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Electric discharge synthesis of HCN in simulated Jovian Atmospheres
ICARUS72, 48--52 (1987)
Electric Discharge Synthesis of HCN in Simulated Jovian Atmospheres ROSCOE STRIBL1NG AND STANLEY I.. MILLER Department of Chemistry, B-OI7, University of California, San Diego, La Jolla, California 92093
Received January 30, 1987; revised April 13, 1987 HCN has been detected in the Jovian atmosphere at a column density of about 2.2 x 10 -7 moles cm -2. While photochemical synthesis from methylamine and aziridine, upwelling, and lightning have been proposed as possible sources of this HCN, corona discharge has not been previously considered. HCN energy yields (moles j - l ) were measured using corona discharge for gas mixtures containing H2, CH4, NH3, with H2/CH4 ratios from 4.4 to 1585. The yields are approximately proportional to the mole fraction of methane in the gas mixture. Assuming that the 3/1 ratio of corona discharge to lightning energy on the Earth applies to Jupiter, HCN column densities from corona discharge could account for approximately 10% of the observed HCN. These estimates are very, dependent on the values used for the energy available as lightning on Jupiter and the eddy diffusion coefficients in the region of synthesis. ,~ 1987AcademicPres~.Inc,
INTRODUCTION
and ammonia, could account for the observed HCN and that the dehydrogenation In 1981, HCN was detected in the Jovian of methylamine (CH3NH2) would be a atmosphere (Tokunaga et al. 1981). An lesser source. Their calculations suggest an HCN column density of about 2.2 x 10 7 HCN column density resulting from the moles cm -2 was inferred from observed photolysis of aziridine of about 3 × 10 7 absorption patterns on the cloud surface of moles cm- 2. the planet. This corresponds to an HCN The synthesis of HCN on Jupiter by mixing ratio of about 2 x 10 -9. The current lightning was calculated by Lewis (1976, models propose that the uppermost layer in 1980a) and Lewis and Fegley (1984) to be the atmosphere of Jupiter contains clouds extremely small. Borucki et al. (1982) and of NH3 down to about the one-bar level Williams et al. (1983) estimated a higher (Orton et al. 1982, Levin 1983, Bjorakcr et lightning rate than Lewis by about a factor al. 1986, West et al. 1986). Tokunaga et al. of I00. This could result in lightning making (1981) suggested three possible sources of a small but substantial contribution to the the observed HCN: upwelling, photochem- HCN production on Jupiter. Recently, calical production from CH3NH2, and culations by Bar-Nun and Podolak (1985) lightning. based on model shock-tube experiments Model calculations seem to rule out suggest that lightning above the water cloud upweiling from deeper layers of the Jovian on Jupiter is sufficient to account for all the atmosphere (Barshay and Lewis 1978. observed HCN. Larson et al. 1977, Fink et al. 1978). Corona discharge, however, has not been Detailed calculations by Kaye and Strobel proposed as a possible energy source for (1983a,b) suggest that aziridine (CzH~N), the production of HCN on Jupiter. Corona formed photochemically from acetylene discharges have been shown to be effective 48 001%1035/87 S3.00 Copyright "!t 1987 by Academic Ibex,,,, Inc. All rights o|" reproduction in any form reserved.
HCN SYNTHESIS ON JUPITER in producing HCN under reducing conditions (Miller 1957, Schlesinger and Miller 1983). In this study we have determined the energy yields for the production of HCN under the very high H2 mixing ratios found on Jupiter and combined thcse yields with an estimate of the energy available on Jupiter as corona discharge in order to derive an HCN column density. Thesc data on the electric discharge synthesis of HCN at high H2/CH4, NH3 ratios are also applicable to parts of the solar ncbula. EXPERIMENTAL
The spark discharge flask previously used to determine carbon yields (Schlesinger and Miller 1983, Stribling and Miller, in press) was modified by the addition of a thermometer well. The spark was provided by a Tesla coil, Cenco Model 80721, which was modified for continuous use by removing the Bakelite cover to allow air circulation and cooling. The tungsten electrodes in the discharge flask were cemented in place to minimize the variability of energy input due to differences in the length of the spark gap. The discharge and calibration flasks were insulated with polyurethane. The total energy input into the discharge flask was estimated from the rise in temperature during the initial stages of a sparking run. This was compared to the temperature rise from a known amount of power generated by a Hewlett-Packard 25 power supply passing through a Nichrome wire connecting two electrodes in a calibration flask. The power generated by the spark coils varied between 1.4 and 2.5 W. The energy of the spark was estimated in each run. Energy yields for the production of HCN were determined for H2/CH,~ ratios of 4.4, 19, 83, 363, and 1585. The discharge flask was dried before each use. The gases were C.P. grade and were used without further purification. The pCH4 and pNH3 were equal in these experiments. For the reaction mixtures with H2/CH4 ratios of less than I00, an NHflCH4 mixture was added directly to the discharge flask through a
