The Moons of Jupiter (continued)
Comparative Planetology is used to infer things about less-explored planetary bodies by comparing them to
better-known ones (and vice versa). The Earth and its moon are well-known...they're the only planetary bodies
that we've stood on! Earth is a geologically ACTIVE planet: volcanoes, fault lines and mountains are proof of
that. The Moon is INACTIVE; no short-term (less than millions of years) processes such as weather, volcanic
flows or mountain-building are operating to destroy the record of crater impacts that has built up over billions
of years.
Based on this information, can you use the technique of Comparative Planetology to determine whether the
Galilean Satellites are geologically active or inactive?
Do you see any trends that correspond to distance from Jupiter?
From December 1995 through December 1997, the Galileo Spacecraft will be on an 11-orbit tour of the Jupiter
System. This tour will bring us closer to Jupiter's moons than we've ever been before. The Io encounter is first
and one of the most exciting. We'll be within 1000 km of what many think is the most volcanically active body
in the Solar System! Throughout the next 2 years we'll have close encounters with Europa three times,
Ganymede four times and Callisto three times. We'll also image the ring and smaller satellites during most
orbits. Stay tuned........
This sketch is a simplified view of the tour that Galileo will take during its 2-year journey. Notice that the
tours' orbits have different shapes. That's because we will use the moons' gravity fields to deflect the
spacecraft into orbits that provide the best "views" of each of the Galilean satellites. The method of using
gravity to change the path of a spacecraft is called a "gravity assist".
Next page Contents
Teacher Resources
Last modified prior to September, 2000 by the Windows Team
The source of this material is Windows to the Universe, at http://windows2universe.org/ from the National Earth Science Teachers Association (NESTA). The Website was developed in part with the support of UCAR and NCAR, where it resided from 2000 - 2010. © 2010 National Earth Science Teachers Association. Windows to the Universe® is a registered trademark of NESTA. All Rights Reserved. Site policies and disclaimer.