Transcript Moon rocks, dust and lunar meteorites

Key Features of the Moon: pages 156 - 164 and 172 - 192
Moon rocks, dust and lunar
meteorites
Physical parameters for the Moon
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1/6th the Earth’s
Why study the Moon?
• The Moon is ancient and preserves an early history
(the first billion years) that is common to all
terrestrial planets.
• Active geologic forces, including plate tectonics and
erosion, continuously destroy the oldest surfaces on
Earth, whereas old surfaces persist with little
disturbance on the Moon.
• Provides a key for unraveling time scales for the
geologic evolution of Mercury, Venus, and Mars
based on their individual crater records.
• Photogeologic interpretation of other planets is
based largely on lessons learned from the Moon.
The Moon’s face
• The highlands (terra)
are brighter and
have more craters
than maria (pl:
mare).
• What caused these
differences?
Topography of the Moon
S. Pole/Aitkin Basin
The types of soil and rock on the Moon
Mare soil (regolith)
The astronaut’s footprint in
the lunar soil (regolith) will
last for millions of years,
until wiped out by impacts
of meteoroids from space.
This lunar soil, recovered by Apollo 11 from Mare Tranquillitatis, was cleaned with acetone to remove ultrafine dust. It consists of impact-produced glass spheres < 1 mm in diameter, brown pyroxene (an Fe,Mg
silicate), white anorthite (a calcium-aluminum silicate), and various rock fragments.
Mare basalts
• Maria
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–
–
–
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Dark
Low in aluminum
High in iron
Poor in plagioclase
High in pyroxene
& olivine
– Exhibit younger
isotopic dates (4.13.1 Ga)
– Have fewer craters
Thin section photomicrograph in transmitted polarized light of an Apollo 15 fine-grained
pyroxene-phyric mare basalt
Thin section photomicrograph in transmitted polarized light of an Apollo 15
Medium-grained pyroxene-phyric mare basalt
Thin section photomicrograph in transmitted polarized light of an Apollo 15
Coarse-grained pyroxene-phyric mare basalt
Explosive volcanism: Fire
fountaining at Pu’u O’o,
Hawaii, on June 2, 1986.
The famous “orange soil” glass spheres from the Apollo 17 landing site. They are thought to
have formed by explosive volcanism (fire fountaining). The spheres are < 1mm in size.
Thin section photomicrograph in polarized light of a crystallized sphere of the famous
“green glass” that is also thought to have formed by explosive volcanism (fire fountaining).
Highlands Crust
• Highlands
–
–
–
–
–
Bright
High in aluminum
Low in iron
Rich in plagioclase
Low in pyroxene &
olivine
– Exhibit old isotopic
dates (4.3-4.1 Ga)
– Have lots of craters
A highlands breccia from the Apollo 16 landing site, consisting of
comminuted anorthositic rocks.
Photomicrograph in transmitted light of one of the few unadulterated, pristine
igneous rocks from the lunar highlands, a spinel troctolite.
Photomicrograph in transmitted polarized light of one of the few unadulterated, pristine
igneous rocks from the lunar highlands, a spinel troctolite.
Search on the “blue ice” of Antarctica for meteorites, including those ejected by
impacts from the Moon
Discovery on the “blue ice” of Antarctica of large numbers of
meteorites, including some ejected by impacts from the Moon.
Antarctica is the best place to find meteorites on Earth, because the ice preserves
them for 106 years, and because the movement of ice concentrates meteorites in
areas of blue ice!
Flow of ice from center of Antarctica to the coast
concentrates meteorites up-slope from mountains
Cross-section through the ice cap in Antarctica
The first lunar meteorite ever recovered on Earth!
Thin section photograph of the first lunar meteorite recovered on Earth, ALHA
81005, a lunar regolith breccia (~ 2mm in diameter).
For comparison, this is a photograph of an Apollo 14 regolith breccia,
which clearly shows the similarity in texture to the lunar meteorite,
ALHA 81005.
The abundances of certain
chemical elements (here La
and K) in rocks are “finger
prints” for their origin on a
particular planet.
Shergottites, nakhlites,
chassignites = Mars;
Eucrites, howardites =
asteroid Vesta.
ALHA 81005 clearly plots
with analyses of Apollo Moon
rocks!!!
The value of the ~ 30 known lunar meteorites is that they, most likely, do not come from the sites were
the Apollo missions landed. Thus, they provide us with rocks from new, previously not visited sites on
the Moon.
Ice at the Poles
1 - 10%
20 - 30%
50 - 60%
60 - 70%
% time in shadows at S. Pole region
Ice at the Poles from neutron data