Role of H2O and CO2 Ices in Martian Climate Changes

In order to study the stability of martian climate, we constructed a two-dimensional (horizontal-vertical) energy balance model. The long-term CO₂ mass exchange process between the atmosphere and CO₂ ice caps is investigated with particular attention to the effect of planetary ice distribution on the climate stability. Our model calculation suggests that high atmospheric pressure presumed for past Mars would be unstabilized if H₂O ice widely prevailed. As a result, a cold climate state might have been achieved by the condensation of atmospheric CO₂ onto ice caps. On the other hand, the low atmospheric pressure, which is buffered by the CO₂ ice cap and likely close to the present pressure, would be unstabilized if the CO₂ ice albedo decreased. This may have led the climate into a warm state with high atmospheric pressure owing to complete evaporation of CO₂ ice cap. Through the albedo feedback mechanisms of H₂O and CO₂ ices in the atmosphere-ice cap system, Mars may have experienced warm and cold climates episodically in its history.     

Extreme Ultraviolet Photon-Induced Chemical Reactions in the C2H2-H2O Mixed Ices at 10 K

Experimental results on the spectral identification of new infrared absorption features and the changes of their absorbances produced through vacuum ultraviolet-extreme ultraviolet (VUV-EUV) photon-induced chemical reactions in the C₂H₂-H₂O mixed ices at 10 K are obtained. To the best of our knowledge, this is the first time that EUV photons have been employed in the study of the photolysis of ice analogues. Two different compositions, i.e., C₂H₂:H₂O=1:4 and 1:1, were investigated in this work. A tunable intense synchrotron radiation light source available at the Synchrotron Radiation Research Center, Hsinchu, Taiwan, was employed to provide the required VUV-EUV photons. In this study, the photon wavelengths selected to irradiate the icy samples corresponded to the prominent solar hydrogen, helium, and helium ion lines at 121.6 nm, 58.4 nm, and 30.4 nm, respectively. The photon dosages used were typically in the range of 1×10¹⁵ to 2×10¹⁷ photons. Molecular species produced and identified in the ice samples at 10 K resulting from VUV-EUV photon irradiation are mainly CO, CO₂, CH₄, C₂H₆, CH₃OH, and H₂CO. In addition to several unidentified features, we have tentatively assigned several absorption features to HCO, C₃H₈, and C₂H₅OH. While new molecular species were formed, the original reactants, i.e., H₂O and C₂H₂, were detectably depleted due to their conversion to other species. The new chemical species produced by irradiation of photons at 30.4 nm and 58.4 nm can be different from those produced by the 121.6-nm photolysis. In general, the product column density of CO reaches saturation at a lower photon dosage than that of CO₂. Furthermore, the production yield of CO is higher than that of CO₂ in the photon irradiation. In the present study, we also observe that the photon-induced chemical reaction yields are high using photons at 30.4 and 58.4 nm. The results presented in this work are essential to our understanding of chemical synthesis in ice analogues, e.g., the cometary-type ices and icy satellites of planetary systems.     

Observation and Study of the CO, CO, HCO and N2H Molecular Lines Towards IRAS 02232+6138

Using the 13.7 m millimeter-wave telescope at the Qinghai Station of Purple Mountain Observatory, we have made observations of ¹³CO, C¹⁸O, HCO⁺ and N₂H⁺ molecular lines towards IRAS 02232+6138. As the excitation density of the probe molecule increases from ¹³CO to HCO⁺, the size of the cloud core associated with IRAS 02232+6138 decreases from 2.40 pc to 0.54 pc, and the virial mass of the cloud core decreases from 2.2 × 10³M to 5.1 × 10²M. A bipolar molecular outflow is found towards IRAS 02232+6138. Using the power function n(r) ∝ r⁻ to fit the spatial density structure of the cloud core, we obtain the power-law index  = 2.3 − 1.2; and we find that, as the probed density increases, the power function becomes more flat. The abundance ratio of ¹³CO to C¹⁸O is 12.4 ± 6.9, comparable with the values 11.8 ± 5.9 for dark clouds and the values 9.0–15.6 for massive cores. The abundance of N₂H⁺ molecules is 3.5 ± 2.5 × 10⁻¹⁰, consistent with the value 1.0 − 5.0 × 10⁻¹⁰ for dark cloud cores and the value 1.2 − 12.8 × 10⁻¹⁰ for massive cores. The abundance of HCO⁺ molecules is 0.9 ± 0.5 × 10⁻⁹, close to the value 1.6 − 2.4 × 10⁻⁹ for massive cores. An increase of HCO⁺ abundance in the outflow region was not found. Combining with the IRAS data, the luminosity-mass ratio of the cloud core is obtained in the range 37–163(L/M). Based on the IRAS luminosity, it is estimated that a main-sequence O7.5 star is probably embedded in the IRAS 02232+6138 cloud core.     

