Stratosphere Of Jupiter Research Articles

Monitoring of the evolution of H2O vapor in the stratosphere of Jupiter over an 18-yr period with the Odin space telescope

Context. The comet Shoemaker-Levy 9 impacted Jupiter in July 1994, leaving its stratosphere with several new species, with water vapor (H2O) among them. Aims. With the aid of a photochemical model, H2O can be used as a dynamical tracer in the Jovian stratosphere. In this paper, we aim to constrain the vertical eddy diffusion (Kzz) at levels where H2O is present. Methods. We monitored the H2O disk-averaged emission at 556.936 GHz with the space telescope between 2002 and 2019, covering nearly two decades. We analyzed the data with a combination of 1D photochemical and radiative transfer models to constrain the vertical eddy diffusion in the stratosphere of Jupiter. Results. Odin observations show us that the emission of H2O has an almost linear decrease of about 40% between 2002 and 2019. We can only reproduce our time series if we increase the magnitude of Kzz in the pressure range where H2O diffuses downward from 2002 to 2019, that is, from ~0.2 mbar to ~5 mbar. However, this modified Kzz is incompatible with hydrocarbon observations. We find that even if an allowance is made for the initially large abundances of H2O and CO at the impact latitudes, the photochemical conversion of H2O to CO2 is not sufficient to explain the progressive decline of the H2O line emission, which is suggestive of additional loss mechanisms. Conclusions. The Kzz we derived from the Odin observations of H2O can only be viewed as an upper limit in the ~0.2 mbar to ~5 mbar pressure range. The incompatibility between the interpretations made from H2O and hydrocarbon observations probably results from 1D modeling limitations. Meridional variability of H2O, most probably at auroral latitudes, would need to be assessed and compared with that of hydrocarbons to quantify the role of auroral chemistry in the temporal evolution of the H2O abundance since the SL9 impacts. Modeling the temporal evolution of SL9 species with a 2D model would naturally be the next step in this area of study.

Jupiter in the Ultraviolet: Acetylene and Ethane Abundances in the Stratosphere of Jupiter from Cassini Observations between 0.15 and 0.19 μm

Abstract At wavelengths between 0.15 and 0.19 μm, the far-ultraviolet spectrum of Jupiter is dominated by the scattered solar spectrum, attenuated by molecular absorptions primarily by acetylene and ethane, and to a lesser extent ammonia and phosphine. We describe the development of our radiative transfer code that enables the retrieval of abundances of these molecular species from ultraviolet reflectance spectra. As a proof-of-concept we present an analysis of Cassini Ultraviolet Imaging Spectrograph (UVIS) observations of the disk of Jupiter during the 2000/2001 flyby. The ultraviolet-retrieved acetylene abundances in the upper stratosphere are lower than those predicted by models based solely on infrared thermal emission from the mid-stratosphere observed by the Composite Infrared Spectrometer (CIRS), requiring an adjustment to the vertical profiles above 1 mbar. We produce a vertical acetylene abundance profile that is compatible with both CIRS and UVIS, with reduced abundances at pressures <1 mbar: the 0.1 mbar abundances are 1.21 ± 0.07 ppm for acetylene and 20.8 ± 5.1 ppm for ethane. Finally, we perform a sensitivity study for the JUICE ultraviolet spectrograph, which has extended wavelength coverage out to 0.21 μm, enabling the retrieval of ammonia and phosphine abundances, in addition to acetylene and ethane.

