Sara S
08-21-2008, 06:46 AM
In today's excerpt--our friend, the asteroid:
"As Steve Ostro of the Jet Propulsion Laboratory has
put it, 'Suppose that there was a button you could
push and you could light up all the Earth-crossing
asteroids larger than about ten meters, there would
be over 100 million of these objects in the sky.' In
short, you would not see a couple of thousand distant
twinkling stars, but millions upon millions of nearer,
randomly moving objects--'all of which are capable of
colliding with the Earth and all of which are moving on
slightly different courses through the sky at different
rates. It would be deeply unnerving.' Well, be unnerved
because it is there. We just can't see it.
"Altogether it is thought--though it is only really a
guess, based on cratering rates on the Moon--that
some two thousand asteroids big enough to imperil
civilized existence regularly cross our orbit. But even a
small asteroid--the size of a house, say--could destroy
a city. The number of relative tiddlers in Earth-crossing
orbits is almost certainly in the hundreds of
thousands and possibly in the millions, and they are
nearly impossible to track.
"The first one [crossing near the Earth] wasn't spotted
until 1991, and that was after it had already gone by.
Named 1991 BA, it was noticed as it sailed past us at
a distance of 106,000 miles--in cosmic terms the
equivalent of a bullet passing through one's sleeve
without touching the arm. Two years later, another,
somewhat larger asteroid missed us by just 90,000
miles. ... It, too, was not seen until it had passed and
would have arrived without warning. According to
Timothy Ferris, writing in the New Yorker, such
near misses probably happen two or three times a
week and go unnoticed.
"An object a hundred yards across couldn't be picked
up by any Earth-based telescope until it was within
just a few days of us, and that is only if a telescope
happened to be trained on it, which is unlikely
because even now the number of people searching
for such objects is modest. The arresting analogy that
is always made is that the number of people in the
world who are actively searching for asteroids is fewer
than the staff of a typical McDonald's restaurant. (It is
actually somewhat higher now. But not
much.)"
Bill Bryson, A Short History of Nearly Everything,
Broadway, Copyright 2003 by Bill Bryson, pp.
194-195.
"As Steve Ostro of the Jet Propulsion Laboratory has
put it, 'Suppose that there was a button you could
push and you could light up all the Earth-crossing
asteroids larger than about ten meters, there would
be over 100 million of these objects in the sky.' In
short, you would not see a couple of thousand distant
twinkling stars, but millions upon millions of nearer,
randomly moving objects--'all of which are capable of
colliding with the Earth and all of which are moving on
slightly different courses through the sky at different
rates. It would be deeply unnerving.' Well, be unnerved
because it is there. We just can't see it.
"Altogether it is thought--though it is only really a
guess, based on cratering rates on the Moon--that
some two thousand asteroids big enough to imperil
civilized existence regularly cross our orbit. But even a
small asteroid--the size of a house, say--could destroy
a city. The number of relative tiddlers in Earth-crossing
orbits is almost certainly in the hundreds of
thousands and possibly in the millions, and they are
nearly impossible to track.
"The first one [crossing near the Earth] wasn't spotted
until 1991, and that was after it had already gone by.
Named 1991 BA, it was noticed as it sailed past us at
a distance of 106,000 miles--in cosmic terms the
equivalent of a bullet passing through one's sleeve
without touching the arm. Two years later, another,
somewhat larger asteroid missed us by just 90,000
miles. ... It, too, was not seen until it had passed and
would have arrived without warning. According to
Timothy Ferris, writing in the New Yorker, such
near misses probably happen two or three times a
week and go unnoticed.
"An object a hundred yards across couldn't be picked
up by any Earth-based telescope until it was within
just a few days of us, and that is only if a telescope
happened to be trained on it, which is unlikely
because even now the number of people searching
for such objects is modest. The arresting analogy that
is always made is that the number of people in the
world who are actively searching for asteroids is fewer
than the staff of a typical McDonald's restaurant. (It is
actually somewhat higher now. But not
much.)"
Bill Bryson, A Short History of Nearly Everything,
Broadway, Copyright 2003 by Bill Bryson, pp.
194-195.