Sky & Telescope - July 2019 - 20

The Moon: First Lunar Samples

brought home Earth's fragility to its inhabitants and inspired
them to take better care of their home.
If only.
My presentation for the SAO group came at 5:20 p.m.
Wednesday afternoon - the last talk of the day, when everyone was tired and looking forward to dinner. But the anorthositic-crust story interested people, and no one else had
told it. Several groups had noticed and described the anorthositic particles in their own samples, but none had pursued
their meaning. Other min-pet groups tended to focus on the
larger rocks, fragments of the titanium-rich basaltic lava that
ﬁlled Mare Tranquillitatis. Still, everybody's reports painted a
picture of a molten history for the Moon.
This consensus would soon answer a burning question the
media had been asking us: Did the Moon form hot or cold?
There was no way of knowing prior to Apollo 11. The betting
had been on a "cold" Moon - one
that slowly accreted alongside Earth,
or perhaps was caught gravitationally - because that was the opinion
of chemist Harold Urey, a highly
respected Nobel laureate. In order to
distance himself from his earlier work
on the atomic bomb, Urey had interested himself in the chemistry of the
solar system. On the basis of much
hard thinking but little observational
evidence, he formulated a model to
account for the solar system. In this
model, small primary objects formed
u BIG NEWS A young girl holds the July
21, 1969, issue of The Washington Post in
this photo taken by her father and posted
decades later online by her son.

J U LY 2 0 1 9 * S K Y & T E L E S C O P E

in dusty gas and then were caught in the cloud that collapsed
to form the Sun and planets. In this model, the Moon is a
surviving primary object that Earth captured into orbit.
The Apollo 11 evidence of a once-molten Moon laid this
concept to rest. Our picture, with the anorthite ﬂoating to
the surface during the crystallization of a magma ocean,
could not be reconciled with it. And ultimately, it was our
magma ocean scenario that itself rose to the top. Within a
few years, scientists realized that the Moon was likely instead
created by a giant planetary collision, in which a Mars-size
body spalled off a disk of molten debris from the early Earth,
with our planet and its orbiting satellite coalescing from the
debris (S&T: Aug. 2018, p. 26). Such a process easily could
have been energetic enough to account for the initial molten
state of the Moon.
It is gratifying that our analysis of just a few rocky chips
changed forever our view of Earth's
companion. Often when we reﬂect
on Apollo 11's importance, we focus
on the political, cultural, and historical sectors. Of course, these are
important. But doubtless one of the
program's greatest impacts was the
revolution it brought to lunar science.

¢ Retired planetary scientist JOHN A.
WOOD has studied meteorites, lunar
samples, and Venus to understand the
solar system's origins. Since 2004 he
has turned his talents to oil painting.
WEBLINK: Listen to the Apollo 11 mission recordings at https://archive.org/
details/Apollo11Audio.

CONFERENCE: LUN A R A ND PL A NE TA RY INSTIT U TE (2); GIRL WITH
PA PER: RUFUS330CI / WIKIMEDIA COMMONS / PUBLIC DOMAIN

p THE CONFERENCE Attendees collect materials (left) and people study samples (right) at the Apollo 11 Lunar Science Conference in Houston. The
meeting was the first of what would become the annual Lunar and Planetary Science Conference, which meets every spring in The Woodlands, Texas.

https://www.archive.org/details/Apollo11Audio https://www.archive.org/details/Apollo11Audio

Sky & Telescope - July 2019

Table of Contents for the Digital Edition of Sky & Telescope - July 2019