http://www.skyandtelescope.com.au 13Far too much to go into in any detail,
but here a few tasters. We know for
example that the oldest lunar rocks
predate the oldest on Earth by some
hundreds of millions of years. We found
evidence, such as from the similarity
between certain moonrocks and some
on Earth, to support the hypothesis that
the Moon was formed when a runaway
body the size of Mars struck the infant
and still molten Earth, throwing up
into orbit around Earth a great mass
of liquid rock that later coalesced and
cooled to form the Moon.
Of course the Apollo missions did
more for lunar studies than just collect
rocks. They left seismometers to detect
‘moonquakes’ as well as reflectors to
bounce back beams of laser light fired
from Earth in order to measure the
Earth-Moon distance with an accuracy
of a few centimetres. From that we
know that the Moon is slowly drifting
away from us, as the rotation of our
planet slows.
We’ve also been able to draw up a
timeline of the Moon’s history. We have
evidence that the whole of the Moon’s
outer crust was molten some 4.4 to
4.6 billion years ago. Bombardment
by massive bodies still roaming the
embryonic Solar System had created
the lunar uplands with their craters by
4.1 billion years, and then the massive
craters in the lowlands by 3.9 billion
years. By 3.1 billion years immense
flows of magma had filled the big craters
to form the smooth, dark plains the old
astronomers called ‘seas’. Since then,
things have been much quieter.
One of the rocks collected by Apollo
17 perhaps did more for diplomacy
than for science. Since it contained
many fragments of different shapes and
sizes, then US President Richard Nixon
ordered that pieces of it be given as
gifts to all the 50 US states and to 135
foreign heads of state. Many of those
gifts are now unaccounted for.■ DAVID ELLYARD presented SkyWatch
on ABC TV. He is the author of Who
Discovered What When and Who
Invented What When.T
hismonthheraldsthe50th
anniversary of probably the
grandest single achievement in
the history of space endeavour. On July
20 (the 21st in Australia), 1969, US
astronauts Neil Armstrong and Buzz
Aldrin stepped onto the Moon, planting
the first-ever human footprints on
another world. The Apollo 11 mission
was a triumph of engineering and of
human courage and skill, and it scored a
major propaganda victory for the US over
its Cold War and space rival the Soviet
Union, which, during the previous decade
had achieved most of the space ‘firsts’.
To a large extent, science just went
along for the ride. Scientific goals were
not the primary ones, but they had a
place. So for me, the date of celebration
I would choose is not July 20, but July
25 (or the 26th in Australia). That
was the day on which scientists had
their first look at some of the 20-or-
so kilograms of rocks the astronauts
brought back (see page 22). These were
the first confirmed lunar rocks we
could examine up close, and so this
could be said to mark the start of themethodicalstudyofthegeologyofthe
Moon. (There are also a few hundred
meteorites that appear to have been
ejected from the Moon, plus there are
a few hundred grams of lunar material
returned to Earth by three of the Soviet
Union’s Luna landers in the 1970s.)
The five Apollo missions that
successfully landed on the Moon
gathered in total nearly 400 kilograms
of rocks from a wide variety of
locations. Indeed, the landing sites
were chosen to provide that diversity.
More than 100 of those kilograms were
gathered by the team of Apollo 17 alone,
the last mission and the only one to
ferry a geologist to the Moon.
The Apollo haul more than doubled
the total mass of moonrocks available
for study. And, unlike the meteorites,
we knew where on the Moon they came
from. Because of their history and origin,
these rocks may be considered priceless.
They are stored in nitrogen to prevent
them from gathering moisture and are
handled only indirectly using tools.
And what have several decades of
study of these priceless samples told us?by David Ellyard DISCOVERIESNASA
Fifty years of
lunar geology
The Apollo 11 mission gave us our first chance
to examine pieces of another world.