49
vacuum system followed by the H2 with the pressure being measured with a Hg manometer. For the higher HJCH4 ratios, the pressure of the NH3/CH4 mixture was measured in a small flask, the mixture allowed to expand into the discharge flask, followed by the addition of the H2. The spark was stopped after the predetermined time and 15 mi of 0.1 M KOH were added to the flask. The solution was stirred for at least 2 hr to allow for complete dissolution of the gaseous HCN into the solution. The solution was then collected, the flask dried, and the procedure repeated. The HCN concentrations in the sample solutions were measured with an Orion cyanide electrode (Model 94-06). The samples were diluted with 0.I M KOH and the pH adjusted to 12.17 to convert the HCN to C N . RESUI.TS
In order to obtain an energy yield applicable to cyanide production in a Jovian atmosphere, it is necessary to obtain the energy yield extrapolated to zero time (Stribling and Miller, in press) as shown in Fig. 1. Long-term spark experiments result in decomposition of the products by the discharge, whereas on Jupiter the diffusion to lower levels in the atmosphere would be fast compared to decomposition of the products. In addition, the CH4 is rapidly depleted, especially in the high H2/CH4 gas mixtures. The energy yields for five gas mixtures are shown in Fig. 2. The zero time energy yields typically differed by less than 30% on repetition. However, it should be emphasized that the accuracy of these energy yields is only about a factor of 2 due to uncertainties of the spark energy and other uncontrolled characteristics of the spark. Since one might expect the energy yields to be a function of the available CH4 present in the gas mixture, we divided the yields by the mole fraction of CH4 in each mixture. These results are also plotted in Fig. 2. With the exception of the H2/CH4 = 4.4
50
STRIBLING AND MILLER
k-
7
.03 /el'44 • 1585
Z
.01
,
t / Spark
2 Time
(hrs)
FIG. I. Energy yields for H C N production vs spark time ( - 2 . 3 - W spark), pNH) = pCH4. P..t,a = 600 Torr.
mixture, the yield/XcH,, is roughly constant and this should allow extrapolation to higher H2/CH4 ratios with some confidence. The mole fraction relationship can be understood on the basis that the energy of the discharge is used to break up the H2, CH4, and NH3 molecules in proportion to their abundances. For the most part, the H atoms recombine to H: without participating in HCN production. The formation of ions and radicals from NH3 and CH4, which does result in HCN formation, would be proportional to their mole fraction. The mole fraction relationship is being investigated for other gas mixtures. Perhaps the most surprising result of this experiment is that easily measurable amounts of HCN can be produced by the action of corona discharge on gas mixtures which have a Hz/CH4 ratio as high as 1585/I. Previous HCN syntheses in simulated Jovian atmospheres have used H2/CH4 ratios smaller than I00/I (e.g., Ferris and Chen 1975, Ferris and Morimoto 1981, Ferris et al. 1982, Raulin et al. 1979, Bar-Nun 1975), although Bar-Nun and Podolak (1985) have extrapolated results from lower mixing ratios to Jovian conditions.
discharge and of the residence time of HCN in the observable region are needed. Due to the limited sampling of the Jovian atmosphere for lightning, there is considerable controversy as to the amount of energy available as lightning on Jupiter (e.g., Lewis 1980a,b, Scarfet al. 1981, Borucki et al. 1982, Lewis and Fegley 1984). Recently, Bar-Nun and Podolak (1985) reviewed the controversy and arrived at a lightning dissipation rate of 10 7 j cm-2 sec ~between the ammonia and water cloud region in the Jovian atmosphere. If the generally accepted 3/I ratio of corona discharge to lightning on the Earth (Schonland 1953) holds for the Jovian atmosphere, then the energy available as corona discharge on Jupiter would be about 3 × I0 7 j cm-_~ sec
I
The residence time for HCN is strongly dependent on the eddy diffusion rates in this region. Residence times were calculated from Bar-Nun and Podolak (1985) which range from 1.3 x 109 to 4.6 × 108 sec for sources 20 and 10 km above the top of the water cloud, respectively. These values are in general agreement with those previously calculated (Lewis 1976, Kaye and Strobel 1983a). While it is difficult to ascertain the exact
.~600
~u
x 400
10-8.
§ 1o, , , o O
10-10
.....
