New Horizons will reach Pluto in July, despite being cancelled twice during development. Alan Sterns determination was crucial to making the mission happen. In this illustration, Plutos moon Charon is the crescent in the background. (Credit: JHUAPL/SwRI)

You dont have to wonder what is on Alan Sterns mind. The planetary scientist and former NASA associate administrator is a relentless champion of all things Pluto; he is both the principal investigator and the prime mover behind the New Horizons mission, which will fly past Pluto and its moons this July 14. In advance of the encounter, Sterns passion is building to a white heat, and he is letting everyone know it.

The excitement is infectious. Pluto is looking far more interesting than researchers realized just a few years ago. Ironically, its scientific importance has skyrocketed in the years since the International Astronomical Union demoted Pluto to dwarf planet. Recent theoretical models indicate that the Kuiper Beltthe population of objects, including Pluto, that orbits beyond Neptuneis key to understanding the early evolution of the outer solar system. It is home to multiple big, round objects that record the movements of water and organic chemicals at the time when Earth was forming.

Call these things in the Kuiper Belt dwarf planets, call them planets (or call them Plutoids and duck before Stern comes after you), whatever. They are major players in the suns family, many of them larger than any asteroid, and Pluto is the brightest and most complex of them all. Stern is a Pluto obsessive, but more and more it looks like the science is on his side: Pluto really is something special, and the New Horizons encounter promises to be a unique experience. Here, Stern makes his caseand reveals surprising details about another great mission that almost happened.

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You describe New Horizons as the first mission to the outer solar systema description that would surprise a lot of people who work on, say, the Cassini mission at Saturn.

Alan Stern: One of the implications of the discovery of the Kuiper Belt and its many small planets is that many scientists now think of the solar system as having not two but three zones. These are, as you go outward from the Sun, the inner rocky terrestrial planets [including Earth], the ice and gas giants [Jupiter and its kin], and the Kuiper Beltthe largest of the three zones, and the one with the most planets. When you think of the architecture of the solar system this way, you see that the missions that explored Jupiter, Saturn, Uranus, and Neptune were really missions to the middle solar system. Then New Horizons becomes the first true mission to the outer planets, the first probe to explore the third zone.

The whole is it a planet debate keeps coming up, but it seems more confusing than enlightening. I liked the recent essay by William McKinnon of Washington University, who defined Pluto in terms of its scientific significance. He called it a beacon to an unexplored solar realm and sentinel of the third zone.

No question, Pluto is the belle of the ball. Its got everything! There are lots of really interesting little planets out there in the Kuiper Belt, but Plutos the only one thats got all the cool attributes. Its the only one with an atmosphere that we know of, its a binary planet, its got seasons and global change, its got more kinds of volatiles on its surface than any other planet out there, and its got a really complicated satellite system.

I think that if you asked 100 leading planetary scientists and said make a table, list the interesting aspects of dwarf planets in the Kuiper Belt, the list for Pluto would be longer than for any other object on every persons list. Thats not me cheerleading, its just a statement of fact. We know more about Pluto, but it seems to have all the goodies. Its the whole package.

See more here:

Alan Stern on Plutos Wonders, New Horizons Lost Twin, and That Whole "Dwarf Planet" Thing