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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Global Warming on Triton

Triton, Neptune's largest moon, has been predicted to undergo significant seasonal changes that would reveal themselves as changes in its mean frost temperature. But whether this temperature should at the present time be increasing, decreasing or constant depends on a number of parameters (such as the thermal properties of the surface, and frost migration patterns) that are unknown. Here we report observations of a recent stellar occultation by Triton which, when combined with earlier results, show that Triton has undergone a period of global warming since 1989. Our most conservative estimates of the rate of temperature and surface-pressure increase during this period imply that the atmosphere is doubling in bulk every 10 years, significantly faster than predicted by any published frost model for Triton. Our result suggests that permanent polar caps on Triton play a c dominant role in regulating seasonal atmospheric changes. Similar processes should also be active on Pluto.

Elliot, J. L.↗
NASA NTRS1999

Water Ice on Triton

We report the spectroscopic detection of H2O ice on Triton, evidenced by the broad absorptions in the near infrared at 1.55 and 2.04 micron. The detection on Triton confirms earlier preliminary studies (D. P. Cruikshank, R. H. Brown, and R. N. Clark, Icarus 58, 293-305, 1984). The spectra support the contention that H2O ice on Triton is in a crystalline (cubic or hexagonal) phase. Our spectra (1.87-2.5 micron) taken over an interval of nearly 3.5 years do not show any significant changes that might relate to reports of changes in Triton's spectral reflectance (B. Buratti, M. D. Hicks, and R. L. Newburn, Jr., Nature 397, 219, 1999), or in Triton's volatile inventory (J. L. Elliot et al., Nature 393, 765-767, 1998).

Cruikshank, Dale P.↗
NASA NTRS2000

Stability of Triton's Albedo from 1985 Through 1997: Implications for the Atmosphere

Recent occultation results indicate that an increase in temperature may have occurred in the atmosphere of Triton during the past 8 years (Elliot et al. 1998; Olkin et al. 1997). The atmosphere is thought to be in vapor pressure equilibrium with the surface frosts, hence changes in frost coverage can have significant implications for atmospheric stability. We have a long- term set of multiwavelength data on Triton spanning more than a decade (the data were obtained for Neptune observations, but Triton is visible in most of the images). Over that time, the data were obtained with nearly identical filters. Thus far, only one year's worth of one wavelength has been analyzed for Triton (Lark et al. 1989). We proposed to complete a comprehensive and self-consistent analysis of the complete Triton data set. One year was funded of a requested three-year program.

Hammel, Heidi B.↗
NASA NTRS2001

Pluto and Triton: Interactions Between Volatiles and Dynamics

Volatiles moving across the surfaces of Pluto and Triton can give rise to interesting dynamical consequences. Conversely, measurement of dynamical states can help constrain the movement of volatiles and interior structure of both bodies. Polar wander may theoretically occur on both Triton and Pluto. Triton's obliquity is low, so that the equatorial regions receive more insolation than the poles. Hence there is a tendency for nitrogen ice to sublime at the equator and condense at the poles, creating polar caps. If the nitrogen supply is large enough, then these caps could move in approximately 10(exp 5) years the global equivalent of 200 m of ice to the poles. At this point the equatorial moment of inertia becomes larger than the moment of inertia measured about the rotation axis, so that Triton overbalances and becomes dynamically unstable. The satellite then undergoes polar wander, restoring stability when the new equator contains the excess matter. Hence the pole may be continually wandering. Neptune raises a permanent tidal bulge on Triton, so that the satellite's surface is elongated like a football, with the long axis pointing at Neptune. This is expected to be the axis about which the pole wanders. Volatile migration would resurface the satellite to some depth and wandering would disturb leading side/trailing side crater statistics. Additional information is contained in the original extended abstract.

Rubincam, D. P.↗
NASA NTRS1984

Large seasonal variations in Triton's atmosphere

Consideration is given to the consequences of Triton's surface covering of volatile substances in view of the circularity of Neptune's orbit, which implies that Triton would have virtually no seasonal variations in either surface temperature or atmospheric bulk despite the complex precessional effects of its orbit. It is hypothesized that Triton's most volatile surface substances are probably relegated to latitudes higher than 35 deg, probably forming polar caps whose temperatures would be nearly equal even during the midwinter/midsummer peak insolation of the summer pole. If the summer pole completely sublimates during one of the 'major' summers, Triton's atmosphere may begin to freeze out over the winter caps and yield large and complex seasonal variations.

