{{Short description|Instrument on the Mars Global Surveyor spacecraft}} [[image:PIA02040 Martian hemispheres by MOLA.jpg|right|thumb|260px|MOLA topographic images of the two hemispheres of Mars. This image appeared on the cover of ''Science'' magazine in May 1999.]] The '''Mars Orbiter Laser Altimeter''' ('''MOLA''') was one of five instruments on the ''[[Mars Global Surveyor]]'' (MGS) [[spacecraft]], which operated in [[Mars]] orbit from September 1997 to November 2006. However, the MOLA instrument transmitted altimetry data only until June 2001. 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 [[topography|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.<ref>This article contains public domain material from [[Goddard Space Flight Center|NASA Goddard Flight Center]] web site.{{Cite web|title=Planetary Laser Altimetry MOLA|publisher=NASA Goddard Space Flight Center|url=http://tharsis.gsfc.nasa.gov/MOLA/index.php|format=General description online|access-date=February 14, 2011|archive-date=August 6, 2021|archive-url=https://web.archive.org/web/20210806071252/https://tharsis.gsfc.nasa.gov/MOLA/index.php|url-status=dead}}</ref>
=={{anchor|Laser altimeter (astronomy)}} Planetary laser altimetry== [[File:mars_elevation.stl|thumb|right|[[STL (file format)|STL 3D model]] of Mars with 20× elevation exaggeration using MOLA data]] A [[laser altimeter]] is an instrument that measures the distance from an [[orbiter|orbiting spacecraft]] to the surface of the [[planet]] 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 body's surface, 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 it by two. With a known [[:wikt:attitude|attitude]] and [[Location (geography)|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.<ref>This article contains public domain material from NASA Goddard Flight Center web site.{{Cite web|title=Planetary Laser Altimetry|publisher=NASA Goddard Space Flight Center|url=http://tharsis.gsfc.nasa.gov/index.php|format=General description|access-date=February 14, 2011}}</ref>
==Pole-to-pole view== [[File:North and south pole view of Martian topography.jpg]] [[File:Mars Observer - MOLAincolor.jpg|right|thumb|The MOLA instrument]] Above is a pole-to-pole view of Martian [[topography]] 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 from NASA Goddard Flight Center web site.<ref>{{Cite web|title=Planetary Laser Altimetry MOLA|publisher=NASA Goddard Space Flight Center|url=http://tharsis.gsfc.nasa.gov/MOLA/index.php|format=General description online|access-date=February 14, 2011|archive-date=August 6, 2021|archive-url=https://web.archive.org/web/20210806071252/https://tharsis.gsfc.nasa.gov/MOLA/index.php|url-status=dead}}</ref><ref>{{cite journal|last=Smith|display-authors=etal|first=D. E.|doi=10.1126/science.284.5419.1495|title=The Global Topography of Mars and Implications for Surface Evolution|pmid=10348732|date=1999|pages=1495–503|issue=5419|volume=284|journal=Science|url=http://tharsis.gsfc.nasa.gov/mola.global.pdf|bibcode=1999Sci...284.1495S|archive-date=2021-05-30|access-date=2011-02-15|archive-url=https://web.archive.org/web/20210530204140/https://tharsis.gsfc.nasa.gov/mola.global.pdf|url-status=dead}} Free PDF download of this peer reviewed article.</ref><ref>Figures from the [[Science (journal)|Science]] Paper {{Cite journal|last=Smith|display-authors=etal|first=David E.|title=The Global Topography of Mars from MOLA|journal=Science |publisher=[[Science (journal)|Science]] and NASA|date=May 28, 1999|volume=284 |issue=5419 |pages=1495–1503 |doi=10.1126/science.284.5419.1495 |pmid=10348732 |bibcode=1999Sci...284.1495S |url=https://www.science.org/doi/full/10.1126/science.284.5419.1495|format=Available online|access-date=February 14, 2011|url-access=subscription}}</ref>
==See also== * [[Protoflight]]
==References== {{Reflist}}
==External links== *[http://sebago.mit.edu/shots// MOLA shot counter] {{Webarchive|url=https://web.archive.org/web/20210621155630/http://sebago.mit.edu/shots// |date=2021-06-21 }}. Individual laser pulses shot by MOLA since launch (approximate).
[[Category:Space laser altimeters]] [[Category:Mars Global Surveyor]]