The double face of Triton: new observational results

Monthly Notices of the Royal Astronomical Society, 2014

Astrometric positions of the Neptunian satellite Triton with a visual magnitude of 13.5 were obtained during three successive oppositions in 2007, 2008 and 2009. A total of 1095 new observed positions of Triton were collected during 46 nights of observations, involving eight missions and three telescopes. We compared our observations to the best ephemerides of Triton available now. This comparison has shown that our observations present a high level of accuracy as they provide standard deviations of residuals hardly higher than 50 mas and mean residuals lower than 30 mas, corresponding to about only 500 km in the position of the very distant satellite Triton. Moreover, we have compared most of the different planetary ephemerides of Neptune available now as well as two recent orbit models of Triton. These new comparisons have clearly shown the differences between all of these ephemerides which can be significant and that are presented in this work.

Journal of Geophysical Research, 1991

The surface properties of Triton have been determined from a threefold approach involving analysis of ground-based and Voyager photopolarimeter subsystem observations of its phase curve, theoretical modeling* and laboratory measurements of the phase functions of a wide variety of materials. The physical parameters derived include the single-scattering albedo, the single-particle phase function, the compaction state of the optically active portion of the regolith, and the degree of macroscopic roughness. We find that Triton has a high single-scattering albedo (0.96 ± 0.01 at 0.75 pm) and an unusually compacted surface possibly similar to that of Europa. Preliminary results 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. Laboratory measurements of the phase curve of a sample of a high-albedo, compact volatile-contaminant analogue are in reasonable agreement with Tritdn's phase curve and provide evidence that the model parameters derived for Triton's surface are physically realistic.

Icarus, 1997

1 Visiting Astronomer at the Infrared Telescope Facility, which is operstructure from the analysis of all ground-based stellar occultaated by the University of Hawaii under contract to the National Aeronaution data recorded to date, including one single-chord occultatics and Space Administration.

Icarus, 2000

Science, 1990

Hapke's photometric model has been combined with a plane-parallel thin atmospheric haze model to describe Voyager whole-disk observations of Triton, in the violet (0.41 urm), blue (0.48 ,um), and green (0.56 urm) wavelength bands, in order to obtain

1996

This paper presents new results about Triton’s atmospheric 1 Visiting Astronomer at the Infrared Telescope Facility, which is oper- structure from the analysis of all ground-based stellar occulta-ated by the University of Hawaii under contract to the National Aeronau- tion data recorded to date, including one single-chord occulta-tics and Space Administration. tion recorded on 1993 July 10 and nine occultation lightcurves

Astronomy & Astrophysics, 2022

Context. A stellar occultation by Neptune’s main satellite, Triton, was observed on 5 October 2017 from Europe, North Africa, and the USA. We derived 90 light curves from this event, 42 of which yielded a central flash detection. Aims. We aimed at constraining Triton’s atmospheric structure and the seasonal variations of its atmospheric pressure since the Voyager 2 epoch (1989). We also derived the shape of the lower atmosphere from central flash analysis. Methods. We used Abel inversions and direct ray-tracing code to provide the density, pressure, and temperature profiles in the altitude range ~8 km to ~190 km, corresponding to pressure levels from 9 µbar down to a few nanobars. Results. (i) A pressure of 1.18 ± 0.03 µbar is found at a reference radius of 1400 km (47 km altitude). (ii) A new analysis of the Voyager 2 radio science occultation shows that this is consistent with an extrapolation of pressure down to the surface pressure obtained in 1989. (iii) A survey of occultation...

Icarus, 1979

New image-tube spectra of Triton are analyzed for a determination of the reflectance of the satellite between 0.32 and 0.74/zm. Comparison of the violet reflectance of Triton with that of terrestrial minerals, lunar samples, and meteorites, gives evidence that the satellite surface is composed largely of rocky material having the same sources of violet opacity (mineral charge transfer and crystal field transitions). New radiometric observations set a stringent upper limit to the satellite radius (r ~ 2600 kin) and a lower limit to the geometric albedo (Pv > 0.19). The albedo can be somewhat higher and still within the range allowed by a rocky surface. No useful constraints can be put on the mean density of Triton because of remaining uncertainties in the radius and the mass. The image-tube spectra show no evidence of gaseous absorption in the methane bands, though a stronger band has been found in the infrared at 2.3 ttm (Cruikshank and Silvaggio, 1979, in press; the near-infrared photometric colors may be affected by the CH4 band. Rayleigh scattering computations of a potential inert atmospheric component of Triton appear to preclude the presence of large quantities of nitrogen and the noble gases.

Planetary and Space Science, 2014

The planet Neptune and its largest moon Triton hold the keys to major advances across multiple fields of Solar System science. The ice giant Neptune played a unique and important role in the process of Solar System formation, has the most meteorologically active atmosphere in the Solar System (despite its great distance from the Sun), and may be the best Solar System analogue of the dominant class of exoplanets detected to date. Neptune's moon Triton is very likely a captured Kuiper Belt object, holding the answers to questions about the icy dwarf planets that formed in the outer Solar System. Triton is geologically active, has a tenuous nitrogen atmosphere, and is predicted to have a subsurface ocean. However, our exploration of the Neptune system remains limited to a single spacecraft flyby, made by Voyager 2 in 1989. Here, we present the high-level science case for further exploration of this outermost planetary system, based on a white paper submitted to the European Space Agency (ESA) for the definition of the second and third large missions in the ESA Cosmic Vision Programme 2015-2025. We discuss all the major science themes that are relevant for further spacecraft exploration of the Neptune system, and identify key scientific questions in each area. We present an overview of the results of a Europeanled Neptune orbiter mission analysis. Such a mission has significant scope for international collaboration, and is essential to achieve our aim of understanding how the Solar System formed, and how it works today.

Icarus, 2006

BVI photometry of Triton and Proteus was derived from HST images taken in 1997. The VEGAMAG photometric technique was used. Triton was found to be brighter by a few percent than observations of the 1970's and 1980's, as expected due to the increasingly greater exposure of the bright south polar region. The leading side was also found to be brighter than the trailing side by 0.09 mag in all filters-50% larger than reported by Franz [Franz, O.G., 1981. Icarus 45, 602-606]. Contrary to our previous results [Pascu, D., et al., 1998. Bull. Am. Astron. Soc. 30, 1101], we found no episodic reddening. Our previous conclusions were based on an inaccurate early version of the Charge Transfer Efficiency (CTE) correction. The present result limits the start of the reddening event reported by Hicks and Buratti [Hicks, M.D., Buratti, B.J., 2004. Icarus 171, 210-218]. Our (B-V ) result of 0.70 ± 0.01 supports the global blueing described by Buratti et al. [Buratti, B.J., Goguen, J.D., Gibson, J., Mosher, J. , 1994. Icarus 110, 303-314]. Our observations of July 1997 agree with the Voyager results and are among the bluest colors seen. We found Proteus somewhat brighter than earlier studies, but in good agreement with the recent value given by Karkoschka [Karkoschka, E., 2003. Icarus 162, 400-407]. A leading/trailing brightness asymmetry was detected for Proteus, with the leading side 0.1 mag brighter. The unique differences in action of the endogenic and exogenic processes on Triton and Proteus provides an opportunity to separate the endogenic and exogenic effects on Triton.