Small impacts on the giant planet Jupiter

Context. Video observations of Jupiter obtained by amateur astronomers over the past 8 years have shown five flashes of light with durations of 1–2 s, each observed by at least two observers that were geographically separated. The first three of these events occurred on 3 June 2010, 20 August 2010, and 10 September 2012. Previous analyses of their light curves showed that they were caused by the impact of objects of 5–20 m in diameter, depending on their density, with a released energy comparable to superbolides on Earth of the class of the Chelyabinsk airburst. The most recent two flashes on Jupiter were detected on 17 March 2016 and 26 May 2017 and are analyzed here. Aims. We characterize the energy involved together with the masses and sizes of the objects that produced these flashes. The rate of similar impacts on Jupiter provides improved constraints on the total flux of impacts on the planet, which can be compared to the amount of exogenic species detected in the upper atmosphere of Jupiter. Methods. We extracted light curves of the flashes and calculated the masses and sizes of the impacting objects after calibrating each video observation. We also present results from a systematic search of impacts on >72 000 video amateur observations with a customized software that is based on differential photometry of the images. An examination of the number of amateur observations of Jupiter as a function of time over the past years allows us to interpret the statistics of these impact detections. Results. The cumulative flux of small objects (5–20 m or larger) that impact Jupiter is predicted to be low (10–65 impacts per year), and only a fraction of them are potentially observable from Earth (4–25 observable impacts per year in a perfect survey). These numbers imply that many observers are required to efficiently discover Jupiter impacts. Conclusions. We predict that more impacts will be found in the next years, with Jupiter opposition displaced toward summer in the northern hemisphere where most amateur astronomers observe. Objects of this size contribute negligibly to the abundance of exogenous species and dust in the stratosphere of Jupiter when compared with the continuous flux from interplanetary dust particles punctuated by giant impacts. Flashes of a high enough brightness (comparable at their peak to a +3.3 magnitude star) could produce an observable debris field on the planet. We estimate that a continuous search for these impacts might find these events once every 0.4–2.6 yr.

Assessing the long-term variability of acetylene and ethane in the stratosphere of Jupiter

Acetylene (C2H2) and ethane (C2H6) are both produced in the stratosphere of Jupiter via photolysis of methane (CH4). Despite this common source, the latitudinal distribution of the two species is radically different, with acetylene decreasing in abundance towards the pole, and ethane increasing towards the pole. We present six years of NASA IRTF TEXES mid-infrared observations of the zonally-averaged emission of methane, acetylene and ethane. We confirm that the latitudinal distributions of ethane and acetylene are decoupled, and that this is a persistent feature over multiple years. The acetylene distribution falls off towards the pole, peaking at ∼ 30°N with a volume mixing ratio (VMR) of ∼ 0.8 parts per million (ppm) at 1 mbar and still falling off at ± 70° with a VMR of ∼ 0.3 ppm. The acetylene distributions are asymmetric on average, but as we move from 2013 to 2017, the zonally-averaged abundance becomes more symmetric about the equator. We suggest that both the short term changes in acetylene and its latitudinal asymmetry is driven by changes to the vertical stratospheric mixing, potentially related to propagating wave phenomena. Unlike acetylene, ethane has a symmetric distribution about the equator that increases toward the pole, with a peak mole fraction of ∼ 18 ppm at about ± 50° latitude, with a minimum at the equator of ∼ 10 ppm at 1 mbar. The ethane distribution does not appear to respond to mid-latitude stratospheric mixing in the same way as acetylene, potentially as a result of the vertical gradient of ethane being much shallower than that of acetylene. The equator-to-pole distributions of acetylene and ethane are consistent with acetylene having a shorter lifetime than ethane that is not sensitive to longer advective timescales, but is augmented by short-term dynamics, such as vertical mixing. Conversely, the long lifetime of ethane allows it to be transported to higher latitudes faster than it can be chemically depleted.

Parameterization of radiative heating and cooling rates in the stratosphere of Jupiter

We present a newly developed parameterization of radiative heating and cooling for Jupiter’s upper troposphere and stratosphere (103 to 10-3hPa) suitable for general circulation models. The scheme is based on the correlated k-distribution approach, and accounts for all the major radiative mechanisms in the jovian atmosphere: heating due to absorption of solar radiation by methane, cooling in the infrared by methane, acetylene, ethane, and collisionally-induced molecular hydrogen–hydrogen, and molecular hydrogen–helium transitions. The results with the scheme are compared with line-by-line calculations to demonstrate that the accuracy of the scheme is within 10%. The parameterization was applied to study the sensitivity of the heating/cooling rates due to variations of mixing ratios of hydrocarbon molecules. It was also used for calculating the radiative–convective equilibrium temperature, which is in agreement with observations in the equatorial region. In midlatitudes, the equilibrium temperature is approximately 10K colder. Our results suggest that the radiative forcing in the upper stratosphere is much stronger than it was thought before. In particular, the characteristic radiative relaxation time decreases exponentially with height from 108s near the tropopause to 105s in the upper stratosphere.

