90
ROCKS FALL
FROM SPACE
ASTEROIDS AND METEORITES
IN CONTEXT
KEY ASTRONOMER
Ernst Chladni (1756–1827)
BEFORE
1718 Isaac Newton proposes
that nothing can exist
between the planets.
1771 A spectacular fireball is
recorded passing over Sussex
in southern England and
continuing to be seen over
northern France.
AFTER
1798 British chemist
Edward Howard and French
mineralogist Jacques-Louis
de Bournon analyze stones
and irons from falls in Italy,
England, and India. They find
similar proportions of nickel
in the stones, indicating a link
between them.
1801 Giuseppe Piazzi
discovers Ceres, the largest
object in the asteroid belt,
now classed as a dwarf planet.
I
n the 18th century, the real
source and nature of what are
now called meteorites was not
known. Interplanetary space was
thought to be empty, and the fiery
lumps of rock and iron that fell from
the sky were believed to originate
either in volcanoes on Earth that
had thrown them up, or from dust
in the atmosphere, perhaps by the
action of lightning.
This idea can be traced back
to Isaac Newton, who wrote that
it was “necessary to empty the
Heavens of all Matter” in order for
the planets and comets to move
unimpeded in their regular orbits.
In the early 1790s, a German
physicist named Ernst Chladni
attempted to solve the mystery
of these “fallen stones” by
examining historical records.
One that he studied had landed in
1768 in France, where it had been
subjected to chemical analysis.
The results showed that it had
formed from a lump of sandstone
that had been struck by lightning
and flung into the air. Chladni
then examined an object found in
1772 that had a mass of more than
1,500 lb (700 kg). It had a rough
surface, was filled with cavities,
and was totally unlike the rock of
the landscape where it was found.
It had also very clearly been melted.
Falling from space
Chladni realized that neither
lightning nor a forest fire could
have produced enough heat to
melt bedrock (the solid rock that
underlies loose deposits). Yet the
rock he examined had become a
mass of metallic iron. This “iron,”
he concluded, could only have come
from space. It had melted on its
passage through the atmosphere.
This iron-nickel meteorite was found
on an Arctic ice sheet. The odd shape
of the meteorite is due to spinning and
tumbling at a high temperature on
entry into the atmosphere.