48 ASTRONOMY • FEBRUARY 2018
Saturn’s volcanic poster child
One moon that certainly does spew water is Saturn’s Enceladus.
Its watery plumes emanate from a series of canyons and ridges
near the south pole. This bizarre terrain is geologically young and
scored by parallel tectonic rifts that encircle four darker troughs
called “tiger stripes.” The dark material apparently erupts or
seeps from the rifts, which measure some 1,650 feet (500 m) deep,
1.2 miles (2 km) across, and up to 80 miles (130 km) long.
Coarse-grained, fresh ice or snow covers the region. And the
temperatures there climb as high as –177 degrees Fahrenheit
(–116 degrees Celsius), some 160 F (89 C) warmer
than expected for this region of Enceladus. The
plumes erupt at velocities up to 900 mph (1,450 km/h)
and eject enough material to constantly replenish
Saturn’s E ring.
The ringed planet hosts another moon that may
feature active volcanism: Titan. Observations from
the Cassini orbiter, whose mission ended this past
September, suggest that cryovolcanism has played a
significant geologic role and may contribute consid-
erably to the moon’s atmospheric methane. Several
large f lows spread across Titan’s landscape. Some
could be the result of erosion from methane rainfall,
and the surface has plenty of branching channels
that indicate rivers of liquid methane run there.
But scientists think most of the f lows are cryovol-
canic. Some of the best evidence lies in northwestern
Xanadu, which showed changes during Cassini’s
13-year reconnaissance. The spacecraft also revealed
features resembling volcanic structures at Hotei Arcus
and Sotra Facula. One site, known as Doom Mons, appears to be a
volcanic mountain with a summit about 0.9 mile (1.5 km) high.
Active volcanism also plays a part in the environment of
Neptune’s largest moon, Triton. Pink nitrogen ice on the surface
cocoons pockets of nitrogen gas. As sunlight filters through the
clear ice, it heats the gas. Eventually, pressure builds to the point
that gaseous nitrogen and hydrocarbons spout into the near
vacuum above, painting the surface with dark trails.
Even Pluto appears to have major volcanic structures. The
mountains informally named Wright Mons and Piccard Mons
exhibit a series of concentric ridges and fractures surrounding
what look like summit calderas — the depressions at a volcano’s
center created when its magma chamber empties and the overlying
surface collapses. Clearly, volcanoes are abundant throughout the
solar system, and researchers should be able to learn more about
them by studying their counterparts on our world.Erebus: Behemoth in the ice
Although Mount Erebus soars “only” 12,448 feet (3,794 m) into
Antarctica’s sky, the air density there is equivalent to that at the
summit of a 14,000-foot (3,270 m) peak on conti-
nents farther north. For those of us in the select
group who would spend more than eight hours on
its snowy slopes, the first required stop was a lay-
over on Fang Glacier. Perched on a ledge of Erebus
real estate at about 9,000 feet (2,740 m), the glacier
allowed us to acclimate to the high altitude we
would be working at.
A stay at Fang is not a stay in comfort. Travelers
hunker down in thin, pyramidal tents (called Scott
tents after polar explorer Robert Scott) that stand
about 9 feet (3 m) tall. Although vented and sturdy,
they are not warm. NSF guidelines call for the front
door to be left open whenever the small propane
stoves are in use to guard against carbon monoxide
poisoning. Our mountaineer, Evan Miller, showed
us how to retain the stove’s heat: boil water and put
it in your drinking bottle. Voilà, hot water bottle!
Although treacherous crevasses and slick ice
cross Fang’s chilly plain, the view of the ocean
below was spectacular. Unfortunately, we could not see the south-
ern night sky — after all, the Sun never sets in austral summer.
But beautiful atmospheric phenomena, including sundogs and
ice-crystal halos, made up for it.
After two long “nights” on the glacier, we were ready to climb. We
took medication to help with the elevation and used our training to
watch each other for symptoms of altitude sickness or hypothermia.
Our next destination was the Lower Erebus Hut base camp at an
altitude of 11,500 feet (3,505 m). Unlike our Scott tents, the hut is
heated. Though the small wooden structure is too small for sleeping,The frozen columns on Ice Tower Ridge take on dramatic and fanciful shapes. Heat from Mount Erebus melts the ice, which then refreezes in the frigid air toWe contented
ourselves with
the study of
aboveground
wonders, the
kinds of scenes
that might
greet future
explorers on
Enceladus
or Titan.