The detection of HCN on Jupiter

We report the detection of HCN on Jupiter. Three R-branch lines of the ν₂ fundamental of HCN near 13.5 μm were observed in absorption, from which the HCN column density is inferred to be 5 × 10^?3 cm-am with an uncertainty of a factor of 2. If emission from the stratosphere exists, then the derived column density is only a lowe limit. We suggest that the Jovian HCN most likely originates from the photolysis of CH₄ and NH₃ in the lower stratosphere and upper troposphere. In addition, an upper limit of 2.5 × 10^?2 cm-am was established for the column density of HCN on Saturn.     

HCN formation on Jupiter: The coupled photochemistry of ammonia and acetylene

A model is presented for the formation of HCN in the upper troposphere and lower stratosphere of Jupiter by ultraviolet photolysis of the C₂H₅N isomer aziridine, a product of the recombination of NH₂ and C₂H₃ radicals, which originate, respectively, from ammonia photolysis and addition of H atoms to acetylene. An HCN column density of ～ 2 × 10¹⁷ cm^?2 in the tropopause region, which is comparable to that observed by A. T. Tokunaga, S. C. Beck, T. R. Geballe, J. H. Lacy, and E. Serabyn (Icarus48, 283–289, 1981), is predicted when vertical mixing is slow above the ammonia cloudtops. Sensitivity of the HCN column density to the individual rate constants and the eddy diffusion coefficient profile is discussed, as is the possibility of the existence of additional HCN-yielding pathways. Ammonia, which is saturated in the upper troposphere, is strongly depleted by photolysis in the lower stratosphere. Phosphine is also strongly depleted by photolysis and its abundance in the upper troposphere is shown to depend strongly on vertical mixing in the tropopause region. The possibility of the formation of phosphirane, the P-containing analog of aziridine, is considered but found to be substantially less probable than aziridine.     

Laboratory simulations of PH3 photolysis in the atmospheres of Jupiter and Saturn

Photolysis of NH₃PH₃ mixtures (11 Torr) at 175°K resulted in the same initial rate of P₂H₄ formation as when the 11 Torr of pure PH₃ was photolyzed. A higher yield of P₂H₄ is obtained at 175°K than at 298°K because some of the P₂H₄ condenses on the cell wall at 175°K and is not subject to further reaction. Some reaction of P₂H₄ is taking place as observed by the decrease in its yield and on the formation of red phosphorus on extended photolysis of PH₃ at 175°K. No NH₂PH₂ or (PN)_x were detected as photoproducts as indicated by the absence of change in the UV spectral properties of the P₂H₄ and red phosphorus fraction, respectively, when NH₃ is present. Although the pathway for PH₃ decomposition is changed, the outcome of the photochemical process is essentially the same in the absence or presence of NH₃. The formation of P₂H₄ and red phosphorus was not inhibited by small amounts of C₂H₄ and C₂H₂, so the low levels of hydrocarbons on Jupiter and Saturn will not have a significant effect on the course of PH₃ photolysis. The ratio of products of PH₃ photolysis are only slightly affected by the wavelength of light used. Use of xenon lamp, with a continuous emission in the ultraviolet where P₂H₄ absorbs, results in only a modest decrease in the yield of P₂H₄ and a modest increase in the rate of formation of red phosphorus as compared to the rates observed with a 206.2-nm light source. The quantum yield for P₂H₄ formation is pressure independent in the 0.5–11 Torr range. This quantum yield is not affected by lowering the temperature to 157°K or by the addition of 100 Torr of H₂. It is concluded that photolysis of PH₃ to P₂H₄ and the subsequent conversion of P₂H₄ to red phosphorus are likely procses on Jupiter and Saturn and that particles of P₂H₄ condense in the atmospheres of these planets. The conversion of some of the P₂H₄ to red phosphorus may take place on Jupiter.     

Observations of NH3 in the atmosphere of Jupiter during 1973, 1974

The 6450 Å ammonia absorption band in the atmosphere of Jupiter was observed during the summers of 1973 and 1974. High-dispersion spectra of this band were obtained and analyzed on a line-by-line basis to derive ammonia abundances in the Jovian atmosphere. The abundances determined this way show strikingly large fluctuations.     

The satellites of Jupiter as a source of very energetic magnetospheric particles

The Jovian satellites and ring are continuously bombarded by high-energy galacic cosmic rays and magnetospheric ions. Nuclear interactions will create very energetic neutrons and pions. The decay of some of these unstable particles within the Jovian magnetosphere wil result in trapped protons and ultrarelativistic electrons and positrons. Although this source is weak compared to those that yield lower-energy magnetospheric particles, it is expected to generate the most energetic Jovian particles. These processes are briefly described.     

