76 Scientific American, July 2019
I was born too late to witness Apollo 11 , but my life
and career as a planetary scientist have been directly
shaped by the samples brought back by the six mis-
sions that landed on the moon. For instance, some
of my re search concerns explosive volcanic deposits
on the lunar surface. The data that I have used come
from samples that were scooped directly off the sur-
face by astronauts during Apollo 15 and 17. Other data
were gathered by orbiting spacecraft that scientists
built and sent to the moon as a direct result of the sci-
entific and technical knowledge gained through the
Apollo missions.
In the past 50 years nasa has received 3,190 unique
lunar sample requests from more than 500 scientists
in more than 15 countries, according to Ryan Zeigler,
nasa’s Apollo sample curator. Over the decades, he
says, the agency has distributed more than 50,000
unique lunar samples, and currently 145 scientists are
studying more than 8,000 samples in diverse fields,
including astronomy, biology, chemistry, engineering,
materials science, medicine and geology. Above all,
the moon rocks have revolutionized our understand-
ing of three major subjects: the nature of the lunar
surface, the origin of the moon and the evolution of
our solar system.ANCIENT SURFACE
Before we sent spacecraft and humans to the moon,
our knowledge of Earth’s natural satellite was largely
speculative, limited to observations that could be
made from Earth.
These studies had suggested that the surface of the
moon is extremely old because it is saturated with
impact craters that must have taken billions of years
to accumulate. When we finally landed on the moon,
we knew for sure. After lunar rocks arrived on Earth,
geochemists analyzed them for isotopes that decay
over well-understood timescales and found that the
moon samples were far older than most terrestrial
rocks—be tween three billion and 4.5 billion years old.
Planetary scientists then made a connection that
would aff ect virtually all subsequent studies of the
moon and the other planetary bodies: they compared
the first measured ages of lunar samples from the
Apollo 11 landing site with the number of impact cra-
ters in the region where each was collected. Then they
used this information to develop a model for how
quickly impact craters form on the surface of the
moon. Through this model, the Apollo sample sites
serve as a kind of Rosetta stone, enabling scientists to
estimate the age of any location on the moon (andT
he apollo missions are most celeBrated for
putting human footprints on the moon, but
their biggest contribution to science was the
collection of rocks the astronauts brought
home with them. To call these 382 kilograms of
stone and regolith (the thick layer of crushed
rock and dust that covers the surface of the
moon and other planetary bodies) a treasure trove
does not do them justice. Studying these samples
in laboratories on Earth helped to establish the
modern field of planetary science and gave us
crucial insights into geologic processes that operate
on all planetary bodies.IN BRIEF
Moon samples
gathered by
Apollo astronauts
have profoundly
influenced plane-
tary science.
By analyzing them
in labs on Earth, sci-
entists clarified the
origin of the moon
and the evolution of
the solar system.
New samples from
different parts of
the moon could
teach us much more.