Jovian Thermosphere Research Articles

Relation between the short‐term variation of the Jovian radiation belt and thermosphere derived from radio and infrared observations

AbstractWe report the first comprehensive observations of Jovian synchrotron radiation (JSR) and H3+ emission from the Jovian thermosphere to investigate the generation process of short‐term (days to weeks) variations in the Jovian radiation belt. The observations were made by the Giant Metrewave Radio Telescope and NASA Infrared Telescope Facility during November 2011. The total flux density of JSR increased by approximately 5% between 6–9 November and 12–17 November, associated with the increased solar UV/EUV flux. From 7 to 14 November, a possible rise in the infrared H3+ emission was observed in the middle‐latitude region, corresponding to a temperature variation of approximately 10 K. These results are consistent with the scenario that the solar UV/EUV heating causes variations in the thermospheric temperature and JSR. Radio images along the equatorial region showed that the JSR intensity decreased inside 1.5 Jovian radii (RJ) and the peak position shifted outward. This implies that energetic electrons are attenuated by some internal loss process, despite the simultaneous increase in radial diffusion. A physical model for the radiation belt shows that such an internal loss process can explain the observed variation of brightness distribution. Typical loss time scale is longer than strong diffusion limit, which suggests the existence of some pitch angle diffusion process such as wave‐particle interaction. Thus, variations of the total JSR flux density and thermospheric temperature seem consistent with the scenario, and the brightness distribution of JSR can be explained by the increase in radial diffusion accompanied by internal loss processes.

Response of the Jovian thermosphere to variations in solar EUV flux

AbstractExamining the response to solar extreme ultraviolet (EUV) radiation is an established diagnostic method used to understand the physics of planetary environments. In this study, we focus on the response of the Jovian thermosphere to variations in the solar EUV flux and discuss the consequences for the coupled thermosphere‐ionosphere‐magnetosphere system. We use a model that simulates both the thermospheric dynamics and the magnetospheric plasma velocity distribution under conditions of angular momentum transport between these regions. The simulations show that when the EUV flux increases by ~100% and 200%, the thermospheric neutral wind velocity at ~45° latitude increases by 16% and 22%, respectively. The short‐term variation over a few Earth days causes an increased velocity at middle latitudes which are magnetically conjugate to the Jovian radiation belt. Increased heating due to solar EUV contributes to this velocity change. The other contribution arises ~30 planetary rotations after the initial solar EUV flux increase. This second (“delayed”) effect is due to propagation of momentum from high latitudes (the auroral region), where Joule heating is dominant, and is related to the behavior of the ionospheric conductance and magnetosphere‐ionosphere coupling currents. The modeled velocity enhancement is smaller than that required to explain the observed enhancement of the synchrotron emission by radial diffusion of the trapped energetic electrons. In this context, we discuss the sensitivity of the underlying thermosphere‐ionosphere response to short‐wavelength solar radiation and the ensuing three‐dimensional wind fields.

Response of the Jovian thermosphere to a transient ‘pulse’ in solar wind pressure

The importance of the Jovian thermosphere with regard to magnetosphere–ionosphere coupling is often neglected in magnetospheric physics. We present the first study to investigate the response of the Jovian thermosphere to transient variations in solar wind dynamic pressure, using an azimuthally symmetric global circulation model coupled to a simple magnetosphere and fixed auroral conductivity model. In our simulations, the Jovian magnetosphere encounters a solar wind shock or rarefaction region and is subsequently compressed or expanded. We present the ensuing response of the coupling currents, thermospheric flows, heating and cooling terms, and the aurora to these transient events. Transient compressions cause the reversal, with respect to steady state, of magnetosphere–ionosphere coupling currents and momentum transfer between the thermosphere and magnetosphere. They also cause at least a factor of two increase in the Joule heating rate. Ion drag significantly changes the kinetic energy of the thermospheric neutrals depending on whether the magnetosphere is compressed or expanded. Local temperature variations appear between ~−45and175K for the compression scenario and ~−20and50K for the expansion case. Extended regions of equatorward flow develop in the wake of compression events – we discuss the implications of this behaviour for global energy transport. Both compressions and expansions lead to a ~2000TW increase in the total power dissipated or deposited in the thermosphere. In terms of auroral processes, transient compressions increase main oval UV emission by a factor of ~4.5 whilst transient expansions increase this main emission by a more modest 37%. Both types of transient event cause shifts in the position of the main oval, of up to 1° latitude.

