Mars Orbiter Laser Altimeter
Encyclopedia
The Mars Orbiter Laser Altimeter (MOLA) was one of five instruments on board the Mars Global Surveyor
(MGS) spacecraft
, which operated in Mars orbit from September 1997 to November 2006. The MOLA instrument transmitted infrared
laser pulses towards Mars at a rate of 10 times per second, and measured the time of flight to determine the range (distance) of the MGS spacecraft to the Martian surface. The range measurements resulted in precise topographic
maps of Mars. The precision maps are applicable to studies in geophysics
, geology
and atmospheric circulation
. MOLA also functioned as a passive radiometer
, and measured the radiance of the surface of Mars at 1064 nanometers.
or asteroid
that the spacecraft is orbiting. The distance is determined by measuring the complete round trip time of a laser pulse from the instrument to the surface of the planet or asteroid and back to the instrument.
The distance to the object can be determined by multiplying the round-trip pulse time by the speed of light
and dividing by two. With a well-known attitude
and position
of the instrument or spacecraft, the location on the surface, which is illuminated by the laser pulse can be determined. The series of the laser spot, or footprint, locations provides a profile of the surface.
from the first MOLA global topographic model [Smith et al., Science, 1999]. The slice runs from the north pole
(left) to the south pole
(right) along the 0° longitude line. The figure highlights the pole-to-pole slope of 0.036°, such that the south pole has a higher elevation than the north pole by ~6 km. This global-scale slope was likely present for most of Mars' history and controlled the surface and subsurface transport of water indicated by images of outflow channels and valley networks. The regional high (in orange) in mid-southern hemisphere latitudes corresponds to the western edge of the topographic annulus that encircles the massive Hellas impact basin. In the figure warm colors correspond to high elevations and cold colors correspond to low elevations. Note the exceedingly flat northern hemisphere in blue. (Image credit: MOLA Science Team).
Mars Global Surveyor
The Mars Global Surveyor was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on 2...
(MGS) spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
, which operated in Mars orbit from September 1997 to November 2006. The MOLA instrument transmitted infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
laser pulses towards Mars at a rate of 10 times per second, and measured the time of flight to determine the range (distance) of the MGS spacecraft to the Martian surface. The range measurements resulted in precise topographic
Topography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
maps of Mars. The precision maps are applicable to studies in geophysics
Geophysics
Geophysics is the physics of the Earth and its environment in space; also the study of the Earth using quantitative physical methods. The term geophysics sometimes refers only to the geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and...
, geology
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
and atmospheric circulation
Atmospheric circulation
Atmospheric circulation is the large-scale movement of air, and the means by which thermal energy is distributed on the surface of the Earth....
. MOLA also functioned as a passive radiometer
Radiometer
A radiometer is a device for measuring the radiant flux of electromagnetic radiation. Generally, the term radiometer denotes an infrared radiation detector, yet it also includes detectors operating on any electromagnetic wavelength....
, and measured the radiance of the surface of Mars at 1064 nanometers.
Planetary laser altimetry
A laser altimeter is an instrument that measures the distance from an orbiting spacecraft to the surface of the planetPlanet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
or asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
that the spacecraft is orbiting. The distance is determined by measuring the complete round trip time of a laser pulse from the instrument to the surface of the planet or asteroid and back to the instrument.
The distance to the object can be determined by multiplying the round-trip pulse time by the speed of light
Speed of light
The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
and dividing by two. With a well-known attitude
Attitude
-Science and engineering:* Attitude as orientation of a geometric figure, such as a line, plane or rigid body* Attitude as strike or dip of a layer of rock in geology* Attitude of a wing or aircraft relative to airflow...
and position
Position
Position may refer to:* Position , a player role within a team* Position , the orientation of a baby prior to birth* Position , a mathematical identification of relative location...
of the instrument or spacecraft, the location on the surface, which is illuminated by the laser pulse can be determined. The series of the laser spot, or footprint, locations provides a profile of the surface.
Pole-to-pole view
Above is a pole-to-pole view of Martian topographyTopography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
from the first MOLA global topographic model [Smith et al., Science, 1999]. The slice runs from the north pole
North Pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets its surface...
(left) to the south pole
South Pole
The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where the Earth's axis of rotation intersects its surface. It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole...
(right) along the 0° longitude line. The figure highlights the pole-to-pole slope of 0.036°, such that the south pole has a higher elevation than the north pole by ~6 km. This global-scale slope was likely present for most of Mars' history and controlled the surface and subsurface transport of water indicated by images of outflow channels and valley networks. The regional high (in orange) in mid-southern hemisphere latitudes corresponds to the western edge of the topographic annulus that encircles the massive Hellas impact basin. In the figure warm colors correspond to high elevations and cold colors correspond to low elevations. Note the exceedingly flat northern hemisphere in blue. (Image credit: MOLA Science Team).
External links
- MOLA shot counter. Individual laser pulses shot by MOLA since launch (approximate).