The Thermal Emission Spectrometer (TES) is an instrument on board Mars Global Surveyor

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...

. TES collects two types of data, hyperspectral thermal infrared data from 6 to 50 micrometers (μm) and bolometric visible-NIR (0.3 to 2.9 μm) measurements. TES has six detectors arranged in a 2x3 array, and each detector has a field of view of approximately 3 × 6 km on the surface of Mars.
The TES instrument uses the natural harmonic vibrations of the chemical bonds in materials to determine the composition of gases, liquids, and solids.
TES identified a large (30,000 square-kilometer) area that contained the mineral olivine

Olivine

The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....

. Olivine was found in the Nili Fossae

Nili Fossae

Nili Fossae is a fracture in the surface of Mars that has been eroded and partly filled in by sediments and clay-rich ejecta from a nearby crater. It is located at approximately 22°N, 75°E, and has an elevation of...

 formation. It is thought that the ancient impact that created the Isidis basin resulted in faults that exposed the olvine. Olvine is present in many mafic

Mafic

Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term is a portmanteau of the words "magnesium" and "ferric". Most mafic minerals are dark in color and the relative density is greater than 3. Common rock-forming mafic minerals include olivine,...

 volcanic rocks. In the presence of water it weathers into minerals such as goethite

Goethite

Goethite , named after the German polymath Johann Wolfgang von Goethe, is an iron bearing oxide mineral found in soil and other low-temperature environments. Goethite has been well known since prehistoric times for its use as a pigment. Evidence has been found of its use in paint pigment samples...

, chlorite

Chlorite

The chlorite ion is ClO2−. A chlorite is a compound that contains this group,with chlorine in oxidation state +3. Chlorites are also known as salts of chlorous acid.-Oxidation states:...

, smectite, maghemite

Maghemite

Maghemite is a member of the family of iron oxides. It has the same structure as magnetite, that is, it is spinel ferrite and is also ferrimagnetic.Maghemite can be considered as an Fe-deficient magnetite with formula...

, and hematite

Hematite

Hematite, also spelled as haematite, is the mineral form of iron oxide , one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum...

. Olivine was also discovered in many other small outcrops within 60 degrees north and south of the equator. Olivine has also been found in the SNC (shergottite, nakhlite, and chassigny

Chassigny

Chassigny is a Mars meteorite which fell on October 3, 1815, at approximately 8:00 am, in Chassigny, Haute-Marne, France. Chassigny is the meteorite for which the Chassignites are named, and gives rise to the "C" in SNCs. Chassigny is an olivine cumulate rock . It consists almost entirely of...

) meteorites that are generally accepted to have come from Mars. Later studies have found the olivine-rich rocks to cover over 113,000 square kilometers. That is 11 times larger than the five volcanoes on the Big Island of Hawaii.