Geology Reference
In-Depth Information
Figure 1.6. An image of the asteroid Itokawa, taken by the JAXA
Hayabusa spacecraft, which touched down on the surface,
collected samples, and returned them to Earth in the fall of 2010.
This asteroid measures 535m by 294m by 209m and appears to
be a
of boulders, the biggest of which is about
50m across. More than 1,500 small grains were collected, and
initial analyses show the presence of silicate minerals, such as
olivine.
“
rubble-pile
”
Figure 1.5. The
first close-up view of an asteroid was obtained
by the Galileo spacecraft in October 1991, shown in this view of
asteroid Gaspra, which is of dimensions 19 kmby 12 kmby 11 km.
Gaspra
Dawn spacecraft will visit Ceres in 2014, and the New
Horizons spacecraft is slated to
fly past Pluto in 2015.
s irregular shape suggests that it might be a piece of a
larger object that fragmented from one or more collisions. More
than 600 impact craters ranging in size from 100 to 500m are
visible on Gaspra
'
1.2 Objectives of Solar System exploration
'
s surface (NASA JPL P-40449).
October 1957 saw the launch of the Soviet orbiter Sputnik
around Earth and the beginning of the
“
Space Age.
”
About the size of a basketball, Sputnik did little more
than send a
1991 and 1993 by NASA
s Galileo spacecraft in the main
asteroid belt (
Fig. 1.5
) and included the discovery that
asteroids could even have their own small moons. In 2003,
Japan launched the Hayabusa spacecraft, which rendez-
voused with the NEO Itokawa (
Fig. 1.6
) in 2005; the
spacecraft touched down on the asteroid and collected
samples that were returned to Earth in 2010 for analyses.
Pluto was discovered telescopically in 1930 and for 76
years was classi
ed as a planet. But it does not
it neatly
into either the terrestrial planet or the giant planet classi-
fication; it is relatively small and has an orbit that is
substantially inclined to the general ecliptic plane and at
times is inside the orbit of Neptune. In the past few
decades, many more large objects have been discovered
in orbit around the Sun, including Eris, which is slightly
larger than Pluto. It is estimated that, as a minimum, some
several dozen large objects reside within the zone of
Pluto
'
s orbit, and many hundreds could well be found in
the Kuiper belt. These factors led the International
Astronomical Union to
“
demote
”
Pluto as a main planet
in 2006 and to de
ne a new category, the so-called
'
radio signal, but it was the
starting gun for the space race. The United States
responded with President Kennedy
'
s decision to send
men to the Moon before the end of the 1960s and the
formation of the National Aeronautics and Space
Administration, or NASA, in October 1958. Although
the decision was motivated by politics and military con-
siderations (an orbiting spacecraft has the ability to deliver
warheads to any place on Earth), the National Academy of
Sciences was asked to de
ne the scienti
c goals for Solar
System exploration. After careful consideration by a
group of distinguished scientists, the principal goals
were de
ned as determining: (1) the origin and evolution
of the Solar System, (2) the origin and evolution of life,
and (3) the processes that shape humankind
'
s terrestrial
environment. Although these goals have evolved over the
years, the basic concepts remain the foundation for Solar
System exploration.
“
beep
-
beep
”
“
dwarf
planets,
currently consisting of Pluto, Ceres (formerly
classi
ed as an asteroid), Haumea, Makemake, and Eris,
some of which have one or more moons. None of
these objects has been visited by spacecraft, but
”
1.2.1 Planetary geology objectives
Geologic sciences
figure prominently in the goals for
Solar System exploration. Basic geologic questions
the