A Search for Variability in the HCCN to H2CO Ratio in Comet Hale-Bopp

We observed submillimeter lines of H₂CO and HCN in comet Hale-Bopp near perihelion. One of our goals was to search for short term variability. Our observations are suggestive, but not conclusive, of temporal and/or spatial changes in the coma's HCN/H₂CO abundance ratio of ∼25%. If due to spatial variability, the ratio on the sunward side of the coma is enhanced over other regions. If due to temporal variability, we find the bulk ratio in the coma changed in less than 16 hours. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Search for Variability in the HCCN to H2CO Ratio in Comet Hale-Bopp

We observed submillimeter lines of H₂CO and HCN in comet Hale-Bopp near perihelion. One of our goals was to search for short term variability. Our observations are suggestive, but not conclusive, of temporal and/or spatial changes in the coma's HCN/H₂CO abundance ratio of ～25%. If due to spatial variability, the ratio on the sunward side of the coma is enhanced over other regions. If due to temporal variability, we find the bulk ratio in the coma changed in less than 16 hours.     

Variability of CO concentrations in the Venus troposphere from Venus Express/VIRTIS using a Band Ratio Technique

A fast method is presented for deriving the tropospheric CO concentrations in the Venus atmosphere from near-infrared spectra using the night side 2.3 μm window. This is validated using the spectral fitting techniques of Tsang et al. [Tsang, C.C.C., Irwin, P.G.J., Taylor, F.W., Wilson, C.F., Drossart, P., Piccioni, G., de Kok, R., Lee, C., Calcutt, S.B., and the Venus Express/VIRTIS Team, 2008a. Tropospheric carbon monoxide concentrations and variability on Venus with Venus Express/VIRTIS-M observations. J. Geophys. Res. 113, doi: 10.1029/2008JE003089. E00B08] to show that monitoring CO in the deep atmosphere can be done quickly using large numbers of observations, with minimal effect from cloud and temperature variations. The new method is applied to produce some 1450 zonal mean CO profiles using data from the first eighteen months of operation from the Visible and Infrared Thermal Imaging Spectrometer infrared mapping subsystem (VIRTIS-M-IR) on Venus Express. These results show many significant long- and short-term variations from the mean equator-to-pole increasing trend previously found from earlier Earth- and space-based observations, including a possible North-South dichotomy, with interesting implications for the dynamics and chemistry of the lower atmosphere of Venus.     

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.     

Characteristics of Massive Star-forming Molecular Cores: The Spectral Observations of CO,CO and CO and the Statistical Comparison

