Deuterated Methane and Ethane in the Atmosphere of JupiterDeuterated Methane and Ethane in the Atmosphere of JupiterChristopher D. Parkinson1,2, Anthony Y.-T. Lee1, Yuk L. Yung1, and David Crisp2

1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA 2Jet Propulsion Laboratory, Pasadena, CA, USA

All D present today synthesised during the first few minutes of the Big Bang All D present today synthesised during the first few minutes of the Big Bang and is a sensitive tracer of the standard Big Bang model and galactic and is a sensitive tracer of the standard Big Bang model and galactic evolutionevolutionJupiter is considered to be an undisturbed deuterium reservoir since the Jupiter is considered to be an undisturbed deuterium reservoir since the formation of the solar system 4.5 billion years ago,formation of the solar system 4.5 billion years ago,Therefore, any measurement of Jovian D abundance may link estimates of Therefore, any measurement of Jovian D abundance may link estimates of primordial values to present time onesprimordial values to present time ones

Sources of HSources of H22(v’):(v’):

HH22(v=0) + h(v=0) + h H H22**

HH22* * H H22(v’) + h(v’) + h (flourescence) (flourescence)

Low densities in thermosphere implies slow quenching of Low densities in thermosphere implies slow quenching of excited Hexcited H22, H, H22

**

HH22(v=0) + e (v=0) + e H H22(v’) + e(v’) + e

HH33++ H H22(v=0) + H(v=0) + H

SinksSinksHH22(v’) + H(v’) + H2 2 H H22(v-1) + H(v-1) + H2 2 + KE+ KE

HH22(v’) + H(v’) + H H H22(v-1) + H(v-1) + H2 2 KE KE

HH22(v’) + H(v’) + H22(v’’) (v’’) H H22(v’-1) + H(v’-1) + H22(v’-1)(v’-1)

Jupiter's D abundance appears to be primarily governed via production by Jupiter's D abundance appears to be primarily governed via production by reaction of Hreaction of Hwith vibrationally hot HD and loss by reaction of D with Hwith vibrationally hot HD and loss by reaction of D with H22

0,1 0,1 and CHand CH33. Below 540 . Below 540 km, CHkm, CH33reacting with D acts to transfer D to deuterated hydrocarbons. reacting with D acts to transfer D to deuterated hydrocarbons. The D Lyman-The D Lyman- emission due to D abundances can be seen quite clearly on the emission due to D abundances can be seen quite clearly on the wings of the H line and we note that subsolar viewing will provide much better wings of the H line and we note that subsolar viewing will provide much better observations since the D Lyman-observations since the D Lyman- is limb darkened and the best contrast is limb darkened and the best contrast between D and H Lyman-between D and H Lyman- is most noticeable at subsolar locations. is most noticeable at subsolar locations.

We have found that a warmer neutral temperature profile in the lower We have found that a warmer neutral temperature profile in the lower thermosphere increases the deuterium abundance in the scattering region and thermosphere increases the deuterium abundance in the scattering region and subsequently results in a brighter Jovian D emission by about 15% when subsequently results in a brighter Jovian D emission by about 15% when compared to the standard reference case.compared to the standard reference case.

Increasing the vibrational temperature above TIncreasing the vibrational temperature above Tvv=2.5T causes dramatic =2.5T causes dramatic increases in the deuterium abundance above increases in the deuterium abundance above CH4CH4=1 for all cases. The CH=1 for all cases. The CH33D, D, and Cand C22HH55D columns increase with increasing vibrational temperature. The CHD columns increase with increasing vibrational temperature. The CH33D D and Cand C22HH55D profiles are enhanced in the lower thermosphere due to the source of D profiles are enhanced in the lower thermosphere due to the source of deuterated non-methane hydrocarbons in the mesosphere.deuterated non-methane hydrocarbons in the mesosphere.

Higher vibrational temperature profiles, viz. THigher vibrational temperature profiles, viz. Tvv = 4T or greater, are expected in = 4T or greater, are expected in auroral regions which should result in brighter D Lyman-auroral regions which should result in brighter D Lyman- airglow at these airglow at these latitudes. However, since latitudes. However, since KKhh should be stronger at higher latitudes (Sommeria should be stronger at higher latitudes (Sommeria et al., 1995), which would affect the D Lyman-et al., 1995), which would affect the D Lyman- emissions in the opposite way, emissions in the opposite way, brighter D Lyman-brighter D Lyman- airglow may not obtain. airglow may not obtain.

