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

of Tritonof Triton

Laura BrennemanLaura Brenneman

ASTR688R Project, 12/9/04ASTR688R Project, 12/9/04

Triton BasicsTriton Basics

• TT ~ 38 ~ 38 4 K (Voyager 4 K (Voyager 2, 1989)2, 1989)

• dd ~ 30 AU, ~ 30 AU, aa ~ 14 R ~ 14 RNep Nep

(icy)(icy)

• ee < 0.0005, < 0.0005, ii ~ 159 ~ 159, , retroretro

• RR ~ 1353 km ~ 1353 km (Europa)(Europa)

• ~ 2 g/cm~ 2 g/cm33

• Varied terrain, Varied terrain, cryovolcanoescryovolcanoes

• How was Triton formed? Still an open How was Triton formed? Still an open question…question…

• Similar to Pluto-Charon, KBOs.Similar to Pluto-Charon, KBOs.

• Understanding equation of state could Understanding equation of state could yield important clues about the early solar yield important clues about the early solar system beyond the frost line.system beyond the frost line.

Polar Regions: NPolar Regions: N22 Frost Frost

Triton’s Tenuous AtmosphereTriton’s Tenuous Atmosphere

The work of Quirico et al. The work of Quirico et al. (1999)(1999)

• Attempted to discern physical state of Attempted to discern physical state of Triton’s surface via IR Triton’s surface via IR spectroscopy on UKIRTspectroscopy on UKIRT (Mauna Kea).(Mauna Kea).

• 6 1-hr. integrations along latitudinal strips at 6 1-hr. integrations along latitudinal strips at ~ 99~ 99 longitude in H, K bands. longitude in H, K bands.

• 2.65 nm spectral resolution, s/n ~ 300.2.65 nm spectral resolution, s/n ~ 300.

• Compared with Compared with lab transmission spectralab transmission spectra of of ice crystals made in liquid phase in closed ice crystals made in liquid phase in closed cryogenic cells cryogenic cells composition, T, composition, T, , crystalline , crystalline lattice phase of Nlattice phase of N22..

• Created Created plane-parallel modelplane-parallel model of radiative of radiative transfer within these icy media (absorption, transfer within these icy media (absorption, single and double scattering).single and double scattering).

• Use this to refine Use this to refine global modelglobal model of observed of observed spectrum spectrum abundances and distribution of abundances and distribution of ices.ices.

Ices Matching the Observed Ices Matching the Observed SpectraSpectra

Ice templates used:Ice templates used: C C22HH22, C, C22HH44, C, C22HH66, C, C33HH88, , NHNH33, NO, NO, NO, NO22, SO, SO22, CH, CH33OH, OH, CHCH44, CO, CO, CO, CO22, , HH22O, NO, N22..

?? ?

Methane Ice: None in Pure Methane Ice: None in Pure Form??Form??

Carbon Dioxide Ice: Carbon Dioxide Ice: Pure Fraction SignificantPure Fraction Significant

Best-Fit Model: Two RegionsBest-Fit Model: Two Regions

Fitting to Temperature and Fitting to Temperature and Grain SizeGrain Size

ConclusionsConclusions

• Two region model of the surface works best: Two region model of the surface works best: 55 % N55 % N22:CH:CH44:CO, 45% H:CO, 45% H220 + CO0 + CO2 2 with CHwith CH44 ~ ~ 0.11%, CO ~ 0.05%0.11%, CO ~ 0.05%

• NN2 2 ice embeds methane, carbon monoxide; T ice embeds methane, carbon monoxide; T 35.6 K inferred since most of solid nitrogen 35.6 K inferred since most of solid nitrogen observed is in observed is in ββ-phase (hexagonal).-phase (hexagonal).

• Radiative transfer model indicates grain size Radiative transfer model indicates grain size of ~ 10 cm: too big for surface to be “granular.” of ~ 10 cm: too big for surface to be “granular.” Probably polycrystalline with large crystals.Probably polycrystalline with large crystals.

• Large concentrations of pure CHLarge concentrations of pure CH44 ice are ice are unlikely: lead to inconsistent global spectral unlikely: lead to inconsistent global spectral fits. fits.

• Still unsure of exact equation of state for the Still unsure of exact equation of state for the HH220 + CO0 + CO22 ice mixture: uncertainty in spectral ice mixture: uncertainty in spectral fits.fits.

Future WorkFuture Work

• Need more dataNeed more data to resolve the equation of to resolve the equation of state more clearly for the Hstate more clearly for the H220 + CO0 + CO22 regions, to further constrain T, and to regions, to further constrain T, and to identify the new spectral features detected.identify the new spectral features detected.

• Some of this can be accomplished nicely Some of this can be accomplished nicely with future ground based observations with with future ground based observations with high signal-to-noisehigh signal-to-noise ratios and ratios and high spectral high spectral resolutionresolution in the 1.0 - 2.5 in the 1.0 - 2.5 m range.m range.

• More of Triton’s surfaceMore of Triton’s surface needs to be needs to be examined!examined!

• It will also be helpful to have It will also be helpful to have future future missionsmissions for the specific purpose of for the specific purpose of observing the outer solar system with observing the outer solar system with greater scrutiny, both in imaging and greater scrutiny, both in imaging and spectroscopy.spectroscopy.

ReferencesReferences

• Cruikshank, D.P. et al. 1993 Cruikshank, D.P. et al. 1993 ScienceScience 261, 742-745.261, 742-745.

• de Pater, I. and Lissauer, J. de Pater, I. and Lissauer, J. Planetary Planetary SciencesSciences..

• Quirico, E. et al. 1999 Quirico, E. et al. 1999 IcarusIcarus 139, 139, 159-178.159-178.

• http://www.solarviews.com/eng/triton.htm