CH4 mixing ratios at microbar pressure levels of Jupiter as constrained by 3-micron ISO data

Infrared Space Observatory (ISO) data of Jupiter are revisited in order to derive CH4 mixing ratios at microbar pressures in the atmosphere. We utilize the most updated radiative transfer programs to construct a 3-μm emission model of CH4 to be compared with the ISO data. From the model-data comparisons, we derive the high-altitude CH4 mixing ratios, which turn out to be at least 10 times smaller than the microbar CH4 mixing ratios assumed in the Galileo probe analysis (Seiff, A. et al., 1998. Thermal structure of Jupiter’s atmosphere near the edge of a 5-μm hot spot in the north equatorial belt. J. Geophys. Res., 103, 22857–22889. doi:10.1029/98JE01766), but which are approximately consistent with ultraviolet airglow observations and with available photochemical models that assume relatively weak atmospheric mixing. We also compare the derived CH4 profile with results from other investigations reported in literature and discuss the implications with respect to photochemistry and vertical transport in the stratosphere of Jupiter.

JOVIAN STRATOSPHERE AS A CHEMICAL TRANSPORT SYSTEM: BENCHMARK ANALYTICAL SOLUTIONS

We systematically investigated the solvable analytical benchmark cases in both one- and two-dimensional (1D and 2D) chemical-advective-diffusive systems. We use the stratosphere of Jupiter as an example but the results can be applied to other planetary atmospheres and exoplanetary atmospheres. In the 1D system, we show that CH_4 and C_2H_6 are mainly in diffusive equilibrium, and the C_2H_2 profile can be approximated by modified Bessel functions. In the 2D system in the meridional plane, analytical solutions for two typical circulation patterns are derived. Simple tracer transport modeling demonstrates that the distribution of a short-lived species (such as C_2H_2) is dominated by the local chemical sources and sinks, while that of a long-lived species (such as C_2H_6) is significantly influenced by the circulation pattern. We find that an equator-to-pole circulation could qualitatively explain the Cassini observations, but a pure diffusive transport process could not. For slowly rotating planets like the close-in extrasolar planets, the interaction between the advection by the zonal wind and chemistry might cause a phase lag between the final tracer distribution and the original source distribution. The numerical simulation results from the 2D Caltech/JPL chemistry-transport model agree well with the analytical solutions for various cases.

Odin space telescope monitoring of water vapor in the stratosphere of Jupiter

The Odin space telescope has monitored the H2O (110–101) line in Jupiter's stratosphere over the 2003–2009 period. When comparing these data with previous spectra obtained with SWAS and Odin over the 1999–2002 period, we see no significant variations in the line-to-continuum ratio of the H2O line over the whole period. We have however tentatively identified a decrease by ∼15% of the line-to-continuum ratio between 2002 and 2007–2009, indicating that there was less H2O in the stratosphere of Jupiter in 2007–2009 than anticipated. We have tested the IDP (interplanetary dust particles) and SL9 (Shoemaker-Levy 9) 1D time-dependent models presented in Cavalié et al. [2008, Observation of water vapor in the stratosphere 613 of Jupiter with the Odin space telescope. Planetary and Space Science 56, 1573–1584]. We present a series of scenarios that lead to satisfactory fits of the whole data set (1999–2002 and 2003–2009 periods) based on IDP and SL9 models. The evolution of Jupiter's stratospheric H2O that we have tentatively observed has however to be confirmed by Herschel/HIFI observations. If the decrease of the line-to-continuum ratio is confirmed by future observations, it would be a direct evidence that Jupiter's H2O comes from SL9. In addition, this study shows that new constraints on Jupiter's eddy diffusion coefficient profile could be obtained (in the pressure ranges that are probed) from the monitoring of SL9 species in its stratosphere.

