Spaceflight Insider

New Horizons scientists study KBO by observing star occultation

South African observation team await the start of the 2014 MU69 occultation

Four members of the South African observation team scan the sky while waiting for the start of the 2014 MU69 occultation, early on the morning of June 3, 2017. The target field is in the Milky Way, seen here from their observation site in the Karoo desert near Vosburg, South Africa. They used portable telescopes to observe the event, as MU69, a small Kuiper Belt object and the next flyby target of NASA’s New Horizons spacecraft, passed in front of a distant star. Photo & Caption Credit: NASA / JHUAPL / SwRI / Henry Throop

A total of 54 New Horizons observation teams successfully obtained crucial data about the spacecraft’s second target, 2014 MU69, when the Kuiper Belt Object (KBO) occulted (or passed in front of) a star on the night of June 2–3.

Approximately 24 members of the mission team, along with additional observers, traveled to locations in South Africa and Argentina, where the shadow cast by the occultation was visible along a path 25 miles (40 kilometers) wide.

New Horizons scientist Alex Parker with telescope

In Argentina, New Horizons scientist Alex Parker sets up to begin collecting data on the stellar occultation of 2014 MU69. Photo Credit: Kai Getrost

Scientists used data on star positions from the Hubble Space Telescope and from the European Space Agency’s (ESA) Gaia mission to identify the path of visibility.

“The Gaia star data has been critical this entire operation,” noted New Horizons Co-Investigator Marc Buie of the Southwest Research Institute (SwRI) in Boulder, Colorado. “Without it, there was no way we could have predicted such an accurate path.”

Narrowing down the path was just one challenge of many faced by the mission team. MU69‘s occultation of the star lasted just two seconds. Though the KBO is located about one billion miles beyond Pluto, it too is located in the constellation Sagittarius, the direction of the galactic center heavily populated with stars.

Observing the occultations gives scientists an opportunity to learn more about the size and reflectivity of the KBO as well as search for any potential debris nearby that could be hazardous to the spacecraft when it flies by MU69 on January 1, 2019.

The presence of clouds at any area along the occultation’s path would preclude scientists from observing the event from that location.

To maximize the chances of collecting good data, mission scientists pointed more than 24 fixed-location ground-based telescopes at the KBO and brought 22 portable 16-inch (40-cm) telescopes to the sites.

They then spaced the teams with portable telescopes every six to 18 miles (10 to 25 kilometers) along the visibility path.

“Deploying on two different continents also maximizes our chances of having good weather,” said mission Deputy Project Scientist Cathy Olkin. If one group were obstructed by a storm, the other one would still be able to collect data.

Notably, all 54 teams succeeded in observing the event and obtaining data.

“A tremendous amount had to go right to correctly execute such a massive observation campaign, but it did,” New Horizons Principal Investigator Alan Stern reported.

Analysis of all the data collected will take scientists several weeks, he added.

International Occultation Timing Association members observe the occultation of Kuiper Belt object 2014 MU69

Paul Maley and Ted Blank, both of the International Occultation Timing Association, observe the occultation of Kuiper Belt object 2014 MU69 on the morning of June 3, 2017, from the Karoo desert near Vosburg, South Africa. Their target field—containing both Pluto and MU69—is in the portion of the Milky Way seen here, in the constellation of Sagittarius. They positioned their telescope next to a small church, shielding it from winds that could arise during the cold winter night. NASA’s New Horizons spacecraft will fly past MU69 on Jan. 1, 2019. Photo & Caption Credit: NASA / JHUAPL / SwRI / Henry Throop

Projected path of the 2014 MU69 occultation shadow

Projected path of the 2014 MU69 occultation shadow, on July 10 (left) and July 17, 2017. Image Credit: Larry Wasserman / Lowell Observatory

MU69‘s small size, estimated to be just 25 miles (40 kilometers) across, is the reason that the occultation happens so quickly.

Little is known about the KBO because it was discovered just three years ago. The images taken during the occultation, even those of the shadow it cast, will shed light on both its brightness and shape.

Two additional occultations of stars by MU69 will occur this summer, one on July 10, and the other on July 17, and mission scientists will take advantage of both opportunities to learn more about New Horizons’ second target.

The July 10 occultation will be viewed using NASA’s airborne Stratospheric Observatory for Infrared Astronomy (SOFIA), equipped with a 100-inch (2.5-meter) telescope, which will fly above the clouds and over the Pacific Ocean, where the shadow will fall.

SOFIA’s telescope is expected to yield better data than the ground-based ones used during the first occultation.

One week later, on July 17, New Horizons scientists will again travel with portable telescopes and cameras, this time to Patagonia in Argentina, to watch MU69 pass in front of a bright star.

“It’s amazing how classical astronomy – from small telescopes to some of the most advanced observatories on Earth – is helping New Horizons plan its next flyby,” commented mission Program Executive Adriana Ocampo of NASA headquarters in Washington, DC. “It shows how truly global space exploration is.”



Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

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