Welcome to Cheshire Starwatch
a weekly column by Keene, NH amateur astronomer James Maynard.
Stardate 08:03:97
Our third week exploring the mysteries of the king of the planets,
Jupiter, concentrates on the enormous wealth of data which has been returned
from the Galileo spacecraft orbiting this largest planet in our solar system.
Galileo, launched October 18, 1989, entered the Jovian system on December 7, 1995 after a journey of over 6 years. One of the people participating in this highly sucessful launch was American astronaut Shannon Lucid, who later spent time aboard the Mir space station.
Galileo came complete with
an atmospheric probe to explore the upper regions of Jupiter's cloud base
first hand. When the probe entered the upper reaches of Jupiter, it was
found that the expected water was nowhere to be found. Data returned to
Earth from the Galileo spacecraft on June 5 of this year explains this as
fluctuations in the moisture content of Jupiter. This massive planet appears
to have at least as much fluctuation in moisture content of it's atmosphere
from place to place as the Earth does.
Just like Earth's deserts, There are areas of the Jovian atmosphere which seem to be 100 times drier than the surrounding areas. It appears as if it was one of these regions where the probe entered. It was as if an alien probe were to land on Earth in the middle of the Sahara, and reported back on finding little water on Earth. These areas cover less than 1 percent of the total surface area of Jupiter, but scientists got initially confusing results due to where the probe happened to enter. It appears these areas are caused by powerful down drafts in the atmosphere of Jupiter.
A thin atmosphere surronding the volcanic moon of Io hinted at by the spacecraft Pioneer 10 has been confirmed by Galileo. This is an atmosphere made largely of Sulfur Dioxide, which, as we discussed last week, is the primary component of the emmisions from the volcanoes of Io.
The moon Callisto, nearly 50 percent larger than our Moon, was
found to be rocky and icy, with little of the extreme tidal forces responsible
for most of the unusual activities on Io and Europa. This is a world much
like we would expect a world of it's size and distance from the Sun to be.
Ganymede was visited for the last time by the Galileo spacecraft on May 7 of this year. This was found to be another Rocky and icy world, much like Callisto.
Perhaps most exciting of all are the new findings from Jupiter's moon Europa. Europa has been found to have not just an atmosphere, but an oxygen atmosphere. Most stunning of all, it appears to have a liquid ocean, heated by the tidal forces of Jupiter acting upon it. This gives all the necessary ingredients for life as we know it. Europa, along with Mars and the Saturnian Moon of Titan, has been used by science fiction writers for decades as a home world for some sort or another of primitive, alien life.
Also found was an ionosphere, perhaps caused by the water molecules present on Europa passing through the powerful magnetic field encompassing Jupiter. An ionosphere is simply an upper atmosphere layer of charged particles.
NASA was considering extending Galileo's mission past it's scheduled end this November in order to concentrate on taking more measurements of Europa. A recent decision to extend the mission for two more years assures more great findings from this strange world, and of Io.
People with access to the world wide web can keep up on the latest findings from Galileo at www.jpl.nasa.gov/galileo.
Don't forget to watch the persied meteor shower, peaking on the night of August 11, in the eastern sky, just about 4 am.
Clear skies, and good viewing.
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