I
10 DISCUSSION
In order to apply energy yields to calculate an HCN column density on Jupiter, estimates of the energy available as corona
O,cO?
. . . . . .
L
100 H2/CH4
. . . . . . . .
I
1000
FIG. 2. Zero time energy yields for H C N synthesis vs H2/CH4 ratio, pNH3 = pCH4, Ptot,l = 600 Torr. Inset: energy yields divided by the CH4 mole fraction vs H2/CH4 ratio.
HCN SYNTHESIS ON JUPITER composition, it is generally accepted that the H2/CH4 ratio in the Jovian atmosphere is about 500 (Strobel 1985, Gautier et al. 1982, Knacke et al. 1982), although estimates as high as 1500/1 had been previously discussed (Sagan 1971, Bar-Nun 1975). In the absence of experimental data at H2/CH4 ratios of 500, Bar-Nun and Podolak (1985) extrapolated earlier results (Bar-Nun 1975) of shock-tube syntheses of acetylene and HCN in N H 3 / C H J H , / A r = I/I/50/150 and acetylene synthesis in CH4/ H2/Ar = 1/500/1500 to calculatc an energy yield for the production of HCN under Jovian conditions of about 0.7 nmoles J-~. This calculation was used to suggest that lightning could be a sufficient energy source to account for the HCN observed on Jupiter. The corona discharge data in Fig. 2 show that the energy yield for an H2/CH4 ratio of 500 would be about 0.1 nmoles j-r. The HCN column densities can be calculated from the product of this HCN energy yield, the cnergy available (3 × 10 -7 J cm 2 sec J), and the residence times of 4.6 × 108 and 1.3 × 109 sec. This gives respective column densities of 13 to 39 nmoles cm -2 or 6 to 18% of the HCN observed on Jupiter. There are a number of uncertainties involved in these calculations which could affect these yields by a factor of I0 or even 100. The greatest source of uncertainty lies in estimating the amount of energy available as lightning, as described above. The amount of corona discharge relative to lightning on Jupiter may also be significantly different from that which occurs on the Earth. Other uncertainties in the Jovian conditions include the structure, composition, and dynamics of the atmosphere, the exact mixing ratios, and the eddy diffusion coefficients in the region of synthesis. Also to be considered are the effect on the yields of the lower NH3/CH4 ratios reported on Jupiter (Knacke et al. 1982, Lutz et al. 1980, Strobel 1985) and whether the corona discharge from the spark coil gives the
51
same energy yields as the corona discharges on Jupiter. The energy yields generated for the high H2/CH4 mixtures in this study suggest that HCN would also have been produced in the CH4 and NH3 rich regions of the solar nebula by corona discharge. This mechanism could account for some of the organic molecules found in the carbonaceous chondrites. It may also have been a mechanism for the retention of carbon on the planetary bodies. Similar synthesis of HCN, as well as H2CO, by corona discharges would also be expected in regions of the solar nebula where H2, CO, and N2 predominated. Experiments are currently underway to investigate this possibility.
ACKNOWLEDGMENT This work NAGW-20.
was
supported
by
NASA
Grant
REFERENCES BAR-NUN, A. 1975. Thunderstorms on Jupiter. lcaru,~ 24, 86-94. BAR-NUN, A., AND M. PODOLAK 1985. The contribution by thunderstorms to the abundances of CO, C:H2, and HCN on Jupiter. Icarus 64~ 112-124. BARSllAY, S. S., AND J. S. LEWIS 1978. Chemical structure of the deep atmospherc of Jupiter. learu.~ 33, 593-611. BJORAKER, O. I.., H. P. I.ARSON, AND V. G. KUNDE 1986. The abundance and distribution of water vapor in Jupiter's atmosphere. Astrophys. J. 311, 1058-1072. BORUCKI. W. J., A. BAR-NUN, F. L. SCARF, A. F. COOK, AND G. E. HUNT 1982. Lightning activity on Jupiter. Icarus 52, 492-502. FERR/S, J. P., J. Y. MORIMOTO. R. BENSON, AND A. BOSSARD 1982. Photochemistry of NH~, CH4, and PH3. Possible applications to the Jovian planets. Origins o f Life 12, 261-265. FERRIS, J. P., AND C. T. CItIEN 1975. Photosynthesis of organic compounds in the atmosphere of Jupiter. Nature 258, 587-588. FERRIS, J. P., AND J. Y. MORIMOTO 1981. Irradiation of NH3-CH4 mixture~ as a model of photochemical processes in the Jovian planets and Titan. Icarus 48, 118-126. FINK, U.. H. P. LARSON, AND R. R. TREFFERS 1978. Germane in the atmosphere of Jupiter. Icarus 34, 344-354.
