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it was estimated that Pluto was
seven times the size of Earth. By
1978, it was clear that Pluto was
smaller than Earth’s Moon. However,
it also had a huge satellite, named
Charon (the boatman of the dead in
Greek mythology), which was about
a third of the size of Pluto, and the
two bodies moved around each
other as a binary system. At launch,
planners also took into account two
more tiny moons, Nix and Hydra,
but by 2012, with New Horizons
already well on the way, it was
found that there were two more—
Kerberos and Styx—which could
potentially disrupt the mission.
Measuring Pluto
In the end, these worries were
misplaced, and LORRI was able
to obtain a measurement for all
of these bodies. Pluto is 1,470 miles
(2,370 kilometers) wide, meaning
that it is larger than Eris (although
Eris is heavier). On July 14, 2015,
New Horizons flew 7,750 miles
THE TRIUMPH OF TECHNOLOGY
(12,472 km) above Pluto, its closest
approach. Its instruments were
collecting huge quantities of
data to be fed back to Earth.
The close-up view of Pluto showed
it to be a world of pale ice plains
and dark highlands. The ice is
largely frozen nitrogen, which
makes Pluto a very bright object
for its size. The highlands are also
ice (although mixed with tar-like
hydrocarbons). The ice is thrust
into lumpy peaks that tower 2 miles
(3 km) above the plains. Quite
how such huge features arose
on such a cold and small body is
one of the mysteries of the New
Horizons mission. In addition,
craterlike structures have been
identified as possible ice volcanoes.Naming the landmarks
Pluto’s surface features have been
given unofficial names by NASA
scientists. Cthulhu Regio is a large
whale-shaped dark patch in the
southern hemisphere. Other regionsare named after past missions:
Voyager, Venera, and Pioneer. Two
main mountain ranges have been
imaged clearly: Norgay Montes and
Hillary Montes, named after the first
two climbers to reach the summit of
Mount Everest. However, the central
feature of New Horizons’ partial
map of Pluto is Tombaugh Regio,
a heart-shaped plain. Half of this
area is made up of Sputnik Planitia,
a vast ice floe riddled with cracks
and troughs, but with no craters,
which suggests it is a young feature
that is carving out new surface
features like glaciers on Earth.
Now past Pluto, the craft is
on course to meet up with other
KBOs. Its nuclear power source
should last until around 2030, and
the mission should make many
more discoveries. ■This view from New Horizons zooms
in on the southeastern portion of
Pluto’s great ice plains, where the
plains border rugged, dark highlands.