This work concerns studies of the thermosphere of Jupiter with the view to This work concerns studies of the thermosphere of Jupiter with the view to better understand some aspects of the chemistry and airglow of deuterated better understand some aspects of the chemistry and airglow of deuterated species. Thermospheric estimates of D/H ratio are difficult due large species. Thermospheric estimates of D/H ratio are difficult due large uncertainties in Tuncertainties in Tvv, but very useful in determining abundances and transport , but very useful in determining abundances and transport properties of deuterated species. What we have seen in this work is that a properties of deuterated species. What we have seen in this work is that a synergistic relationship exists between the modelling and the measurements synergistic relationship exists between the modelling and the measurements which may reveal surprises, viz., HD vibrational chemistry impacts D in the which may reveal surprises, viz., HD vibrational chemistry impacts D in the thermosphere, CHthermosphere, CH33D and CD and C22HH55D are vibrationally enhanced in the thermosphere, D are vibrationally enhanced in the thermosphere, and variations in abundance of CHand variations in abundance of CH33D and CD and C22HH55D in the thermosphere may reflect D in the thermosphere may reflect dynamical activity (i.e. dynamical activity (i.e. KKhh) in the Jovian upper atmosphere. These are examples ) in the Jovian upper atmosphere. These are examples of testable phenomena and an observing program dedicated providing such of testable phenomena and an observing program dedicated providing such measurements would provide further insight to the aeronomy of the Jovian measurements would provide further insight to the aeronomy of the Jovian atmosphere.atmosphere.

H + HD(H + HD(=1) --> HD (=1) --> HD (=0) + H=0) + HH + HD(H + HD(=0) --> D + H=0) --> D + H22

H + HD(H + HD(=1) --> D + H=1) --> D + H22((=0,1)=0,1)H + CHH + CH22D --> D + CHD --> D + CH33

D + HD + H2 2 ((=0) --> HD + H=0) --> HD + HD + HD + H2 2 ((=1) --> H=1) --> H22((=0,1) + H=0,1) + HD + CHD + CH33 --> H + CH --> H + CH22DDD + H + M --> HD + MD + H + M --> HD + MH + CHH + CH22D --> CHD --> CH33D D CHCH22D + CHD + CH3 3 --> C --> C22HH55DDCC22HH55 + C + C22HH44D --> CD --> C22HH55 + C + C22HH55DD

Why we are solving this problemWhy we are solving this problem

Relevant ThermochemistryRelevant Thermochemistry

Vibrationally Hot H2 in the Jovian Vibrationally Hot H2 in the Jovian ThermosphereThermosphere

ConclusionsConclusions

Figure Captions

Figure 1: The model atmosphere of some of the more relevant species considered, viz., H2, CH4, CH3, CH2D, CH3D, C2H5D, HD, H and D. Here, the standard reference temperature profile with Tv = 3T was used.

Figures 2, 3, and 4: Various D profiles resulting from calculations utilising vibrational temperature profiles corresponding to Tv = nT, where n = 1, 2, 2.5, 3 and 4.

Figure 5: H and D Lyman- intensity profiles for several solar zenith angleswith the same viewing angle (i.e. SZA = viewing angle) for the standard reference atmosphere,

Figure 6: D Lyman- subsolar intensities as a function of vibrational temperature.

Solving the problemSolving the problemParkinson et al. (2002) previously consider D, HD, CHParkinson et al. (2002) previously consider D, HD, CH33D abundances and D D abundances and D & H Ly-& H Ly-emissions emissions assuming mixing ratio of D to Hassuming mixing ratio of D to H22 is given by HD/H is given by HD/H22 and and well determined by the GPMS instrument (Mahaffy et al., 1998) well determined by the GPMS instrument (Mahaffy et al., 1998) thermospheric HD will be vibrationally excitedthermospheric HD will be vibrationally excitedSolve continuity equation treating He as a minor constituent in a Solve continuity equation treating He as a minor constituent in a background gas of varying mean molecular mass (allowing for Hbackground gas of varying mean molecular mass (allowing for H22, He, and , He, and CHCH44))

utilise Cutilise C22HH55D reactions from Lee et al. (2000).D reactions from Lee et al. (2000).

Figure 1 Figure 2

Figure 3 Figure 4

Figure 5 Figure 6