52
STRIBLING AND MILLER
GAUTIER, D., B. BEZARD, A. MARTEN, J. P. BALUTEAU, N. SCOTT, A. CHEI)IN, V. KUNDE, AND R. HANEI. 1982. The C/H ratio in Jupiter from the Voyager infrared investigation. Astrophys. J. 257, 901-912. KAYE, J. A., AND n. F. STROBEI. 1983a. Formation and photochemistry of methylamine in Jupiter's atmosphere. Icarus 55, 399-419. KAYE, J. A., AND D. F. STROBEI_ 1983b. HCN formation on Jupiter: The coupled photochemistry of ammonia and acetylene, h'arus 54, 417-433. KNACKE, R. F., S. J. KIM, S. T. RIDGEWAY, AND A. T. TOKUNAGA 1982. The abundances ofCH4, CH3D, NH3, and PH3 in the troposphere of Jupiter derived from high-resolution 1100-1200 cm-I spectra. Astrophys. J. 262, 388-395. LARSON, H. P., R. R. TREFFERS, AND U. FINK 1977. Phosphine in Jupiter's atmosphere: The evidence from high altitude observations at 5 micrometers. Astrophys. J. 211, 972-979. LEVIN, Z., W. J. BORUCKI. AND O. B. TOON 1983. Lightning generation in planetary atmospheres. Icarus 56, 80- I 15. LEWIS, J. S. 1976. Equilibrium and disequilibrium chemistry of adiabatic solar composition planetary atmospheres. In Chemical Evolution of the Giant Planets (C. Ponnamperuma, Ed.), pp. 13-25. Academic Press, New York. LEwis, J. S. 1980a. Lightning synthesis of organic compounds on Jupiter. Icarus 43, 85-95. LEWlS, J. S. 1980b. Lightning on Jupiter: Rate, energetics, and effects. Science 210, 1351-1352. LEWIS, J. S., AND M. B. FEGI.EY, JR. 1984. Vertical distribution of disequilibrium species in Jupiter's troposphere. Space Sci. Rev. 39, 163-192. L u r z , B. L., AND T. OWEN 198(I. The visible bands of ammonia: Band strengths, curves of growth, and the spatial distribution of ammonia on Jupiter. Astrophys. J. 235, 285-293. MXLLER, S. 1.. 1957. The mechanism of synthesis of
amino acids by electric discharges. Biochim. BiD-
phys. Acta 23, 480-489. OR'I-ON, G. S., J. F. APPLEBY, AND J. V. MARTONCHIK 1982. The effect of ammonia ice on the outgoing thermal radiance from the atmosphere of Jupiter. Icarus 52, 94-116. RAULIN, F.. A. BOSSARD, G. TOUPANCE. AND C. PONNAMPERUMA 1979. Abundance of organic compounds photochemically produced in the atmospheres of the outer planets. Icarus 38, 358-366. SAGAN, C. 1971. The solar system beyond Mars: An exobiological survey. Space Sci. Rev. 11,827-866. SCARF. F. L., D. A. GURNETT, W. S. KURTII, R. R. ANDERSON, AND R. R. SHAW 1981. An upper bound to the lightning flash rate in Jupiter's atmosphere. Science 213, 684-685. SCHLESINGER, G., AND S. L. MIIA_ER 1983. Prebiotic synthesis in atmospheres containing CH4, CO. and CO2. II. Hydrogen cyanide, formaldehyde, and ammonia. J. Mol. Evol. 19, 383-390. SCltONLAND, B. F. J. 1953. Atmospheric Electricity. pp. 42-63. Methuen, London. STRIBI.iNG, R.. AND S. 1.. MII.I.ER 1987. Energy yields for hydrogen cyanide and formaldehyde syntheses: The HCN and amino acid concentrations in the primitive ocean. Origins of Life (in press). STROBEL, 1). F. 1985. The photochemistry of the atmospheres of the outer planets and their satellites. In The Photochemistry ~)f Atmospheres (J. S. Levine, Ed.), pp. 393-434. Academic Press, Orlando, FL. TOKUNAGA. A. T., S. C. BEC'K.T. R. GEBAI I t-:. J. H. I.ACY, AND E. SERABYN 1981. The detection of HCN on Jupiter. h'arus 48, 283-289. WEST, R. A., D. F. STROBEL. AND M. G. "I'OMASKO 1986. Clouds. aerosols, and photochemistry in the Jovian atmosphere, h.arus 65, 161-217. WILLIAMS, M. A., E. P. KRIDER, AND D. M. HUNTEN 1983. Planetary lightning: Earth, Jupiter, and Venus. Rev. Geophys. Space Phys. 21,892-902.