Trafton, L.↗
NASA NTRS1989

A predicted Triton plasma torus in Neptune's magnetosphere

The possibility of the formation of a plasma torus generated by the satellite Triton in the magnetosphere of Neptune is investigated. A set of coupled differential equations is solved that describe the evolution of material sputtered from the surface of atmosphere of Triton in the conditions likely to exist in an assumed Neptunian magnetosphere for various combinations of nitrogen and methane that may exist on Triton. The model assumes a mechanism for transport that gives upper limits for predicted torus concentrations. It is concluded that a successful detection of plasma by the Voyager Plasma Science instrument may be possible and could be an important source of information about the composition of Triton's surface and atmosphere.

Delitsky, Mona L.↗
NASA NTRS1990

Triton torus and Neptune aurora

Triton is shown to be the dominant source of plasma for L equal to or greater than 7 in the magnetosphere of Neptune. Triton maintains a neutral hydrogen torus of average density comparable to a greater than that of the Titan torus at Saturn. The Triton torus may be detectable in H Lyman-alpha emissions. However, the energy source from plasma outward transport and mass loading in the Triton torus is insufficient to explain the Neptune aurora. It is proposed that Neptune's aurora is driven mainly by a solar wind interaction.

Cheng, Andrew F.↗
NASA NTRS1990

The Triton torus revisited

Prior to the Voyager encounter with Neptune, Delitsky et al. (1989) predicted that a torus of ions emanating from Triton would be discovered. These predictions are reexamined in light of the Voyager results. Sputtering of Triton's atmosphere can produce the heavy ion densities inferred at Triton's orbit by the Voyager plasma experiment if the ion residence time is about 30 days. The torus is found to be longitudinally asymmetric near Triton, with peak densities at longitudes of 170 and 350 deg. The total nitrogen flux due to sputtering is about 2 x 10 to the 21st/s. The consequences of larger escape fluxes of both N2 and H2 are investigated; it is difficult to reconcile large escape fluxes with the plasma and ultraviolet spectrometer observations.

Richardson, John D.↗
NASA NTRS1990

Triton - Topside ionosphere and nitrogen escape

The principal ion in the ionosphere of Triton is N(+). Energetic electrons of magnetospheric origin are the primary source of ionization, with a smaller contribution due to photoionization. To explain the topside plasma scale height, it is postulated that N(+) ions escape from Triton. The loss rate is 3.4 x 10 to the 7th/sq cm per sec or 7.9 x 10 to the 24th ions/sec. Dissociative recombination of N2(+) produces neutral exothermic fragments that can escape from Triton. The rate is estimated to be 8.6 x 10 to the 6th N/sq cm per sec or 2.0 x 10 to the 24th atoms/sec. Implications for the magnetosphere of Neptune and Triton's evolution are discussed.

Yung, Y. L.↗
NASA NTRS1990

Temperature and thermal emissivity of the surface of Neptune's satellite Triton

Analysis of the preliminary results from the Voyager mission to the Neptune system has provided the scientific community with several methods by which the temperature of Neptune's satellite Triton may be determined. If the 37.5 K surface temperature reported by several Voyager investigations is correct, then the photometry reported by the imaging experiment on Voyager requires that Triton's surface have a remarkably low emissivity. Such a low emissivity is not required in order to explain the photometry from the photopolarimeter experiment on Voyager. A low emissivity would be inconsistent with Triton having a rough surface at the about 100-micron scale as might be expected given the active renewal processes which appear to dominate Triton's surface.

Nelson, Robert M.↗
NASA NTRS1991

Rotationally resolved midultraviolet studies of Triton and the Pluto/Charon system. I - IUE results

The present uniform analysis of the full set of IUE spectra of Pluto + Charon and Triton attempts to characterize these objects' UV photometric properties variation with rotational phase, giving attention to the 2550-3200 A range. The visible-UV color differentiation increases as Pluto reaches its maximum bolometric brightness; the IUE data suggests that this could be due to a UV surface absorption feature on Pluto or Charon. Typical UV albedos are found on Triton which agree with Voyager photopolarimeter results; Pluto's albedo is much lower than that of Triton, but the amplitude of the Pluto UV lightcurve is greater than that of Triton.

Stern, S. A.↗
NASA NTRS1991

Triton's surface properties - A preliminary analysis from ground-based, Voyager photopolarimeter subsystem, and laboratory measurements

The surface properties of Triton were investigated using data from the ground-based and Voyager photopolarimeter subsystem (PPS) observations of Triton's phase curve. The results indicate that Triton has a high single-scattering albedo (0.96 +/-0.01 at 0.75 micron) and an unusually compacted surface, possibly similar to that of Europa. Results also suggest that Triton's single-particle phase function and the macroscopically rough character of its surface are similar to those of most other icy satellites.

