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Occultation data raises questions about New Horizons’ target KBO

Occultation data: Artist's impression of NASA's New Horizons spacecraft encountering a distant Kuiper Belt Object (KBO)

Occultation data will give scientists new insight of KBO 2014 MU69. The image is an artist’s impression of NASA’s New Horizons spacecraft encountering the object. Image Credit: NASA / JHU-APL / SwRI / Steve Gribben

Data collected on NASA’s New Horizons spacecrafts second flyby target, 2014 MU69, during its June 3 occultation of a star, may indicate that the Kuiper Belt Object (KBO) is smaller and brighter than previously thought.

Located approximately one billion miles beyond Pluto, which New Horizons flew by in July 2015, MU69 was discovered in June 2014 by scientists using the Hubble Space Telescope (HST) to find a second flyby target for an extended mission.

One month after the Pluto flyby, the KBO was officially selected as the spacecraft’s next target, to be visited on January 1, 2019.

MU69 passed in front of, or occulted, a star on June 3 and will occult two other stars this summer – one on July 10, and the other on July 17.

More than 50 mission scientists and others assisting them observed the occultation via both fixed and portable ground-based telescopes placed strategically along the narrow path of the KBO’s shadow in South Africa and Argentina.

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

Hubble and the European Space Agency’s (ESA) Gaia space telescope viewed the event from space.

The shadow cast by MU69 during the occultation lasted just two seconds, yet all of the observing teams successfully collected data from the event, including more than 100,000 images of the occultation star.

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

Significantly, the KBO itself was not observed although the data collected is already providing mission scientists with crucial information about the object’s environment.

New Horizons Principal Investigator Alan Stern of the Southwest Research Institute (SwRI) in Boulder, Colorado, said: “These results are telling us something really interesting.

“The fact that we accomplished the occultation observations from every planned observing site but didn’t detect the object itself likely means that either MU69 is highly reflective and smaller than some expected, or it may be a binary or even a swarm of smaller bodies left from the time when the planets in our Solar System formed.”

Less than one percent the size of Pluto, MU69 orbits in the same location where it formed about four billion years ago.

“These data show that MU69 might not be as dark or as large as some expected,” confirmed New Horizons science team member and occultation team leader Marc Buie, also of SwRI.

Mission scientists plan to observe MU69‘s next two stellar occultations, which will occur on July 10 and July 17.

The July 10 event will be studied using NASA’s airborne Stratospheric Observatory for Infrared Astronomy (SOFIA), equipped with a 100-inch (2.5-meter telescope), which will search for debris near the KBO that could pose a potential hazard to the spacecraft.

On July 17, mission scientists will again set up a line of portable telescopes along the predicted path of the shadow MU69 will cast, located in southern Argentina.

Hubble will observe that occultation to aid the search for debris in the KBO’s environment and possibly obtain an accurate estimate of its size.



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.

Reader Comments

Pablo Bonifacio

Hola podrán informar hora y posición del cielo para observar la ocultación. Vivo en Comodoro Rivadavia, donde se observará el evento el 17 de julio. Gracias!

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