DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

California, Berkeley Space Sciences Laboratory,
for the Mars Polar Lander (launched on
January 3, 1999, and destroyed on landing in
Mars on December 3, 1999).
Mars Microprobe The Mars Microprobe
Mission, also known as Deep Space 2 (DS2)
was launched aboard the Mars Polar Lander on
January 3, 1999.
The microprobes were two basketball-sized
aeroshells designed to crash onto the Martian
surface at a velocity of about 200 m per second
and release a miniature two-piece science
probe into the soil to a depth of up to 2 m. The
microprobes were to have separated from the
Mars Polar Lander on December 3, 1999 prior
to entry into the Martian atmosphere, and return
signals relayed through the Mars Global Surveyor.
However, no signal was received from
them. Subsequent studies indicated severe design
defects in the probes. The Mars Polar Lander
also crashed on Mars on December 3, 1999.
See Deep Space 2, Mars Polar Lander.
Mars Pathfinder Mission The second of
NASA’s low-cost planetary Discovery missions,
originally called Mars Environmental Survey, or
MESUR, Pathfinder. It was launched on December
4, 1996, arrived at Mars on July 4, 1997,
and continued to operate for 4 months. The
mission consisted of a stationary lander and a
surface rover (Sojourner), which was controlled
by an Earth-based operator. The rover survived
for 3 months, significantly longer than its designated
lifetime of 1 week. After landing, Mars
Pathfinder returned 2.6 billion bits of information,
including more than 16,000 images from
the lander and 550 images from the rover (which
infer that some of the rocks may be sedimentary,
thus implying a significant fluvial history), as
well as more than 15 chemical analyses of rocks
and extensive data on winds and other weather
phenomena.
The spacecraft entered the Martian atmosphere
without going into orbit and landed on
Mars with the aid of parachutes, rockets and
airbags, taking atmospheric measurements on
the way down. It impacted the surface at a velocity
of about 18 m/s (40 mph) and bounced
about 15 m (50 ft) into the air, bouncing and
rolling another 15 times before coming to rest
© 2001 by CRC Press LLC
Martian meteorites
approximately 2.5 minutes after impact, about
1 km from the initial impact site. The landing
site, in the Ares Vallis region, is at 19.33 ◦ N,
33.55 ◦ W and has been named the Sagan Memorial
Station.
Mars Polar Lander (MPL) A spacecraft
launched on January 3, 1999, that crashed on
landing on Mars on December 3, 1999. The
lander was designed to directly enter the atmosphere,
deploy a parachute, then fire rockets and
soft land on the surface. Subsequent studies
have indicated that a coupled software/hardware
error led to premature shutdown of the landing
rocket. Instruments on the Mars Polar Lander
included cameras, a robotic arm, soil composition
instruments, a light detection and ranging
instrument (LIDAR), and two microprobes
which were presumably deployed before the lander
entered the atmosphere but were also lost.
Martian geophysical epochs Similar to assignments
on Earth, names have been assigned
to geophysical epochs on the planet Mars. The
names and their approximate age correspondences
are: Amazonian, 0 to 1.8 Gy BP; Hesperian,
1.8 to 3.5 Gy BP; Noachian, more than
3.5 Gy BP.
Martian meteorites Currently 13 meteorites
display characteristics that indicate they are
probably from Mars. Twelve of these meteorites
have very young formation ages (ranging from
1.8 × 10 8 yr to 1.3 × 10 9 yr) and have compositions
indicative of formation in basaltic lava
flows. These young meteorites are called the
Shergottites, Nakhlites, and Chassigny (or SNC
meteorites), after the three meteorites which display
the major chemical characteristics of each
group. The young, basaltic compositions suggested
a body that was volcanically active very
recently. This process of elimination resulted in
the Earth, Venus, and Mars as the likely parent
bodies for these meteorites. Other chemical evidence
(primarily from oxygen isotopes) eliminated
the Earth from consideration and orbital
dynamic considerations eliminated Venus as a
possibility. The Martian origin of these meteorites
was largely confirmed by the discovery
of trapped gas within some of the meteorites;
the isotopic composition of this gas is statisti-
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