The Prediction and Observation of the 1997 July 18 Stellar Occultation by Triton: More Evidence for Distortion and Increasing Pressure in Triton's Atmosphere
✍ Scribed by J.L. Elliot; M.J. Person; S.W. McDonald; M.W. Buie; E.W. Dunham; R.L. Millis; R.A. Nye; C.B. Olkin; L.H. Wasserman; L.A. Young; W.B. Hubbard; R. Hill; H.J. Reitsema; J.M. Pasachoff; T.H. McConnochie; B.A. Babcock; R.C. Stone; P. Francis
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 294 KB
- Volume
- 148
- Category
- Article
- ISSN
- 0019-1035
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✦ Synopsis
establish the global shape of Triton's atmosphere at about 20-km altitude by modeling the detailed shape of the central flash), (ii) obtaining one or more light curves of high signal-to-noise ratio from a large telescope (to accurately determine the thermal structure of Triton's atmosphere), and (iii) obtaining light curves distributed across Triton's disk (to probe the thermal structure of Triton's atmosphere above different areas and to establish the shape of the atmosphere at about 100-km altitude by modeling the half-light surface). Although the large, fixed telescopes proved to be outside of the occultation shadow and observations with some of the portable telescopes were foiled by clouds, light curves were successfully recorded from Brownsville, Texas, and Chillagoe, Queensland. These were combined with data from another group to determine the radius and shape of the half-light surface in Triton's atmosphere and the equivalent-isothermal temperatures at the sub-occultation latitudes on Triton. A circular solution for the half-light surface (projected into Triton's shadow) yielded a radius of 1439 ± 10 km. However, the data are indicative of a global shape more complex than a sphere. Such a figure is most likely caused by strong winds. Light-curve models corresponding to the best fitting circular and elliptical atmospheres were fit to the data. The mean pressure at 1400-km radius (48-km altitude) derived from all of the data was 2.23 ± 0.28 µbar for the circular model and 2.45 ± 0.32 µbar for the elliptical model. These values suggest a global pressure increase at this level since a previous Triton occultation in 1995 August. The mean equivalentisothermal temperature at 1400 km was 43.6 ± 3.7 K for the circular model and 42.0 ± 3.6 K for the elliptical model. Within their (sometimes large) uncertainties, the equivalent-isothermal temperatures agree for all Triton latitudes probed.