Oct 19, 2004
Credit: top, Wal
Thornhill, bottom, Galileo Project, JPL, NASA
If the ancient
thunderbolt legends are taken at face value, then we are faced with
the possibility that our neighboring planets waged celestial wars
with thunderbolts in the time of human myth-makers. If this
happened, what "smoking guns" should we expect to find?
Jupiterís moon, Europa, offers an excellent
example. The images above show a plasma ball as an
electric discharge flows across it (top) and a view of
Europaís scarred surface (bottom). Europaís
rotation has been captured by Jupiter, so the same
side faces Jupiter all the time. (The same is true of our own moon
and the Earth.) The parts of Europa directly facing
Jupiter and those exactly opposite are rugged and chaotic
(hence the name chaos regions). These regions are where the
thunderbolts struck and where they departed. The
surface areas connecting the two chaos regions (bottom
of top image) are characterized by long, looping scars in patterns
similar to those seen on the plasma ball.
displays a frozen record of strikes by Jupiterís
thunderbolts in the recent past. Just as lightning looks
for the easiest path to ground, Jupiterís thunderbolts
preferred to run across the surface of Europa rather
than through the near vacuum of space. The result is a filamentary
pattern of superimposed furrows running this way and that for
hundreds and thousands of kilometers across the face of the moon.
Europa was not a target itself, but it bears the scars
from being caught in the crossfire
(click image left). Even if
future missions to Europa discover continued "erosion"
by tidal or electrical connections with Jupiter,
most of the scars we see today were created in brief catastrophic
episodes, not gradually at a uniform rate.
As the surface lightning blasted its way across the moon, it heaped
material to either side to form levees. It ripped across earlier
channels as if they were not there. Jupiterís lightning was so
powerful that it converted some of the oxygen in the water ice to
sulfur - creating the dark coloration down the center and to either
side of the large furrows.
Europa is completely covered with this type of plasma scarring, and
other moons are partially covered with similar patterns. Among them
are Jupiterís Ganymede and Callisto,
Saturnís Enceladus, and Uranusí
Miranda. Continued study of these moons offers an opportunity to
learn more about the recent electrical history of the solar system
and our own human heritage.