New Horizon’s Next Target Is an Oddly Shaped Asteroid

New data shows that MU69 is less than 20 miles long and may actually be two asteroids orbiting one another

MU69 Double
Asteroid 2014 MU69 may be composed of two spheres NASA/JHUAPL/SwRI/Alex Parker

In 2015, NASA’s New Horizons probe began sending back photos and data from Pluto, revolutionizing what we know about the dwarf planet with its massive heart-shaped basin as well as its moon Charon. After that successful mission, the agency has pointed the probe at another target, 2014 MU69, a Kuiper Belt Object (KBO) in the region of space beyond Pluto full of comets, asteroids, space debris and dwarf planets. Now, as Kenneth Chang at The New York Times reports, astronomers have gotten a better glimpse of the MU69, and it might be more interesting than previously thought.

As Chang reports, astronomers using the Hubble Space Telescope first located MU69 in 2014 as they looked for a post-Pluto mission for New Horizons. Measuring just 20 miles wide, MU69 appeared to be a measly speck in the sky. But the sighting provided just enough information for researchers to calculate its orbit. Though it zipped through space a billion miles beyond Pluto, New Horizons could reach it.

Now, researchers have learned a lot more about the space rock, according to a press release. That’s because MU69 happened to pass in front of three different stars in just two months. The events, called occultations, happen when the object blocks out the star and casts a tiny shadow on Earth. Using that data, researchers can calculate the speed and size of the object.

But after an exhausting scramble to prepare for the big moment, the scientists missed the first pass, Kelly Beatty at Sky & Telescope reports. On June 3 the star never darkened in the glass eyes of the 24 telescopes in South Africa and Argentina that were watching for the wink, Chang reports. They also missed a second occultation on July 10 while observing the asteroid from Fiji.

“I was physically and emotionally exhausted, psychically damaged,” Marc Buie, a member of the New Horizons team, tells Chang.

In late June and early July, measurements from Hubble of the space rock helped the astronomers refine their search. They set up a line of amateur astronomers along a three mile-long path in a remote stretch of Argentina, reports Chang. The winds were so strong, locals positioned tractor-trailers trucks as wind breaks.

But the waiting paid off. Five out of 24 observers detected the light cutting out as MU69 passed in front of a star.

Based on those observations, astronomers now believe MU69 is either one long, skinny, potato-shaped asteroid less than 20 miles in length. The other possibility is that it is two spheres, each 9 to 12 miles wide, circling each other or even touching, something known as a contact binary.

“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,” Alan Stern, principal investigator for New Horizons says in the press release. “I could not be happier with the occultation results, which promise a scientific bonanza for the flyby.”

As Beatty reports, observations of MU69 conducted by Susan Benecchi of the Planetary Science Institute between June and July also suggest the object may be a binary asteroid.

While the shape of MU69 is interesting, the occultation observation also had a bigger purpose. It also showed that there’s  no debris around MU69 that could damage New Horizons when it makes it’s anticipated pass of the KBO on January 1, 2019.