Via Reuters: The
passage of asteroid 2012 DA14 through the Earth-moon system, is depicted
in this handout image from NASA. On February 15, 2013, an asteroid, 150
feet (45 meters) in diameter will pass close, but safely, by Earth. The
flyby creates a unique opportunity for researchers to observe and learn
more about asteroids.
(NASA)
Early Friday afternoon (2:24 p.m. EST), planet Earth will be buzzed
by an asteroid some 150 feet wide, identified as 2012 DA14, as it
intersects Earth’s orbit just 17,500 miles above our heads.
According to NASA, this is the closest documented encounter of an
asteroid this large (excluding ones which actually smashed into the
Earth). While this might not seem at first even a close miss, on the
cosmic scale of the solar system, it certainly qualifies as a very close
call.
Only last December a somewhat smaller asteroid,
XE54, passed within about 140,000 miles of Earth, and was about as
close to crashing into Earth as an asteroid can without actually doing
so.
(Note: For perspective, a relatively simple calculation shows that
DA14’s closest approach corresponds proportionately to two commercial
aircraft approaching to within about 150 feet of one another. That is
far below FAA requirements for the minimum safe horizontal separation
between airliners - 3 to 10 miles. There is little doubt that coming as
close as 150 feet, which is less than the wingspan of even most
mid-sized commercial passenger planes, is as close one can imagine
without having a disastrous mid-air collision.)
The path of asteroid
2012 DA14's approach to earth is shown in this handout graphic from
NASA obtained by Reuters February 8, 2013. The 50-metre in diameter
asteroid will pass inside the Earth's geosynchronous orbit, reaching its
closest point February 15, 2013. Scientists say there is no danger of
it hitting the earth.
(NASA - REUTERS)
Several recent asteroids have come closer than DA14 but were much
smaller (tens of feet in size). And, when it comes to the consequences
of an Earth-asteroid collision, size really matters.
The smallest asteroids (better described as large rocks) to threaten
Earth most likely would burn up in the atmosphere creating eye-opening
fireballs racing across the sky, possibly with some fragments (referred
to as meteorites) reaching the ground. (Note, by comparison, the
“shooting stars” seen annually in association with meteor showers are
typically pebble sized).
Meteor Crater
(NASA)
An asteroid the size of DA14 is capable of blasting a
crater - with the equivalent of hundreds of Hiroshima atomic bombs –
like the one mile wide hole known as Meteor Crater blasted into the ground 50 thousand years ago in Arizona.
Just 105 years ago (June, 1908) a 300 foot asteroid (or comet
comprised of mostly water ice rather than hard rock) exploded over the Tunguska River in Siberia\
with more power than anything before or since (including thermo-nuclear
hydrogen bombs) in recorded history. Thousands of square miles of
territory were devastated, but the only victims were trees and wild
life.
An equivalent strike today near a metropolitan area would obviously
cause tremendous damage and take a terrible toll on life and societal
infrastructure. However, it’s much more likely that the asteroid would
either produce a big splash (and possible tidal waves) somewhere over
the vastness of earth’s oceans, or create a humongous bang (and possible
earthquakes) over some relatively large and sparsely populated land
mass. In either case, though, the event would not wipe out humanity.
Scientists believe that any space rock larger than about 1 kilometer
(.62 mile) across could cause a global catastrophe. The asteroid which
led to the mass extinction of dinosaurs 75 million years ago was about
10 kilometers (6.2 miles) wide.
“Extinction event” asteroid collisions appear highly improbable (but
possible) on time scales less than millions of years. But objects larger
than about 100 feet like DA14 are believed to strike Earth every few
hundred years. At this time there are no known asteroids of this size on a collision course with Earth for at least 100 years.
What’s of interest and concern, however, is that scientists believe
there are literally tens to hundreds of thousands of objects, mostly
with dimensions in the hundreds of feet, whizzing around in space that
have not yet been discovered. Consider the fact that XE54 was first
observed only the day before its closest approach. Even though it has
been crossing Earth’s orbit about once per year for millennia, DA14 was
discovered less than one year ago.
(Note: the discovery of DA14 reads like the opening of a SciFi movie.
Last February, a young dental surgeon sailing along the Mediterranean
coast of Spain just happened to spot a speck of light moving across the
sky in images on his laptop from an observatory several hundred miles
away. He alerted the Minor Planet Center
in Cambridge, Massachusetts. Telescopes around the world then began
determining the previously unknown object’s orbit placed it on a
near–collision with the Earth.)
For the foreseeable future, then, Earth will continue to reside in a
cosmic shooting gallery with an enormous number of currently unknown
objects, some of which may have a direct bead on us without our knowing.
While it is probably much more unlikely than likely, a potentially
disastrous collision with an asteroid of at least the dimensions
comparable to DA14 could occur anytime possibly with little or no
warning in our lifetimes.
Over the next decade or so, ongoing and proposed (but not yet
approved and/or funded) improvements in earth and space-based asteroid
monitoring capabilities should (could) reduce the number of possible
close encounters of the asteroid kind. For example, most of the sky seen
from the southern hemisphere is currently unobserved by asteroid
watchers. However this void is expected to be at least partially filled
in 2019 by the Large Synoptic Survey Telescope (LSST) on Cerro Pachón Mountain in Chile.
Because ground-based telescopes can operate only at night, objects
coming from the direction of the sun cannot be monitored. Only
space-based platforms can overcome this problem. Despite a recent United
Nations meeting of experts designed to review issues and discuss plans
for the future, the only hard and potentially realistic proposal on the
books comes from a non-profit charitable organization
organized by notable scientists and two former NASA astronauts. All
well and good, except the project depends upon contributions to move
forward.
(Note: the company is also planning
to mine asteroids for minerals and water for future manned exploration
of space. While it’s not feasible to return very much of an asteroids
resources back to Earth, it’s estimated that, if it were possible, the
value of the asteroid belt between the orbits of Mars and Jupiter
amounts to the equivalent of about 100 billion dollars for every person
on Earth today!)
Suppose we were able to spot an asteroid on a trajectory that
threatens Earth. What, if anything, could be done to avoid a potential
disaster? The answer depends mostly on how much advance warning is
available, especially for a potential “extinction event” sized object.
Without advanced planning and defenses of some sort in place (not
likely, politically and economically speaking), estimates are that it
would take 10-20 years to spin up and effectively implement an
operational system and strategy. As discussed previously,
this would most likely take the form of deflecting the asteroid from
its trajectory by gradually bumping (“nudging”) it with a robot space
vehicle.
(Science fiction author Larry Niven is quoted as saying:“The
dinosaurs became extinct because they didn’t have a space program. And
if we become extinct because we don’t have a space program, it’ll serve
us right!” If dinosaurs had been able to divert the killer asteroid, we
wouldn’t be around to contemplate the event.)
If we were threatened by the more common mid-sized asteroid like
DA14, the same deflection approach could be applied, but this class of
asteroid would unlikely provide adequate warning time for this bumping
strategy to sufficiently alter the trajectory.
Then what? Probably just sit back and watch coverage of the
awe-inspiring (not panic-generating) event on 24/7 cable TV assuming
there was total confidence (never possible with weather forecasts) the
asteroid would crash into the ocean (but be wary of a tsunami from the
impact.)
If ground zero were a populated region for an incoming medium-sized
aseroid, blowing it up with a nuclear missile is a possibility.
However, this probably would result in large fragments raining down on
the surface. The net result might be a more extreme hazard over a larger
area than a direct hit. Either way, the scenario becomes one of
evacuating the affected population and massive disaster mitigation
efforts.
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