Page 49 - Astronomy - October 2017 USA

by a large fraction: about one-third the To mark the final flyby, NASA’s Jet
planet’s radius for Uranus, and nearly half Propulsion Laboratory hosted a special
a radius for Neptune. Both planets could event celebrating Voyager’s journey and
have oceans of conductive icy slush that accomplishments. Scientists shared images
perform the work of the liquid metallic with the public, and rock-’n’-roll legend
cores at Earth and Jupiter, but inconclusive Chuck Berry, whose music lives on as part
models and observations have left scientists of Voyager’s Golden Record, played in a
with little more than guesswork as to what special concert.
exactly drives the magnetic fields that At the edge of our planetary system,
Voyager observed. 2.75 billion miles (4.43 billion km) from
Voyager also detected aurorae on Earth, Voyager turned its cameras back for
Neptune. Due to the strange and complex a last look, imaging farewell shots of a cres-
nature of the planet’s magnetic field, these cent Neptune. Dodd recalls her reaction to
aurorae don’t occur only at the poles; the images: “Wow. The planetary mission
instead they are scattered across Neptune’s is done. We’re going off into the deep dark
upper atmosphere. and cold realms of space. Who knows how
long the mission will last?”
End of an era
Voyager also closed a contentious chapter Epilogue Voyager 2 captured a crescent Neptune
in astronomy history by revising Neptune’s When she left her position with the as it sped away from its final planetary
encounter. Now, 28 years later, the
mass downward by around half a percent Neptune team, Dodd says, no one then spacecraft continues to explore the
— or roughly the mass of Mars. This mis- imagined Voyager would continue as long outer realm of the solar system. NASA/JPL
calculation had sent astronomers on a wild as it has. She returned to Voyager’s inter-
goose chase through the years as they tried stellar mission in 2010, 21 years after she
to make sense of Uranus’ and Neptune’s left the project. In many ways, she admits Voyager continues to measure magnetic
orbits, usually by invoking the existence of that the spacecraft is an artifact — memory fields, charged particles, plasma density,
a mysterious Planet X tugging on both of and power limited, with many of its spe- and more as it cruises the solar system’s
them. (Pluto was found as a direct result cialists long since retired or passed on. hinterlands, teaching scientists about the
of this hunt, but its small size was never Since Voyager’s departure from Neptune, subtle edges of the solar system’s boundar-
enough to resolve the initial problem.) many of its instruments have gone quiet. ies. Voyager 1 has passed beyond the reach
Voyager settled the issue, as Neptune’s There is no need for imaging cameras in of the solar wind, and thus is sampling
smaller mass means it and Uranus orbit the dark void of space. But that does not aspects of interstellar space, though it still
just as they should. mean the project is defunct. lies well within the Sun’s gravitational
influence. Voyager 2, following a slower
trajectory from its two-planet detour, tags
behind, still sampling the solar wind. From
their distance, it takes more than 15 hours
for their signals to reach Earth.
Sometime in the next decade, the space-
craft will lose power and begin to shut
down. Dodd’s team will turn the Voyagers’
heaters off first, and one by one, the science
instruments will succumb to the cold of
space. But the spacecraft themselves and
their Golden Records will journey on, car-
rying humanity’s imprint into the cosmos.
It will be years before any spacecraft
retreads Voyager’s path to Uranus or
Neptune. With at least half a century of
technological advances behind it, any
future craft will undoubtedly revolutionize
our understanding of the ice giants all over
again. But it’s safe to say that nothing will
match Voyager for sheer adventure and
scope. Decades after its primary mission,
Voyager continues to teach, to inspire,
and to explore.
Neptune’s largest moon, Triton, boasts some of the solar system’s most unusual landscapes.
The unique “cantaloupe terrain” in the top half of this image is riddled with crevices and Korey Haynes is a contributing editor to
depressions but few impact craters. The south polar region at bottom shows dark streaks
Astronomy. You can find her on Twitter
deposited by huge geysers that were active during the Voyager 2 flyby. NASA/JPL/USGS
@weird_worlds.
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