Page 30 - Astronomy - October 2017 USA

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3. Voyager was the first to image out dark streaks in the rings. The streaks from Delta Scorpii as the rings passed in
Saturn’s rings in enough detail to make didn’t circle the planet, but instead looked between that background star and the
out features like the “spokes” seen
here in the B ring on August 22, 1981, like they radiated away from it. These spacecraft. Called an occultation, this fil-
from a distance of 2.5 million miles “spokes” were the first of many unexpected tered view allowed researchers to see even
(4 million km). These dusty features, details in the ring system. finer details in the rings. In fact, they saw
which can stretch up to 12,400 miles As Voyager 1 neared closest approach the particles in the rings with a resolution
(20,000km) in length, vary with time and
and the resolution improved, the team 10 to 20 times better than by just photo-
have no agreed-upon origin. NASA/JPL-CALTECH
could make out more details. “It looked graphing the rings directly.
4. Saturn’s skinny F ring, imaged like grooves on a phonograph record,” On the evening of nearest approach,
November 12, 1980, from 466,000 miles
(750,000km), is a complex structure says Spilker of the rings. Hundreds of when Voyager 2 was just over 100,000 miles
composed of two bright rings encircling concentric rings circled Saturn. Scientists (161,000km) from Saturn, the photopola-
a third, fainter ring. Clumps, kinks, and saw waves along the edges of gaps between rimeter (an instrument that records how
other structures in these rings give them
those rings, as well as braided features light scatters off particles) observed the
a braided appearance. NASA/JPL-CALTECH
and spiral structures within the rings — rings for two and a half hours. Those data
5. The Voyagers unveiled not only a all due to the gravitational influence were printed on a roll of paper using a pen-
dynamic planet, but an intriguing of small moons embedded in and sitting plotter. “I remember unrolling it out in the
and varied system of moons as well.
Voyager imaged Mimas on November just outside of the rings. They even saw hallway, putting a book on one end and a
12, 1980, from a distance of 264,000 patterns that looked like propeller wings book on the other end and walking
miles (425,000km). The moon’s terrain spiraling out from moonlets, showing through and just looking at the data,”
is marred by the huge Herschel crater, how large boulders clear material along recalls Spilker. “It was like walking
which is 80 miles (130km) across and
covers more than a quarter of Mimas’ gaps in their orbit. Studying the behavior through the rings.”
of moonlets in a “debris disk” such as With those data, scientists could esti-
surface. NASA/JPL
Saturn’s rings has allowed scientists to mate the thickness at the edge of each ring:
6. Tethys, imaged by Voyager 2, showed indirectly study how planets form around between 33 and 656 feet (10–200m). They
areas of both old (brighter, more heavily
cratered areas) and new (darker) crust, stars in protostellar disks. “The rings were saw smaller structures in the rings: clumps,
as well as a vast system of canyons that just so much more than I had imagined,” twists, and waves — all due to the gravity
nearly encircles the small moon from top adds Spilker. of Saturn’s satellites. That occultation using
to bottom. NASA/JPL-CALTECH
But it wasn’t just the beautiful images of Delta Scorpii was one of the most crucial
the photogenic ring system that surprised observations Voyager made at Saturn. And
scientists. When Voyager 2 approached with only one such event, the data was
Saturn in August, it observed starlight extremely precious, says Spilker.

30 ASTRONOMY • OCTOBER 2017