Pluto’s Atmosphere Probed from Carter Observatory

For Immediate Release

25 July 2012

Pluto’s Atmosphere Probed from Carter Observatory

Carter Observatory has helped in an international collaboration to probe the depths of Pluto’s atmosphere.

On the evening of June 4 Pluto passed in front of a faint star in the constellation Sagittarius, so that from certain parts of New Zealand and southeast Australia Pluto’s atmosphere was expected to partially obscure the star’s light. By monitoring any change in brightness as Pluto moved past the star, astronomers hoped to determine whether Pluto’s atmosphere has changed in size in the last few years. This information is of critical importance in planning the flyby of NASA’s New Horizons spacecraft in July 2015 after its ten year flight from Earth.

Observations of this event, called an occultation, were planned from 17 sites in Australia and New Zealand, in addition to the Carter Observatory in Wellington. However bad weather over most of eastern Australia and southern New Zealand only allowed data to be obtained from three places in New Zealand. And of these, the Carter Observatory 41cm “Ruth Crisp” telescope was the only one to experience perfect conditions and see the star’s light diminish as it passed through the upper reaches of Pluto’s atmosphere.

Marc Buie, a Staff Scientist from the Southwest Research Institute in Boulder, Colorado, assisted by local astronomers Graham Blow and Gordon Hudson have spent many long hours and cold nights observing occultations of Pluto from right here in Wellington.

“It’s wonderful that Wellington’s amateur astronomers are able to use our Carter Observatory to participate in this co-ordinated international effort to explore more of our Solar System”, says Director Dr Sarah Rusholme. “We’re really proud to have participated, and are looking forward to more of this type of research being conducted here at Carter”.

The observations were made using Carter’s Ruth Crisp telescope, a research-grade 41-cm (16-inch) Cassegrain reflector made by Boller and Chivens of the USA, and gifted to the observatory in the 1960s thanks to a donation by the New Zealand writer and philanthropist Ruth Crisp.

Pluto was discovered in 1930 and follows a much more elliptical orbit around the Sun than do the other planets. This means that during its orbital period of 248 years, Pluto’s distance from the Sun varies from 7,311 million km to 4,437 million km, so making the extent of Pluto’s atmosphere change enormously depending on where it is in its orbit.

Pluto was last closest to the Sun in 1989, so astronomers are keen to find out whether Pluto’s atmosphere has now started to contract again, and if so, by how much. The rate at which such a contraction would take place depends very much on what gases are present in its atmosphere and how quickly they release stored heat from the Sun.

The program to observe this occultation was co-ordinated by astronomers from Lowell Observatory (Flagstaff, Arizona), Southwest Research Institute (Boulder, Colorado) and the Paris Observatory.

This is the third occasion the Carter Observatory has been involved in observations to detect and measure Pluto’s atmosphere. The 41cm Ruth Crisp telescope was part of the international team which made the initial discovery of Pluto’s atmosphere in 1988. In 2006 Carter Observatory data from another occultation was combined with information from other sites to help refine our knowledge of both the extent and composition of the atmosphere at that time.

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