Electric Discharge Synthesis of HCN in Simulated Jovian Atmospheres ROSCOE STRIBL1NG AND STANLEY I.. MILLER Department of Chemistry, B-OI7, University of California, San Diego, La Jolla, California 92093
Received January 30, 1987; revised April 13, 1987 HCN has been detected in the Jovian atmosphere at a column density of about 2.2 x 10 -7 moles cm -2. While photochemical synthesis from methylamine and aziridine, upwelling, and lightning have been proposed as possible sources of this HCN, corona discharge has not been previously considered. HCN energy yields (moles j - l ) were measured using corona discharge for gas mixtures containing H2, CH4, NH3, with H2/CH4 ratios from 4.4 to 1585. The yields are approximately proportional to the mole fraction of methane in the gas mixture. Assuming that the 3/1 ratio of corona discharge to lightning energy on the Earth applies to Jupiter, HCN column densities from corona discharge could account for approximately 10% of the observed HCN. These estimates are very, dependent on the values used for the energy available as lightning on Jupiter and the eddy diffusion coefficients in the region of synthesis. ,~ 1987AcademicPres~.Inc,
INTRODUCTION
and ammonia, could account for the observed HCN and that the dehydrogenation In 1981, HCN was detected in the Jovian of methylamine (CH3NH2) would be a atmosphere (Tokunaga et al. 1981). An lesser source. Their calculations suggest an HCN column density of about 2.2 x 10 7 HCN column density resulting from the moles cm -2 was inferred from observed photolysis of aziridine of about 3 × 10 7 absorption patterns on the cloud surface of moles cm- 2. the planet. This corresponds to an HCN The synthesis of HCN on Jupiter by mixing ratio of about 2 x 10 -9. The current lightning was calculated by Lewis (1976, models propose that the uppermost layer in 1980a) and Lewis and Fegley (1984) to be the atmosphere of Jupiter contains clouds extremely small. Borucki et al. (1982) and of NH3 down to about the one-bar level Williams et al. (1983) estimated a higher (Orton et al. 1982, Levin 1983, Bjorakcr et lightning rate than Lewis by about a factor al. 1986, West et al. 1986). Tokunaga et al. of I00. This could result in lightning making (1981) suggested three possible sources of a small but substantial contribution to the the observed HCN: upwelling, photochem- HCN production on Jupiter. Recently, calical production from CH3NH2, and culations by Bar-Nun and Podolak (1985) lightning. based on model shock-tube experiments Model calculations seem to rule out suggest that lightning above the water cloud upweiling from deeper layers of the Jovian on Jupiter is sufficient to account for all the atmosphere (Barshay and Lewis 1978. observed HCN. Larson et al. 1977, Fink et al. 1978). Corona discharge, however, has not been Detailed calculations by Kaye and Strobel proposed as a possible energy source for (1983a,b) suggest that aziridine (CzH~N), the production of HCN on Jupiter. Corona formed photochemically from acetylene discharges have been shown to be effective 48 001%1035/87 S3.00 Copyright "!t 1987 by Academic Ibex,,,, Inc. All rights o|" reproduction in any form reserved.
HCN SYNTHESIS ON JUPITER in producing HCN under reducing conditions (Miller 1957, Schlesinger and Miller 1983). In this study we have determined the energy yields for the production of HCN under the very high H2 mixing ratios found on Jupiter and combined thcse yields with an estimate of the energy available on Jupiter as corona discharge in order to derive an HCN column density. Thesc data on the electric discharge synthesis of HCN at high H2/CH4, NH3 ratios are also applicable to parts of the solar ncbula. EXPERIMENTAL
The spark discharge flask previously used to determine carbon yields (Schlesinger and Miller 1983, Stribling and Miller, in press) was modified by the addition of a thermometer well. The spark was provided by a Tesla coil, Cenco Model 80721, which was modified for continuous use by removing the Bakelite cover to allow air circulation and cooling. The tungsten electrodes in the discharge flask were cemented in place to minimize the variability of energy input due to differences in the length of the spark gap. The discharge and calibration flasks were insulated with polyurethane. The total energy input into the discharge flask was estimated from the rise in temperature during the initial stages of a sparking run. This was compared to the temperature rise from a known amount of power generated by a Hewlett-Packard 25 power supply passing through a Nichrome wire connecting two electrodes in a calibration flask. The power generated by the spark coils varied between 1.4 and 2.5 W. The energy of the spark was estimated in each run. Energy yields for the production of HCN were determined for H2/CH,~ ratios of 4.4, 19, 83, 363, and 1585. The discharge flask was dried before each use. The gases were C.P. grade and were used without further purification. The pCH4 and pNH3 were equal in these experiments. For the reaction mixtures with H2/CH4 ratios of less than I00, an NHflCH4 mixture was added directly to the discharge flask through a