Effect of solar UV/EUV heating on the intensity and spatial distribution of Jupiter's synchrotron radiation

We analyzed the Very Large Array archived data observed in 2000 to determine whether solar ultraviolet (UV)/extreme ultraviolet (EUV) heating of the Jovian thermosphere causes variations in the total flux density and dawn‐dusk asymmetry (the characteristic differences between the peak emissions at dawn and dusk) of Jupiter's synchrotron radiation (JSR). The total flux density varied by 10% over 6 days of observations and accorded with theoretical expectations. The average dawn‐dusk peak emission ratio indicated that the dawn side emissions were brighter than those on the dusk side and this was expected to have been caused by diurnal wind induced by the solar UV/EUV. The daily variations in the dawn‐dusk ratio did not correspond to the solar UV/EUV, and this finding did not support the theoretical expectation that the dawn‐dusk ratio and diurnal wind velocity varies in correspondence with the solar UV/EUV. We tried to determine whether the average dawn‐dusk ratio could be explained by a reasonable diurnal wind velocity. We constructed an equatorial brightness distribution model of JSR using the revised Divine‐Garrett particle distribution model and used it to derive a relation between the dawn‐dusk ratio and diurnal wind velocity. The estimated diurnal wind velocity reasonably corresponded to a numerical simulation of the Jovian thermosphere. We also found that realistic changes in the diurnal wind velocity could not cause the daily variations in the dawn‐dusk ratio. Hence, we propose that the solar UV/EUV related variations were below the detection limit and some other processes dominated the daily variations in the dawn‐dusk ratio.

Influence of upstream solar wind on thermospheric flows at Jupiter

The coupling of Jupiter's magnetosphere and ionosphere plays a vital role in creating its auroral emissions. The strength of these emissions is dependent on the difference in speed of the rotational flows within Jupiter's high-latitude thermosphere and the planet's magnetodisc. Using an azimuthally symmetric global circulation model, we have simulated how upstream solar wind conditions affect the energy and direction of atmospheric flows. In order to simulate the effect of a varying dynamic pressure in the upstream solar wind, we calculated three magnetic field profiles representing compressed, averaged and expanded ‘middle’ magnetospheres. These profiles were then used to solve for the angular velocity of plasma in the magnetosphere. This angular velocity determines the strength of currents flowing between the ionosphere and magnetosphere. We examine the influence of variability in this current system upon the global winds and energy inputs within the Jovian thermosphere. We find that the power dissipated by Joule heating and ion drag increases by ∼190% and ∼185% from our compressed to expanded model respectively. We investigated the effect of exterior boundary conditions on our models and found that by reducing the radial current at the outer edge of the magnetodisc, we also limit the thermosphere's ability to transmit angular momentum to this region.

Processes of auroral thermal structure at Jupiter: Analysis of multispectral temperature observations with the Jupiter Thermosphere General Circulation Model

