The thermal structure of Triton's atmosphere: Results from the 1993 and 1995 occultations

C. B. Olkin, J. L. Elliot, H. B. Hammel, A. R. Cooray, S. W. McDonald, J. A. Foust, A. S. Bosh, M. W. Buie, R. L. Millis, L. H. Wasserman, E. W. Dunham, L. A. Young, R. R. Howell, William B. Hubbard, R. Hill, R. L. Marcialis, J. S. McDonald, D. M. Rank, J. C. Holbrook, H. J. Reitsema

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Abstract

This paper presents new results about Triton's atmospheric structure from the analysis of all ground-based stellar occultation data recorded to date, including one single-chord occultation recorded on 1993 July 10 and nine occultation lightcurves from the double-star event on 1995 August 14. These stellar occultation observations made both in the visible and in the infrared have good spatial coverage of Triton, including the first Triton central-flash observations, and are the first data to probe the altitude level 20-100 km on Triton. The small-planet lightcurve model of J. L. Elliot and L. A. Young (1992,Astron. J.103,991-1015) was generalized to include stellar flux refracted by the far limb, and then fitted to the data. Values of the pressure, derived from separate immersion and emersion chords, show no significant trends with latitude, indicating that Triton's atmosphere is spherically symmetric at ~50-km altitude to within the error of the measurements; however, asymmetry observed in the central flash indicates the atmosphere is not homogeneous at the lowest levels probed (~20-km altitude). From the average of the 1995 occultation data, the equivalent-isothermal temperature of the atmosphere is 47 ± 1 K and the atmospheric pressure at 1400-km radius (~50-km altitude) is 1.4 ± 0.1 μbar. Both of these are not consistent with a model based on Voyager UVS and RSS observations in 1989 (D. F. Strobel, X. Zhu, M. E. Summers, and M. H. Stevens, 1996,Icarus120,266-289). The atmospheric temperature from the occultation is 5 K colder than that predicted by the model and the observed pressure is a factor of 1.8 greater than the model. In our opinion, the disagreement in temperature and pressure is probably due to modeling problems at the microbar level, since measurements at this level have not previously been made. Alternatively, the difference could be due to seasonal change in Triton's atmospheric structure.

Original languageEnglish (US)
Pages (from-to)178-201
Number of pages24
JournalIcarus
Volume129
Issue number1
DOIs
StatePublished - Sep 1997

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occultation
thermal structure
atmospheres
atmosphere
stellar occultation
atmospheric structure
flash
double stars
emersion
atmospheric temperature
limbs
atmospheric pressure
submerging
limb
planets
asymmetry
planet
air temperature
temperature
probe

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Olkin, C. B., Elliot, J. L., Hammel, H. B., Cooray, A. R., McDonald, S. W., Foust, J. A., ... Reitsema, H. J. (1997). The thermal structure of Triton's atmosphere: Results from the 1993 and 1995 occultations. Icarus, 129(1), 178-201. https://doi.org/10.1006/icar.1997.5757

The thermal structure of Triton's atmosphere : Results from the 1993 and 1995 occultations. / Olkin, C. B.; Elliot, J. L.; Hammel, H. B.; Cooray, A. R.; McDonald, S. W.; Foust, J. A.; Bosh, A. S.; Buie, M. W.; Millis, R. L.; Wasserman, L. H.; Dunham, E. W.; Young, L. A.; Howell, R. R.; Hubbard, William B.; Hill, R.; Marcialis, R. L.; McDonald, J. S.; Rank, D. M.; Holbrook, J. C.; Reitsema, H. J.

In: Icarus, Vol. 129, No. 1, 09.1997, p. 178-201.

