WWW.ASTRONOMY.COM 33wobble — if there is any — has been too
subtle to see before now. Researchers hope
that as Cassini f lies through the gap
between rings and planet, they’ll get high
enough resolution in their magnetic field
data to tease out any wobble. “If there’s
even just a tiny angle we can measure, we’ll
see the length of the day,” Spilker says.
With this data in hand, researchers will
also be able to more precisely measure the
relative winds on Saturn, which are some
of the strongest in the solar system.
Beginning of the end
Cassini will not go quietly into the night.
Its demise will bequeath a last treasure-
trove of in situ data for investigators, fol-
lowed by an end that will be both brief
and spectacular. Cassini will enter the
planet’s hydrogen/helium atmosphere at
74,000 mph (119,100 km/h) on the dayside,
just a little off noon in Saturn’s local time.
The vehicle’s thrusters will fire constantly,
desperately trying to keep the spacecraft
antenna pointed toward Earth for a few last
data bits. Atmospheric drag from the huge
magnetometer boom, which extends to one
side, will eventually overcome the attitude
thrusters, turning Cassini away from Earth.
“Once we lose the signal,” says Spilker, “I
think things will happen pretty fast.”
For Carolyn Porco, the end of the mis-
sion will mark one of her life’s milestones.
“My whole life — and the lives of all of us
who were part of this — has been defined
by this. These things define your lifebecause they are your life. For me, it’s been
all consuming. I missed a lot during those
years, things that other people take for
granted, but in its place I got to do some-
thing that not many people get to do.”
In those final moments, as the space-
craft begins to glow in Saturn’s cloudy
skies, most of Cassini’s main engine fuel
will already have been exhausted. Though
it likely won’t be visible on the face of the
second-largest planet, many earthbound
observers will nevertheless watch, waiting
for a possible f lash as the mission sings its
swan song.On September 15, Cassini will end its mission as a man-made meteor streaking through Saturn’s
atmosphere, as imagined in this artist’s rendering. NASA/JPL-CALTECHMichael Carroll is both a science writer
and an astronomical artist. His latest book is
Earths of Distant Suns (Springer, 2017).Cassini snapped this false-color image of Saturn’s
famous polar hexagon from a distance of 261,000
miles (419,000km). The hexagonal jet stream was
first identified by scientists while reviewing data
from the Voyager probes. NASA/JPL-CALTECH/SSI
Pandora’s entire surface (above)
appears coated with fine particles of
icy material, which have softened its
edges in contrast with other moons,
such as Hyperion (left). Like its nearby
neighbor Prometheus, Pandora’s
surface also has peculiar ridges and
grooves. ABOVE: NASA/JPL-CALTECH/SPACE SCIENCE
INSTITUTE; LEFT: NASA/JPL/SPACE SCIENCE INSTITUTE