We use our three‐dimensional Jupiter Thermosphere General Circulation Model (JTGCM) to quantify thermal processes that take place in the auroral thermosphere. These processes tend to control the thermal budget in the Jovian ovals and polar caps and maintain thermospheric temperatures consistent with those derived from multispectral observations of Jupiter's aurora. The main heat source in the JTGCM that drives the thermospheric flow is high‐latitude joule heating resulting from frictional motion of the ions relative to the neutrals. A secondary source of heating that dominates the exospheric region of the Jovian ovals is the auroral process of particle precipitation. Both sources of high‐latitude heating in the JTGCM are strongly related to the current system in the outer magnetosphere that allows plasma to flow in and out of the Jovian ionosphere. The mapping of this flow to ionospheric altitudes gives rise to an ion drag process that dominates the neutral momentum forcing near the altitude of the ionospheric peak. We find that the ion drag and joule heating inputs in the JTGCM significantly intensify the underlying global thermospheric circulation, thereby affecting the distribution of the neutral temperature. Global simulations of the Jovian thermospheric dynamics indicate strong neutral outflows from the auroral ovals with velocities up to 1.9 km s−1 and subsequent convergence and downwelling at the Jovian equator. Such circulation is shown to be an important mechanism for transporting significant amounts of auroral energy to the rest of the planet and for regulating the global heat budget in a manner consistent with temperature observations of Jupiter's oval and polar cap regions. Adiabatic expansion of the neutral atmosphere resulting from outward flows is found to be an important source of cooling for the auroral exosphere. The distribution of neutral temperature from 1 μbar to 1 nbar is determined by the thermal balance between the total heating caused by joule and adiabatic heating processes and dynamical cooling mainly from the hydrodynamic advection process. The thermal balance of the Jovian thermosphere below the homopause (≥1 μbar) is shown to be dominated primarily by wind transport processes. The heating in this region both for the Jovian ovals and polar caps is due to hydrodynamic advection and adiabatic compression processes. This dynamical heating is efficiently dissipated by hydrocarbon cooling through CH4 and C2H2 infrared radiation at 7.8 and 12.6 μm, respectively.

Deuterium chemistry and airglow in the jovian thermosphere

We present a detailed study of the distribution of key deuterated species (viz., atomic D and HD) and the associated deuterium Lyman- α airglow in the jovian thermosphere. The reactions that appear to govern the abundances of these deuterated species are used in conjunction with C 2-chemistry in a 1-D photochemical-diffusion model. While the D abundance is mainly sensitive to H densities and the vibrational temperature profile, the D vertical distribution also depends on other parameters such as eddy mixing and the uncertain values of some of the reaction rate constants. We consider different scenarios by varying several parameters controlling the D distribution in the thermosphere. A radiative transfer model with coupling of the H and D Lyman- α lines is employed to obtain line profiles and total intensities at disk center for these scenarios. This allows a comparison of the impact of various parameters on the jovian D Lyman- α emission. A consequence of these chemical processes in the jovian thermosphere is the formation of CH 2D, CH 3D, and C 2H 5D, and other deuterated species. We also discuss the source of these deuterated hydrocarbons and their abundance. We find that HD vibrational chemistry impacts D in the thermosphere, CH 3D and C 2H 5D are vibrationally enhanced in the thermosphere, and variations in abundance of CH 3D and C 2H 5D in the thermosphere may reflect dynamical activity (i.e., K h ) in the jovian upper atmosphere. An observing program dedicated to providing such measurements of these testable phenomena would provide further insight into the synergistic coupling between chemistry, energetics and airglow in the jovian upper atmosphere.

Heating of Jupiter’s thermosphere by the dissipation of upward propagating acoustic waves

