In the
most comprehensive lunar map yet, the moon looks like it’s been playing
paintball.

Each
splash of color identifies a discrete rock or sediment formation, including
craters, basins and ancient lava fields. For instance, “the darker, more earth
tones are these highland-type terrains, and the reds and the purples tend to be
more of these volcanic and lava flow materials,” says geologist James Skinner
of the U.S. Geological Survey in Flagstaff, Ariz., who helped make the map,
released April 20 by the USGS. (For more details on exactly what those colors
mean, check out the map in all its glory here.)

The Unified Geologic Map of the Moon, as it’s called, combines
information from six regional lunar maps created during the Apollo era, as well
as recent spacecraft observations. The modern data include views of the north
and south lunar poles made by NASA’s Lunar Reconnaissance Orbiter, and observations around the
equator from the Japanese Aerospace Exploration Agency’s SELENE lunar orbiter (SN: 7/10/19).

This
lunar cartography project was trickier than just fitting Apollo-era maps
together like puzzle pieces and using new data to tweak the details — in part,
because the edges of the regional maps didn’t line up. Many surface features
that should have been visible at the edges of two separate maps were identified
as different types of features on each map, or features of different ages.

Different colors on a new geologic map of the moon designate different types of rock and sediment formations on the moon. For instance, many of the blue-shaded areas are associated with the Mare Imbrium basin, and greens highlight the Eratosthenian crater.

Those discrepancies
arose because the Apollo-era maps were created by separate research groups, and
two different teams looking at the same parts of the moon could interpret what
they saw differently. For instance, one group might have seen something jagged
on the surface and called it a fault, whereas another team could have read it
as a fragment ejected during the formation of a crater.

Skinner
and colleagues reconciled those discrepancies by analyzing information from all
six regional maps, along with the new lunar orbiter observations, to figure out
the proper identifications for different surface features. That allowed the
team to draw up a comprehensive geologic map of the whole moon.

Detailed
observations from the lunar orbiters were especially helpful for clearing up
uncertainties in how different craters overlapped with each other, which
revealed the craters’ relative ages. Hammering out crater formation timelines gives
insight into the moon’s history (SN: 3/26/18).

The new map could also inform future human missions to the moon by revealing regions that may be rich in useful resources or areas that need more detailed mapping to land a spacecraft there safely (SN: 12/16/19).