Encyclopedia of the Solar System 2nd ed

332 Encyclopedia of the Solar System

TABLE 1 Landing Sites on Mars

Site Latitude (deg.+N) Longitude (deg.+E) Elevation (km, MOLA) Region

Viking 1 22.27 311.81 −3.6 Chryse Planitia

Viking 2 47.67 134.04 −4.5 Utopia Planitia

Mars Pathfinder 19.09 326.51 −3.7 Ares Vallis

MERSpirit −14.57 175.47 −1.9 Gusev crater

MEROpportunity −1.95 354.47 −1.4 Meridiani Planum

surface morning temperatures, and the first measurement
of small wind vortices or dust devils. The mission captured
the imagination of the public, garnered front-page head-
lines during the first week of operations, and became one
of NASA’s most popular missions by becoming the largest
Internet event in history at the time. Much of the flight sys-
tem, lander, and rover design were used for the next two
successful landings.
The Mars Exploration Rover (MER) landed twin mod-
erately sized rovers in early 2004, and they have explored
over 6 km of the surface at two locations. Each rover car-
ries a moderately sophisticated payload that includes multi-
ple imaging systems including the color, stereo Panoramic
Camera (Pancam) and the Miniature Thermal Emission
Spectrometer (Mini-TES). The rovers also carry an arm that
can brush and grind away the outer layer of rocks (the Rock
Abrasion Tool or RAT) and can place an APXS, M ̈ossbauer
Spectrometer (MB), and Microscopic Imager (MI) against
rock and soil targets (Table 2). The rover and payload par-
tially mimic a field geologist (eyes, legs, rock hammer, and
hand lens) in that they are able to identify interesting tar-
gets using the remote sensing instruments (a field geologist’s
eyes), can rove to those targets (legs), and can remove

the outer weathering rind of a rock (equivalent to a rock

hammer) and identify the rock type (equivalent, or better

than a geologist’s hand lens) using the chemical composi-

tion (APXS), iron mineralogy (MB), and rock texture (MI).

These rovers have lasted years (well beyond their 3 month

design lifetime) and returned a treasure trove of basic field

observations along their traverses as well as sophisticated

measurements of the chemistry, mineralogy, and physical

properties of rocks and soils encountered. They have re-

turned compelling information that indicates an early wet

and likely warm environment on Mars.

2. Landing Sites on Mars

The five landing sites (Table 1) that constitute the “ground

truth” for orbital remote sensing data on Mars were all se-

lected primarily on the basis of safety considerations, in

which surface characteristics appeared to match the engi-

neering constraints based on the designed entry, descent,

and landing system, with scientific desires being subsidiary.

The most important factor controlling the selection of the

five landing sites is elevation, as all landers used an aeroshell

TABLE 2 Instruments Used to Examine Rocks at Spacecraft Landing Sites

Alpha Particle X-ray Spectrometer (APXS) on Mars Exploration Rovers— measures rock chemistry, using interactions of

alpha particles with the target

Alpha Proton X-ray Spectrometer (APXS) on Mars Pathfinder— measured rock chemistry, using interactions of alpha

particles and protons with the target

Imager for Mars Pathfinder (IMP)— lander-mounted digital imaging system for stereo, color images and visible near-infrared

reflectance spectra of minerals

Microscopic Imager (MI) on Mars Exploration Rovers— equivalent to a geologist’s hand lens, a high-resolution (∼ 100

microns) camera used to image textures and fabrics

Miniature Thermal Emission Spectrometer (Mini-TES) on Mars Exploration Rovers— identifies minerals by thermal

infrared spectra caused by crystal lattice vibrations

Mossbauer Spectrometer (MB) on Mars Exploration Rovers ̈ — identifies iron-bearing minerals and distribution of iron

oxidation states by measuring scattered gamma rays

Panorama Camera (Pancam) on Mars Exploration Rovers— digital imaging system for stereo, color images and visible

near-infrared reflectance spectra of minerals

Rock Abrasion Tool (RAT) on Mars Exploration Rovers— brushes or grinds rock surfaces to reveal fresh interiors