Is MU69 A Double-lobed World?

In just under a year and a half, the New Horizons spacecraft will pass by a distant Kuiper Belt Object called 2014 MU69.

Earth-based observations gave the New Horizons scientists a tantalizing look by watching what’s called a “stellar occultation”. They watched as MU69 passed in front of a star on July 17, 2017,  watching a little eclipse-type event more accurately called an “occultation”. This was after a first occultation observation mission on June 3, 2017, was set up for observers in South Africa and Argentina, and a crew aboard the airborne Strategic Observatory for Infrared Astronomy (SOFIA) watched the event on July 10. The observations, plus high-resolution scans using Hubble Space Telescope (which looked for debris in the area right around MU69) gave clues to this little world’s shape.

Unlike eclipses, which can last for minutes, the MU69 occultations lasted only a few seconds. That was precious little time to gather information about the size and shape of the object. Scattering observers along pre-selected sites from where the event could be seen (and imaged) gave the New Horizons team much more data. That gave a better feel for what MU69’s shape must be.

What Does 2014 MU69 Look Like?

It turns out 2014 MU69 is pretty weird-looking, at least from our great distance from it. The measurements reveal what looks like a double-lobed object or maybe a tiny world with a big bite taken out of it. It’s not a perfectly round place. It’s also possible that 2014 MU69 could be two objects orbiting very close to (or even touching) one another — too close to be distinguished from each other. Right now, MU69 is more than 6.5 billion kilometers from Earth and its tiny size (about 30 km) makes it difficult to get a final answer about that oddball shape. Still, it’s a pretty amazing feat to use occultations and high-resolution measurements to get this far 17 months ahead of the flyby. It will be interesting to see how it all pans out as the spacecraft gets closer and returns better images. That won’t happen until later in 2018.

Threading the Needle at MU69

Not only is this information pretty cool to know for its own sake, but the observations made this summer also help the New Horizons mission planners do a more accurate job of targeting the flyby. That’s set for January 1, 2019. The closer they can get for a safe flyby, the better the science will be. However, it’s like threading an incredibly tiny needle. Obviously, it’s good to know if there’s a debris field orbiting along with 2014 MU69. We don’t want to see New Horizons whack into something that could be avoided.

Mission Science

The science to be gained at MU69 itself is incredibly important. However, the upcoming flyby will also tell us a lot about its environment. The Kuiper Belt, the third “regime” of the solar system, contains many objects that range in size from fairly small to some larger than Pluto. This one is among the smaller worldlets out there. The short-period comets also come from this region, and Pluto is among its more famous planetary bodies. MU69 lies on the way “out” of the solar system along the New Horizons trajectory from Pluto (which it explored on a quick flyby in July 2015). The mission is essentially sampling KBOs as it goes. From its data, we may see more than just this oddball world; if there’s debris, then that will also give clues to the population of objects in the neighborhood.

Questions about 2014 MU69

I can imagine all kinds of questions to be answered by the next flyby, all aimed at figuring out just how MU69 (and any companions) formed. Is nearby debris the result of an ancient collision? Or, could it be left over from MU69’s formation (which itself could be the result of a collision)? What’s it all made of? Are they mostly rocks? Mostly ice? A mix? If so, which ices are predominant out there? What do the surfaces look like? These are all questions to be answered with images and data from the flyby. New Horizons is our “forward scout”, exploring the territory ahead and giving ever-more-detailed answers about the outer frontiers of the solar system.

Addendum:  Check out the comments below, where artist Adolph Schaller shares his interpretation of the occultation data for MU69. He does a remarkable job of extrapolating the possible shape of this object.