Occultation data suggests New Horizons' next target could be a binary

Shape of distant KBO surprises scientists.
By Laurel Kornfeld | Aug 06, 2017
Observations of New Horizons' second target, Kuiper Belt Object (KBO) 2014 MU69 conducted when it passed in front of a star on July 17 suggest it could be a binary system of two objects that orbit very close together.

Five out of 24 ground-based observing teams in remote parts of Argentina saw the background star disappear for three seconds as MU69 passed in front of it.

This was the third time the KBO occulted or passed in front of a background star since early June. Mission scientists also observed the previous two events, the first with a similar network of ground-based telescopes in Argentina and South Africa, and the second using NASA's airborne Strategic Observatory for Infrared Astronomy (SOFIA) over the Pacific Ocean.

The third effort was the most successful, with teams spaced three miles (4.5 km) apart perpendicular to the expected occultation path, using cameras that recorded five frames per second.

Based on the occultation timings, mission scientists estimate MU69 is either an elongated object, a roundish object with a large chunk missing, an object with two lobes, or two separate objects that either touch each other or orbit very close to one another.

If it is a single object, MU69 is at most 20 miles (30 km) long. If it is two separate objects, each one has a diameter ranging between nine and 12 miles (15 and 20 km).

"This new finding is simply spectacular. The shape of MU69 is truly provocative, and could mean another first for New Horizons going to a binary object in the Kuiper Belt," said mission principal investigator Alan Stern of the Southwest Research Institute (SwRI) in Boulder, Colorado.

"I could not be happier with the occultation results, which promise a scientific bonanza for the flyby."

Scientists used the Hubble Space Telescope and the European Space Agency's (ESA) Gaia satellite to identify the exact path of MU69's shadow for all three occultations.

Data from the occultations will help the mission team refine the spacecraft's trajectory for January 1, 2019, flyby as well as more accurately pin down MU69's orbit.

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