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 The 3 billion-mile (5 billion-km) journey to Pluto, an
unexpectedly peach-hued world with contrasting dark and light
regions across its face, has taken more than nine years.
For most of the voyage – the equivalent of flying 120,477 times
around Earth – the probe hibernated, saving wear-and-tear on its
systems and trimming ground control costs to help the mission meet
its $720 million budget.
Clipping along at 9 miles per second (14 km per second), New
Horizons awoke in January to begin observations of Pluto and its
primary moon, Charon, located beyond Neptune in the Kuiper Belt
region, which was discovered in 1992.
Before then, Pluto was considered an odd, outlier ninth planet of
the solar system, smaller than Earth’s moon and out of place among
the gas giants that occupy what was previously considered the outer
solar system.
 Six months after New Horizons launched and with more than 40 Kuiper
Belt objects on the books, the International Astronomical Union made
a controversial call to reclassify Pluto as a “dwarf planet.”
Astronomers have since discovered about 2,000 more Kuiper Belt
residents out of a population estimated at hundreds of thousands.
Ironically, it was the discovery of the Kuiper Belt that provided
the scientific motivation and money for a mission to Pluto.
Scientists believe the Kuiper Belt holds fossils from the formation
of the solar system 4.6 billion years ago. New Horizons will conduct
its science on the fly, much like NASA’s Pioneer, Mariner and
Voyager missions of the 1960s to the 1980s, when exploration of the
solar system began. Built lean, New Horizons does not carry
propellant for a braking burn to slow down and slip into orbit
around Pluto.
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A computer program to orchestra every aspect of the spacecraft’s
pass by Pluto began on Tuesday, following a nail-biting computer
crash that suspended science operations for three days.
Timing is crucial. New Horizons will have just 30 minutes to conduct
the most important part of the mission, including photographing
Pluto and Charon, determining what the icy worlds are made of and
scanning Pluto’s atmosphere - all done while the probe and Pluto
finally cross paths.
“After traveling for nine and half years, we have to know within 100
seconds where Pluto is,” said project manager Glen Fountain.
New Horizons is expected to come as close as 7,800 miles (12,500 km)
from Pluto at 7:49 a.m. EDT/1149 GMT on Tuesday.
(Editing by Steve Orlofsky)
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