Mars Global Surveyor
Science Instruments
Collectively, Mars Global Surveyor's five scientific instruments cover
much of the electromagnetic spectrum and form a complementary array. Each
instrument produces a set of data that contribute to a wide variety of scientific
investigations. The Mars Observer instruments included in the new mission
are: Thermal Emission Spectrometer (TES), Mars Orbiter Camera (MOC), Mars Orbiting
Laser Altimeter (MOLA), Radio Science, and Magnetometer. Also included is the Mars
Relay, which is an antenna provided by France that will be used to relay data from
landers placed on Mars between 1997 and 2000 by Russia and the U.S. The
Mars Observer instruments not included in the new mission will be placed
on another orbiter for launch in 1998, pending Congressional approval of the funds:
Gamma Ray Spectrometer (GRS) and the Pressure Modulator Infrared Radiometer (PMIRR).
Thermal Emission Spectrometer (TES)
The TES will measure infrared thermal radiation emitted by the martian atmosphere
and surface. The thermal properties of the surface materials and their mineral
content may be determined from these measurements. When viewing the surface beneath
the spacecraft, the spectrometer has six fields of view, each covering an area of
3 by 3 kilometers (1.9 by 1.9 miles). The TES has three sets of these 6 fields of
view: the Spectrometer (143 spectral bands), the Bolometer (1 broad thermal infrared
band), and the Reflectance or Albedo channel (1 broad visble/near-infrared band).
The spectrometer, a Michelson interferometer, will determine the composition of
surface rocks and ice and map their distribution on the martian surface. Other
capabilities of the instrument will investigate the advance and retreat of the polar
ice caps, as well as the amount of radiation absorbed, reflected, and emitted by
these caps. The distribution of atmospheric dust and clouds will also be examined
over the 4 seasons of a martian year.
Mars Orbiter Camera (MOC)
The MOC will photograph the martian surface with the highest resolution
(1.5 meters; 4.6 ft) ever accomplished by an orbiting civilian spacecraft.
Resolution is a measure of the smallest object that can be seen in an image.
Low-resolution global images of Mars-- a daily "weather map"-- will also be
acquired each day using two wide-angle cameras operated at 7.5 kilometer
(4.7 miles) resolution per picture element (pixel). These same cameras will
acquire moderate-resolution photographs at 240 meters (787 feet) per pixel.
The low-resolution camera system will capture global views of the martian
atmosphere and surface so that scientists may study the martian weather and
related surface changes on a daily basis. Moderate-resolution images will
monitor changes in the surface and atmosphere over hours, days, weeks, months,
and years. The high-resolution camera system will be used selectively because
of the high data volume required for each image.
Mars Orbiting Laser Altimeter (MOLA)
The MOLA uses a very short pulse of laser light to measure the distance from
the spacecraft to the surface with a precision of several meters. These
measurements of the topography of Mars will provide a better understanding
of the relationship among the martian gravity field, the surface topography,
and the forces responsible for shaping the the large-scale features of the
planet's crust.
Radio Science Investigations
The radio science investigation will use the spacecraft's telecommunication
system and the giant parabolic (dish) antennas of NASA's Deep Space Network
to probe the martian gravity field and atmosphere. These measurements will
help scientists determine the structure, pressure, and temperature of the
martian atmosphere. Each time the spacecraft passes behind the planet or
reappears on the opposite si\de, its radio beam will pass through the martian
atmosphere briefly on its way to Earth. The way in which the radio waves are
bent and slowed will provide data about the atmospheric structure at a much
higher vertical resolution than any other Mars Global Surveyor
experiment. During that part of the orbit when the spacecraft is in view of
the Earth, precise measurements of the frequency of the signal received at
the ground tracking stations will be made to determine the velocity change
(using the Doppler effect) of the spacecraft in its orbit around Mars.
These Doppler measurements, along with measurements of the distance from the
Earth to the spacecraft, will be used to navigate the spacecraft and to study
the planet's gravitational field. Gravitational field models of Mars will
be used along with topographic measurements to study the martian crust and
upper mantle. By the end of the mission, as a result of the low altitude of
the orbit and uniform coverage of Mars Global Surveyor, scientists will
have obtained unprecedented global knowledge of martian gravity.
Magnetic Fields Investigation
Mars is now the only planet in the Solar System, except Pluto, for which a
planetary magnetic field has not yet been detected. In addition to searching
for a martian planetary magnetic field, this instrument also will scan the
surface material for remnants of a magnetic field that may have existed in
the distant past. The magnetic field generated by the interaction of the
solar wind with the upper atmosphere of Mars will also be studied. Unlike
Mars Observer, the magnetometer on Mars Global Surveyor will
not be at the end of a boom but instead will be fixed to the spacecraft.
Without the boom, however, it will be more difficult to isolate the effects
of the martain magnetic field from fields generated by the spacecraft.
Mars Relay
The spacecraft will carry a radio system supplied by the French Centre
National d'Etudes Spatiales (CNES, the French space agency) to support the
Russian Mars 96 mission. Mars 96 consists of an orbiter,
two small landers and 2 penetrators (amounting to four landed spacecraft).
This Russian mission was formerly scheduled to launch in October 1994 but
will now wait until 1996 for launch. The landers will carry instruments
to directly sample both the atmosphere and surface. The landers will send
data to Earth via the Mars 96 orbiter, using the relay antenna as a
back-up. Other U.S., Russian, and European landers launched in 1998
may be able to use this relay as well.
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Table of Contents.
TES 1994-1995 Curriculum Guide / Arizona Mars K-12 Education Program