The surreal je ne sais
quoi of Saturn has
captivated observ-ers for centuries. That’s largely because
the world’s stunning rings span some
170,000 miles (274,000 kilometers), or
about 2.5 times the width of the planet
itself. But get this: They might be as
little as 30 feet (10 meters) thick in some
places. So, when the planet is tilted just
so to our line of sight, presenting its ring
system side-on, those rings all but vanish
from our view.
The world’s glimmering rings are
made of countless pieces of dirty water ice
that range in size from dust grains to
mountains. Although it’s unclear exactly
how or when the rings formed, Cassini
data indicate they are the result of a moon
(or moons) being torn asunder 10 million
to 100 million years ago. Considering the
planets are some 4.5 billion years old and
scientists expect the rings to last just
another couple of hundred million years,
we’re quite fortunate to bear witness to
this relatively brief celestial show.
Launched in 1997, the Cassini space-
craft spent some 13 years exploring all
Saturn has to offer (despite mission plan-
ners initially banking on only four years
of scientific study there). During that
time, the craft returned thousands of
awe-inspiring images, tracked Saturn’sseasonal changes, analyzed its icy rings,
and studied its raging storms, including
the massive hexagonal hurricane that
churns around the world’s north pole.
As part of Cassini’s Grand Finale in 2017,
the spacecraft even skirted past the inner
edge of Saturn’s rings before plunging
into the gas giant’s multilayered,
ammonia-laced clouds. During its final
orbits, Cassini not only sampled ring
particles that are magnetically drawn
into Saturn’s atmosphere, but also created
highly detailed maps of the world’s gravi-
tational and magnetic fields.
While exploring the Saturn system,
Cassini also dropped off an ESA-built
lander named Huygens near the intrigu-
ing moon Titan. Despite all odds, the
craft managed to survive its descent
through the moon’s dense clouds, reveal-
ing one of the most surprisingly Earth-
like worlds yet found in our solar system.WWW.ASTRONOMY.COM 21
SATURN
STATS
Mass: 95 Earth masses
Equatorial diameter: 74,900 miles
(120,500 km)
Average temperature: –218 F (–139 C)
Rotation period (day):
10 hours 39 minutes
Orbital period (year): 29.5 Earth years
Moons: At least 82 moonsCassini carried with it the ESA’s ambitious Huygens
lander, which floated through Titan’s atmosphere
and landed (after bouncing) on the surface in
January 2005. This mosaic shows Huygens’ view
of Titan’s complex terrain from an altitude of about
6 miles (10 km). ESA/NASA/JPL-CALTECH/UNIVERSITY OF ARIZONAOn July 19, 2013, Saturn
eclipsed the Sun from
Cassini’s vantage point.
This majestic mosaic of
141 images is only
slightly enhanced and
hides a surprise. Can
you spot our blue home
planet just beneath
Saturn’s rings at lower
right? NASA/JPL-CALTECH/SSIThe massive moon
Titan stands before
Saturn and the
planet’s rings in this
natural-color view
captured by NASA’s
Cassini spacecraft.
NASA/JPL-CALTECH/SPACE
SCIENCE INSTITUTE