planetary image interpretation and mapping phil stooke usgs map i-515
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Planetary image interpretation and mapping
Phil Stooke
USGS map I-515
Copernicus region
The first area mapped using these methods
E. M. (Gene) Shoemaker and
R. Hackman, 1962.
“Stratigraphic Basis for a Lunar
Timescale”, available HERE.
Image from the Consolidated Lunar Atlas, available online
at LPI
Names:
Many other named features not shown here.
Details at the USGS Planetary Nomenclature
website
Scale: Copernicus is about 100 km
across
Observations:
Craters: produced by
asteroid impacts
Secondary craters: made by
big blocks thrown out of the
primary crater
Rays: surface material
disturbed by ejecta and/or thrown out of
primary
Mountains: part of the rim of a gigantic crater
(basin)
Impact is the dominant
process here
Context
Context is crucial to understanding
Here we see Copernicus near the bottom. The mountains above it (north) are part of a circular pattern – the rim of a giant crater (called a basin).
Without context you don’t know that.
Lunar Orbiter 4 image 4-114-M(always identify your images)
The image is available from LPI’sLunar Orbiter Photo Gallery
Observations:
Smooth plains: lava flows filling low areas inside and outside the
giant ‘basin’
Domes: small volcanoes
Ridges: deformed
surfaces of lava flows
Dark hills: in a few cases,
volcanic ash deposits
Volcanism has also contributed to the landscape
Units:
Geologic (lithostratigraphic)
units are individual bodies of rock or other material formed
by a specific event or process.The landscape is a patchwork of
these units
We can recognize them on Earth by
composition, texture, fossils
etc.
We can try to recognize them on other worlds by morphology
and texture (and composition with more recent data)
Units:
Forgive the very crude outlines!
Brown: material of mountains
Pink: material of hills
Note: I’m describing the
rock – the material – not the
landform (mountain or hill)
I think not just of the surface
appearance – this goes down into
the crust as a 3D mass of rock.
Units:
Yellow: material of craters with
rays
green: material of craters without
rays
Purple: material of partly filled craters
Note: I’m mapping ejecta deposits, impact melt, all
materials associated with the crater. They
could be subdivided
(Smaller features omitted for clarity)
Units:
Blue: material of smooth plains
red: material of domes
Note: I have not mapped rays
separately, but I could if needed, especially in a
detailed map of a small area.
(Smaller features omitted for clarity)
Units:
Here’s the USGS version, much
prettier but basically doing the same thing
(all such maps available at the
LPI website under Resources -
Lunar Atlases – Lunar Map
Catalog
USGS map I-515, Geologic Map of the
Copernicus Quadrangle of the Moon.
Schmitt, H., Trask, N. and Shoemaker, E.,
1967.
Ages – young or old?
Copernicus must be young – its rays lie on
top of the smooth plains
Plains must be younger than
the basin – they fill it and cover
most of its ejecta
Craters without rays: older, their rays mixed into
the local regolith by small
impacts
Ages – young or old?
Crater at left – Copernicus
secondaries on its rim – older
than Copernicus
Crater at right – very few
superposed craters and no
Copernicus secondaries on its rim or ejecta – younger than
Copernicus
Lunar Orbiter 4 image 4-126-H2 (always identify your source images)
Ages – young or old?
One of the ‘filled craters’
Covered with Copernicus
secondaries – older than
Copernicus
But… it lies on the basin rim,
so must be younger than the mountains
and hills
Lunar Orbiter 4 image 4-126-H2
Ages – young or old?
Domes – older than
Copernicus – secondaries
cross the dome at middle left
Younger or older than
plains? No real evidence here, one way or the
other
Lunar Orbiter 4 image 4-126-H1
Unit description and interpretation
We try to keep these separate. If the interpretation is wrong, the unit mapping
may still be useful with a new interpretation
Examples:
Mountain material:Material of large steep-sidedelevated areas. Interpretation:rim materials of large impact basin
Hill material:Material of small isolated hills and regions of many hills. Interpretation:ejecta of large impact basin
Dome material:Material of smooth round to elongatedelevated hills, most with summit pits.Interpretation: volcanic shields and cinder cones, pits are calderas or vents
Geologic history
We try to put it all together. How did the surface get to be the way it is now?
1. Organize materials by order of formation:
Youngest- craters with rays - craters without rays- plains and domes- filled craters- the materials of the large impact basin (Imbrium basin)
Oldest
2. Describe as a narrative:
A very large impact formed the Imbrium basin, destroying any older features in this map area and producing a mountainous rim and hilly ejecta deposit. Some craters formed on top of those materials. Lava flows flooded low areas inside the basin and on its ejecta, forming Mare Imbrium and Oceanus Procellarum. Some cones and domes formed at about the same time. Numerous craters formed after that. Older craters, including Eratosthenes, had their rays removed by small impacts (gardening of the regolith). Younger craters such as Copernicus still show rays and many secondaries.
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