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Composition, Physical State and Distribution of Ices at the Surface of Triton

Composition, Physical State and Distribution of Ices at the Surface of Triton. Laura Brenneman ASTR688R Project, 12/9/04. Triton Basics. T ~ 38  4 K (Voyager 2, 1989) d ~ 30 AU, a ~ 14 R Nep (icy) e < 0.0005, i ~ 159, retro R ~ 1353 km (Europa)  ~ 2 g/cm 3

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Composition, Physical State and Distribution of Ices at the Surface of Triton

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  1. Composition, Physical State and Distribution of Ices at the Surface of Triton Laura Brenneman ASTR688R Project, 12/9/04

  2. Triton Basics • T ~ 38  4 K (Voyager 2, 1989) • d ~ 30 AU, a ~ 14 RNep (icy) • e < 0.0005, i ~ 159, retro • R ~ 1353 km (Europa) •  ~ 2 g/cm3 • Varied terrain, cryovolcanoes • How was Triton formed? Still an open question… • Similar to Pluto-Charon, KBOs. • Understanding equation of state could yield important clues about the early solar system beyond the frost line.

  3. Polar Regions: N2 Frost

  4. Triton’s Tenuous Atmosphere

  5. The work of Quirico et al. (1999) • Attempted to discern physical state of Triton’s surface via IR spectroscopy on UKIRT (Mauna Kea). • 6 1-hr. integrations along latitudinal strips at ~ 99 longitude in H, K bands. • 2.65 nm spectral resolution, s/n ~ 300. • Compared with lab transmission spectra of ice crystals made in liquid phase in closed cryogenic cells  composition, T, , crystalline lattice phase of N2. • Created plane-parallel model of radiative transfer within these icy media (absorption, single and double scattering). • Use this to refine global model of observed spectrum  abundances and distribution of ices.

  6. Ices Matching the Observed Spectra ? ? ? Ice templates used: C2H2, C2H4, C2H6, C3H8, NH3, NO, NO2, SO2, CH3OH, CH4, CO, CO2, H2O, N2.

  7. Methane Ice: None in Pure Form??

  8. Carbon Dioxide Ice: Pure Fraction Significant

  9. Best-Fit Model: Two Regions

  10. Fitting to Temperature and Grain Size

  11. Conclusions • Two region model of the surface works best: 55 % N2:CH4:CO, 45% H20 + CO2 with CH4 ~ 0.11%, CO ~ 0.05% • N2 ice embeds methane, carbon monoxide; T  35.6 K inferred since most of solid nitrogen observed is in β-phase (hexagonal). • Radiative transfer model indicates grain size of ~ 10 cm: too big for surface to be “granular.” Probably polycrystalline with large crystals. • Large concentrations of pure CH4 ice are unlikely: lead to inconsistent global spectral fits. • Still unsure of exact equation of state for the H20 + CO2 ice mixture: uncertainty in spectral fits.

  12. Future Work • Need more data to resolve the equation of state more clearly for the H20 + CO2 regions, to further constrain T, and to identify the new spectral features detected. • Some of this can be accomplished nicely with future ground based observations with high signal-to-noise ratios and high spectral resolution in the 1.0 - 2.5 m range. • More of Triton’s surface needs to be examined! • It will also be helpful to have future missions for the specific purpose of observing the outer solar system with greater scrutiny, both in imaging and spectroscopy.

  13. References • Cruikshank, D.P. et al. 1993 Science 261, 742-745. • de Pater, I. and Lissauer, J. Planetary Sciences. • Quirico, E. et al. 1999 Icarus 139, 159-178. • http://www.solarviews.com/eng/triton.htm

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