Observation of water vapor in the stratosphere of Jupiter with the Odin space telescope

The water vapor line at 557 GHz has been observed with the Odin space telescope with a high signal-to-noise ratio and a high spectral resolution on November 8, 2002. The analysis of this observation as well as a re-analysis of previously published observations obtained with the submillimeter wavelength astronomy satellite seem to favor a cometary origin (Shoemaker-Levy 9) for water in the stratosphere of Jupiter, in agreement with the ISO observation results. Our model predicts that the water line should become fainter and broader from 2007. The observation of such a temporal variability would be contradictory with an IDP steady flux, thus supporting the SL9 source hypothesis.

Meridional Transport in the Stratosphere of Jupiter

The Cassini measurements of C_2H_2 and C_2H_6 at ~5 mbar provide a constraint on meridional transport in the stratosphere of Jupiter. We performed a two-dimensional photochemical calculation coupled with mass transport due to vertical and meridional mixing. The modeled profile of C_2H_2 at latitudes less than 70° follows the latitude dependence of the solar insolation, while that of C_2H_6 shows little latitude dependence, consistent with the measurements. In general, our model study suggests that the meridional transport timescale above 5-10 mbar altitude level is ≳1000 yr, and the time could be as short as 10 yr below 10 mbar level, in order to fit the Cassini measurements. The derived meridional transport timescale above the 5 mbar level is 100 times longer than that obtained from the spreading of gas-phase molecules deposited after the impact of Shoemaker-Levy 9 comet. There is no explanation at this time for this discrepancy.

STRATOSPHERIC IMAGES OF JUPITER DERIVED FROM HYDROCARBON EMISSIONS IN VOYAGER 1 AND 2 IRIS SPECTRA

Spectroscopic data obtained by the Infrared Interferometer Spectrometer (IRIS) aboard Voyager 1 and 2 have been re-visited. Using the spectroscopic data and footprints of the IRIS aperture on the planet, we constructed images of the stratosphere of Jupiter at the emission bands of hydrocarbons including , and . Thermal emission from the hydrocarbons on Jupiter originates from a broad region of the stratosphere extending from 1 to 10 millibars. We averaged the data using a bin of 20 degrees of longitude and latitudes in order to increase signal-to-noise ratios. The resultant images show interesting wave structure in Jupiter`s stratosphere. Fourier transform analyses of these images yield wavenumbers 5 - 7 at mid-Northern and mid-Southern latitudes, and these results are different from those resulted from previous ground-based observations and recent Cassini CIRS, suggesting temporal variations on the stratospheric infrared pattern. The comparisons of the Voyager 1 and 2 spectra also show evidence of temporal intensity variations not only on the infrared hydrocarbon polar brightenings of hydrocarbon emissions but also on the stratospheric infrared structure in the temperate regions of Jupiter over the 4 month period between the two Voyager encounters. Short running title: Stratospheric Images of Jupiter derived from Voyager IRIS Spectra.

Radiative Balance and Dynamics in the Stratosphere of Jupiter: Results from a Latitude-Dependent Aerosol Heating Model

An updated dynamical model for the circulation in the jovian stratosphere has been developed. For computation of the heating and cooling rates in the stratosphere, required to obtain the radiative flux convergence, the model makes use of exponential-sum derived coefficients from laboratory and correlated-kdistributions from line listing data for the various atmospheric gases. The aerosol distribution at different latitudes was determined from comparisons of results from microphysical models and near-UV jovian images obtained by the Wide Field and Planetary Camera 2 on the Hubble Space Telescope. The largest aerosol content is found at latitudes south of 65°S planetographic, the aerosols being produced at higher atmospheric levels and at higher rates than those at the corresponding northern latitudes. At midlatitudes, the aerosol production rate is less than about two orders of magnitude than that found at high latitudes. The distinct imaginary refractive index spectra of the aerosols found at the different latitudes reflect a compositional difference in the material being produced as a result of chemical reactions. This difference is evident in the shortest wavelength explored (λeff= 230 nm) between low to midlatitudes and the polar regions.The resulting heating rates are much higher in the stratosphere than those given by previous estimates. The corresponding radiative equilibrium temperatures are therefore hotter than previously reported, mainly above the 10-mbar level. A north–south asymmetry in the stratospheric aerosol distribution was found, which, in turn, produces a different pattern in the derived quantities from the dynamical model. In particular, the Eliassen–Palm flux divergence (ϵ) shows a different pattern when compared with that inferred by Conrathet al.(1990,Icarus83, 255–281) and Westet al. (1992,Icarus100, 245–259). At the base of the stratosphere we inferred the same circulation pattern as found by Gieraschet al. (1986,Icarus67, 456–483) and Westet al. (1992) with upwelling over the zones and subsidence in belts, but with higher values in the magnitude of the vertical winds at low latitudes.

