaccounted flux deficit. This remaining flux deficit is explained by the presence of a large polar spot extending down to latitude 42 ±6 °.Marie Curie Intra-European Fellow     

Synthetic spectra of simulated terrestrial atmospheres containing possible biomarker gases.

NASA's proposed Terrestrial Planet Finder, a space-based interferometer, will eventually allow spectroscopic analyses of the atmospheres of extrasolar planets. Such analyses would provide information about the existence of life on these planets. One strategy in the search for life is to look for evidence of O3 (and hence O2) in a planet's atmosphere; another is to look for gases that might be present in an atmosphere analogous to that of the inhabited early Earth. In order to investigate these possibilities, we have calculated synthetic spectra for several hypothetical terrestrial-type atmospheres. The model atmospheres represent four different scenarios. The first two, representing inhabited terrestrial planets, are an Earth-like atmosphere containing variable amounts of oxygen and an early Earth-type atmosphere containing methane. In addition, two cases representing Mars-like and early Venus-like atmospheres were evaluated, to provide possible "false positive" spectra. The calculated spectra suggest that ozone could be detected by an instrument like Terrestrial Planet Finder if the O2 concentration in the planet's atmosphere is > or = 200 ppm, or 10(-3) times the present atmospheric level. Methane should be observable on an early-Earth type planet if it is present in concentrations of 100 ppm or more. Methane has both biogenic and abiogenic sources, but concentrations exceeding 1000 ppm, or 0.1% by volume, would be difficult to produce from abiogenic sources alone. High methane concentrations in a planet's atmosphere are therefore another potential indicator for extraterrestrial life.     

Intensity and polarization line profiles in a semi-infinite Rayleigh-scattering planetary atmosphere. I. Integrated flux

Absorption and polarization line profiles as well as the curves of growth in the integrated light of a planet over the whole range of phase angles have been computed assuming a semi-infinite atmosphere scattering according to Rayleigh’s phase-matrix which takes polarization into account. The relative change in line depth and equivalent widths qualitatively agree with the observations of the CO₂ bands in Venus reported by Young, Schorn and Young (1980). It is pointed out that the bands might be formed in a part of the atmosphere which is different from that where continuum polarization originates.