With the 13.7 m millimeter wave telescope of Purple Mountain Observatory at Qinghai Station, the simultaneous mapping observations at the ¹²CO(J=1-0), ¹³CO(J=1-0) and C¹⁸O(J=1-0) lines were performed towards the 24 Galactic high-mass star-forming cores, which are associated with water masers and have available Spitzer's infrared data. The average mapping range was 8′ × 8′. The C¹⁸O line emission was detected in all the cores, in which 11 cores were observed to the half maximum of their C¹⁸O integrated intensities and the rather extended (5′ − 8′) C¹⁸O maps were obtained, while the others were failed to make such a large scale mapping because of the low SNR or the intrinsically extended morphology of the cores. On the 11 completely mapped dense cores, we analyzed their characteristics and made the statistics and comparisons on the integrated intensity ratios between ¹²CO and ¹³CO (R_12/13), ¹³CO and C¹⁸O(R_13/18), as well as ¹²CO and C¹⁸O(R_12/18). We concluded that as a tracer of dense gas, C¹⁸O is absolutely optically thin and can be used to detect the detailed structures of the cores, and that in general the 3 ratios increase gradually from the core center to the periphery. We found that the integrated intensity ratio R_12/13 ranges from 2 to 6; R_13/18 fluctuates between 4 and 20, but in central regions it is concentrated in the range 6–12 with a small fluctuation; and R_12/18 occupies a wider range 13–90, but it is concentrated between 13 and 50 in the denser regions of the cores.     

CO2 production by ion irradiation of H2O ice on top of carbonaceous materials and its relevance to the Galilean satellites

In this work we report on new experiments of ion irradiation of water ice deposited on top of solid carbonaceous materials to study the production of CO₂ at the interface ice/refractory material and discuss the possibility that this mechanism accounts for the quantity of CO₂ ice detected on the surfaces of the Galilean satellites. The used experimental technique has been in situ infrared spectroscopy. We have irradiated thin films of H₂O frost on carbonaceous layers with 200 keV of He⁺ and Ar⁺, and 30 keV of He⁺ at 16 and 80 K. The used carbonaceous layers have been asphaltite, a natural bitumen, and solid organic residues obtained by irradiation of frozen benzene. In both cases the results show that CO₂ is produced very efficiently after irradiation obtaining a maximum quantity of the order of . These results are, also quantitatively similar, to those recently obtained for water ice deposited on amorphous carbon films [Mennella, V., Palumbo, M.E., Baratta, G.A., 2004. Formation of CO and CO₂ molecules by ion irradiation of water ice covered hydrogenated carbon grains. Astrophys. J. 615, 1073-1080]. Thus we suggest that, whatever is the carbonaceous residue, CO₂ will be produced efficiently by the studied process. These results have interest in the context of the surfaces of the icy Galilean satellites in which CO₂ has been detected mainly trapped in the non-ice material, not in the pure water ice. We suggest that radiolysis of mixtures of water ice and refractory carbonaceous materials is the primary formation mechanism responsible for the CO₂ formation on the surfaces of the Galilean satellites.     

The nature of the solar wind interaction with CO2/CO-dominated comets

The varying overall nature of the solar wind interaction with the ionospheres of CO and CO₂-dominated comets is investigated and compared with previous results for H₂O-dominated comets. It is shown that as a comet approaches the sun, it may exhibit one of two types of ionospheric transitions. (In rare circumstances, the cometary ionosphere may display a third type of transition in addition to one of the first two). For both transitions, the ionosphere turns from being hard (in other words, the ionosphere is not susceptible to compression under sudden solar wind pressure increases) to soft. However, for one type of transition, the bow shock changes from being weak (M2) to being strong (M10), whereas for the other type of transition, the bow shock remains weak. The heliocentric distance at which these transitions may occur is found to be a function of the cometary nuclear radius, the latent heat of sublimation of the surface volatiles, the surface bolometric albedo and the following ionospheric properties: the optical depth, the average ionization time scale and the amount of heat addition. Two important consequences of the strong shocks are the large solar wind velocity modulation of the energization of electrons at the bow-shock and the relatively quick formation of cometary plasma tails.These results are applied to the case of comet Humason (1962 VIII). It is shown that either a CO or CO₂ dominated surface can explain not only the strong coma and tail activity of this comet at large heliocentric distances, but it can also explain the irregular activity of this comet at such distances.     

