The Gulf War was also the first battlefield test of
the Tomahawk cruise missile (BGM-109). Early ver-
sions were 6 meters (20 feet) long, had a 2,500-
kilometer (1,500-mile) range, and could carry 450
kilograms (1,000 pounds) of explosives. Tomahawks
fly low, 15 to 30 meters (50 to 100 feet) above the
ground, and fast, 880 kilometers per hour (550 miles
per hour), to avoid detection. At first, they navigated
by recognizing the ground terrain; later versions
used GPS for navigation. They are the ideal weapon
for striking air-defense radar and missile sites deep
behind enemy lines. During the Gulf War, 297 Toma-
hawk missiles were launched. Of these, 282 success-
fully began flights to their targets, and between two
and six Tomahawks were shot down. Once the air de-
fenses were softened up, piloted aircraft were used.
Originally designed to bring down airplanes, Pa-
triot missiles were modified to destroy incoming mis-
siles. A single radar antenna located the incoming
missile, guided the Patriot to the target, and helped
the Patriot hit the enemy missile. Earlier Patriots
used a proximity fuse to explode their warheads
near the enemy missile, destroying it with shrapnel.
Later Patriots were modified to use the more certain
“hit to kill” tactic. There has been considerable de-
bate about just how effective the Patriots were in the
Gulf War. Most of the controversy can be resolved by
agreeing on what akillis, how it is to be verified, and
how it is to be counted. For example, if four Patriots
are launched at an incoming Scud missile, and the
Scud is hit by at least one Patriot, is that four kills, or
one kill and three misses? The U.S. Army reasonably
claimed a Patriot success rate of 70 percent in Saudi
Arabia and 40 percent in Israel.
Astronomy and Space Science Comet Hale-Bopp
was a spectacular sight as it moved rather swiftly
across Earth’s skies during 1997. Five years earlier,
astronomers Eugene and Carolyn Shoemaker and
David Levy were studying the Shoemaker-Levy
group of comets. These comets were unknown to the
general public since they were invisible to the naked
eye. The three astronomers watched comet number
9 of that group break apart as it passed close to Jupi-
ter. It broke into twenty-one pieces that traveled one
after the other like railroad cars in a train. Comets
are made of water ice along with frozen carbon diox-
ide and perhaps ices of ammonia and methane. The
ice is riddled with grains of carbon, flecks of iron,
and other bits of rock. The accepted model is that of
a dirty, fragile iceberg. Comets coming within the
same distance from the Sun as the planet Mars begin
to sublimate—the ice turning to great clouds of
water vapor. The solar wind drags out some of this va-
por into spectacular tails. Astronomers soon real-
ized that the fragments of Shoemaker-Levy 9 were
on a collision course with Jupiter, and that they
would hit at 60 kilometers per second (36 miles per
second). At this speed, their impact energies would
be several hundred times that of the same mass of dy-
namite. Various telescopes, including the Hubble,
monitored the resulting fireballs in July, 1994. Had
they hit the Earth, any of the larger fragments could
have ended civilization, or worse.
The Galileo mission to Jupiter proved to be one of
the most successful planetary probes. Launched
from Earth in October, 1989, Galileo released a
probe in July, 1995. Both the probe and Galileo
reached Jupiter on December 7, 1995, but while Ga-
lileo entered Jupiter orbit, the probe plunged into
Jupiter’s atmosphere. As the probe descended be-
neath its parachute, it continued to broadcast data
for fifty-seven minutes until it reached a hellish re-
gion 156 kilometers (97 miles) below the cloud tops,
where the pressure was twenty times Earth’s surface
pressure, the temperature was 127 degrees Celsius
(260 degrees Fahrenheit), and the wind blew at 550
kilometers per hour (330 miles per hour). The Gali-
leo spaceship itself explored Jupiter and its inner
moon system, finding evidence that the moons
Callisto, Ganymede, and Europa all had subsurface
oceans. It is possible that Europa’s vast ocean har-
bors life around undersea vents. Low on fuel after
fourteen years of exploration, Galileo was pushed
headlong into Jupiter’s atmosphere so that it could
not accidently contaminate Europa’s surface some
time in the future.
In 1996, NASA called a news conference to an-
nounce that organic compounds and other possible
evidence for life had been found in a meteorite from
Mars. Study has since shown that the various evi-
dences for life could have had nonlife origins, so the
case for life on Mars is yet to be proved. On July 4,
1997, the Mars Pathfinder carrying the rover So-
journer landed on Mars. Sojourner was used to pho-
tograph and analyze various rocks near the landing
site. Pathfinder continued to function for three
months, and sent over 16,000 images back to Earth.
Mars Global Surveyor orbiter arrived at Mars in Sep-
tember of 1997. An early surprise from Surveyor was756 Science and technology The Nineties in America