49
vacuum system followed by the H2 with the pressure being measured with a Hg manometer. For the higher HJCH4 ratios, the pressure of the NH3/CH4 mixture was measured in a small flask, the mixture allowed to expand into the discharge flask, followed by the addition of the H2. The spark was stopped after the predetermined time and 15 mi of 0.1 M KOH were added to the flask. The solution was stirred for at least 2 hr to allow for complete dissolution of the gaseous HCN into the solution. The solution was then collected, the flask dried, and the procedure repeated. The HCN concentrations in the sample solutions were measured with an Orion cyanide electrode (Model 94-06). The samples were diluted with 0.I M KOH and the pH adjusted to 12.17 to convert the HCN to C N . RESUI.TS
In order to obtain an energy yield applicable to cyanide production in a Jovian atmosphere, it is necessary to obtain the energy yield extrapolated to zero time (Stribling and Miller, in press) as shown in Fig. 1. Long-term spark experiments result in decomposition of the products by the discharge, whereas on Jupiter the diffusion to lower levels in the atmosphere would be fast compared to decomposition of the products. In addition, the CH4 is rapidly depleted, especially in the high H2/CH4 gas mixtures. The energy yields for five gas mixtures are shown in Fig. 2. The zero time energy yields typically differed by less than 30% on repetition. However, it should be emphasized that the accuracy of these energy yields is only about a factor of 2 due to uncertainties of the spark energy and other uncontrolled characteristics of the spark. Since one might expect the energy yields to be a function of the available CH4 present in the gas mixture, we divided the yields by the mole fraction of CH4 in each mixture. These results are also plotted in Fig. 2. With the exception of the H2/CH4 = 4.4
50
STRIBLING AND MILLER
k-
7
.03 /el'44 • 1585
Z
.01
,
t / Spark
2 Time
(hrs)
FIG. I. Energy yields for H C N production vs spark time ( - 2 . 3 - W spark), pNH) = pCH4. P..t,a = 600 Torr.
mixture, the yield/XcH,, is roughly constant and this should allow extrapolation to higher H2/CH4 ratios with some confidence. The mole fraction relationship can be understood on the basis that the energy of the discharge is used to break up the H2, CH4, and NH3 molecules in proportion to their abundances. For the most part, the H atoms recombine to H: without participating in HCN production. The formation of ions and radicals from NH3 and CH4, which does result in HCN formation, would be proportional to their mole fraction. The mole fraction relationship is being investigated for other gas mixtures. Perhaps the most surprising result of this experiment is that easily measurable amounts of HCN can be produced by the action of corona discharge on gas mixtures which have a Hz/CH4 ratio as high as 1585/I. Previous HCN syntheses in simulated Jovian atmospheres have used H2/CH4 ratios smaller than I00/I (e.g., Ferris and Chen 1975, Ferris and Morimoto 1981, Ferris et al. 1982, Raulin et al. 1979, Bar-Nun 1975), although Bar-Nun and Podolak (1985) have extrapolated results from lower mixing ratios to Jovian conditions.
discharge and of the residence time of HCN in the observable region are needed. Due to the limited sampling of the Jovian atmosphere for lightning, there is considerable controversy as to the amount of energy available as lightning on Jupiter (e.g., Lewis 1980a,b, Scarfet al. 1981, Borucki et al. 1982, Lewis and Fegley 1984). Recently, Bar-Nun and Podolak (1985) reviewed the controversy and arrived at a lightning dissipation rate of 10 7 j cm-2 sec ~between the ammonia and water cloud region in the Jovian atmosphere. If the generally accepted 3/I ratio of corona discharge to lightning on the Earth (Schonland 1953) holds for the Jovian atmosphere, then the energy available as corona discharge on Jupiter would be about 3 × I0 7 j cm-_~ sec
I
The residence time for HCN is strongly dependent on the eddy diffusion rates in this region. Residence times were calculated from Bar-Nun and Podolak (1985) which range from 1.3 x 109 to 4.6 × 108 sec for sources 20 and 10 km above the top of the water cloud, respectively. These values are in general agreement with those previously calculated (Lewis 1976, Kaye and Strobel 1983a). While it is difficult to ascertain the exact
.~600
~u
x 400
10-8.
§ 1o, , , o O
10-10
.....
I
10 DISCUSSION
In order to apply energy yields to calculate an HCN column density on Jupiter, estimates of the energy available as corona
O,cO?