Thunderstorms in Jupiter’s atmosphere are likely to be prodigious generators of acoustic waves, as are thunderstorms in Earth’s atmosphere. Accordingly, we have used a numerical model to study the dissipation in Jupiter’s thermosphere of upward propagating acoustic waves. Model simulations are performed for a range of wave periods and horizontal wavelengths believed to characterize these acoustic waves. The possibility that the thermospheric waves observed by the Galileo Probe might be acoustic waves is also investigated. Whereas dissipating gravity waves can cool the upper thermosphere through the effects of sensible heat flux divergence, it is found that acoustic waves mainly heat the Jovian thermosphere through effects of molecular dissipation, sensible heat flux divergence, and Eulerian drift work. Only wave-induced pressure gradient work cools the atmosphere, an effect that operates at all altitudes. The sum of all effects is acoustic wave heating at all heights. Acoustic waves and gravity waves heat and cool the atmosphere in fundamentally different ways. Though the amplitudes and mechanical energy fluxes of acoustic waves are poorly constrained in Jupiter’s atmosphere, the calculations suggest that dissipating acoustic waves can locally heat the thermosphere at a significant rate, tens to a hundred Kelvins per day, and thereby account for the high temperatures of Jupiter’s upper atmosphere. It is unlikely that the waves detected by the Galileo Probe were acoustic waves; if they were, they would have heated Jupiter’s thermosphere at enormous rates.

Excitation of the FUV Io tail on Jupiter: Characterization of the electron precipitation

Spectral observation of both polar regions of Jupiter in the far ultraviolet (FUV) obtained with the Space Telescope Imaging Spectrograph (STIS), on board the Hubble Space Telescope from July 1997 to January 2001 have been combined with FUV images to map the FUV color ratio along the STIS slit. Spatially resolved spectra of the aurora carried at ∼12 Å resolution have been used to determine the amount of methane absorption as measured by the FUV color ratio of the Io magnetic footprint and its trailing tail. It is found that the absorption is systematically less than in the main polar aurora, indicating a higher altitude source region. The color ratio of the north tail is shown to slowly decrease downstream from the footprint. The combination of these spectral data with a two‐stream model of the interaction of energetic electrons with the Jovian thermosphere indicates that the mean energy of the electrons creating the north FUV emission ranges from ∼55 keV at the Io footprint to ∼40 keV, 20 degrees downstream in the tail. In parallel, the incident electron energy flux drops by a factor ∼6 over the same angular distance. These observations are consistent with the steady state slippage picture where the subcorotating flux tube is accelerated very slowly up to corotation owing to the nonideal coupling. It is argued that small deviations from corotation can supply sufficient energy to fuel the observed auroral emissions. It is suggested that the parallel electric field accelerating electrons out of the flux tube only moderately depends on the time elapsed since the contact with Io, although the mapping between a point in the tail and Io is very uncertain in the presence of magnetic field line slippage.

On the Dynamics of the Jovian Ionosphere and Thermosphere: II. The Measurement of H 3+ Vibrational Temperature, Column Density, and Total Emission

We present the first reported measurements of the intensity of a “hotband” transition for the H 3 + molecular ion in the northern auroral/polar region of Jupiter. This transition is identified as the R(3, 4 +) line of the (2 v 2( l=0)→ v 2) hotband, with a wavelength of 3.94895 μm. This is the first time such a transition has been measured outside the laboratory, and the wavelength as measured on Jupiter is within the experimental accuracy of the lab measurement. This detection makes it possible to investigate H 3 + transitions that simultaneously originate from different vibrational levels. We use the intensity ratio between this line and the Q(1, 0 −) fundamental transition to derive effective vibrational temperatures, column densities, and total emission parameters as a function of position across the auroral/polar region. Effective temperatures range from ∼900 to ∼1250 K; an increase in average temperature during our observing run of ∼100 K is noted. The derived temperatures are toward the high end or in excess of the auroral temperature range that has been reported in the literature to date. The relationship among emission intensity, temperature, and density is shown to be complex. This may reflect the nonthermalization of the vibrational levels at the gas densities prevailing in the jovian thermosphere. An alternative analysis allowing for this effect is presented. But this approach requires thermospheric temperatures to be ∼1500 K at the level that the majority of H 3 + is being produced, higher than has previously been proposed.

