Overview (The Solar System)
The Neptunian satellite Triton is 2,706 kilometers in diameter. The satellite’s density is 2.07 grams/centimeter3. With this density, models of the satellite can be constructed. It is thought that there is a metallic core, a Silicate mantle, a layer of ice, a possible ocean, and a top layer of ice. The core is expected to have a radius of about 600 kilometers and the mantle a thickness of about 350 kilometers, with a 150-kilometer layer of ice below the ocean and a 250-kilometer layer above the ocean.
William Lassell, a brewer by trade, found Triton on October 10, 1846, using a telescope he built himself. An amateur astronomer, Lassell had been asked by Sir John Herschel to look for satellites of the newly discovered planet, Neptune. Triton is 355,000 kilometers from Neptune. The Eccentricity of Triton’s orbit is zero, meaning that the orbit is circular. Triton is a most unusual satellite. Its orbit is retrograde, that is, it rotates around Neptune in the opposite direction to the rotation of Neptune. It is synchronous with Neptune, meaning it presents the same face to Neptune at all times. Being synchronous also means that the rotation time of Triton is the same as the time for one orbit around Neptune, 5 days and 21 hours. The angle of inclination is 23° . The angle between the orbit of Triton and the equator of Neptune is 23° .
This large angle of inclination, coupled with the retrograde direction of Triton’s...
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Knowledge Gained (The Solar System)
Much of what has been discovered about Triton has come from Earth-based instruments and the Hubble Space telescope (HST). Hale Observatory used narrow-band spectrophotometry to determine that Triton had a constant spectral reflectance. Astronomers have compared data from HST, the Infrared Telescope Facility at the University of Hawaii, and Voyager 2 over a period of years to see if there is a seasonal change in Triton’s surface. It appears that there is a change, but since the climate cycle is so long, the data remain inconclusive. Both types of surface composition, methane ice and solid nitrogen, were detected by infrared spectra from an Earth-based instrument.
Voyager 2 provided more information in a short time than the land-based instruments had been able to gather in the years since Triton’s discovery. The spacecraft’s small changes in Flight path caused by Triton’s mass allowed that mass to be calculated. Pictures allowed the size to be determined. Density could then be calculated. Models of the structure of the satellite could then be developed. The density, 2.07 grams/centimeter, indicates that there is a large component of silicate materials, even though they do not show in infrared spectra because they are under ice. Voyager also detected the nitrogen atmosphere.
Pictures showed the effects of wind on Triton, a phenomenon that was unexpected. Varied terrain and plumes were also noticed in the...
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Context (The Solar System)
The density of Triton is close to that of the Pluto-Charon system. Is that a coincidental fact, or are Triton and Pluto related? Could Pluto at one time have been a satellite of Neptune that was knocked off by Triton? The orbital inclination, rotational speed, and retrograde motion all point to some cataclysmic occasion that produced Triton as a satellite.
Triton’s surface features raise interesting questions about its energy source. Triton’s is the coldest surface in the solar system, yet it also appears to be active, given the plumes and smoothness observed. How can these conditions coexist? The idea that enough sunlight penetrates a deep sheet of solid nitrogen to produce a Greenhouse effect under the ice is startling but may be true; it does appear that the ice sublimes and then refreezes in another place. Yet where does Triton get the energy to produce plumes rising 8 kilometers into the satellite’s tenuous atmosphere? Even given the satellite’s rather low gravitational acceleration, this phenomenon completes the satellite’s overall mystery. Is Triton’s interior heated radiogenically? Is there another heat source?
It is possible that scientists do not understand as much about the effect of very low atmospheric pressure, low temperature, and heavy mass as was previously thought, because the planet’s heat is generated somewhere. The theory that Triton is heated radiogenically will have to wait until the...
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Further Reading (The Solar System)
Bond, Peter. Distant Worlds: Milestones in Planetary Exploration. New York: Copernicus Books, 2007. The author discusses each of the planetary systems, including planets, moons, and rings. Exploratory space missions and how they have developed our knowledge of each system are also addressed. Illustrations, bibliography, appendix, index.
Corfield, Richard. Lives of the Planets. New York: Basic Books, 2007. The author takes the reader through the different planets and the information gathered by space missions that investigated them. Index.
Croswell, Ken. Ten Worlds: Everything That Orbits the Sun. Honesdale, Pa.: Boyds Mills Press, 2007. Basic information on each system is presented separately. Illustrations, bibliography, index. For younger readers.
Cruikshank, Dale P., ed. Neptune and Triton. Tucson: University of Arizona Press, 1995. Voyager 2’s 1989 encounter with Neptune revealed Triton to be a frozen, icy world with clouds, haze layers, and vertical plumes of particles rising high into the thin atmosphere. Originally presented as papers at a 1992 conference, the chapters in this volume are all by experts on Neptune, its many satellites, and its near-space environment. Until engineers can design propulsion systems for the next mission to the outer solar system, this 1,249-page tome will remain the most authoritative one-volume resource on Neptune and its satellites....
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