Sky & Telescope - August 2023 - 53

USGS UNIFIED GEOLOGIC MAP OF THE MOON: UNITED STATES GEOLOGICAL SURVEY
/ ASTROGEOLOGY SCIENCE CENTER / WILHELMS, D.E. ET AL.; MAP DETAIL: JINZHU JI
ET AL. / INSTITUTE OF GEOCHEMISTRY / CHINESE ACADEMY OF SCIENCES / CC BY 4.0
North Pole
South Pole
The USGS Unified Geologic Map of the
Moon (above) and the new, larger-scale Chinese
geologic map (facing page)
even plans for human exploration in
the next decade. To support these missions,
the Chinese Academy of Sciences
has produced a large-scale map (fortunately
in English) that contains even
more information than the USGS map.
The Chinese map is sourced from the
nation's own lunar exploration program
as well as from data provided by the
U.S., Japan, and India lunar missions.
The most obvious difference between
the two maps is the color scheme. The
USGS map uses mostly saturated colors:
Maria are shaded red, while impact
craters of different ages are of various
other bright colors. Young craters, such
as Copernicus and others that formed
in the last 800 million years, are colored
yellow, and craters older than about 3.8
billion years, including Ptolemaeus,
are tinted brown. The Chinese map
color-codes geological differences with
subdued pastels - all the better to read
data and names on the map. Still, the
Chinese map looks very much like the
USGS one in that both accurately depict
the same Moon. Perhaps as an homage
to Earth's oceans, the lunar maria on
the Chinese map are blue.
The real differences between the
maps lie in the details included and how
they are depicted. Both show craters
and their floors, their rims and ejecta
fields, mare ridges, rills, and mountains.
But the Chinese map displays more of
all these features in better detail. For
example, impact basins are depicted
with inner rims and multiple outer
rings, differing from the way they've
been depicted in the past. This shows
our understanding of complex features
is still evolving.
The Chinese map also displays the
ages of maria (based on the work of
Harold Hiesinger and colleagues at the
University of Münster) with five shades
of blue indicating different compositions
of basalts, from very low to very
high titanium levels. A glance at the
lavas in Mare Imbrium reveals that the
ones with flow fronts that erupted from
the basin's western rim area are 2.3 billion
years old with a medium titanium
composition, and the surrounding
lavas are about a billion years older and
contain a low titanium content. I'm not
aware of any other place where such
information is so readily available.
The good news for observers is
that both maps are freely available for
download at https://is.gd/USGS_Moon
and https://is.gd/CN_Moon; the files
are a few hundred megabytes in size
but worth the wait. Don't try looking at
them on a mobile phone; they deserve
large screens. And while both the USGS
and Chinese maps are digital versions
of traditional paper maps, the revised
USGS map is included on the Lunar
Reconnaissance Orbiter QuickMap site
at https://is.gd/USGSmap. You can use
this site to compare its data to gravity
data, topographic data, and many other
geologic data sets superposed on top of
high-resolution LRO mosaics.
¢Contributing Editor CHUCK WOOD will
be spending many evenings pouring over
these new maps.
This detail of the Chinese map shows Plato and surrounding regions, including multiple outer
basin rings as well as mare ages and compositions.
sk yand tele scope .o r g * AUGUST 2023 53

https://www.is.gd/USGS_Moon https://www.is.gd/CN_Moon https://www.is.gd/USGSmap http://skyandtelescope.org

Sky & Telescope - August 2023

Table of Contents for the Digital Edition of Sky & Telescope - August 2023