Delicate clouds in the predawn Martian sky, as seen by Mai-s
Pathnder in 1997.
Bruce M. Jakosky
PLANET's ATMOSPHERE is arguably one of its most imporr
taut features. We live at die bottom ofa sea of air and
breathe it every day in order to stay alive. Thi
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Patterns of ironinickel alloys in the acid~etched
surface of an iron meteorite.
Harer. McSween Jr.
ACH YEAR AS it swings around the Sun, the Earth sweeps
up perhaps 78,000 tons of ex
The asteroid 951 Gaspra, like a number of others, has now
been studied by spacecraft at close range.
Clark R. Chapman
ARLIER "rt-us CENTURY, asteroids were dismissed as unintcrr
esting planetary dregs or as the vermin of the skies.
However, we now realize
The western edge of Mare Serenitatis, as photographed by the
crew of Apollo 17.
Paul D. Spudis
HE MOON OF Earth has been a source of inspiration and
curiosity throughout history. For millennia, people have
gazed at its changing shape and wondered about it
R. Stephen Saunders
N THE PAST few years, planetary scientists have studied in
detail a world that can perhaps teach us a great deal about 97
Earth. Venus was expected to be like our planet in many
ways. It is nearly as large as Earth (Fayette 1), and e
A portion of Mercurys Caloris basin, a multiring impact more
than 1,300 km in diameter.
5 THE CLOSEST planet to the Sun, Mercury guards the
secrets of its planetary properties very tightly. Its mean
heliocentric distance is only 0.3871 AU, a