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.