Triton

Triton, the largest moon of Neptune, is the seventh largest moon in the solar-system. It has an atmosphere consisting primarily of nitrogen. It had warmed slightly between the 1989 voyager II flyby and our 1997 occultation, so our 1998 paper in the scientific journal Nature was entitled “Global Warming on Triton.”

For the October 5, 2017, event, NASA’s SOFIA aircraft was based at the Daytona airport, where Embry Riddle Aeronautical University is located, and it made its first Atlantic flights, a test flight on Tuesday and the data-gathering flight on Thursday (Oct 5), the latter lasting about 8 hours.  They went out about halfway to Europe, and then went a bit south by a few hundred kilometers as the latest astrometric predictions came in from colleagues, led by Amanda Bosh of MIT, working with the Discovery Channel Telescope in Flagstaff, AZ.  Michael Person of MIT was the scientist in charge of the observations with the HIPO (High Speed Imaging Photometer for Occultations) instrument, mounted so it could see through the 2.5-m aperture of SOFIA’s telescope.  (HIPO is being retired, in spite of its successes with this occultation and with two Pluto occultations.)  Jay Pasachoff was in charge of ground-based support with the 1-m telescope of ERAU in Daytona, where he was working with Williams College undergraduate Christian Lockwood and our alumnus and present Yale graduate student Allen Davis. We were assisted there by observatory director Ted von Hippel.  Williams College undergraduate student Ross Yu headed our successful observations with our Portable Occultation, Eclipse, and Transit System (POETS) with our 24-inch telescope at Williams College, Williamstown, MA.  We had a second POETS at Embry-Riddle.  The other four POETSs that Williams College and MIT purchased with a NASA grant a dozen years ago were deployed in the Canary Islands and in Europe, where other observatories also observed the occultation.

We have a successful light curve from SOFIA, with a central flash, which brightening in the middle of the two minutes of occultation allows sampling of Triton’s atmosphere closer to its surface than is otherwise possible.  We have a light curve from the 24” at Williams College, which helps constrain the shape of Triton’s atmosphere, since it is around the curve of its shape.  It was too cloudy to observe with the 1-m at ERAU, though we had had enough clear sky to observe a star to focus the night before.  Stephen Levine of Lowell Observatory and MIT was successful with a light curve from the Canary Islands using the Jacobus Kapteyn Telescope of the Isaac Newton Group.

Refereed Papers

• Global Warming on Triton (Elliot et al., Nature 393, 765-767, 25 June 1998)
• More Evidence for Distortion and Increasing Pressure in Triton’s Atmosphere (Elliot et al., Icarus 148, 347-369, 2000)
• J. L. Elliot, M. J. Person, and S. Qu, 2003, Analysis of Stellar Occultation Data. II. Inversion, with Application to Pluto and Triton,* Astronomical Journal 126, 1041, doi: 10.1086/375546

Abstracts

• Further Evidence for Increasing Pressure and a Non-spherical Shape in Triton’s Atmosphere (Person et al., B.A.A.S. 32, No. 3, 1082, October 2000)
• Probing small bodies in the outer solar system with stellar occultations (Person et al., European Planetary Science Conference 2008, Münster)

Informational Links

David Dunham’s Sky and Telescope report on the October 5, 2017, occultation