SOFIA in the right place at the right time for Pluto observations

The SOFIA Science Center Press Release

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a joint project of NASA and the German Aerospace Center (DLR). It is a Boeing 747SP wide-body aircraft that has been modified to include a large door in the aft fuselage that can be opened in flight to allow a 2.5-metre diameter reflecting telescope access to the sky. This telescope is designed for infrared astronomy observations in the stratosphere at altitudes of about 41,000 feet (12 kilometres). Image credit: NASA / Jim Ross.
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a joint project of NASA and the German Aerospace Center (DLR). It is a Boeing 747SP wide-body aircraft that has been modified to include a large door in the aft fuselage that can be opened in flight to allow a 2.5-metre diameter reflecting telescope access to the sky. This telescope is designed for infrared astronomy observations in the stratosphere at altitudes of about 41,000 feet (12 kilometres). Image credit: NASA / Jim Ross.
In a special celestial event visible only from the Southern Hemisphere, Pluto passed directly between a distant star and the Earth on the morning of 30 June, New Zealand time. As the dwarf planet and its atmosphere were backlit by the star, this “occultation” caused a faint shadow of Pluto to move across the surface of Earth at more than 53,000 mph, creating a ripe opportunity to perform scientific analysis – if instruments and observers could be in the right place at the right time. The only observatory capable of positioning itself above terrestrial weather and directly in the centre of Pluto’s shadow was NASA’s SOFIA, a Boeing 747SP jetliner modified to carry a 100-inch (2.5-metre) diameter telescope built by NASA’s partner, the German Aerospace Center.

SOFIA, the Stratospheric Observatory for Infrared Astronomy, is operating from a base in Christchurch, New Zealand between 15 June and 24 July, 2015. Flying out of New Zealand enables SOFIA to study celestial objects that are more easily observed, or can only be observed, from southern latitudes. The occultation observations were conducted during one flight in the observatory’s science plan that includes studies of 40 celestial targets to be observed during a 15-flight program.

“SOFIA observations of Pluto demonstrate a capability to make detailed measurements of Pluto’s atmospheric density and structure,” said Pamela Marcum, SOFIA Program Scientist at NASA’s Ames Research Center. “SOFIA conducted its first occultation observation, also involving Pluto, in July 2011. This flight adds to our understanding of how the atmosphere of Pluto evolves over multiple-year time scales as its elongated orbit takes it farther away from the Sun.”

The occultation happened at a unique time, just two weeks before NASA’s New Horizons mission will make its nearest approach to Pluto on 14 July 2015. New Horizons will use cameras, spectrometers, and other instruments to perform the first close-up studies of that world. Members of the New Horizons team who are co-investigators on the SOFIA observing proposal will have immediate access to the occultation data. Those data will be available to the general scientific community and the public in July 2016 via SOFIA’s scientific data archive.

Three diagonal lines trending southwest to northeast, respectively, indicate the centre and boundaries of Pluto's shadow track on 30 June 2015 (NZ time), travelling at more than 53,000 mph across Earth's surface. Note how the centreline of the track passed over the heart of New Zealand's South Island. Image credit: MIT.
Three diagonal lines trending southwest to northeast, respectively, indicate the centre and boundaries of Pluto’s shadow track on 30 June 2015 (NZ time), travelling at more than 53,000 mph across Earth’s surface. Note how the centreline of the track passed over the heart of New Zealand’s South Island. Image credit: MIT.
“New Horizons will give us comprehensive ‘snapshot’ measurements of Pluto for which ongoing occultation studies provide context. This unique opportunity to connect what SOFIA observes remotely with in-situ measurements from New Horizons will allow future analyses of Pluto from Earth by SOFIA and other observatories to be considerably enhanced,” Marcum said.

The principal investigator (P.I.) for these SOFIA occultation observations is Michael Person of MIT. Three scientific instruments were mounted together on SOFIA’s telescope and used to make simultaneous measurements: HIPO (High-speed Imaging Photometer for Occultations; P.I. Ted Dunham, Lowell Observatory, Flagstaff, Arizona), FLITECAM (First Light Infrared TEst CAMera, P.I. Ian McLean, University of California, Los Angeles), and the FPI+ (Focal Plane Imager-plus, P.I. Juergen Wolf, German SOFIA Institute, University of Stuttgart).

Infographic illustrating how SOFIA flew in Pluto's shadow to observe the light passing through the dwarf planet's atmosphere to analyse its characteristics. Image credit: NASA/SOFIA/USRA/ASP/L. Proudfit.
Infographic illustrating how SOFIA flew in Pluto’s shadow to observe the light passing through the dwarf planet’s atmosphere to analyse its characteristics. Image credit: NASA/SOFIA/USRA/ASP/L. Proudfit.
Speaking for the entire team, Ted Dunham said, “Lowell Observatory’s Discovery Channel Telescope made last-minute precise measurements of Pluto’s position that were analysed at MIT and relayed to us on SOFIA. A 135 mile (220 kilometre) shift in SOFIA’s flight path was worked out and precisely executed. Thanks to the hard work and dedication of so many people, excellent data were obtained with all three instruments, including observing a flash at the moment the star was exactly centered behind Pluto and illuminated its entire atmosphere as a bright ring.”