New Horizons Explores the “Third Zone” of the Solar System

A tiny spacecraft with seven powerful instruments is hurrying to Pluto, on its way to return images of a planet that we have only ever seen as a dot in the distance orbiting the Sun in a previously unexplored zone of the solar system. New Horizons will fly by Pluto on July 14, 2015, visiting the last of the known “planets” in our solar system. The last flyby like this, where a spacecraft encountered a previously unexplored world, was made by the Voyager 2 mission when it swept past Neptune in 1989.

“About half the people on our planet have never seen a flyby like this,” said New Horizons PI Alan Stern during today’s NASA press conference about the mission. “This is really unique and historic. I know it sounds like science fiction, but it’s not. Three months from today, we will make the first exploration of Pluto and the Kuiper Belt, which is farther than any shore ever explored by humankind. We will all get to watch as a point of light turns into a planet in a matter of weeks.”

New Horizons started out as a Pluto fast flyby, with a great deal of planning at NASA over a period of a decade before it was built and launched. It may sound like hyperbole, but this mission is going to change our view of the solar system yet again, just as the Pioneer, Voyager, Galileo, and Cassini missions did before it. All but Cassini were flybys, the first tentative “pokes” at new worlds.  This mission  is also a flyby, giving us the first up-close look at a distant world. But, its significance is even bigger than that.  New Horizons is probing what planetary scientists now think of as the “third zone” of the solar system.  And, that’s a big change from the way we’ve always understood our Sun and planets.

Until now, we all knew about two types of planets that inhabited two different zones of the solar system. The rocky, terrestrial-type worlds circle within the inner solar system. The gas giant planets inhabit a colder region beyond the Asteroid Belt that used to be simply referred to as the “outer solar system”.

With Pluto’s discovery, and the more recent discoveries of objects orbiting beyond Neptune and Pluto, a “third zone” is coming into view: the Kuiper Belt zone. It’s populated with small worlds and planetary building blocks, and its contents are relics of the great age of planetary formation that took place about 4.5 billion years ago after the Sun was born. Many of the worlds in the third zone are big enough to be dwarf planets. Stern pointed out that the numbers of dwarf planets discovered are rising. “Dwarf planets are the most common type of planet now,” he said. “They outnumber the combined population of the terrestrial and giant planets.”

This realm has dwarf planets with very different properties, even from each other. Most do not have known atmospheres, some have moons while others do not, and they have different colors. The Kuiper Belt, not known to us before the 1990s, is turning out to be a biggest, massive and amazing new frontier of the solar system, and New Horizons is aimed right at it, via Pluto. If all goes well, after it finishes at Pluto, the spacecraft has its sights set on two other worlds that lie beyond Pluto. Hubble Space Telescope discovered them last year and the followup mission should allow New Horizons to take a peek at them.

Starting in the next few weeks, we should start to see higher resolution images coming from the spacecraft as it zooms in toward its flyby target. By mid-May, those images will be better than the best efforts of the Hubble Space Telescope (but remember, it’s doing its observing from Earth orbit, some 4.8 billion kilometers (3 billion miles) away. The flyby will take the spacecraft through the escaping outer atmosphere of Pluto, and at that close range, the cameras will be returning images as sharp any returned by a satellite flyover of a city on Earth. That means they’ll be able to resolve objects the size of a large building. So, we’ll get to see whatever’s on the surface of Pluto and learn more about its interior and atmosphere from the spacecraft’s suite of instruments.

If you’re interested in following the New Horizons mission, check out the NASA New Horizons page as well as the mission page at Johns Hopkins Applied Physics Laboratory. I’ll be writing reports at least once a week for the next few weeks, bringing you up to speed about the spacecraft and its accomplishments. You can also go back and check some of my earlier reports: On the Approach to Pluto and information on its dwarf planet status, plus some news about a contest to name Pluto features. Stay tuned for more!  I plan to be at Applied Physics Lab for the historic flyby week, and I’ll report from there, too.

I’m psyched for this! 2500 Americans who designed and built New Horizons are psyched for it.  And, I hope you will be, as well.

For now, I’ll let Alan Stern have the last word about how HE feels:  “We’re on Pluto’s doorstep and we ARE excited!”