Research output: Contribution to journalArticle

Olkin, CB, Elliot, JL, Hammel, HB, Cooray, AR, McDonald, SW, Foust, JA, Bosh, AS, Buie, MW, Millis, RL, Wasserman, LH, Dunham, EW, Young, LA, Howell, RR, Hubbard, WB, Hill, R, Marcialis, RL, McDonald, JS, Rank, DM, Holbrook, JC & Reitsema, HJ 1997, 'The thermal structure of Triton's atmosphere: Results from the 1993 and 1995 occultations', Icarus, vol. 129, no. 1, pp. 178-201. https://doi.org/10.1006/icar.1997.5757
Olkin CB, Elliot JL, Hammel HB, Cooray AR, McDonald SW, Foust JA et al. The thermal structure of Triton's atmosphere: Results from the 1993 and 1995 occultations. Icarus. 1997 Sep;129(1):178-201. https://doi.org/10.1006/icar.1997.5757
Olkin, C. B. ; Elliot, J. L. ; Hammel, H. B. ; Cooray, A. R. ; McDonald, S. W. ; Foust, J. A. ; Bosh, A. S. ; Buie, M. W. ; Millis, R. L. ; Wasserman, L. H. ; Dunham, E. W. ; Young, L. A. ; Howell, R. R. ; Hubbard, William B. ; Hill, R. ; Marcialis, R. L. ; McDonald, J. S. ; Rank, D. M. ; Holbrook, J. C. ; Reitsema, H. J. / The thermal structure of Triton's atmosphere : Results from the 1993 and 1995 occultations. In: Icarus. 1997 ; Vol. 129, No. 1. pp. 178-201.
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abstract = "This paper presents new results about Triton's atmospheric structure from the analysis of all ground-based stellar occultation data recorded to date, including one single-chord occultation recorded on 1993 July 10 and nine occultation lightcurves from the double-star event on 1995 August 14. These stellar occultation observations made both in the visible and in the infrared have good spatial coverage of Triton, including the first Triton central-flash observations, and are the first data to probe the altitude level 20-100 km on Triton. The small-planet lightcurve model of J. L. Elliot and L. A. Young (1992,Astron. J.103,991-1015) was generalized to include stellar flux refracted by the far limb, and then fitted to the data. Values of the pressure, derived from separate immersion and emersion chords, show no significant trends with latitude, indicating that Triton's atmosphere is spherically symmetric at ~50-km altitude to within the error of the measurements; however, asymmetry observed in the central flash indicates the atmosphere is not homogeneous at the lowest levels probed (~20-km altitude). From the average of the 1995 occultation data, the equivalent-isothermal temperature of the atmosphere is 47 ± 1 K and the atmospheric pressure at 1400-km radius (~50-km altitude) is 1.4 ± 0.1 μbar. Both of these are not consistent with a model based on Voyager UVS and RSS observations in 1989 (D. F. Strobel, X. Zhu, M. E. Summers, and M. H. Stevens, 1996,Icarus120,266-289). The atmospheric temperature from the occultation is 5 K colder than that predicted by the model and the observed pressure is a factor of 1.8 greater than the model. In our opinion, the disagreement in temperature and pressure is probably due to modeling problems at the microbar level, since measurements at this level have not previously been made. Alternatively, the difference could be due to seasonal change in Triton's atmospheric structure.",
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AU - Cooray, A. R.

AU - McDonald, S. W.

AU - Foust, J. A.

AU - Bosh, A. S.

AU - Buie, M. W.

AU - Millis, R. L.

AU - Wasserman, L. H.

AU - Dunham, E. W.

AU - Young, L. A.

AU - Howell, R. R.

AU - Hubbard, William B.

AU - Hill, R.

AU - Marcialis, R. L.

AU - McDonald, J. S.

AU - Rank, D. M.

AU - Holbrook, J. C.

AU - Reitsema, H. J.

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N2 - This paper presents new results about Triton's atmospheric structure from the analysis of all ground-based stellar occultation data recorded to date, including one single-chord occultation recorded on 1993 July 10 and nine occultation lightcurves from the double-star event on 1995 August 14. These stellar occultation observations made both in the visible and in the infrared have good spatial coverage of Triton, including the first Triton central-flash observations, and are the first data to probe the altitude level 20-100 km on Triton. The small-planet lightcurve model of J. L. Elliot and L. A. Young (1992,Astron. J.103,991-1015) was generalized to include stellar flux refracted by the far limb, and then fitted to the data. Values of the pressure, derived from separate immersion and emersion chords, show no significant trends with latitude, indicating that Triton's atmosphere is spherically symmetric at ~50-km altitude to within the error of the measurements; however, asymmetry observed in the central flash indicates the atmosphere is not homogeneous at the lowest levels probed (~20-km altitude). From the average of the 1995 occultation data, the equivalent-isothermal temperature of the atmosphere is 47 ± 1 K and the atmospheric pressure at 1400-km radius (~50-km altitude) is 1.4 ± 0.1 μbar. Both of these are not consistent with a model based on Voyager UVS and RSS observations in 1989 (D. F. Strobel, X. Zhu, M. E. Summers, and M. H. Stevens, 1996,Icarus120,266-289). The atmospheric temperature from the occultation is 5 K colder than that predicted by the model and the observed pressure is a factor of 1.8 greater than the model. In our opinion, the disagreement in temperature and pressure is probably due to modeling problems at the microbar level, since measurements at this level have not previously been made. Alternatively, the difference could be due to seasonal change in Triton's atmospheric structure.

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