I. INTRODUCTION
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The past decade has seen p werful gr und- and space-based techniques applied
t the investigati n f the c mp siti n f uter s lar system b dies, including the
spectacular measurements f He/H, is t pe rati s, and n ble gas abundances in
the j vian atm sphere by the pr be; impr ved deuterium and trace species
measurements in the atm spheres f the giant planets and Titan; and first detecti n
f abs rpti n features n the surface f a Kuiper Belt bject. In this chapter we
review the new bservati ns and discuss h w they c nstrain the c mp siti n f
prim rdial reserv irs supplying material t the giant planets, their m ns, and
ther uter s lar system b dies. Planned r anticipated planetary missi ns in the
next decade, al ng with impr ved gr und-based capability n giant telesc pes,
will enable m dels f the early ev luti n f the uter s lar system t be tested and
impr ved, ultimately t pr vide a picture f h w the f ur giant planets and their
m ns came t be.
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CNR-Istituto di Astrofisica Spaziale and Uni ersity of Arizona
Uni ersity of Hawaii
Uni ersity of Arizona
Galileo
THE OUTER SOLAR SYSTEM:
CHEMICAL CONSTRAINTS AT LOW
TEMPERATURES ON PLANET FORMATION
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JONATHAN I. LUNINE
TOBIAS C. OWEN
and
ROBERT H. BROWN
The uter s lar system is the pr vince f f ur giant planets, their retinue
f m re than 60 m ns, and an ass rtment f small b dies that represent
left ver planet-f rming material scattered by the giant planets. The c ndensati
n fr nt f water ice in the later stages f ev luti n f the pr t s lar
disk (als called the s lar nebula) pr vides a c nvenient inner b undary
f r the regi n. This fr nt existed r ughly in the regi n 4–5 AU fr m the
Sun. There is a c rresp nding c mp siti nal thresh ld in present-day bjects.
Inward f the fr nt lie b dies wh se c mp siti n is largely r ck and
metal, with water present primarily as water f hydrati n. The ice that sits