Pluto or Bust: Possible Extended Mission for NASA's New Horizons

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Portrait of Pluto and its large moon Charon.  (New Horizons/NASA)

July 14th was a fantastic ride. NASA's New Horizons mission took us through the Pluto system on the adventure of a lifetime, an adventure that will continue to unfold for many months as the large batch of data captured by the tiny spacecraft is sent back to Earth in radio trickles.

The encounter with Pluto and its large moon Charon dealt us far more surprises than expected. Far from being the icy, crater-scarred orbs that conventional thinking might have prepared us for, both appear to have relatively young, nearly crater-free surfaces--which means that some form of activity has taken place in their recent history—sometime in the past 100 million years or so.

Tectonic activity? Cryo-volcanism? A sub-surface ocean? Atmospheric meteorological phenomena? We don't know, yet—but that's part of the ongoing journey of discovery that we can enjoy for years.

But even as Pluto data continues to flow in with fresh food for thought on these questions, mission scientists have their eyes on a further adventure, beyond Pluto. Though no definite decisions have been carved in ice yet, the opportunity to expand on the exploration of Pluto's realm, the Kuiper Belt, is open wide before New Horizons' flight trajectory.

New Horizons is in good condition, having survived its decade-long trek to Pluto, mostly in a preserving state of robotic hibernation. Powered by plutonium, the spacecraft's energy source can last for, well, thousands of years.


The Kuiper Belt is a wide band ringing the Sun, extending from just beyond the orbit of Neptune to about 50 astronomical units (AU--1 AU being the Earth-Sun distance of about 93 million miles). It is populated by an unknown number of icy objects—dwarf planets like Pluto, Eris, Haumea, and Makemake; smaller Kuiper Belt Objects (KBOs); and comets—and is estimated to contain between 20 and 200 times the material of the main Asteroid Belt.

A lot of territory to explore—and very interesting territory, if New Horizons' revelations of the Pluto system are an indication.

One of the reasons for exploring Pluto and the Kuiper Belt—maybe the most important reason, scientifically—is that these objects possess clues about the formation of the solar system. They are basically "left overs" from the solar system's earliest times, chunks of primordial material that didn't get swept up in the formation of the planets, or were ejected from regions closer to the sun by their gravitational influence.

While New Horizons is still officially engaged in its Pluto flyby mission, continuing observations of the dwarf planet system as it flies away, it is also poised on the point of a decision: where to go next.

Mission scientists would like to send New Horizons to another encounter, and have a pair of candidates in mind: two Kuiper Belt Objects, called 2014 MU69 and 2014 PN70. We can only visit one of these, and to achieve either destination the spacecraft must expend some fuel to adjust its course—and by no later than the Fall of 2015. The actual encounter would occur in 2019.

Both of these objects are quite different from Pluto. They are smaller, estimated to be a few tens of miles across—compared to Pluto's newly refined diameter of 1,473 miles. And they are much farther from the sun—about a billion miles farther than Pluto, deep within the Kuiper Belt. A flyby sampling of either would likely tell us things about that region of the solar system that Pluto can only hint at.

However, this further encounter can only take place if NASA approves funding for an extended mission, for which proposals are due in 2016, with funding granted in 2017.

Worst-case scenario: New Horizons is sent to one of these objects, but flies by without collecting or sending data back to Earth.

Best case: we have another close encounter with a far-flung, exotic, and mysterious world to look forward to.