Jovian acoustics: Short‐range observation and long‐range prediction

Waves were observed propagating in the stratosphere of Jupiter near the impact sites of several of the fragments of Comet Shoemaker‐Levy 9. Concentric rings appearing in Hubble Space Telescope images have tentatively been identified as gravity and acoustic waves based on their horizontal group speeds of 450 and 900 m/s. Interpreting the images is complicated by the fact that the outer ring is located amidst the debris of the collapsed fireball. Since the fireball rose back through the obliquely oriented path of the incoming fragment, the debris field is asymmetric and offset from the impact site. It is therefore unlikely that the outer ring is part of the debris. If waves are observed far from the impact sites, they might provide new information about the Jovian atmosphere. A three‐dimensional adiabatic mode solution predicts that the Jovian zonal winds cause horizontal caustics to form to the east and west of the impact sites about 10 h after impact. An adiabatic mode solution has also been derived for gravity waves, which exhibit similar horizontal caustics. Although the acoustic and gravity wave equations are drastically different, the horizontal wave equations for the mode coefficients are identical.

Detectability of water-ice clouds expected after the P/Shoemaker-Levy 9 impact with Jupiter at near-infrared molecular bands

The predicted crash of periodic comet Shoemaker-Levy 9 into Jupiter in mid-July 1994 is expected to release a considerable amount of cometary material, which is mainly composed of water, into Jupiter's atmosphere. This released water will form a water-ice cloud layer in the stratosphere. We estimated the reflected sunlight from the impact cloud at near-infrared wavelengths using a radiative transfer model. It was found that the cloud is likely to be observable when we choose some strong molecular absorption band such as methane for imaging observation, because we get higher contrast between the cometary ice cloud and background scattered light from the lower ammonia clouds at these wavelengths. This cometary cloud can be used as an atmospheric tracer of the upper troposphere and the stratosphere of Jupiter.

The photolysis of NH 3 in the presence of substituted acetylenes: A possible source of oligomers and HCN on Jupiter

Photolysis of NH 3 in the presence of propyne yields dimethylketazine (4) as the main product along with dimethylketimine, isopropylamine, and propioazine (7). Dimethylketazine and isopropylamine are the principal reaction products when the protolysis is performed at 198 K. The conversion to dimethylketazine is about 35 times greater at 198 K because it is not volatile and condenses on the wall of the protolysis cell out of the UV flux. Protolysis of dimethylketazine at 185 nm yields acetonitrile and small amounts of N-methyldimethylketamine (8). Protolysis of 8 gives acetonitrile. Photolysis of NH 3 in the presence of 2-butyne gives the cis and trans isomers of 2-butane as the principal products along with the corresponding azine (9). Photolysis of azine 9 yields acetonitrile and propionitrile. Photolysis of hydrazine in the presence of propyne yields acetonitrile and isopropylamine but no azines were detected as reaction products. Quantum yields and percentage conversion to products are reported. These studies show that acetylenic hydrocarbons formed by the photolysis of methane in the stratosphere of Jupiter may react with radicals formed by NH 3 photolysis to give nonvolatile yellow-brown polymers, dialkylazines, alkylnitriles, and eventually HCN. This scenario accounts for the observation of both HCN and chromophores on Jupiter.