Sunrise and sunset effects on solar heating in the Jovian thermosphere and ionosphere

We present some calculations on the effects of oblateness on the solar heating process as considered in the Jovian Ionospheric Model by Achilleos et al. (1998). Since Jupiter has significant oblateness we have to use a new approach for the investigation of sunrise/sunset variations in the Jovian ionosphere. We introduce the modified Chapman function ( Che) and point to its importance for the sunrise and sunset time periods where this function significantly deviates from the “classic” Chapman function ( Ch). Because of the dependence of the Che function on latitude and solar declination we have included latitudinal variations in all thermospheric and ionospheric parameters. The Jovian Ionospheric Model assumes plane stratified atmospheric layers. We consider one part of this model, the solar heating, and more precisely take into account the shape of the planetary body. We model it with a rotational ellipsoid and calculate the optical depth parameter, used in evaluation of the neutral volume heating rate due to solar radiation. We use secants for the flat model, the Ch function for spherical model, and the Che function for the ellipsoidal model. We use all other physical inputs of the Jovian Ionospheric Model to explore the effects due to oblateness only. Calculations show that only the modified Chapman function Che can really describe sunrise/sunset and latitudinal variations in the Jovian thermosphere and ionosphere.

Gravity Wave Heating and Cooling in Jupiter's Thermosphere

A numerical model to explore the possibility that the dissipation of two upward propagating internal gravity waves, identified in the temperature measurements of the Galileo Probe, provide the energy to maintain Jupiter's high thermospheric temperatures ∼900 K is used. The propagation and dissipation of the gravity waves are simulated by a full-wave model that is used to calculate the thermal mean-state forcing. The observed temperature is the result of this forcing and other energy sources. The equation of heat transfer, including the effects of eddy and molecular thermal diffusion, is solved to provide the gravity wave contribution to the steady-state temperature distribution. For the smallest values of eddy diffusion considered, the waves can heat the entire thermosphere, while for the largest values of eddy diffusion, the waves can cool the entire thermosphere. However, in all cases considered the net heating and cooling effects are not large, being typically ∼15–20 K or less. To the extent that the Galileo data characterize gravity waves in Jupiter's atmosphere, gravity wave dissipation is unlikely to be the source of energy maintaining Jupiter's high thermospheric temperatures. Other waves not identified in the Galileo data or other energy sources must be responsible for heating the jovian thermosphere. We demonstrate that the viscous heating can only be calculated using the viscous stress tensor, and that the use of the wave mechanical energy flux divergence for this purpose in previous studies is invalid.

The chemical effects of auroral oxygen precipitation at Jupiter

Energetic oxygen precipitation is one possible explanation for the auroral molecular hydrogen emissions observed by the Voyager ultraviolet spectrometer. These ions deposit their energy in the Jovian thermosphere by means of ionization, dissociation, excitation, and heating processes. The photochemistry of both the neutral gas and the ionosphere is altered by the influx of atomic oxygen. The auroral oxygen flux is about 10 7 cm −2 sec −1 if all the observed Lyman and Werner band emissions are due to heavy ion precipitation rather than to energetic electron precipitation. The O atoms react with H + ions forming O + ions, which then react with H 2, starting a chain of chemical reactions involving H 2O + and H 3O + that ultimately leads to the formation of water. The O atoms can also react with CH 3 and will eventually form CO deeper in the atmosphere. A numerical model has been developed to study the effects of odd oxygen (i.e., O, OH, and H 2O) on the auroral ionosphere of Jupiter. In particular, we show that the electron density is reduced by about a factor of 4 due to the removal of H + ions by chemistry associated with odd oxygen species, whereas the electron density reduction required for consistency with observations is more than a factor of 20 suggesting that other H + loss mechanisms must be operating or that sources of oxygen or water other than auroral precipitation are present. The globally averaged flux of oxygen from the aurora is also about a factor of 20 too low to explain the Jovian CO measurements.

Heating by Alfven wave dissipation in the Jovian thermosphere

An estimate of heating rates by the dissipation of Io‐generated Alfven waves by ion‐neutral collisions in the Jovian thermosphere is made. Heating rates at the foot of the Io flux tube are found to be significant.

