Almost five billion years ago, our solar system began as a vast cloud of dust and gas. The cloud began to collapse. It flattened into a giant disk that rotated faster and faster, just as an ice skater spins faster as she brings her arms in close to her body. The Sun formed at the center, and the swirling gas and dust in the rest of the spinning disk clumped together to produce the planets, moons, asteroids, and comets. The reason so many objects orbit the Sun in nearly the same plane (called the ecliptic) and in the same direction is that they all formed from this same rotating disk.
While the planets were forming, the young solar system was a wild place. Clumps of matter of all sizes often collided and either stuck together or side-swiped each other, knocking off pieces and sending each other spinning. Sometimes the gravity of big objects would capture smaller ones in orbit. This could be one way the planets acquired their distant moons.
Investigating the Aftermath
NASA has sent many spacecraft to explore the four rocky planets closest to the Sun (Mercury, Venus, Earth, and Mars) and the four giant gas planets farther out (Jupiter, Saturn, Uranus, and Neptune). All these spacecraft have helped scientists understand how our solar system formed. But still many questions remain. And no spacecraft has yet visited the most distant planet, the Pluto-Charon system, or any of the other icy objects on the outskirts of our solar system called the Kuiper Belt. Stretching for tens of billions of miles beyond Neptune, the Kuiper belt may hold at least 100,000 icy relics from the solar system's birth.
Despite being the smallest, Pluto, the ninth planet from the Sun, remains a big mystery. For example, we know Pluto is solid, like the four inner planets, rather than gaseous, like the four large outer planets. But Pluto seems to be made of very different stuff from the inner planets, having a much greater portion of ices. So what is Pluto exactly and what's it doing out there beyond the orbits of the gas giants? Why is Pluto's orbit so lopsided? Why is its orbit around the Sun so tilted from the plane in which the other planets orbit? And why is Pluto's companion moon, Charon, so big relative to Pluto and so different from Pluto itself?
Scientists have these and many more questions about Pluto and Charon, and it looks like they're going to finally get some answers--or at least start the process. In January 2006, NASA plans to launch the New Horizons spacecraft to Pluto-Charon and on to one or more of the icy Kuiper Belt Objects. Although it will be the fastest spacecraft ever built, New Horizons won't get to Pluto until 2015!
The first step in designing any mission of discovery is to decide what questions to ask. Then you either find or invent the instruments that will help find the answers. For a mission to Pluto-Charon, NASA scientists are asking such questions as, what does the surface of Pluto look like? What is Pluto's atmosphere made of? Are there big geological structures? How does the solar wind (particles ejected by the Sun) interact with the atmosphere at Pluto?
Designing a Mission to Pluto-Charon and Beyond
What scientists do know about Pluto-Charon makes them very curious to know a lot more. Based on their questions, the New Horizons team selected instruments that would measure or make images of the things in which NASA scientists are interested. In addition, they picked instruments that would provide backup to other instruments on the spacecraft should one instrument fail during the mission.
The Science Payload
Whatever a spacecraft is carrying that fulfills the main purpose of the mission is called the payload. In the case of New Horizons, the payload is the collection of instruments that will gather the information that scientists hope will help them answer their questions. The New Horizons payload includes these instruments:
New Horizons Planned Science Instrument Payload [ILLUSTRATION OMITTED] Baseline Design * PERSI is a group of instruments that can sense the visible, infrared, and ultraviolet parts of the spectrum. …