The atmosphere of Jupiter: An analysis of the Voyager radio occultation measurements

Coherently related S (2.3 GHz) and X band (8.4 GHz) signals transmitted from Voyager 1 and 2 have been used to probe the Jovian atmosphere during occultations of the spacecraft by Jupiter. The observations have yielded profiles in height of the gas refractivity, molecular number density, pressure, temperature, and microwave absorption in the troposphere and stratosphere of Jupiter at latitudes ranging from 0° to about 70°S. The data cover a pressure range from 1000 to 1 mbar over a height interval of 160 km. At the 1000‐mbar level, the temperature was 165±5 K, and the lapse rate was equal to the adiabatic value of 2.1 K/km, within the resolution of the measurements. The ammonia abundance in this region of the atmosphere was about 0.022±0.008%, in approximate agreement with the value derived from cosmic abundance considerations. The tropopause, which was detected near the 140‐mbar level, had a temperature of 110 K. Above the tropopause, the temperature increased with increasing altitude, reaching 160±20 K in the 10‐ to 1‐mbar region of the stratosphere. Significant horizontal density variations were detected in the stratosphere. This may imply a nonuniform temperature and aerosol distribution across the Jovian disk or high‐ and low‐pressure regions due to local atmospheric dynamics. The zenoid or gravity equipotential surface which best fits the 100‐mbar isobaric surface has an equatorial radius of 71,541±4 km and a polar radius of 66,896±4 km.

Models of the Jovian upper atmosphere

Recent developments in photochemical models of the upper atmosphere of Jupiter and Titan are reviewed. Measurements of the Jovian Lyman alpha airglow favor a homopause value of approximately 107 cm² s−1 for the eddy diffusion coefficient. A relatively hot exosphere as implied by the electron density measurements results in an extended atmosphere of hydrogen. Larger than solar C/H and N/H ratios are obtained on reinterpretation of the sunlight reflected from Jupiter; and substantially lower ultraviolet photoabsorption cross sections measured for methane and ethane influence the distribution of CH4, NH3, and their photochemical products. Possible coupling between PH3 and NH3 may inhibit ultraviolet destruction of NH3 on Jupiter. The red color of the Great Red Spot and other minor spots may be due to the presence of red phosphorus crystals formed after photolysis of PH3. The detection of such gases as PH3, GeH4, and CO in the stratosphere of Jupiter gives an indication of the presence of thermochemical nonequilibrium processes, and a strong vertical mixing may be required to explain their large observed upper atmospheric abundances. This argument is further strengthened by a laboratory finding that C2H2 can efficiently scavenge photolysis products of PH3. Other alternate mechanisms to account for the presence of CO in the stratosphere are the oxygen atom transfer from the Galilean satellites to Jupiter either by radial diffusion, or along magnetic flux tubes, or on ablation of meteoroidal material. Subsequent reactions of the thermal oxygen atoms with photolysis products of methane lead to the production of CO. Finally, the discussion of reducing atmospheres is extended to include Titan. It is found that if NH3 has outgassed from Titan and if the surface temperature during the initial phases of its evolution was 150°K or greater, due perhaps to a CH4‐H2 greenhouse, it is inevitable that Titan would have accumulated a thick atmosphere of nitrogen over geologic time. The pressure‐induced thermal opacity of 20 bars of nitrogen can also explain the recently measured 200°K surface temperature of Titan. On the other hand, the composition of Titan's atmosphere would be far less certain if the surface temperature were as low as 100°K.

The role of phosphorus in the upper atmosphere of Jupiter

The reaction of elemental phosphorus and H atoms to form PH 3 was observed and should be a major factor in the recycling of PH 3 in the stratosphere of Jupiter. The formation of PH 3 in this manner should predominate at high altitudes where, due to the very low temperatures, reactions that require higher activation energies than these atom reactions cannot occur. At lower altitudes, in the troposphere, the rapid formation of H atoms from the strong absorption of light by NH 3 will contribute to phosphine production also in this same manner. Recent experiments have also shown that elemental phosphorus reacts readily with aqueous ammonia to form PH 3. This reaction may also be important in the recycling of PH 3 in the upper troposphere of Jupiter if water-ammonia clouds, as had been previously thought, exist. Considerations of the coloration of the Great Red Spot have been made based upon the nature of the phosphorus obtained by decomposition of phosphine.