Geoscience Reference
In-Depth Information
entists, led by Urey, were glad to provide one. Although most astronomers had
disdained the study of the Moon—Carl Sagan said it was boring—Urey had per-
suaded many that the Moon is a deeply important object, possibly the key to the
origin of the Earth and the solar system.
By 1965, though Kennedy had not lived to see it, the stage was set to fulfill his
challenge. The United States had broken out of a dismal pattern of launch failures
and had assembled and trained a team of photogenic, crew-cut astronauts, each ex-
emplifying the “right stuff.” The USGS Astrogeology Branch had mapped the near
side of the Moon in detail from photographs and identified possible landing sites.
The United States was getting ready.
Covered with Craters
Before sending men to the Moon, NASA had to learn whether the surface would
bear the weight of a landing vehicle and the tread of an astronaut. The iconoclastic
astrophysicist Thomas Gold had predicted that a layer of dust deeper than an as-
tronaut is tall blanketed the Moon. That would present difficulties with the second
half of JFK's summons: “return safely to earth.”
On July 28, 1964, a Ranger mission finally succeeded when
Ranger 7
struck
only a few kilometers from its intended landing site on a ray of the bright crater
Copernicus. The 4,300 photos telemetered back to Earth revealed a surface car-
peted with craters, but no lunites, manbats, or obvious volcanic features. Craters
covered everything down to the limit of resolution: about fifty centimeters, or six-
teen inches, just as Alfred Wegener had written in 1921. Ranger's images showed
rocks resting in small indentations, suggesting that if Gold's dust were present, it
formed only a thin layer.
The volcanists, or hot-mooners, thought the Moon had been and still is geolo-
gically active, like the Earth. The impacters, or coldmooners, typified by Urey,
thought the Moon had accumulated from cold particles elsewhere in the solar sys-
tem and been captured by the Earth when it got too close: the spouse theory. In
that case, the Moon's internal fires had died long ago, and its surface features must
be caused largely by meteorite impact. The debate was not merely academic: a
hot Moon would presumably have generated lava flows that, having cooled, would
likely bear the weight of a spacecraft and astronaut; a cold Moon would be more
likely to be covered with dangerous moon dust.
One clue to the Moon's history would be the age of its surface features. If they
are truly ancient—billions of years old—then the Moon has been cold for almost
all of its history. But how to measure the age of something that you cannot get
