Dr. Jim Green, Director, Planetary Science Division, NASA Headquarters, Washington, DC

NTB: And you had no technology to figure out whether they were planets or not, right?

Dr. Green: Correct!   

NTB: So you assumed they were planets.

Dr. Green: That’s right! You called them planets. But by 1852, when the astronomers got together and really began to noodle on “What’s going on here?” you recognized that this was really a different class of objects, and that class was defined as asteroids. We now know there are probably a million or more asteroids in the asteroid belt, which exists between Mars and Jupiter.

We are right now in the same part in our history – in exactly an analogous way – by thinking about Pluto as a planet or other type of solar system body. Pluto turns out to be what we call a Kuiper Belt object. Another class of objects. This is fantastic! How did this occur? Well, around 1990, because telescopes on Earth were getting quite outstanding and they continue to improve with time, a series of astronomers were observing and finding what were objects – they could be planets – but they were objects at distances greater than Pluto. Since 1990 we’ve found about 1300 of these objects, one of which is bigger than Pluto. That object is called Eris, and it’s about twice as far as Pluto is from us right now.

So this whole new set of objects that we’re finding, we now call the Kuiper Belt, after astronomer Gerard Kuiper. He suggested that comet-like debris left over from the formation of the solar system should exist just beyond Neptune, and now we want to study them. So, our mission called New Horizon, which will fly by Pluto in 2015, will be our first fabulous glimpse of a completely new type of object – once again, a Kuiper Belt object – and it will be quite fascinating to understand a lot more about its structure, its shape, and see how these objects are really part of the origin and evolution of our solar system.

This next decade in planetary science is going to be incredibly rich with fabulous amounts of data, and I think we’ll continue to make some really outstanding and astounding discoveries as we move into the future.

For more information, contact Dr. Green at This email address is being protected from spambots. You need JavaScript enabled to view it..

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