Electron precipitation and related aeronomy of the Jovian thermosphere and ionosphere

Voyager ultraviolet spectrometer (UVS) measurements provided the first unassailable evidence for particle precipitation in the Jovian atmosphere. Strong Lyman and Werner band emissions at high latitudes indicate particle precipitation energy fluxes of about 10 ergs cm−2 s−1. On the other hand dayglow Lyman and Werner emissions at mid‐ and low‐latitudes may indicate additional particle precipitation fluxes on the order of 0.3 ergs cm−2 s−1 at all latitudes. Such particle precipitation can have significant aeronomical effects on the Jovian thermsophere and ionosphere. A one‐dimensional theoretical model is used to study these effects for the case of electron precipitation, although ion precipitation produces similar effects. Diffusion equations are solved for all the major neutral species and for H+, and photochemical solutions are given for the short lived ions. These neutral and ionospheric components of the model are coupled with the electron and ion energy equations and a two‐stream electron transport code that calculates the energy deposition of precipitating electrons (considered to be the precipitating particles) and photoelectrons. An independent calculation of the vertical neutral temperature is also obtained. The results of the model calculations can be broadly categorized as effects of electron precipitation (1) on the neutral composition and temperature of the thermosphere, and (2) on the composition and structure of the ionosphere. Auroral electron precipitation by 10‐keV electrons with a total energy flux of 10 ergs cm−2 s−1 produces 4.7×1011 H atoms cm−2 s−1 and 5 ergs cm−2 s−1 of heat, over 2 orders of magnitude larger than solar EUV processes that produce 3.3×109 H atoms cm−2 s−1 and 0.03 ergs cm−2 s−1 of heat. Thus, Jovian auroral H production coupled with aurorally driven meridional winds in the thermosphere can possibly explain the high concentration of atomic hydrogen in the low‐latitude Jovian upper atmosphere. Furthermore, aurorally produced changes in composition can create important feedback which affects the relative airglow efficiencies and heating rates in the high‐latitude thermosphere. In addition, ionization and vibrational heating of H2 from precipitation processes appear to play a central role in determining the structure of the high‐latitude ionosphere. Theoretical fits to the Voyager radio occultation electron density profiles at high latitudes suggest a 10‐keV electron aurora with an energy flux of 10 ergs cm−2 s−1 coupled with a height‐dependent H2 vibrational temperature that reaches 3000 K in the topside ionosphere.

Solar wind energy as a source of upper-atmosphere heating on Earth and Jupiter

Measurements of thermospheric composition by the Esro 4 gas analyzer reveal a permanent increase of exospheric temperature at high latitudes. It is argued that the required energy is ultimately derived from the solar wind and that 5 × 10−4 of the total solar wind flux intercepted by the magnetosphere of the earth will maintain the observed temperature increase. Heating of a planetary upper atmosphere by solar wind will be proportional to the cross-sectional area of the magnetosphere of the planet and the leakage rate of solar wind energy into the atmosphere. It is estimated that the ratio of heat input from solar wind with respect to the EUV heat input will be about 20 times higher on Jupiter than it is on earth if similar leakage rates at both planets are assumed. The solar wind may thus contribute to the high temperatures observed in the Jovian thermosphere.

The roles of particle precipitation and Joule heating in the energy balance of the Jovian thermosphere

Order of magnitude calculations have been carried out to compare particle precipitation and Joule heating with solar radiation as sources of energy in the Jovian thermosphere. Calculations based on a detailed atomic cross section approach to energy deposition show that the efficiency of conversion of energetic particle precipitation energy into thermal energy is 0.33, larger than on Earth. This emphasizes the role of particle precipitation heating, which may serve as a source for gravity waves. In contrast to the terrestrial case, Joule heating is found to be of only minor significance in the Jovian atmosphere.