. . . . . .
L
100 H2/CH4
. . . . . . . .
I
1000
FIG. 2. Zero time energy yields for H C N synthesis vs H2/CH4 ratio, pNH3 = pCH4, Ptot,l = 600 Torr. Inset: energy yields divided by the CH4 mole fraction vs H2/CH4 ratio.
HCN SYNTHESIS ON JUPITER composition, it is generally accepted that the H2/CH4 ratio in the Jovian atmosphere is about 500 (Strobel 1985, Gautier et al. 1982, Knacke et al. 1982), although estimates as high as 1500/1 had been previously discussed (Sagan 1971, Bar-Nun 1975). In the absence of experimental data at H2/CH4 ratios of 500, Bar-Nun and Podolak (1985) extrapolated earlier results (Bar-Nun 1975) of shock-tube syntheses of acetylene and HCN in N H 3 / C H J H , / A r = I/I/50/150 and acetylene synthesis in CH4/ H2/Ar = 1/500/1500 to calculatc an energy yield for the production of HCN under Jovian conditions of about 0.7 nmoles J-~. This calculation was used to suggest that lightning could be a sufficient energy source to account for the HCN observed on Jupiter. The corona discharge data in Fig. 2 show that the energy yield for an H2/CH4 ratio of 500 would be about 0.1 nmoles j-r. The HCN column densities can be calculated from the product of this HCN energy yield, the cnergy available (3 × 10 -7 J cm 2 sec J), and the residence times of 4.6 × 108 and 1.3 × 109 sec. This gives respective column densities of 13 to 39 nmoles cm -2 or 6 to 18% of the HCN observed on Jupiter. There are a number of uncertainties involved in these calculations which could affect these yields by a factor of I0 or even 100. The greatest source of uncertainty lies in estimating the amount of energy available as lightning, as described above. The amount of corona discharge relative to lightning on Jupiter may also be significantly different from that which occurs on the Earth. Other uncertainties in the Jovian conditions include the structure, composition, and dynamics of the atmosphere, the exact mixing ratios, and the eddy diffusion coefficients in the region of synthesis. Also to be considered are the effect on the yields of the lower NH3/CH4 ratios reported on Jupiter (Knacke et al. 1982, Lutz et al. 1980, Strobel 1985) and whether the corona discharge from the spark coil gives the
51
same energy yields as the corona discharges on Jupiter. The energy yields generated for the high H2/CH4 mixtures in this study suggest that HCN would also have been produced in the CH4 and NH3 rich regions of the solar nebula by corona discharge. This mechanism could account for some of the organic molecules found in the carbonaceous chondrites. It may also have been a mechanism for the retention of carbon on the planetary bodies. Similar synthesis of HCN, as well as H2CO, by corona discharges would also be expected in regions of the solar nebula where H2, CO, and N2 predominated. Experiments are currently underway to investigate this possibility.
ACKNOWLEDGMENT This work NAGW-20.
was
supported
by
NASA
Grant
REFERENCES BAR-NUN, A. 1975. Thunderstorms on Jupiter. lcaru,~ 24, 86-94. BAR-NUN, A., AND M. PODOLAK 1985. The contribution by thunderstorms to the abundances of CO, C:H2, and HCN on Jupiter. Icarus 64~ 112-124. BARSllAY, S. S., AND J. S. LEWIS 1978. Chemical structure of the deep atmospherc of Jupiter. learu.~ 33, 593-611. BJORAKER, O. I.., H. P. I.ARSON, AND V. G. KUNDE 1986. The abundance and distribution of water vapor in Jupiter's atmosphere. Astrophys. J. 311, 1058-1072. BORUCKI. W. J., A. BAR-NUN, F. L. SCARF, A. F. COOK, AND G. E. HUNT 1982. Lightning activity on Jupiter. Icarus 52, 492-502. FERR/S, J. P., J. Y. MORIMOTO. R. BENSON, AND A. BOSSARD 1982. Photochemistry of NH~, CH4, and PH3. Possible applications to the Jovian planets. Origins o f Life 12, 261-265. FERRIS, J. P., AND C. T. CItIEN 1975. Photosynthesis of organic compounds in the atmosphere of Jupiter. Nature 258, 587-588. FERRIS, J. P., AND J. Y. MORIMOTO 1981. Irradiation of NH3-CH4 mixture~ as a model of photochemical processes in the Jovian planets and Titan. Icarus 48, 118-126. FINK, U.. H. P. LARSON, AND R. R. TREFFERS 1978. Germane in the atmosphere of Jupiter. Icarus 34, 344-354.
