Scientists flock to NIWA site for rare show of Pluto


Scientists from around the world will be at NIWA’s atmospheric research station in Central Otago next week to observe a rare astronomical event that is likely to last just 90 seconds.

Called a stellar occultation, it occurs when light from a star is blocked by a planet, much like a solar or lunar eclipse. Next Tuesday about 5am, Pluto will pass in front of a star which will shine light on the planet, giving scientists the best possible opportunity in nearly a decade to observe its atmosphere.

Visible only through powerful telescopes, astronomers say Central Otago offers the best chance of seeing the occultation, but it may also be visible from Tasmania or Australia’s South-eastern seaboard. NIWA’s atmospheric research station is based at Lauder, 35km from Alexandra, and is renowned for its clear skies.

NIWA atmospheric scientist Dr Richard Querel says that as the star shines its light through Pluto’s atmosphere it will enable spectroscopic measurements to be made, allowing its atmosphere to be probed and studied.  “This is a pretty rare event for Pluto – the last one where some significant discoveries were made was about 10 years ago. It was around that time that a couple of new moons were discovered near Pluto that weren’t known about before.”

Scientists are particularly interested in this stellar occultation because it occurs just two weeks before NASA’s spaceship, New Horizons, flies past Pluto collecting data and images that have never been gathered this close before. Comparisons will then be made between the ground-based and satellite observations. It is expected that the New Horizons mission will provide greater understanding of the origin and evolution of the solar system.

Occultations can be as short as a few seconds, so the expected length of Tuesday’s one will enable longer camera exposures to be used and more video footage to be collected. Dr Querel said they were still fine-tuning the precise timing and expected path of the shadow of the occultation but there was a good chance of seeing something from Central Otago, provided the weather was clear.

Several groups of scientists from the US and Europe are coming to New Zealand to observe the occultation. Some were also hosted at Lauder during the last significant Pluto occultation just after New Horizons was launched in 2006.  Observations were attempted from Lauder and Mount John as well as Wanaka. 

This time they are bringing two 14-inch portable telescopes with infrared and visible wavelength cameras. A Spanish-operated telescope installed at Lauder (BOOTES-3 60cm) will also be attempting to observe the event.

Quick facts 

  • A stellar occultation occurs when the light from a star is blocked by something like a planet, moon or asteroid – much like a solar eclipse
  • The occultation of Pluto happens on Tuesday, June 30 about 04:52 AM NZST (June 29  16:52 UT). It will last about 90 seconds and will only be visible through powerful telescopes
  • Pluto is 5.8 billion kilometres from Earth and about two-thirds the size of Earth’s moon
  • The occultation will enable scientists to make measurements of Pluto’s atmosphere about which little is known
  • Current predictions show Southern New Zealand as the best place to observe this occultation.

Further information

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Lauder Atmospheric Research Station - Dobson station. Credit: Dave Hansford