Geology Reference
In-Depth Information
If such a ten-mile asteroid hits land, the immediate devastation may be more localized.
Everything within a thousand miles would be obliterated, and massive fires would sweep
across whatever continent is the unlucky target. For a short time, more distant lands might
be spared the violence, but such an impact would vaporize immense quantities of rock and
soil, sending Sun-obscuring clouds into the high atmosphere for a year or more. Photosyn-
thesis would all but shut down. Plant life would be devastated and the food chain would
collapse. A few humans might survive the horror, but civilization as we know it would be
destroyed.
Smaller impactors would cause less death and destruction, but any asteroid over a few
hundred feet, whether it smacks the land or the sea, would cause a natural disaster great-
er than anything we have known. What to do? Should we ignore the threat as too remote,
too insignificant in a world that has so many more immediately pressing problems? What
could we do to divert a big rock?
The late Carl Sagan, perhaps the most charismatic and influential spokesperson for sci-
ence in the last half century, thought a lot about asteroids. In public and private, most fam-
ouslyinhisepicTVseries
Cosmos,
headvocated concerted international action.Hesetthe
stage by telling the vivid tale of the monks of Canterbury Cathedral, who in the summer
of 1178 saw a violent explosion on the Moon—an asteroid impact so very close to us less
than a thousand years ago. If such an impact occurred on Earth, countless millions would
die. “The Earth is a very small stage in a vast cosmic arena,” he said. “There is no hint that
help will come from elsewhere.”
The simplest, first step in avoiding such an event is to look as hard as we can for those
elusive Earth-crossing destroyers—to know the enemy. We need dedicated telescopes,
automated with digital processors, to locate the Earth-crossing projectiles, to plot their or-
bits and predict their future pathways. Such an endeavor is relatively cheap and already
under way. More could be done, but at least the effort is being made.
And what if we found a large rock that is projected to smash into us a few years from
now? For Sagan, along with others in both the scientific and the military communities, as-
teroid deflection is an obvious strategy. If initiated early enough, even a small nudge by a
rocket engine or a few well-placed nuclear explosions could shift an asteroid's orbit suf-
ficiently to change a collision course to a near-miss. Such an eventual necessity is reason
enough for a robust program of space exploration, he argued. In a prescient 1993 essay,
Sagan wrote, “Since hazards from asteroids and comets must apply to inhabited planets all
over the Galaxy, if there are such, intelligent beings everywhere will have to unify their
homeworldspolitically,leavetheirplanets,andmovetosmallnearbyworldsaround.Their
eventual choice, as ours, is spaceflight or extinction.”
Spaceflight or extinction. To survive in the long run, we must journey outward to col-
onize neighboring worlds. First will come bases on the Moon, though our luminous satel-
