New Horizons Extends Planetary Exploration

Musings on Exploration

Pluto north pole region exploration
The north polar region of Pluto, with canyons running vertically across the region, named Lowell Regio. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

We got another green light from the New Horizons mission this week, indicating its journey of exploration of continues. It means the spacecraft is alive and well, although mostly hibernating on its way out to its next target. The spacecraft is speeding along, continuing its headlong outward journey from Earth, exploring “new worlds” out there. If what it saw at Pluto is any indication, planetary scientists will likely have a few surprises in store.

Already, they’re puzzling over the shape of the next target world, 2014 MU69 (first spied by Hubble Space Telescope). Could it be two worlds in close orbit? A bi-lobed world in the deeps of the Kuiper Belt? We’ll all find out much later this year.

Targeting a Distant Planet

Pluto atmosphere exploration
Sunlight filters through and illuminates Pluto’s complex atmospheric haze layers.  Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Pluto has always been a target for exploration, although the launch windows don’t open very often. Heck, it wasn’t even discovered until early in the 20th century. Missions to the nearby planets didn’t begin until the 1960s, and the outer planets in the late 1970s.

Pluto started getting taken seriously as the most distant known planet in the late 1980s. Eventually, the New Horizons project was selected after a few tentative starts and a competition. In September 1989, a group of us students put together a Pluto Perihelion party to celebrate the planet’s closest approach to the Sun.

Over beers and volleyball, we got into a fairly heated discussion about when Pluto’s tenuous atmosphere would freeze out and fall to the surface. And, that was a concern for any mission that would head out that way. Would it get there in time to measure the atmosphere before it “fell down”? To be sure, that “freezing out” wouldn’t take place for many years, and we speculated when that might happen. It was a subject of much debate. We all had to wait until a spacecraft could actually get out there. But, no doubt about it, Pluto was definitely an object of fascination years before we got there with a spacecraft.

The Attempt to Demote a Distant Planet

Pluto also became an object of controversy. In the years since its perihelion, only a few months after New Horizons was launched, nobody expected the IAU to decide Pluto wasn’t a planet. That happened even before it had been explored. Most planetary scientists weren’t sure what to expect from a world so far out that it takes a decade to get there, even for a spacecraft that is the fastest ever sent. So, why pre-judge the world before it’s explored? I still wonder that to this day. Nothing about that “decision” made sense, except perhaps for the proffering of the term “dwarf planet” to cement Pluto’s planetary status.

Moving on to the Next Distant World

MU69 exploration and artist's concept
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 on December 31, 2018. Courtesy JHU/APL/SWRI/Alex Parker

Fast-forward to now, when we get those weekly “green lights” from New Horizons. It’s kind of heartening to know that a tiny outpost of human intellect is speeding out through the solar system, extending our senses to such a cold, dark, and distant region.

New Horizons has done a great deal at Pluto. However, it’s really just getting started in the Kuiper Belt. We’re ready for the next stop on the tour, even as we look back to see that the pesky Plutonian atmosphere still hasn’t fallen down. Even more fascinating, Pluto’s fascinating surface belies activity deep inside the planet.

What will 2014 MU69 tell us? I can’t wait to find out!


  1. It is important to note that only four percent of the IAU voted on the controversial 2006 demotion, and most were not planetary scientists but other types of astronomers. Their decision was immediately opposed in a formal petition led by Alan Stern, Principal Investigator of New Horizons, and signed by several hundred planetary scientists.

    There is already some discussion about following up New Horizons with a Pluto orbiter and lander!

  2. C.C. Petersen

    Yes, this is all well known. However, I elected purposely not to go into those details because this is a reminiscence of the entire mission and not focused on the IAU.

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