Possible new Jovian thermospheric models

view Abstract Citations (2) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Possible new Jovian thermospheric models. Prasad, S. S. Abstract Possibilities of models for the Jovian thermosphere, based upon mechanical heating, have been explored. Under certain reasonable assumptions about the magnitude of the critical Richardson number, the correction to the conventional expression for the eddy heat flux, and the height dependence of the eddy diffusion coefficient, a very hot thermosphere could result, yielding exospheric temperatures more in tune with the bounds being suggested by the recent optical and radio occultation experiments. Publication: The Astrophysical Journal Pub Date: September 1975 DOI: 10.1086/181924 Bibcode: 1975ApJ...200L.171P Keywords: Astronomical Models; Atmospheric Heating; Atmospheric Models; Jupiter Atmosphere; Planetary Temperature; Thermosphere; Atmospheric Temperature; Exosphere; Turbulent Diffusion; Solar Physics full text sources ADS |

On the Temperature of the Jovian Thermosphere

Abstract A theoretical study is made to assess the importance of the solar EUV flux in the thermal energy balance of the Jovian thermosphere. A global averaged vertical temperature contrast in the thermosphere of 15K is calculated and the mesopause is located at a particle density of 5×1013 cm−3. Thus, the upper atmosphere of Jupiter is approximately isothermal. At the mesopause IR cooling by C3H2 is an order of magnitude more important than IR cooling by CH4. Only the location of the mesopause is a sensitive function of the IR cooling agent in the upper atmosphere. The exospheric temperature depends principally on the mesopause temperature and the solar flux. Eddy heat transport plays a negligible role in the thermal energy balance of the Jovian thermosphere. For the thermospheres of Saturn and Titan the global averaged vertical temperature contrasts are estimated to be ∼10K and 90K, respectively, if their compositions are similar to Jupiter's and the same physics is applicable.

Thermodynamic Equilibria in Planetary Atmospheres

view Abstract Citations (53) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Thermodynamic Equilibria in Planetary Atmospheres Lippincott, Ellis R. ; Eck, Richard V. ; Dayhoff, Margaret O. ; Sagan, Carl Abstract The thermodynamic equilibrium composition of all possible combinations of the elements carbon, hydrogen, oxygen, and nitrogen at average pressures and temperatures have been calculated for the atmospheres of Earth, Venus, Mars, and Jupiter. All regions of the composition diagram consistent with the observed molecular abundances are located and discussed. The constituents of the terrestrial atmosphere considered as a closed system are in approximate thermodynamic equilibrium in spite of the continual addition of trace compounds by biological activity, lightning, radiation, and vulcanism. Under some circumstances, the presence of atmospheric organic molecules far in excess of their thermodynamic equilibrium proportions can be an indication of indigenous biological activity. The atmosphere of Venus seems likely to be in thermodynamic equilibrium. It then follows that the measured upper limits on the abundances of C114, NHl, and CO are all inconsistent with the possibility of elemental carbon or hydrocarbons in contact with the atmosphere, either on the surface or as clouds. The evidence for Mars is not inconsistent with thermodynamic equilibrium. The computations do not indicate whether small quantities of free Ol exist. The equilibrium abundances of all oxides of nitrogen on Mars are extremely low even if computed with a considerable excess of 01. For Mars and Venus there are no molecular species with a large predicted equilibrium abundance and spectroscopically accessible absorption features which have not already been identified. Under equilibrium conditions at low temperatures Jupiter also cannot contain significant amounts of any molecule not yet observed. However, at high temperatures such as would be produced by lightning discharges or in the Jovian thermosphere, simple hydrocarbons and cyanides, polycyclic aromatics, and a variety of nitrogen compounds would be expected. Some of these compounds are brightly colored, and it seems possible that such organic compounds contribute to the observed variable coloration of Jupiter. Publication: The Astrophysical Journal Pub Date: February 1967 DOI: 10.1086/149051 Bibcode: 1967ApJ...147..753L full text sources ADS |