Until recently, active volcanism was known to exist
only on two planets, Venus and Earth, and on Jupiter’s moon Io. However, it has
now been confirmed that Enceladus, a moon of Saturn, also exhibits this
phenomenon.
This satellite orbits Saturn at a distance of 238,040
km, doing so synchronously (always showing the same face) in 32.9 hours. It is
nearly spherical, with a diameter of 499 km, and its icy surface displays
remarkable diversity: some regions are almost smooth, devoid of geological
features, while others show fracture lines from tectonic activity, and still
others are dotted with impact craters. The most striking feature, however, lies
at its South Pole.
There, scientists have identified what they’ve dubbed
“tiger stripes”—grooves stretching 130 km long, 2 km wide, and 500 meters deep.
From these, massive jets of water vapor, solid materials like sodium chloride
crystals and ice, volatile compounds, and—surprisingly—organic material are
continuously ejected into space at a rate of up to 200 kg per second. The
Cassini spacecraft, which explored this moon, detected over 100 such geysers,
confirming the presence of an internal heat source. The concentration of this
activity at the South Pole may be due to centrifugal forces pushing denser
material toward the equator and lighter material toward the poles. Some of the
expelled water vapor falls back as snow, while the rest escapes, contributing
to Saturn’s outermost and faintest E ring, within which Enceladus orbits.
This internal heat source drives volcanoes and
hydrothermal vents, similar to those found on Earth’s ocean floors. Beneath its
icy surface, Enceladus harbors a liquid water ocean about 30 km deep and 10 km
thick, situated above its central core. Yet, there may be additional, unknown
heat sources at play. For instance, Enceladus is in an orbital resonance with
its neighboring moon Dione (completing two orbits around Saturn for every one
of Dione’s), which helps maintain its orbital eccentricity and generates extra
heat through geological activity. Between these factors, scientists are left
astounded—especially upon discovering that the heat output at the South Pole
reaches nearly 16 million watts, ten times higher than previously estimated, with
no clear explanation yet uncovered.
At the surface, Enceladus is blanketed in ice, with an
average temperature of -198°C. This varies by location and time, ranging from
-240°C to -128°C—except, of course, in the South Pole regions where the
constant geysers emerge.
Its atmosphere consists of water vapor (91%), nitrogen
(4%), carbon dioxide (3.2%), and methane (1.7%). This composition, along with
its subsurface ocean and hydrothermal activity, has sparked significant
scientific interest, positioning Enceladus as one of the most promising
locations in our solar system for potential life, particularly near its
hydrothermal vents.
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