Io and Europa -- The Role of Tidal Heating
- Io is the innermost satellite of the four large Galilean
satellites of Jupiter.
- Io is covered with active volcanoes which are constantly
resufacing this small world.
- Impact craters are non-existent since they are quickly
erased after they form.
- It takes just a million years for Io to resurface itself to a depth of 100 meters!
- The surface coloration arises from sulfur compounds and
sulfur dioxide frost.
- Io actually has a diffuse transient atmosphere which is continually being lost as it is produced
by the eruptions.
- It's surface gravity is too weak to hold on to the gasses.
- Io's interior is warmed by constant gravitational stretching
of the Moon due to its non-circular orbit around Jupiter.
- Like the Earth's Moon, Io's rotation is tidally
locked so that it always keeps the same face toward Jupiter.
- In fact, all of the Galilean satellites rotate
in this way.
- The same forces which lead to the tidal locking of
rotation also try to make Io's orbit perfectly circular.
- The influence of the other large satellites,
however, drive Io's orbit away from being a perfect circle.
- Io is more stretched by tides when it is close to
Jupiter and less stretched when it is farther away. The
tides in the solid body of Io are estimated to be 100-meters high!
- Since Io completes an orbit around Jupiter in 42
hours, it is regularly stretched and released. This process
generates sufficient internal heat to melt the interior
- Tidal heating becomes less effective with increased distance
- Tidal heating plays a smaller (but very significant)
role on Europa and is insignificant for Ganymede and Callisto.
- Europa is covered with a frozen-over ocean 100 km thick.
- Europa harbors several times more water on its surface than all of Earth's oceans combined.
- Few craters appear on this surface, suggesting recent resurfacing.
- However, there is no evidence for active volcanism on this object.
- Icebergs frozen in place suggest that liquid water could have been present at the
surface in the "recent" past.
- Apparently tidal heating (which can vary with time) occasionally is significant enough to melt regions of the crust and permit liquid
water to reach the surface.
- Volcanic vents at the bottom of the global ocean may be hospitable to life!
- Life on Earth may have originated near and derived its energy
from such submerged volcanic vents.
- The most primitive (from an evolutionary perspective) organisms on Earth survive in near boiling water near volcanic vents and in hot springs.
Revised April 17, 2002