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Is 2014 MU69 composed of 2 objects?

The next target for the New Horizons spacecraft – which passed Pluto in 2015 – reveals itself, intriguingly, to be a possible contact binary, that is, 2 objects in 1.

View larger. | New Horizons, heading out of the solar system, has been given the nod for an extended mission to 2014 MU69. Astronomers are trying to learn all they can about this little body in the Kuiper Belt before the spacecraft’s January 1, 2019 encounter.

The New Horizons spacecraft – which visited the dwarf planet Pluto in July, 2015 – is headed now toward any icy remnant leftover from the formation of our solar system, called 2014 MU69. This object resides in the Kuiper Belt, a region of our solar system beyond Neptune’s orbit, believed to contain many small asteroid- or comet-like bodies. This summer, astronomers have been watching occultations of stars by 2014 MU69, watching for telltale dips in the stars’ light that might reveal characteristics of the little Kuiper Belt body – which is less than a few dozen miles in size – prior to its January 1, 2019 New Horizons encounter. And, voila! Jackpot! The occultations have revealed that MU69 might be a weird shape. A press release from the New Horizons team on August 3, 2017 said:

Based on these new occultation observations, team members say MU69 may not be not a lone spherical object, but suspect it could be an ‘extreme prolate spheroid’ – think of a skinny football – or even a binary pair. The odd shape has scientists thinking two bodies may be orbiting very close together or even touching – what’s known as a close or contact binary – or perhaps they’re observing a single body with a large chunk taken out of it.

Here are 2 possibilties for the shape of 2014 MU69. It’s either highly elongated and up to 30 km long (as depicted at left) or a binary body whose halves are each about 15 to 20 km across. Image via NASA/ JHU-APL/ SwRI/ Alex Parker.

Based on the occultation data, 2014 MU69 definitely appears to have an odd shape. In a press release, NASA officials said that it’s either football shaped or a type of object called a contact binary. The size of MU69 or its components also can be determined from these data. It appears to be no more than 20 miles (30 km) long, or, if a binary, each about 9-12 miles (15-20 km) in diameter.

Marc Buie, the New Horizons co-investigator who led the observation campaign, said:

These exciting and puzzling results have already been key for our mission planning, but also add to the mysteries surrounding this target leading into the New Horizons encounter with MU69, now less than 17 months away.

Follow the mission and observation campaign at the NASA New Horizons website and the mission’s KBO Chasers page.

In recent months, the small Kuiper Belt object 2014 MU69 occulted (covered over) 3 faint stars as seen from various parts of Earth. Here are the predicted tracks, each only about 50 km wide, from which those disappearances were visible. Astronomers traveled to points along these paths to observe the occultations. Dips in the stars’ light during the July 17, 2017 event suggest that MU69 may be a contact binary. Image via skyandtelescope.com.

By the way, some other known objects in our solar system are known to be contact binaries, composed of two objects close enough that they actually touch. For exmaple, Comet 67P/Churyumov–Gerasimenko, recently explored by ESA’s Rosetta probe, also appears to be a contact binary.

This is another contact binary, Comet 67P/Churyumov–Gerasimenko, as captured by the Rosetta spacecraft March 25, 2015 from a distance of 54 miles (87 km.) Read more about this image from ESA.

Bottom line: The next target for the New Horizons spacecraft – which passed Pluto in 2015 – is a Kuiper Belt Object (KBO) called 2014 MU69. This object occulted, ove covered over, three stars this summer, thereby revealing itself to be a possible contact binary, that is, 2 objects in 1.

Deborah Byrd