Broadband Submillimeter Spectroscopy of HCN, NH3, and PH3in the Troposphere of Jupiter

We report measurements of the Jupiter brightness spectrum in the 850-μm and 1100-μm atmospheric windows with a spectral resolution of 125 MHz, obtained with a Fourier transform spectrometer on the James Clerk Maxwell Telescope. Three results were obtained. First, the predicted absorption features due to the rotational lines of HCN at 266 and 354 GHz were not detected within our error limits of less than 1%. We establish new upper limits for the HCN abundance in the jovian troposphere for five assumed abundance distributions and for two assumed NH₃abundances. The upper limits are 1.7 to 13 times smaller than the abundance value obtained in the only reported detection of HCN in Jupiter prior to the impact of Shoemaker–Levy 9. Second, the continuum brightness temperature spectrum at 850 μm was determined and is in agreement with previous measurements, but has large error bars due to uncertainties in the photometric calibration. We estimate the ammonia abundance in the 1–2 bar region to be 1.7 times solar, but this result is tentative since scattering by NH₃cloud particles and absorption by gaseous H₂S were neglected in our atmospheric model. Finally, the first rotational line of PH₃at 267 GHz was not detected, a result which we demonstrate is consistent with the statistical noise level in these measurements, with current values of the spectroscopic parameters, and with phosphine measurements at other wavelengths.     

The atmospheric influence, size and possible asteroidal nature of the July 2009 Jupiter impactor

Near-infrared and mid-infrared observations of the site of the 2009 July 19 impact of an unknown object with Jupiter were obtained within days of the event. The observations were used to assess the properties of a particulate debris field, elevated temperatures, and the extent of ammonia gas redistributed from the troposphere into Jupiter’s stratosphere. The impact strongly influenced the atmosphere in a central region, as well as having weaker effects in a separate field to its west, similar to the Comet Shoemaker-Levy 9 (SL9) impact sites in 1994. Temperatures were elevated by as much as 6 K at pressures of about 50-70 mbar in Jupiter’s lower stratosphere near the center of the impact site, but no changes above the noise level (1 K) were observed in the upper stratosphere at atmospheric pressures less than ∼1 mbar. The impact transported at least ∼2 × 10¹⁵ g of gas from the troposphere to the stratosphere, an amount less than derived for the SL9 C fragment impact. From thermal heating and mass-transport considerations, the diameter of the impactor was roughly in the range of 200-500 m, assuming a mean density of 2.5 g/cm³. Models with temperature perturbations and ammonia redistribution alone are unable to fit the observed thermal emission; non-gray emission from particulate emission is needed. Mid-infrared spectroscopy of material delivered by the impacting body implies that, in addition to a silicate component, it contains a strong signature that is consistent with silica, distinguishing it from SL9, which contained no evidence for silica. Because no comet has a significant abundance of silica, this result is more consistent with a “rocky” or “asteroidal” origin for the impactor than an “icy” or “cometary” one. This is surprising because the only objects generally considered likely to collide with Jupiter and its satellites are Jupiter-Family Comets, whose populations appear to be orders of magnitude larger than the Jupiter-encountering asteroids. Nonetheless, our conclusion that there is good evidence for at least a major asteroidal component of the impactor composition is also consistent both with constraints on the geometry of the impactor and with results of contemporaneous Hubble Space Telescope observations. If the impact was not simply a statistical fluke, then our conclusion that the impactor contained more rocky material than was the case for the desiccated Comet SL9 implies a larger population of Jupiter-crossing asteroidal bodies than previously estimated, an asteroidal component within the Jupiter-Family Comet population, or compositional differentiation within these bodies.     

The contribution by thunderstorms to the abundances of CO,C2H2, and HCN on Jupiter

The lightning energy dissipation rate on Jupiter from Voyager's observation is used, together with shock-tube experimental results and reasonable eddy diffusion coefficients for the various atmospheric layers, to compute the column abundances of lightning-produced CO, C₂H₂, and HCN. Shock-tube experiments on the hydrogenation of CO clearly rule out chemical “freezing” of CO at the 1064°K and 400-bar level and its subsequent upwelling to the upper atmosphere. Also, lightning in the water cloud cannot produce enough CO to meet its observed abundance. Hence, the CO is formed from an external source of oxygen or water. The production of acetylene both by lightning above the water cloud and by startospheric methane photolysis is required to maintain its observed abundance against destruction processes. This explains the decrease in the C₂H₂/C₂H₆ ratio from the equator to the pole, as observed in the IR. HCN production by lightning above the water cloud is sufficient to account for its observed abundance and meets the observational requirement of a tropospheric HCN source.     

Methane on Mars: A product of H2O photolysis in the presence of CO

We suggest that the methane observed on Mars can be formed by photolysis of water vapor in the presence of CO, in addition to possible geological sources, rather than biologically.     

The possible presence of C2 lines in sunspot spectra

Indirect evidence against the presence of C₂ lines in umbral spectra is discussed. The dominant role of CO in the molecular equilibrium of C at umbral temperatures ensures that CN, CH and C₂ lines are formed in the same atmospheric regions. Observations of CN and CH umbral lines are in good accord with predictions based on accepted umbral model atmospheres. This implies that C₂ must follow the predictions and that it is too weak to contribute to the umbral spectrum. C₂ lines in the photosphere and penumbrae are in excellent quantitative agreement with predictions. Additional tests are proposed.     

