Planetary scientist Alan Stern continues his exclusive series of blogs with details of what awaits the New Horizons spacecraft when it reaches its next objective.

It sounds like science fiction, but it's not: NASA's New Horizons mission explored the Pluto system this summer — and we're not done yet! For the next year, New Horizon will be downloading data virtually daily from its encounter with Pluto and its moons. We will also be making preparations for our next flyby, which will explore an ancient, intermediate-size Kuiper Belt Object (KBO) called 2014 MU69.

New Horizons in Kuiper Belt
Its Pluto flyby now over, New Horizons is moving farther from the Sun and deeper into the Kuiper Belt.
Dan Durda

When the National Academy of Sciences' 2003 Planetary Decadal Survey rocketed the exploration of Pluto to the top of NASA's science budget queue, it also made very clear that the mission was to be a broader approach than simply a Pluto flyby and should include one or more flybys of KBOs 30 to 50 km in diameter. In fact, the Decadal Survey's drafters felt so strongly about this that they dubbed the mission "Kuiper Belt Pluto Flyby." NASA managers felt the same way, ultimately requiring us to build a spacecraft and payload fully capable of operating all the way out to at least 55 astronomical units (8¼ billion km) from the Sun — and to carry the fuel necessary to conduct at least one flyby of an ancient KBO far beyond Pluto.

The motivation for studying small KBOs is straightforward. These bodies are valuable for understanding the accretion of distant small planets like Pluto, Eris, Makemake, Haumea, Sedna, and their siblings. Why is that? It's because KBOs of this size are thought to be the building blocks that led to these larger bodies. And because medium-size KBOs are both about 1,000 times more massive than comets like 67P/Churyumov-Gerasimenko (which Rosetta is studying up close) and yet still 1,000 to 10,000 times less massive than Pluto, their study can help connect the dots of the accretion 4½ billion years ago of the small planets now found abundantly throughout our solar system.

Our target, 2014 MU69 (initially dubbed "PT1" for Potential Target 1), was found in 2014 by the Hubble Space Telescope as part of a dedicated search for New Horizons KBO targets. Actually, HST found several potential targets, but this one was selected for several reasons. One is that it is the most accessible — New Horizons will need the least fuel and shortest flight time to reach it. But 2014 MU69 also hits the sweet spot scientifically. It's about 45 km across (assuming a 4% surface reflectivity), and it's a member of the "cold, classical" dynamical population of objects that formed right there in the Kuiper Belt directly from the primordial solar nebula.

New Horizons trajectory to PT1
New Horizons must travel a billion miles past Pluto to reach 2014 MU69 (initially designated PT1).
Alex Parker

Following NASA's approval of 2014 MU69 in August, we began planning a series of trajectory adjustments so that New Horizons can get there. Those engine burns will take place between October 22nd and November 4th. The result of that will be a roughly 1,150-day flight of about a billion miles, culminating with an intercept on January 1, 2019, at a point 44.2 a.u. from the Sun. The flyby speed will be 14.4 km (8.9 miles) per second.

This flyby is contingent on NASA approving and funding a 4-year extension to the New Horizons mission — a decision planned for late summer 2016 (about when the last of our Pluto data reaches Earth). If that approval comes, then along the way to 2014 MU69 the spacecraft will also make observations of the heliosphere using our SWAP and PEPSSI plasma instruments, our dust impact counter, and our ultraviolet spectrograph.

We'll also be taking images of about 20 other KBOs that New Horizons will pass distantly. We won't see them resolved, but the resulting images will allow us to study how light reflects off their surfaces at varying Sun-object-camera angles — the kind of photometric studies of their surface properties that can't be made from Earth. We'll also use the spacecraft's camera to search more deeply for satellites around these KBOs than any Earth-based instrument or Hubble can do. These studies of small KBO surface properties and satellite populations will be a significant and completely unique contribution that only New Horizons can make.

Of course, the main science of the KBO mission, if funded, will be the flyby of 2014 MU69 itself. Our objectives for that flyby include:

  • mapping the surface geology to learn how it formed and has evolved
  • measuring the surface temperature
  • mapping the 3D surface topography
  • mapping the surface composition to learn how it is similar to and how it is different from comets like 67P and small planets like Pluto
  • searching for any signs of activity, such as a cloud-like coma
  • searching for (and studying any) satellites or rings
  • measuring or constraining its mass
PT1 compared to Cape Cod
Astronomers don't yet know the exact shape of "PT1" (2014 MU69), but its estimated 45-km diameter is much larger than that of a typical comet.

Our team is already determining how close we can come to 2014 MU69. We hope to approach much closer than we did to Pluto, so that the imaging and spectral observations collected will have higher resolution than we obtained at Pluto. We also intend to employ all seven of the instruments aboard New Horizons. If the extended mission is approved, we'll build a much more detailed encounter observation plan in 2017 followed by development and testing the following year.

We expect New Horizons to begin making observations of 2014 MU69 in October 2018, beginning with satellite searches and navigation sightings to home in on the target. We won't see it resolved as a disk (or whatever shape it has) until the spacecraft begins its intensive operations just a few days before the encounter.

So mark January 1, 2019, on your long-range calendar. Although this flyby probably won't be as dramatic as the exploration of Pluto we just completed, it will be a record-setter for the most distant exploration of an object ever made. It will also be a KBO science bonanza — something we'll share with you and the world — that's unlikely to be repeated for decades.

This is the fifth of six blogs written by Alan Stern exclusively for Previous ones are:


Image of GerryP


October 3, 2015 at 1:54 am

A thought occurred to me when I viewed the images of Charon in the article from the Sky and Telescope newsletter of 2015-10-02: the darker patch appears to match (colourwise) the area surrounding Tombach Regio on Pluto so could it possibly be that at some time in the past Charon indeed struck Pluto and the dark area near Charon's pole is where it hit Pluto and perhaps can be implicated in causing the brighter area of Tombach Regio on Pluto?

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October 3, 2015 at 11:51 am

A very interesting article, that makes my S&T subscription the best money spent in amateur astronomy. Thank you

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Image of James-Anderson


October 5, 2015 at 9:53 am

Thank you for posting!
I was wondering,
Were plans made for a parallax experiment using both ground based observations in conjunction with New Horizons for a more deeper space experiment?
Thank you.

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