Sky & Telescope - January 2021 - 40

Lunar Exploration

W WHAT NEUTRON SPECTROSCOPY DETECTS Cosmic rays constantly strike the Moon and liberate neutrons, which either get absorbed
or scattered by interactions with rocks before escaping to space. But the
neutrons lose a bit of energy if they glance off hydrogen atoms before
leaving - hydrogen that's very likely bound up in molecules of water. So
by recording these less-energetic "moderated" neutrons, scientists can
map the extent and abundance of water-ice deposits in the top meter or
so of the lunar surface.

Directly
escaping
neutrons

Moderated
neutrons

The rover will land in an "unbelievably cold" and "very
strange, never-seen-before region" that may have very little
resemblance to the Moon we think we know, says Andrews.
Already mission planners are sifting through thousands of
candidate landing sites and traverse patterns, factoring in
science needs, access to sunnier terrain, temperatures, sight
lines with Earth for communication, and obstacle avoidance.
We'll learn more about such mission needs from a smaller
rover called MoonRanger, under joint development by Carnegie Mellon University and CMUspinoff company Astrobotic. Set to arrive in
2022, it will test navigation, communications,
and mapping tools before VIPER lands.
This large-scale lunar exploration effort -
joined as well by China (S&T: June 2020, p. 34)
and other countries - would not be happening if not for the combined allure of scientiﬁc
discovery and natural resources.
The cache of water and other volatiles stored
at the lunar poles will provide valuable information about the creation and evolution of the
X WHERE'S THE ICE? These maps show the icefavorability index (IFI), a predictive assessment of which
regions near the lunar poles contain the most favorable
ice deposits for future mining operations. They apply
desired characteristics such as older crater ages, ice
stability closer to the surface, and higher areal fraction of
cold traps - but not ease of access. North pole on top.

terrestrial planets, including Earth, says Deutsch. "If we don't
have the opportunity to study these records in detail, we lose
access to the most accessible and potentially most complete
record of the processes that have delivered and modiﬁed volatiles in the inner solar system."
Understanding the timing and processes for the deposition
of surface and subsurface lunar water ice can also help us
understand impact rates over time, Cohen points out.
But although science is in many ways driving the lunar
revival, it might be economic activity and even settlements
that translate to further progress. Researchers are also studying which deposits would be best for in situ resource utilization, processed for crew consumption or rocket fuel.
"On Earth, we've learned a tremendous [amount] about
geologic processes and materials in the course
of exploring for resources," says Kevin Cannon
(Colorado School of Mines). "I think scientists
should welcome economic prospecting and
development of these ices, because it will result
in them getting more data, samples, and new
ﬁndings than they ever could have hoped for
with scientiﬁc exploration alone." Given that
there might be trillions of metric tons of ice
present, it won't be gone any time soon, he adds.
Somewhere, W. H. Pickering may be smiling.
There are no blizzards in Theophilus, but there
are places on the Moon locked in a kind of interplanetary winter. It's a season that heralds breakthroughs for our understanding of the Moon.

IFI+
Low

High

CHRISTOPHER COKINOS is coeditor of the
anthology Beyond Earth's Edge: The Poetry of
Spaceﬂight. He teaches at the University of Arizona and is writing a book about the Moon.

Where Is
the Ice?
NASA scientists
use four categories for where to
look for ice on
the Moon.

50 cm
100 cm

Surface region
Soils on the surface
where ice is expected
to be stable, such as
in permanently shadowed craters

JANUARY 2 021 * SK Y & TELESCOPE

Shallow region
Soils where ice
is expected to
be stable within
50 cm (20 in) of
the surface

Deep region
Soils where ice is
expected to be
stable at depths
of 50-100 cm
(20-40 in)

Dry region
Soils where
no ice is expected within
the top 100
cm (40 in)

NEU TRONS ESCA PING M OON: G REGG DINDER M A N / S&T, SOURCE:
LUN A H-M A P / A RIZON A STATE UNIV ERSIT Y; M OON M A PS: K E VIN
CA NNON & DA NIEL BRIT T / UNIV ERSIT Y OF CEN TR A L FLORIDA

Galactic cosmic-ray protons

Sky & Telescope - January 2021

Table of Contents for the Digital Edition of Sky & Telescope - January 2021