The structure of the planets Jupiter and Saturn

Planetary models for Jupiter and Saturn are computed using a fourth-order theory and a new molecular equation of state. The equation of state for the molecular hydrogen and helium planetary envelopes is taken from the Monte Carlo calculations of Slattery and Hubbard [Icarus 29, 187–192 (1976)]. Models for Jupiter are found that have a small amount of heavy elements either mixed with hydrogen and helium throughout the interior of the planet or concentrated in a small dense core. Saturn is modeled with a solar-composition hydrogen and helium envelope and a small derse core. We conclude that the molecular equation of state linked with suitable interior equations of state can produce Jovian models which satisfy the observational data. The planetary models show that the enrichment of heavy elements (relative to solar composition) is approximately 3 times for Jupiter and 10 times for Saturn.     

Constraints on the NH3 and PH3 distributions in the great red spot

Spatially resolved IUE observations of the Great Red Spot and the South Tropical Zone in the wavelength region of the NH₃ predissociation bands between 1900 and 2200 Å show slightly stronger absorption in the Great Red Spot than in the South Tropical Zone. Neglecting stratopheric haze, vertically inhomogeneous Rayleigh scattering radiative transfer models find an enhanced [NH₃]/[H₂] mixing ratio at the 80- to 125-mbar pressure level in the Great Red Spot of a factor of 3 to 10 with respect to the South Tropical Zone. Upper limits on the mixing ratio of PH₃ and the eddy diffusion coefficient above the Great Red Spot are considerably lower than earlier predictions.     

The WKB approximation and the plasma ring of Jupiter

In this note we study the behaviour of hydromagnetic oscillations along the field lines of Jupiter's magnetosphere crossing the Io plasma ring. We compare the shape and period of these oscillations, as found by a direct numerical calculation, with those obtained with the WKB method, in order to show the unaccuracy of this approximation.     

The abundance of ammonia in the atmosphere of Jupiter

A laboratory curve of growth analysis was made on the lines in two ammonia bands located at 6450 Å and 10800 Å and the abundance of ammonia in the atmosphere of Jupiter was determined. Lines in the 6450 Å band appear to fall on the weak line section of the curve of growth, while those in the 10800 Å band fall in the transition region. The abundance values obtained from these bands are 13.0±3 m atm and 15±8 m atm, respectively.Measurements of the intensity distribution in the 6450 Å band in the laboratory and in the Jovian spectra show that the intensity of several lines in this band is highly dependent on the temperature. Strengths for some of the lines in the 6450 Å band were determined and half-widths of some strong lines were also measured. The effective pressure found from these half-width values is 2.5 atmospheres.Contributions from the University of Illinois, Chicago Circle Physics Department, No. 12.     

The predicted infrared spectrum of ZrO and its possible presence in S stars

The unidentified absorption feature at 9730±5 Å observed in the spectra of pure S stars is provisionally identified with the predicted 9732 Å (0,0) band of thee ¹II-c ¹ transition of ZrO molecule. Relative band strengths and band head positions ofthis transition in the 8300–12 500 Å region are presented to assist both laboratory and stellar spectral studies. The insistent need for the laboratory study of gas phase infrared spectrum of ZrO is accentuated.     

Irregular Satellites of Jupiter: a study of the capture direction

The irregular satellites of Jupiter are believed to be captured asteroids or planetesimals. In the present work is studied the direction of capture of these objects as a function of their orbital inclination. We performed numerical simulations of the restricted three-body problem, Sun-Jupiter-particle, taking into account the growth of Jupiter. The integration was made backward in time. Initially, the particles have orbits as satellites of Jupiter, which has its present mass. Then, the system evolved with Jupiter losing mass and the satellites escaping from the planet. The reverse of the escape direction corresponds to the capture direction. The results show that the Lagrangian points L1 and L2 mainly guide the direction of capture. Prograde satellites are captured through these two gates with very narrow amplitude angles. In the case of retrograde satellites, these two gates are wider. The capture region increases as the orbital inclination increases. In the case of planar retrograde satellites the directions of capture cover the whole 360° around Jupiter. We also verified that prograde satellites are captured earlier in actual time than retrograde ones. This paper was presented at the Asteriods, Comets and Meteors meeting held at Búzios, Rio de Janeiro, Brazil in August 2005 and could not be included in the special issue related to that conference.     

The abundance of acetylene in the atmosphere of Jupiter

The Q and R branches of the C₂H₂ ν₅ fundamental, observed in emission in an aircraft spectrum of Jupiter near 750 cm^?1, have been analyzed with the help of an improved line listing for this band. The line parameters have been certified in the laboratory with the same interferometer used in the Jovian observations. The maximum mixing ratio of C₂H₂ is found to be between 5 × 10^?8 and 6 × 10^?9, depending on the form of its vertical distribution and the temperature structure assumed for the lower stratosphere. Most consistent with observations of both Q and R branches are: (1) distributions of C₂H₂ with a constant mixing ratio in the stratosphere and a cutoff at a total pressure of 100 mbar or less, and (2) the assumption of a temperature at 10^?2 bar which is near 155°K.