Category Archives: New Horizons mission

Kuiper Belt, New Horizons mission

The Shadow of 2014 MU69 Tells a Tantalizing Tale

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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.

No one was quite sure what shape this tiny world is, and the mission scientists needed to know. So, they put together an ingenious plan.
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?

MU69
The Kuiper Belt object 2014 MU69 may be a double-lobed object or possibly a more spherical one with a chunk missing. The New Horizons spacecraft will fly by this object in January 2019. Courtesy JHU/APL/SWRI/Alex Parker

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.

astronomy, New Horizons mission

New Horizons Team Does Science in the Shadow

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2015 MU69 Occults a Star

sofia occultation run
SOFIA cartoon showing flight path of airborne observatory catching the occultation; observers also watched it from the ground. Courtesy NASA

On January 1, 2019, the New Horizons spacecraft is going to pass close to a Kuiper Belt object called 2014 MU69. Not much is known about this distant little world, so it’s important to know how big it is, whether it has companions or a debris field or even a ring around it. Most importantly, the New Horizons team needs to get a very precise fix on the object’s position and orb it so they can plan the flyby to gather maximum science with minimum danger to the spacecraft. This is very similar to work done by the team as their spacecraft approached Pluto in 2015 during the fantastic flyby exploration of the distant planet.

One way to get that information is to watch as MU69 passes in front of (occults) a star. As the star “winks out” and then reappears, the team can get a much better guide on the position and size of the object. So, the team gathered star position data using a star catalog amassed by observations using the European Space Agency’s GAIA telescope, and the positions of the object gathered by the Hubble Space Telescope to plot out a series of occultation observations. The second of those observation runs took place on July 10th aboard the SOFIA aircraft high over the southern hemisphere skies. Groups of ground-based observers also looked for the occultation, as well.

This is an incredibly tough set of measurements to make. MU69 is not very bright, it’s small, and its very far away. The good news is, the SOFIA observers reported they were able to fly through the “shadow” of this tiny world and get occultation measurements. It’ll be a short while (perhaps a few days) before we know the full results, but coupled with the ground-based info, the chances are very good that we’ll know more about this little object. That’ll be of immense help to the New Horizons planners as they chart the close flyby in less than a year and a half.

Occultations and their Meaning for New Horizons

So, how can an object occulting a distant star reveal information about the object?
If you know the distance of the object, you can use simple geometry to figure out at least one of its dimensions using time it takes for the object to traverse in front of the star. The starlight winks out (or dims) at one point and then some minutes (or hours) later, it comes back. Astronomers can use that to plot an angular distance that the object traveled as it passed in front of the star. Imagine watching a car pass in front of a tree. You note the time it begins the pass, and then note when its rear bumper clears the tree. That gives you the time it took to occult the tree. If you know how far away it is, you can the figure out how long the car is. Occultations by asteroids are most commonly studied, as well as occultations of stars by the Moon.

Multiple occultations from different places can also help astronomers understand more about the object’s shape. Different parts of the object will occult the star at different times, and when you put all that data together, you will get a rough estimate of the “roundedness” or “lumpiness” of its shape (what planetary scientists refer to as its “morphology”). If there are multiple occultations before and after the main occultation, that might be a clue to the existence of a ring system or moons or co-orbital objects (maybe it has a clump of objects traveling with it).

For planets and other solar system objects, the more distant stars act as an indirect measuring stick that reveals a lot more information than you’d think. While it’s likely not an issue at MU69 (but never say “never”), an occultation could also reveal whether it has an atmosphere or not. The starlight passing through that atmosphere would absorb certain wavelengths of light, and that would show up in a spectrum of the starlight taken during the occultation.

We Should Hear Soon from the New Horizons Team

I hope we hear soon from the New Horizons team about this set of occultation studies. The first one was somewhat inconclusive, but this one appears to be successful. You can follow the news at the New Horizons mission web site, and on Twitter using the hashtag #mu69occ — presumably, there’ll be an announcement in the next few weeks, once the data analysis is complete.

Other Observations Today

Also, keep an eye out for images from the Juno spacecraft. It’s flying over Jupiter’s Great Red Spot today and the images should be downright amazing! Look for those in a few days, too.