Troctolite 76535
Encyclopedia
Troctolite 76535 is a lunar sample discovered and collected on the Apollo 17
mission in 1972 in the Taurus-Littrow valley
. It has a mass of about 156 grams and is about 5 centimeters across at its widest point.
76535 is a coarse-grained plutonic rock that is believed to have had a slow cooling history. The rock originates from early in the Moon's history
. Geologists have described it as a coarse-grained olivine
-plagioclase
cumulate with a granular polygonal texture.
Olivine and plagioclase are of about equal quantities within 76535, while the remaining approximate 4% is made up of primarily orthopyroxene. Studies have shown that the rock is plutonic in origin and originates from about the middle to lower crust of the Moon.
Investigations have shown that the rock may have formed as a cumulate at depth, thus possibly making the sample an important link in the understanding of the geologic timeline of the Moon
.
As Troctolite 76535 is the oldest known unshocked lunar rock, it has been used for thermochronological
calculations in order to determine whether the Moon formed a metallic core
or generated a core dynamo
. The results of these studies have been shown to support the core dynamo hypothesis.
According to some studies, 76535 shows evidence of having cooled slowly at a depth of about 10-20 kilometers (6.21-12.43 mi), as well as reequilibration and annealing.
Troctolite 76535 has been called the most interesting sample returned from the Moon.
Apollo 17
Apollo 17 was the eleventh and final manned mission in the American Apollo space program. Launched at 12:33 a.m. EST on December 7, 1972, with a three-member crew consisting of Commander Eugene Cernan, Command Module Pilot Ronald Evans, and Lunar Module Pilot Harrison Schmitt, Apollo 17 remains the...
mission in 1972 in the Taurus-Littrow valley
Taurus-Littrow (lunar valley)
Taurus–Littrow is a lunar valley located on the near side at the coordinates . It served as the landing site for the American Apollo 17 mission in December 1972, the last manned mission to the Moon to date....
. It has a mass of about 156 grams and is about 5 centimeters across at its widest point.
Description
TroctoliteTroctolite
Troctolite is a mafic intrusive rock type. It consists essentially of major but variable amounts of olivine and calcic plagioclase along with variable minor pyroxene. It is an olivine-rich, pyroxene-depleted relative of gabbro. However, unlike gabbro, no troctolite corresponds in composition to a...
76535 is a coarse-grained plutonic rock that is believed to have had a slow cooling history. The rock originates from early in the Moon's history
Lunar geologic timescale
The lunar geological timescale divides the history of Earth's Moon into five generally recognized periods: the Copernican, Eratosthenian, Imbrian , Nectarian, and Pre-Nectarian...
. Geologists have described it as a coarse-grained 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....
-plagioclase
Plagioclase
Plagioclase is an important series of tectosilicate minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series...
cumulate with a granular polygonal texture.
Olivine and plagioclase are of about equal quantities within 76535, while the remaining approximate 4% is made up of primarily orthopyroxene. Studies have shown that the rock is plutonic in origin and originates from about the middle to lower crust of the Moon.
Investigations have shown that the rock may have formed as a cumulate at depth, thus possibly making the sample an important link in the understanding of the geologic timeline of the Moon
Lunar geologic timescale
The lunar geological timescale divides the history of Earth's Moon into five generally recognized periods: the Copernican, Eratosthenian, Imbrian , Nectarian, and Pre-Nectarian...
.
As Troctolite 76535 is the oldest known unshocked lunar rock, it has been used for thermochronological
Thermochronology
Thermochronology is the study of the thermal evolution of a region of a planet. Thermochronologists use radiometric dating along with the closure temperatures that represent the temperature of the mineral being studied at the time given by the date recorded, to understand the thermal history of a...
calculations in order to determine whether the Moon formed a metallic core
Planetary core
The planetary core consists of the innermost layer of a planet.The core may be composed of solid and liquid layers, while the cores of Mars and Venus are thought to be completely solid as they lack an internally generated magnetic field. In our solar system, core size can range from about 20% to...
or generated a core dynamo
Dynamo theory
In geophysics, dynamo theory proposes a mechanism by which a celestial body such as the Earth or a star generates a magnetic field. The theory describes the process through which a rotating, convecting, and electrically conducting fluid can maintain a magnetic field over astronomical time...
. The results of these studies have been shown to support the core dynamo hypothesis.
According to some studies, 76535 shows evidence of having cooled slowly at a depth of about 10-20 kilometers (6.21-12.43 mi), as well as reequilibration and annealing.
Troctolite 76535 has been called the most interesting sample returned from the Moon.