Oxidation of CO on surface hematite in high CO2 atmospheres

We propose a mechanism for the oxidation of gaseous CO into CO₂ occurring on the surface mineral hematite (Fe₂O₃(s)) in hot, CO₂-rich planetary atmospheres, such as Venus. This mechanism is likely to constitute an important source of tropospheric CO₂ on Venus and could at least partly address the CO₂ stability problem in Venus’ stratosphere, since our results suggest that atmospheric CO₂ is produced from CO oxidation via surface hematite at a rate of 0.4 petagrammes (Pg) CO₂ per (Earth) year on Venus which is about 45% of the mass loss of CO₂ via photolysis in the Venusian stratosphere. We also investigated CO oxidation via the hematite mechanism for a range of planetary scenarios and found that modern Earth and Mars are probably too cold for the mechanism to be important because the rate-limiting step, involving CO(g) reacting onto the hematite surface, proceeds much slower at lower temperatures. The mechanism may feature on extrasolar planets such as Gliese 581c or CoRoT-7b assuming they can maintain solid surface hematite which, e.g. starts to melt above about 1200 K. The mechanism may also be important for hot Hadean-type environments and for the emerging class of hot Super-Earths with planetary surface temperatures between about 600 and 900 K.     

The Correct Evaluation of the Sublimation Rate of Dusty Ices under Solar Illumination, and Its Implication on the Properties of P/Halley Nucleus

This note (1) provides a formal derivation of an algorithm proposed precedingly without proof for evaluating the sublimation rate of dusty ice under solar illumination, and (2) illustrates the importance of adopting a correct algorithm for such a purpose, by rediscussing the basic characteristics of P/Halley nucleus activity derived from the 1996 flyby data.     

The KOSMA large-scale CO survey of clouds in the Galactic Molecular Ring

We present the status of the KOSMA large-scale observations of clouds in the Galactic Molecular Ring (GMR) in CO J=3-2, 2-1 and ¹³CO 2-1 following up on the BU-FCRAO ¹³CO 1-0 survey. The GMR is one of the prominent large scale structures in the Milky Way and an interesting laboratory to studystar formation. Whereas the ¹³CO data yield a good measureof the overall column density structure, the new observations of CO 2-1provide a picture of the thin extended gas and the CO 3-2 data show thedistribution of the dense and warm molecular gas. The combination of observations of these lines thus allows to distinguish between extended,quiescent gas, dense cold parts, and warm regions, influenced by star formation. In performing large scale observations we are able to analysethe structure of this material.     

A comparison of the spectral characteristics of the Wolf Sunspot Number (RZ) and Group Sunspot Number (RG)

The objective of this paper is to compare the spectral features of the recently derived Group Sunspot Numbers (R _G) and the traditional Wolf Sunspot Numbers (R _Z) for the 1700–1995 period. In order to study the spectral features of both time series, two methods were used, including: (a) the multitaper analysis and (b) the wavelet analysis. Well-known features of the solar variability, such as the 98.6-yr (Gleissberg cycle), 10–11-yr (Schwabe cycle) and 5-yr (second solar harmonic) periodicities were identified with high confidence using the multitaper analysis. Also observed was a larger amount of power spread in high frequencies for R _Z than for R _G spectra. Furthermore, a multitaper analysis of two subsets, A (1700–1850) and B (1851–1995), has indicated that the main differences occurred in the first subset and seem to be due to uncertainties in the early observations. The wavelet transform, which allows observing the spectra evolution of both series, showed a strong and persistent 10–11-yr signal that remained during the whole period. The Meyer Wavelet Transform was applied to both R _Z and R _G. This study indicates that the main spectral characteristics of both series are similar and that their long-term variability has the same behavior.     

State-to-state rotational transition rates of the HCO+ ion by collisions with helium

The rates of rotational transitions for HCO⁺, the most abundant ion in interstellar space, induced by collision with helium are obtained for temperatures ranging from 10 to 80 K. The calculations are based on a new potential energy surface for the He–HCO⁺ interaction and on a scattering matrix whose accuracy was checked by pressure broadening and shift measurements. The rates     decrease for increasing values of j and  Δ j   , with a temperature trend depending on the energy involved in the transitions: if it is small, the rates are almost constant, while an increase with T is found for other cases. Comparison with previous and less accurate results shows an agreement within 50 per cent. Comparison between state-to-state and pressure broadening cross-sections allows us to discuss importance and influence of elastic and inelastic collisions.