Buratti, B. J.↗
NASA NTRS1991

On the microphysical state of the surface of Triton

The microphysical processes involved in the pressureless sintering of particulate materials and the physical conditions likely to prevail on Triton are examined in order to investigate the processes leading to the frost metamorphism on Triton. It is argued that the presence of a well-annealed transparent nitrogen layer offers a natural explanation for most of what is seen on the surface of Triton; results of observations suggest that such a layer can form on Triton at 37 K on a seasonal time scale (about 100 earth years), provided the initial grain diameter is less than 1 micron. Grains up to 10 microns are allowed if grain growth does not hinder densification.

Eluszkiewicz, Janusz↗
NASA NTRS1991

Search for glazed surfaces on Triton

The paper summarizes arguments leading to suggestions that Triton's icy surface may be unusual in texture, sith special attention given to the hypothesis of the existence of glazed areas on Triton. Results are presented of a search for an evidence of specular reflection diagnostic of 'glazed' icy surfaces on Triton, using high-resolution Voyager 2 images of three regions on Triton: the South Polar Cap Mottled Unit, the Bright Fringe, and the Frost Band. No such evidence was found in these three different terrains.

Lee, Pascal↗
NASA NTRS1991

A new spectrum of Triton near the time of the Voyager encounter

A 5200-10,000 A spectrum of Triton that was telescopically obtained during the summer of 1989, just before the Voyager II encounter with the Neptune system, exhibits a measurable 8900 A CH4 ice absorption band. A combination of these data with those of Voyager indicates that the absorption is caused solely by Triton surface CH4 ice. A Hapke-type model for the Triton spectrum (1) sets a 20-micron lower limit on the CH4 ice's mean grain size (although it is suspected that actual grain size is closer to 100 microns), and (2) indicates that CH4 ice is widely distributed on the southern-hemisphere surface of Triton.

Grundy, William M.↗
NASA NTRS1992

Triton - Voyager's finale

The investigation of the Neptunian satellite Triton by the Voyager 2 is described with interpretations of the object's nature and composition. The orbit, seasonal cycle, and southern-hemisphere solstice are described, and the composition of the satellite is discussed. Triton's mass and radius are known, and the objects is made up of about 70 percent rock and organics and 30 percent ice by mass. Triton's interior is warm and geologically active considering its distance from the sun, and large amounts of frozen methane and nitrogen are theorized to contribute to the object's high reflectivity. Also noted in the Voyager color images are creeping ice, cryogenic lava, and dark streaks on the south polar cap from nitrogen gas leaks driven by a type of greenhouse effect. Triton represents a class of satellite that has not been observed previously: a moon-sized body in a retrograde inclined orbit from the class of objects that coalesced to form Neptune.

Brown, R. H.↗
NASA NTRS1992

Voyager imaging of Triton's clouds and hazes

Results are presented from a detailed analysis of Voyager images of Triton obtained at the highest solar phase angles; these have been fit to Mie scattering models in order to obtain the mean particle sizes, number densities, and the vertical extent of the two different scattering components of the Triton atmosphere. The 0.001-0.01 optical depths of about 0.17 micron particles are vertically distributed with scale heights of about 10 km throughout Triton. A number of properties of the haze particles in question suggest that they are composed of photochemically produced gases which have condensed in the cold lower atmosphere of Triton.

Rages, Kathy↗
NASA NTRS1993

Spectroscopic determination of the phase composition and temperature of nitrogen ice on Triton

Laboratory spectra of the first overtone band (2.1480 microns, 4655.4 reciprocal cm) of solid nitrogen show additional structure at 2.1618 microns (4625.8 reciprocal cm) over a limited temperature range. The spectrum of Neptune's satellite Triton shows the nitrogen overtone band as well as the temperature-sensitive component. The temperature dependence of this band may be used in conjunction with ground-based observations of Triton as an independent means of determining the temperature of surface deposits of nitrogen ice. The surface temperature of Triton is found to be 38.0 +2.0 or -1.0 K, in agreement with previous temperature estimates and measurements. There is no spectral evidence for the presence of alpha-nitrogen on Triton's surface, indicating that there is less than 10 percent carbon monoxide in solid solution with the nitrogen on the surface.

Tryka, Kimberly A.↗