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NASA Readies to Launch Pluto Mission
The spacecraft has no moving parts, so engineers will program it to use 16 hydrazine fuel thrusters to turn the spacecraft so it can point individual instruments at targets, a process Kusnierkiewicz described as "a fairly involved ballet." Communications between Earth and New Horizons will take four hours and 25 minutes.
"We're going to see things we've never even dreamed of," said astronomer Marc Buie, a deep space specialist from Arizona's Lowell Observatory. "Over the years I've used every tool at my disposal to learn about Pluto, but there's absolutely no way from Earth to understand the geologic context -- craters, impact basins and whatever else has happened."
In fact, Pluto remains largely an enigma 75 years after it was discovered. It is an "ice dwarf" composed of water, carbon monoxide, nitrogen, methane ices and rocky material. It is yellowish red in color and bright, probably from the ice, but with darker regions. Pluto is the smallest planet in the solar system, with a diameter two-thirds that of Earth's moon.
When Pluto was discovered, "astronomers thought it was a solar system misfit," Stern said, but since then scientists have estimated there are 500,000 objects with a diameter of at least 60 miles in the Kuiper Belt, making the belt the "largest structure in the solar system," he added. "It turns out that we and Mars and Jupiter are the misfits. Pluto is typical."
But what does that mean? "There are very clearly surface features of some sort, and we have no idea at all what those features are," said astronomer Michael Brown, a Kuiper Belt expert from the California Institute of Technology. "We don't understand this body at all."
Besides taking pictures of Pluto and Charon with three imagers, New Horizons will also analyze Pluto's atmosphere and geology, measure temperatures and space dust, and document the effects of the solar wind as it peels ions from the upper atmosphere.
Brown said Pluto undergoes tremendous temperature changes during a 248-year elliptical orbit that takes it as close as 2.8 billion miles from the sun and as far as 4.6 billion miles. When the temperature gets low enough, scientists suspect, the atmosphere "collapses," with the gas freezing and falling back to the surface. Charon is too small to hold on to an atmosphere, and has none.
Buie said bright surfaces usually mean "there's been some activity down there," perhaps from an atmospheric collapse, while darkness usually means that meteors and other "space weathering" phenomena have pocked the surface enough to dissipate light. Charon is considerably less bright than Pluto.
After New Horizons passes Pluto and Charon, it will almost certainly have enough power left for both the thrusters and the generator to search out and explore at least one other Kuiper Belt object, maybe two.
"We're not even looking yet," Stern said. "Anything I pick now will seem quaint in 10 years. It would be like planning a trip to Paris in 2015 and making a restaurant reservation today."