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Triton: The World that should not be.: 

Triton: The World that should not be. Adric Riedel

Things that are wrong with Triton: 

Things that are wrong with Triton Wasn’t officially named for nearly 100 years Largest retrograde orbiter in the solar system Has an atmosphere Has geysers Looks like a cantaloupe Might even have an underground ocean or magnetic field

History of Triton: Discovery: 

History of Triton: Discovery Discovered less than a month after Neptune itself, by William Lassell Unusual orbit was spotted very soon after discovery, possibly Neptune rotated retrograde By the 1920s it was known that Triton does indeed rotate retrograde relative to Neptune

Properties of Triton (Voyager): 

Properties of Triton (Voyager)

A History of Triton: Properties: 

A History of Triton: Properties Triton was not officially named until 1948, when Gerard Kuiper discovered Nereid (Wikipedia) Long believed to be the largest moon in the solar system In 1936, R. A. Lyttleton published a paper suggesting Pluto was an escaped moon of Neptune, and the event that separated it reversed Triton’s momentum. This is impossible; Triton is actually more massive.

A History of Triton: Atmosphere: 

A History of Triton: Atmosphere In 1978, astronomers detected a methane (CH4) band in Triton’s spectra; interpreted as a thin atmosphere. Further observations showed it was methane ice Triton is yellow-pink! (due to methane) In 1980, Nitrogen is detected on Triton Triton’s Nitrogen believed frozen or in pools

Voyager 2: 

Voyager 2 Encountered Neptune on August 25, 1989 Triton was imaged during late spring in its southern hemisphere Voyager 2 found an atmosphere Pressure: 14×10-9 bar Temperature: 38°K Composition: 99.9% N2, 0.01% CH4

The Interior: 

The Interior Believed to be differentiated rock and ice (Ruiz, J.; Torices, A. 2000) Some models (Ruiz, J.; Torices, A. 2000) suggest temperatures of 176 K between different layers of ice, sufficient to melt ammonia-methane ice. Possible tidal heating Practically nothing is known for sure

The Surface: 

The Surface Surface of Triton appears to be new; oldest is the cantaloupe terrain. Dimpled seems to be the youngest. (S.K. Croft, 1990) Surface is entirely ice, apparently a smooth, reflective glaze (no fine particle effects observed) Cryovolcanism via as-yet unknown mechanism Cryovolcanism possibly linked the odd cantaloupe terrain

The Surface: 

The Surface Wide variety of terrain Cantaloupe terrain possibly due to tectonics (S.K. Croft 1990) Possibly due to collapse Some dimples (#5, #6, #7) appear volcanic (S.K. Croft 1990)

The Surface: 

The Surface The current active area (as of 1989) is the south pole, which seems to be retreating There is more N2 in the south polar cap than there is in the atmosphere (Triton’s atmosphere is the relocation of the polar ice caps) More cantaloupe terrain may be discovered underneath Cap disputed by Schenk & Moore (1993)

The Atmosphere: Structure: 

The Atmosphere: Structure Various proposed thermal structures (Elliot et al. 1999) based on occultation. Note the area from 50-25 km. Elliot had to assume that to allow for the known (by Voyager) surface temperature profile. The cooling process is unknown, or Triton may not be in atmospheric equilibrium (Elliot et al. 1999)

The Atmosphere: Structure: 

The Atmosphere: Structure Principal model is solar heating, conducted down to the surface where it’s radiated away. Geyser plumes level off at 8 km, clouds seen at 30 km. (Olkin 1997) Troposphere to 10 km (more recently 50 km, with energy radiating away above the surface) (Elliot et al. 1999). The lower regions are not homogenous (Elliot, 1998).

The Atmosphere: Structure: 

The Atmosphere: Structure Apparent ionosphere from 125-130 km (Stevens et al. 1992, Elliot et al. 1999) Thermosphere is spherically symmetric and isothermal (?) above 400 km (Stevens et al. 1992) Thermosphere reaches peak temperature of 102 K at 600 km (Olkin et al. 1997 using the early Voyager model), drops to 96K (75K with old model)

The Atmosphere: Future: 

The Atmosphere: Future Olkin et al. (1997) find that either the atmosphere was twice as thick at 50 km during a 1995 occultation or the models are wrong Initially believed to be evidence of asymmetric atmosphere due to high winds and gravitational anomalies (unlikely given the 5.9 day rotation) (Elliot 1997) Eventually deemed to be an actual temperature (+5K) and pressure (x1.8) increase (Elliot 1998, Sicardy 1998)

The Future: 

The Future Currently accepted hypothesis for Triton is that it’s a captured Kuiper Belt Object like Pluto. This explains the similarities to Pluto/Charon and the retrograde motion The current model requires Triton to hit one of the original Neptunian sattelites, and then pick off most of the rest as its orbit stabilized

The Future: 

The Future Triton is tidally locked to Neptune, and may be subject to tidal heating (if not, it will be soon) The tidal forces may be responsible for the unusually high winds seen on Neptune Triton’s orbit seems stable enough that Triton won’t be destroyed in the next 5 Gyr

The Future: 

The Future Proposals have been made since 2000 to fund a return mission to Neptune, and determine the state of the rings, the composition and structure of Triton’s atmosphere, electromagnetic fields and physical composition. (Hammel et al. 2002 and subsequent) Current hopes are for a Cassini/Gallileo style orbiter mission, scaling from a simple orbiter to a mission with a Triton lander, Triton orbiter, Neptune Orbiter and Neptune atmospheric probe. Since Triton seems to be entering summer, we have time…


Bibliography Croft, S.K. (1990) LPI 21 248C Elliot, J.L (1997) hst.prop 3833E Elliot, J.L (1998) STIN 9914316E Elliot, J.L. et al. (1999) Icarus 143 425-428 Hammel, H.B. et al. (2002) ASPC 272 297H Herbert, F. & Sandel, B.R. (1991) JGR 9619241H Olkin et al. (1997) Icarus 129 178-201 Schenk, P. & Moore, J.M. (1993) LPI 24 1247S Sicardy, B. et al (1998) DPS 30 4902S Rothery, David. “Sattelites of the Outer Planets: Worlds in their own right”. 2nd ed. New York, Oxford: 1999 Ruiz, J. & Torices, A. (2000) LPI 31 1298R Weissman, Paul; McFadden, Lucy-Ann and Johnson, Torrence. “Encyclopedia of the Solar System”. San Diego, Academic Press: 1999 Wikipedia. “Triton (moon)”. January 29, 2005. Images from and

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