Star date: 09:29:98
Jupiter, with It's mighty moons dominates the southern
skies this week, and it's dozens of moons dominates the Jovian system. There
are now nearly 20 moons known which circle this mighty planet, and all of
them have some interesting aspect about them which sets them apart from
the rest.
Mighty Io is the only object in the solar system, other than the Earth, known to have an active volcano system. The volcanos on Io spew glow in the dark gas which forms a gaseous ring around the king of the planets. In addition, the tidal forces from Jupiter make the surface of Io flex up and down, keeping the inner core of this moon molten. If it were not for these tidal forces, the inner layers of Io would have cooled long ago, leaving this moon without any volcanic system.
Callisto and Ganymede were shown to have strange
markings on their surfaces, and are full of mystery.
The last of the large Jovian moons is perhaps the most enigmatic, and full of the deepest mysteries. This is the moon Europa. First discovered in 1610 by Galileo, along with the moons Callisto, Ganymede, and Io, Europa is a world of questions waiting to be answered.
Perhaps the oldest question in astronomy is "Are we alone in
the universe". The answer to this question seems to evade human knowledge
time and time again. At one time, Mars seemed to be the best place anywhere
in our solar system to find other life. The astronomer Percival Lowell once
believed that he could see what he thought were water channels on Mars.
Using the Italian word for channels, he called them canalli. This was then
badly retranslated into English as canals, and the idea of an intelligent
race of 
Martians building a huge canal system
to save their planet from desertfication became popular. Although later
astronomers using better equiptment were able to prove that Mars did not
even have channels, the question of life on Mars is uncertain, even today.
The Viking probes of the 1970's ran tests on the soil of Mars, but the results
of the tests were inconclusive. There was some reaction which mimiced life,
but the results may have also been caused by a chemical reaction. It appears
that if there is life on Mars, it will likely be found in the form of bacteria
like life, at least partly underground. The discovery last year of possible
microscopic fossils in a Martian rock may further strengthen this idea.
The surface of Mars, however, is pummeled with ultraviolet light, as Mars
has no ozone layer to protect it from these occasionally deadly rays.
Another possible abode for life in our solar system
is Saturns moon Titan. Larger than the planets Mercury and Pluto, Titan
has an atmosphere thicker than the Earth. Measurements from Earth also seem
to suggest that Titan has oceans (probably of liquid methane), and continents,
or possibly groupings of islands. the atmosphere of Titan is teeming with
hydrocarbons, the building blocks of protiens and amino acids, which are,
on Earth, the building blocks of life. Titan, however, is frigid cold (which
is one of the reasons it has such a thick atmosphere). There are not enough
tidal forces at Titans distance from Saturn to warm this large world.
Europa, however, seems to have it all. There are large oceans of liquid water on this Jovian moon which are perhaps ten times deeper than the oceans of the Earth. In addition, Europa also has a substantial oxygen atmospere. This makes Europa the only body in the solar system, other than the Earth, known to have such a large portion of oxygen in it's atmosphere. Also, although the tidal forces on Europa are not as great as those on Io, there is enough tidal warming to keep this world from freezing. Dissolved material in these mighty oceans may also serve to help keep these oceans liquid so far from the Sun.
Europa can be easily seen with any back yard telescope.
Consult a chart of the moons of Jupiter, and see where Europa can be found
on a given day. Then, point a telescope at Jupiter, and sets your eyes on
what may be the greatest mystery in the solar system.
Clear skies, and good viewing.
James Maynard is head of the astronomy department at Earth Treasures in Keene, N.H.