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GAUTIER, D., B. BEZARD, A. MARTEN, J. P. BALUTEAU, N. SCOTT, A. CHEI)IN, V. KUNDE, AND R. HANEI. 1982. The C/H ratio in Jupiter from the Voyager infrared investigation. Astrophys. J. 257, 901-912. KAYE, J. A., AND n. F. STROBEI. 1983a. Formation and photochemistry of methylamine in Jupiter's atmosphere. Icarus 55, 399-419. KAYE, J. A., AND D. F. STROBEI_ 1983b. HCN formation on Jupiter: The coupled photochemistry of ammonia and acetylene, h'arus 54, 417-433. KNACKE, R. F., S. J. KIM, S. T. RIDGEWAY, AND A. T. TOKUNAGA 1982. The abundances ofCH4, CH3D, NH3, and PH3 in the troposphere of Jupiter derived from high-resolution 1100-1200 cm-I spectra. Astrophys. J. 262, 388-395. LARSON, H. P., R. R. TREFFERS, AND U. FINK 1977. Phosphine in Jupiter's atmosphere: The evidence from high altitude observations at 5 micrometers. Astrophys. J. 211, 972-979. LEVIN, Z., W. J. BORUCKI. AND O. B. TOON 1983. Lightning generation in planetary atmospheres. Icarus 56, 80- I 15. LEWIS, J. S. 1976. Equilibrium and disequilibrium chemistry of adiabatic solar composition planetary atmospheres. In Chemical Evolution of the Giant Planets (C. Ponnamperuma, Ed.), pp. 13-25. Academic Press, New York. LEwis, J. S. 1980a. Lightning synthesis of organic compounds on Jupiter. Icarus 43, 85-95. LEWlS, J. S. 1980b. Lightning on Jupiter: Rate, energetics, and effects. Science 210, 1351-1352. LEWIS, J. S., AND M. B. FEGI.EY, JR. 1984. Vertical distribution of disequilibrium species in Jupiter's troposphere. Space Sci. Rev. 39, 163-192. L u r z , B. L., AND T. OWEN 198(I. The visible bands of ammonia: Band strengths, curves of growth, and the spatial distribution of ammonia on Jupiter. Astrophys. J. 235, 285-293. MXLLER, S. 1.. 1957. The mechanism of synthesis of
amino acids by electric discharges. Biochim. BiD-
phys. Acta 23, 480-489. OR'I-ON, G. S., J. F. APPLEBY, AND J. V. MARTONCHIK 1982. The effect of ammonia ice on the outgoing thermal radiance from the atmosphere of Jupiter. Icarus 52, 94-116. RAULIN, F.. A. BOSSARD, G. TOUPANCE. AND C. PONNAMPERUMA 1979. Abundance of organic compounds photochemically produced in the atmospheres of the outer planets. Icarus 38, 358-366. SAGAN, C. 1971. The solar system beyond Mars: An exobiological survey. Space Sci. Rev. 11,827-866. SCARF. F. L., D. A. GURNETT, W. S. KURTII, R. R. ANDERSON, AND R. R. SHAW 1981. An upper bound to the lightning flash rate in Jupiter's atmosphere. Science 213, 684-685. SCHLESINGER, G., AND S. L. MIIA_ER 1983. Prebiotic synthesis in atmospheres containing CH4, CO. and CO2. II. Hydrogen cyanide, formaldehyde, and ammonia. J. Mol. Evol. 19, 383-390. SCltONLAND, B. F. J. 1953. Atmospheric Electricity. pp. 42-63. Methuen, London. STRIBI.iNG, R.. AND S. 1.. MII.I.ER 1987. Energy yields for hydrogen cyanide and formaldehyde syntheses: The HCN and amino acid concentrations in the primitive ocean. Origins of Life (in press). STROBEL, 1). F. 1985. The photochemistry of the atmospheres of the outer planets and their satellites. In The Photochemistry ~)f Atmospheres (J. S. Levine, Ed.), pp. 393-434. Academic Press, Orlando, FL. TOKUNAGA. A. T., S. C. BEC'K.T. R. GEBAI I t-:. J. H. I.ACY, AND E. SERABYN 1981. The detection of HCN on Jupiter. h'arus 48, 283-289. WEST, R. A., D. F. STROBEL. AND M. G. "I'OMASKO 1986. Clouds. aerosols, and photochemistry in the Jovian atmosphere, h.arus 65, 161-217. WILLIAMS, M. A., E. P. KRIDER, AND D. M. HUNTEN 1983. Planetary lightning: Earth, Jupiter, and Venus. Rev. Geophys. Space Phys. 21,892-902.