Cover: Many fanciful solar systemswere onceenvisaged;examplesappear in this 1798copper engraving by
J. Pass,whose original motivation for the work is unknown. Amazingly, extrasolar planetary systemshave
recently beenfound with planetary orbits that resemblesome of those earlier imaginings. Planetary science
has made great strides in recent years, and much of the excitement is captured in this special issue, beginning with Guest Editor David Stevenson'soverview article on page43. (Courtesy of Ewine F. van Dishoeck
and P. T. de Zeeuw.)
,
43
ARTICLES
Special Issue: Planetary
Diversity
Planets come in a wide variety of types and exhibit a wide range of complexbehavior.
Still, we can ask-and answer-some fundamental questions about them
-David J. Stevenson,Guest Editor
49
The Kuiper Belt
The hundreds of objects lying beyond Neptune's orbit provide data that enable scientists
to trace the history of the outer planets. They also present an intriguing mystery
-Michael E. Brown
:
56
Origin of the Terrestrial
Planets and the Earth-Moon
System
Increasingly sophisticated computer simulations show how the four solid planets could
have emerged through collisions and accretion. One late, giant collision with Earth is
the likely origin of the Moon -Robin M. Canup
p.21
Probing the Giant Planets
More than a hundred extrasolar giant planets have been discoveredin the past few
years. Th understand how they were formed, we must study in detail the giants closest
to us: Jupiter and Saturn -1tistan Guillot
71
Water on Mars
Mars is cold enough that its meager water content appears to exist today simply in frozen
and gas phases. But as recent evidence suggests,that may not have always been the case
-Bruce M. Jakosky and Michael 1; Mellon
A Look at the Galilean Satellites
After the Galileo Mission
From volcanic eruptions hotter than those typically found on Earth to oceansandwiches
with water trapped between ice layers, the Galileo mission revealed fascinating
phenomena on Jupiter's four largest moons -Thrrence v: Johnson
p.27
DEPARTMENTS
9
10
Physics
Update
Reference
Frame
Total relativity: Mach 2004 -Frank
Wilczek
1321 Letters
Search and Discovery
Evidence reported for a "supersolid" phase ofhelium-4 ...Dubna-Liverniore
collaboration forms two new superheavy elements. ..New silicon-baseddevice
modulates light at 1 GHz
p.43
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DEPARTMENTS
27
Issues and Events
DOE warms to cold fusion. ..French scientists take to the streets to
save research. ..Bush administration accusedof misusing science. ..
Semesterabroad to SOAR in Chile. ..Magnet lab attracts Boebinger ...
US physics job market holds steady. ..News Notes. ..Web Watch. ..
Special Report: Bush R&D budget remains focused on war, terrorism,
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