Sky and Telescope - July 2015 - 20

New Horizons at Pluto

Pluto
at Last

After a 9½-year ﬂight, NASA's New Horizons spacecraft
is making a long-awaited visit to Pluto and its moons.

Emily Lakdawalla
Beyond any planet that's ever been
explored before lies the frozen "Third
Zone" of the solar system: the Kuiper
Belt. It's dark, cold, and sluggish, a place so remote that
its small, icy inhabitants take hundreds of years to complete a single orbit of the distant, dim Sun. We've only
seen a handful of Kuiper Belt objects from Earth - and
none of those as anything more than vague smudges.
But after nearly a decade of interplanetary travel, NASA's
New Horizons spacecraft is about to change the status
quo. Now we're about to see, up close, the region's most
famous member: Pluto.
New Horizons is not the ﬁrst spacecraft to traverse
this region of space, but it will be the ﬁ rst to study any of

its denizens. The spacecraft follows a trail blazed by four
others - twin pairs of Pioneers and Voyagers - that are
well on their way to escaping our solar system entirely.
Yet New Horizons is "less" in every way than its predecessors: a smaller vehicle, smaller data volume, smaller
instrument package, and a price tag only 40% that of the
Voyager mission.
Nor will it be the ﬁrst craft to study a dwarf planet.
That distinction goes to Dawn, which started orbiting
asteroid 1 Ceres in March and has settled in for a yearlong mission there (S&T: Apr. 2015, p. 20).
For New Horizons, orbiting Pluto will be impossible
- like the Pioneers and Voyagers, New Horizons is a
ﬂyby mission. At 11:50 Universal Time on July 14, 2015,
it will zip past Pluto at nearly 14 kilometers (8.6 miles)
per second, never to return. And although it will gather
observations throughout most of 2015, all of its highestpriority reconnaissance is squeezed into a 48-hour
period around closest approach. How much can such a
constrained spacecraft accomplish in only two days of
work? Will it be worth the 9½-year wait?

NASA

A Challenging Assignment

FAST START Propelled by an Atlas V rocket, New Horizons
left Earth on January 19, 2006, and attained 58,537 km (36,373
miles) per hour - so fast that the spacecraft reached the
Moon's orbit only 9 hours after its launch.

20

July 2015 sky & telescope

The mission's highest-priority goals are to map the
global geology of Pluto and its moon Charon, to determine their surface composition, and to study Pluto's
wispy atmosphere. The target system's conﬁguration
presents several challenges that make New Horizons'
task harder than it might otherwise be. For one thing,
Pluto's spin axis is tilted sideways, much like that of
Uranus. So, just as Voyager 2 saw only half of the planet

Sky and Telescope - July 2015

Table of Contents for the Digital Edition of Sky and Telescope - July 2015

Contents
Sky and Telescope - July 2015 - Cover1
Sky and Telescope - July 2015 - Cover2
Sky and Telescope - July 2015 - 3
Sky and Telescope - July 2015 - Contents
Sky and Telescope - July 2015 - 5
Sky and Telescope - July 2015 - A
Sky and Telescope - July 2015 - B
Sky and Telescope - July 2015 - 6
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Sky and Telescope - July 2015 - Cover3
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