Ice Dwarf
Pluto is an ice dwarf that differs fundamentally from more familiar planet types, such as rocky planets (Mercury, Venus, Earth, and Mars) and gas giants (Jupiter, Saturn, Uranus, and Neptune).
Some scientists question whether Pluto should be considered a planet at all.
Surface temperatures on Pluto are estimated to hover around –387° F (–233° C).
"We discovered in the 1990s, much to our surprise, that the solar system is littered with these little icy planets," Stern said. "They are the most populous category, and we haven't been to a single one. It's as if we explored only the extreme northern climates on Earth and never visited the more typical climes."
"In fact, we think that these icy planets are very common across the entire galaxy."
The 700-million-U.S.-dollar mission will also study Pluto's primary moon, Charon, and the Kuiper Belt.
A huge swath of icy, rocky bodies in the outermost solar system, the Kuiper belt is believed to contain more than a hundred thousand miniature worlds. They orbit in the frigid realm beyond Neptune.
The materials found in the belt are thought to be leftovers from planet formation and may reveal secrets of the origins of our solar system.
Pluto and other Kuiper belt objects appear to contain large amounts of organic compounds, such as frozen methane and water ice.
Scientists theorize that Kuiper belt objects may have delivered these materials to Earth billions of years ago, providing the raw ingredients for life.
Early "Earth"?
The New Horizons design is ultraefficient. If successful, the spacecraft will conduct its Pluto and Charon observations using less power than two hundred-watt lightbulbs.
During a five-month study the piano-size probe will map and measure Pluto's geology and landform origins, as well as its surface compositions and temperatures. The probe will also study the planet's atmosphere and two smaller moons that were discovered last year.
The craft will also deliver dramatic high-resolution images and will analyze space-dust particles.
Pluto's primary moon, Charon, is about half Pluto's size. The pair constitute a "double planet" locked in dual orbit that is unique in our solar system but likely more common elsewhere in space.
Astronomers hope to learn more about how the double planet system formed. Many believe that Pluto collided with some celestial body eons ago and that the resulting debris eventually condensed to form Charon.
A similar scenario may have spawned our own Earth-moon system.
Pluto's atmosphere is also believed to be leaking rapidly into space.
The process, called hydrodynamic escape, may have caused the rapid depletion of hydrogen from Earth's early atmosphere—making our planet suitable for life.
"I think that a thousand years from now the U.S. will be known for space exploration in much the same way that Spain is known for its exploration of the Americas in the 1500s," Stern said.
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