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Fri, Oct. 18

Lowell scientists essential to airborne Pluto observation

Courtesy NASA/Jim Ross<br>
NASA’s Stratospheric Observatory for Infrared Astronomy opens its 
telescope cavity doors while a NASA F/A-18 mission support aircraft keeps pace during a test flight.

Courtesy NASA/Jim Ross<br> NASA’s Stratospheric Observatory for Infrared Astronomy opens its telescope cavity doors while a NASA F/A-18 mission support aircraft keeps pace during a test flight.

A team of scientists from Flagstaff's Lowell Observatory led a recent airborne observation of Pluto's passing in front of a distant star, thereby learning more about Pluto while also proving the plane's worth in space observation.

The Lowell-built High-Speed Imaging Photometer for Occultation (HIPO) - an extremely fast and accurate electronic camera - was essential to the June 23 observation of the occultation.

The specially designed 747 plane is called the Stratospheric Observatory for Infrared Astronomy (SOFIA).

"Occultations give us the ability to measure pressure, density, and temperature profiles of Pluto's atmosphere without leaving the Earth," explained Lowell's Dr. Ted Dunham, who led the team of scientists aboard SOFIA during the Pluto observations and is HIPO's principal investigator. "Because we were able to maneuver SOFIA so close to the center of the occultation we observed an extended, small, but distinct brightening near the middle of the occultation.

"This change will allow us to probe Pluto's atmosphere at lower altitudes than is usually possible with stellar occultations."

SOFIA is a highly modified Boeing 747SP aircraft that carries a telescope with a 100-inch (2.5-meter) reflecting mirror. By operating in the stratosphere at altitudes up to 45,000 feet, SOFIA flies above the water vapor in Earth's lower atmosphere and can conduct astronomical research not possible with ground-based telescopes.

"This was the first demonstration in practice of one of SOFIA's major design capabilities," said Bob Meyer, SOFIA's program manager. "Pluto's shadow traveled at 53,000 mph across a mostly empty stretch of the Pacific Ocean. SOFIA flew more than 1,800 miles out over the Pacific Ocean from its base in Southern California to position itself in the center of the shadow's path, and was the only observatory capable of doing so."

Finding the proper position in the shadow's path proved difficult. Pluto's precise position in relation to Earth could not be adequately computed until a few hours before the event.

That evening, Lowell astronomer Dr. Stephen Levine used facilities at the U.S. Naval Observatory's Flagstaff Station to take digital images of Pluto and the star.

Collaborators at the Massachusetts Institute of Technology (MIT) received Dr. Levine's data and refined their prediction of the exact position and timing of Pluto's shadow track.

Two hours before the occultation, the MIT scientists contacted the airborne SOFIA with news that the center of the shadow would cross 125 miles north of the position cited in the observatory's flight plan.

After recalculating and filing a revised flight plan, SOFIA's flight crew and science team anxiously waited 20 minutes before air traffic control approved the change.

Dunham was a member of the group that originally discovered Pluto's atmosphere by observing a stellar occultation from SOFIA's predecessor, the Kuiper Airborne Observatory, in 1988. Pluto itself was discovered at Flagstaff's Lowell Observatory in 1930.

"We have already shown that SOFIA is a first-rank international facility for infrared astronomy research. This successful occultation observation adds substantially to SOFIA's ability to serve the world's scientific community," said Dr. Pamela Marcum, SOFIA project scientist.

SOFIA is a joint project of NASA and the German Aerospace Center (DLR), and is based and managed at NASA's Dryden Aircraft Operations Facility in Palmdale, Calif.

NASA's Ames Research Center in Moffett Field, Calif., manages the SOFIA science and mission operations in cooperation with the Universities Space Research Association headquartered in Columbia, Md., and the German SOFIA Institute (DSI) at the University of Stuttgart.

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