New Horizons team to observe stellar occultation from Senegal and Colombia

Data from distant observation will help guide plans for New Year’s flyby.

NASA’s New Horizons team is preparing to view the spacecraft’s second target, Kuiper Belt Object (KBO) Ultima Thule, pass in front of a star less than five months ahead of its scheduled New Year’s flyby.

When Ultima Thule, also known as 2014 MU69, passes in front of or occults a star on August 4, mission scientists will observe the event from two 18.5-mile (30-km) locations in Senegal and Colombia identified by data from the Hubble Space Telescope (HST) as the places on Earth where the KBO will cast its shadow.

Last summer, the mission team observed three occultations, when Ultima Thule passed in front of three separate stars in June and July. Observing from Patagonia and Argentina, the team successfully viewed the event from five separate sites in spite of extreme winter weather.  Data obtained from the event helped mission scientists learn more about the KBO and set the flyby distance at 2,175 miles (3,500 km).

As then, scientists will set up telescopes on various locations along the shadow’s path to observe the occultation, which this year will be viewed from Senegal and Colombia.

“Gathering occultation data is an extremely difficult task. We are literally at the limit of what we can detect with Hubble, and the amount of computer processing needed to resolve the data is staggering,” said Marc Buie of the Southwest Research Institute (SwRI), who is leading the observation team, as he did last year.

“Our team of almost 50 researchers using telescopes in Senegal and Colombia are certainly hoping lightning will strike twice, and we’ll see more blips in the stars. This occultation will give us hints about what to expect at Ultima Thule and help us refine our flyby plans,” he explained.

The observation team is grateful to the governments of Senegal and Colombia, US embassies in both countries, and the French, Senegalese, Colombian, and Mexican astronomy communities for their support in the project, which requires detailed and painstaking preparations.

Ultima Thule is located more than four billion miles from Earth. Like other Kuiper Belt Objects, it is made of pristine materials unchanged from the time the solar system formed.

Based on last year’s occultations, mission scientists determined the KBO is either a binary system of two objects that orbit close to one another or actually touch one another or a two-lobed object. Its size is estimated at 20 miles (30 km) long if it is a single object or nine to twelve miles (15-20 km) long each if it is two objects.

“If the team is successful, the results will help guide our planning for the flyby,” said New Horizons principal investigator Alan Stern, also of SwRI.



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