Planetary Exploration Missions 885
one at Mars. It is also targeted to flyby asteroids 2867
Steins in 2008 and 21 Lutetia in 2010. (See rosetta.esa.int/
science-e/www/area/index.cfm?fareaid=13.)
Deep Impact
With the goal of determining the physical and chemical
makeup of a cometary nucleus, NASA’sDeep Impactmis-
sion, launched in January 2005, successfully delivered a
370-kg projectile to a 10 km/s collision with Comet Tem-
pel 1 on July 4, 2005. Imaging from the impactor and the
flyby spacecraft returned the highest resolution pictures of
a comet to date and documented the impact event which
provided new insights into the nature of cometary nuclei.
(See deepimpact.jpl.nasa.gov/mission/facts.html.)
Dawn
Dawn,an ion-propelled spacecraft to be launched in 2007
(after its mission was cancelled and quickly reinstated in
2006) will investigate the surface and interior properties
of Vesta and Ceres, the two large asteroids that telescopic
observation shows to be quite different from each other.
(See dawn.jpl.nasa.gov.)
10. Outer Planets and Moons
In 1610 when Galileo observed four bright specks moving
near Jupiter, he set in motion a quest that culminated in
the 20th century with history’s greatest robotic exploration
program, giving never-to-be-repeated first close looks at the
giant outer planets and their retinue of moons and rings.
(See http://www.solarsystem.nasa.gov./index.cfm.))
Pioneers 10 and 11
Two NASA missions launched the first two of four human
artifacts to escape forever from the Sun’s domain. Leav-
ing Earth in 1972,Pioneer 10flew by Jupiter in 1973 with
imaging and magnetospheric measurements. Its signal con-
tinued to be detected at Earth until 2003. After launch in
1973,Pioneer 11’s flyby trajectory was adjusted so that, at its
encounter in 1974, Jupiter’s gravity would fling it onward
toward Saturn, where it flew by in 1979. Each spacecraft
carried a golden plaque illustrating humans and encoded
information on where and when in the cosmos the flight had
originated. (See http://www.solarsystem.nasa.gov/missions/profile
.cfm?Sort=Target&Target=Saturn&MCode=Pioneer11.)
Voyagers 1 and 2
Launched in 1977 by Titan-Centaurs and still operating in
2006, the NASA missionsVoyagers 1and 2 are a mighty
achievement.Voyager 1flew by Jupiter in 1979 and Saturn
in 1980, whence it is headed toward the heliopause, the
boundary between the Sun’s realm and that of interstellar
space.Voyager 2was targeted to a Jupiter flyby and then
to Saturn, where Saturn’s gravity would send it on to
Uranus and Neptune, taking advantage of a planetary
alignment that happens at intervals of 173 years.Voyager
2 passed Uranus in 1986 and Neptune in 1989. The two
Voyagersreturned a vast harvest of imagery, geochemical
and geophysical data on the giant planets and their moons
and rings, and magnetospheric information. Each one
carried a golden phonograph and video record showing
characteristics of our planet, its inhabitants, and human
civilization. In 2005Voyager 1detected the heliopause,
and in 2006 it passed 100 astronomical units from the Sun.
(See http://www.solarsystem.nasa.gov/missions/profile.cfm?Sort=
Chron&MCode=Voyager2&StartYear=2000&EndYear=
2009.)Galileo
NASA’sGalileomission was launched by the space shuttle
plus theInertial Upper Stagein 1989 after a fraught history
of replanning and delays.Galileoentered Jovian orbit in
1995, having made one Venus and two Earth gravity assist
flybys en route. During the flybys, some science data were
collected, including multispectral observations of the Earth
and Moon. Galileo performed the first two asteroid flybys
and was in position to image the Comet Shoemaker-Levy 9
impacts on Jupiter. At arrival in the Jovian system the space-
craft delivered a probe into the huge planet’s atmosphere.
Despite the failure of the orbiter’s high-gain antenna to
deploy, the mission returned a large volume of imaging,
spectra and other data on the planet and its moons. In
2003 the craft was commanded to a Jupiter impact, with
destruction in Jupiter’s atmosphere to keep it from be-
coming a contamination risk toward any possible biology in
the putative subsurface oceans of Europa and Ganymede.
(See http://www.solarsystem.nasa.gov/missions/profile.cfm?Sort=
Target&Target=Jupiter&MCode=Galileo.)Cassini-Huygens
Launched in 1997 by a Titan-Centaur, NASA Saturn-
orbiter spacecraftCassini-Huygenscarried ESA’sHuygens
probe designed to enter the dense atmosphere of the huge
moon Titan (Fig. 11). With a 1998 Venus gravity assist and
a 2000 Jupiter flyby with some scientific observations en
route, the combination entered Saturn orbit in 2004. The
probe descended to Titan in 2005, delivered remarkable
images and survived impact on the surface for many hours.
Both spacecraft returned unique new observations that will
cause active scientific analysis and argument for years to
come. (See saturn.jpl.nasa.gov.)