Sky & Telescope - January 2021 - 34

LUNAR EXPLORATION

by Christopher Cokinos

Several tiny spacecraft are launching to tell
us more about the water ice that lurks in
shadowed craters on the Moon.

F

lashlights help us find our way through pitch-black
forests or a house that's just lost power. But researchers want to use a flashlight in another way: to find and
characterize water ice in one of the darkest, coldest places in
the solar system - the Moon.
Astronomers already know that patches of ice exist on
the lunar surface at both the north and south poles. Hidden
from direct sunlight and thus extremely cold, these regions
are where ice delivered by comet impacts and other processes
can gradually accumulate and survive on geologic time
scales. The distribution of water ice in these cold traps varies
between the poles, from place to place, and even within a
single deposit.

T SUNLESS SECRETS Located almost exactly at the Moon's south
pole, the crater Shackleton has a rim 21 km (13 miles) across that's
bathed in near-constant sunlight - and a floor that never sees even a
glint of it. A new generation of spacecraft will soon probe such permanently shadowed regions for the abundant water ice that scientists think
lies hidden from view.

But scientists know little about this ice. To explore these
frozen regions, Barbara Cohen (NASA Goddard) leads the
Lunar Flashlight mission, a CubeSat about the size of a box
of detergent that will fly to the Moon in late 2021. The probe
will scan dark craters near the lunar south pole to better
understand deposits of water ice there. It's one of several to
be carried aboard Artemis 1, the first (and uncrewed) trip
of NASA's new astronauts-to-the-Moon program. Other
upcoming probes will also investigate lunar ice, helping to
pave the way for the first NASA-built Moon rover and, perhaps, the eventual development of a cislunar economy.

Ground Truth
Water on the Moon is not a new idea. In pretelescopic times,
people speculated that the lava plains called maria (Latin for
seas) actually were seas. In the early 20th century, William
H. Pickering even penned wildly speculative articles about
vegetation and insect migrations in the crater Eratosthenes
and wrote of "The Snow Peaks of Theophilus."
In 1952, geochemist Harold Urey noted that because the
Moon's spin axis is tilted a mere 1½° from the axis of its
orbit around the Sun, permanently shadowed regions (PSRs)
should exist at the lunar poles, in which frozen water molecules and other volatile compounds might be present. In

Looking for Ice

in the Dark

34

JANUARY 2 021 * SK Y & TELESCOPE



Sky & Telescope - January 2021

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

Contents
Sky & Telescope - January 2021 - Cover1
Sky & Telescope - January 2021 - Cover2
Sky & Telescope - January 2021 - 1
Sky & Telescope - January 2021 - Contents
Sky & Telescope - January 2021 - 3
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Sky & Telescope - January 2021 - Cover3
Sky & Telescope - January 2021 - Cover4
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