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OCR for page 12
n 1977, twin spacecraft lifted off
from the same launch pad at the
Kennedy Space Center in Florida,
only a few months apart. These
spacecraft, Voyager 1 and Voyager 2,
were Earth's first emissaries to the
outer solar system. The information
that they returned about the giant
planets and their moons revolution-
ized our understanding of the solar
system. Voyager stands as one of the
greatest missions of planetary discov-
ery in the space age. For all the
Voyager program's success, however,
Voyager 1 and 2 left the reconnais-
sance of the outer solar system incom-
plete. To date, no missions have
explored the ninth planet, Pluto, and
its satellite, Charon.
At the time of the Voyager mis-
sions, Pluto was thought to be less
important than other planetary bodies,
such as Neptune and Saturn's moon
Titan, which were also easier to reach.
In 1992, however, scientists found the
first direct evidence for the existence
of the Kuiper Belt a region of icy
planets in orbit around other stars.
Many of these extrasolar planets reside
in large disks of material orbiting
young stars, which scientists believe
resemble our solar system in its youth.
If current theory holds, objects in
these extrasolar disks are similar in
composition to objects in the Kuiper
Belt. Most KBOs are thought to have
undergone relatively little change
since their formation in the solar neb-
ula some 4.6 billion years ago. If that
is the case, they would be relics of the
building blocks from which the planets
were formed. Thus, analyzing the
structure and composition of these
objects will provide new insights into
the early history of planetary systems
and help scientists understand the
processes that formed Earth and other
planets.
Studies of the surface composi-
tions of KBOs undertaken with Earth-
based telescopes suggest that these
objects likely contain organic matter
and volatile materials such as water.
This is an exciting discovery because
.
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Even the most detailed map of Pluto's surface, assembled from observations made with
the Hubble Space Telescope, reveals little about the most distant planet from the Sun.
The nature of the surface features remains unknown.
planetary debris on the edge of the
solar system. The discovery of the
Kuiper Belt refocused attention on
Pluto. Instead of an afterthought,
Pluto became the largest and most
important member of an entirely
unexplored type of body the Kuiper
Belt objects (KBOs).
Another exciting discovery came
within a few years of the detection of
the first KBO the identification of
~ ~ Faze {~: ~~ ~~f~ ~;f5~:ffff~ ~f/~'f:~
researchers believe that the water and
carbon-rich materials essential for the
development of life on Earth are not
indigenous to our planet. In other
words, these life-giving materials were
delivered to the primordial Earth dur-
ing impacts with objects originating
elsewhere in the solar system. A likely
source of the impactors, and thus of
the building blocks of life, may have
been the Kuiper Belt.
The first exploratory voyage to an
unexplored region always turns up
new and unexpected findings. As the
first spacecraft specifically targeted to
study this distant part of the solar sys-
tem, the Kuiper Belt-Pluto Explorer
will undoubtedly lead to a new
understanding of the KBOs and, per-
haps, inform us about the role played
by KBOs in the origin and evolution
of other parts of the solar system.
Collisions, for example, are a ubiq-
uitous process in planetary formation
and in shaping planetary environ-
ments. But next to nothing is known
about the 4.6 billion-year-old colli-
sional history of the Kuiper Belt. A
comparison of the density of craters
on Pluto, its moon Charon, and sever-
al KBOs will provide our first hard
data on the history of impacts in the
extreme outer solar system.
If indeed KBO material is as
ancient and relatively unaltered as sci-
entists believe, characterizing the
composition will provide an impor-
tant reference for comparison with the
surface materials on other related bod-
ies, including the Centaurs, the nuclei
of comets, and certain near-Earth
asteroids. Such observations may pro-
vide information on whether comets
are fragments of large KBOs or are
themselves primordial bodies. Kuiper
Belt-Pluto Explorer data will also allow
researchers to compare the surface
compositions of KBOs with Pluto,
Charon, and Triton a satellite of
Neptune suspected of being a captured
KBO. This may allow us to determine
how primitive material in the outer
solar system is changed over the
course of planetary evolution.
Telescopic observations to date
indicate that KBOs have diverse and
sometimes unexpected characteris-
tics most display wide color varia-
tions from object to object, some
have rapid rotation rates, a few exist
in loosely bound double systems,
and Pluto even has a tenuous atmos-
phere. Because of the incredible
variety in color, size, composition,
and orbit among KBOs, the value of
the Kuiper Belt-Pluto Explorer mis-
sion increases as it observes more
KBOs and, thus, samples more of the
OCR for page 13
Kuiper Belt-Pluto Explorer
physical and chemical diversity dis-
played by these objects.
NASA has been working for more
than a decade to develop a mission to
Pluto, and much of the planning and
design has already been done. The
compelling scientific investigations
outlined above and the body of exist-
ing technology and planning led the
SSE Survey to conclude that a flyby
mission to multiple KBOs, including
Pluto and Charon, should be NASA's
highest priority for medium-size mis-
sions in the decade 2003-2013.
Profile
Kuiper Be~-P~uto Explorer
Mission Type: Muiti-object Flyby
Cost Class: Medium
Priority Measurements:
· Determine the dimensions and
shapes of the KBOs visited.
· Assess their crater density.
· Measure their surface composition
through imaging spectroscopy.
· Detect their atmospheres.
· Search for evidence of ongoing
geological activity (e.g., geysers).
· Assess the dust density with
increasing distance into the
Kuiper Belt.
Guiding Themes Addressed Important Planetary Science Questions Addressed
Artist's impression of New Horizons, the Kuiper Belt-Pluto Explorer.
Representative terms from entire chapter:
outer solar
