History Channel
Season. 5 Episode. 6
http://www.history.com/shows/the-universe
http://en.wikipedia.org/wiki/The_Universe_%28TV_series%29
EXCERPTS:
ASTEROID ATTACK
APOPHIS,
will pass close by 2029,
if it hits the KEYHOLE,
a region in space of one mile wide
then it will hit Earth in 2036.
Apohis was discovered in 2004.
1 in 250,000, possibility to impact on Earth.
Objects that are one km or 2/3 of a mile in diameter or larger,
we think there's about 940 of those, and we've discovered 86% of the population.
If you move to smaller objects,
say 100 meters and larger,
we think there's about 50,000
of those and we've discovered 10%.
And if you move to smaller still objects, 30 meter
and larger-sized objects we think there's about
2 million of those objects and we've discovered much less than 1%.
Now, down here, we've got a basketball-sized rock.
On average, about two of these slam into the Earth's atmosphere
EVERY SINGLE DAY.
Next is the small car-sized object.
This happens about ONCE EVERY TWO WEEKS.
But even something this big is probably gonna burn up completely
before reaching the Earth's surface.
For a typical object hitting the Earth's atmosphere,
it needs to be at least 100 feet in diameter.
But according to recently uncovered fossil records,
the-one-mile-wide Chesapeake bay asteroid
didn't seem to have the same globar effects as the
massive extinctions triggered by the
6-mile asteroid that killed the dinosaurs.
2001, NASA's "NEAR" landed asteroid Eros.
"The NEAR spacecraft even transmitted information back to Earth
for about two weeks while on the surface.
But it has lost its radio link with teh Earth.
and so now, it's simply sitting there, mute for million of years."
"The asteroid explorer Hayabusa, of the
Japan Aerospace Exploration Agency (JAXA)
recently one-upped NEAR.
It's the first spacecraft to ever land on an asteroid
and then return to earth.
It arrived in June 2010 after a four billion mile round trip.
DAWN
DAWN will arrive at 3200-mile-wide Vesta in 2011,
orbit for a year, then reach 600-mile-wide Ceres in 2015.
Asteroids are trackable, because they are close (Near Earth Objects).
Comets come from farther space, and they are not visible until they are 6 months away from Earth. so we have little time to react.
WISE (Wide field Infrared Survey Explorer)
2009 launched
WISE has already found 25,000 asteroids and more than a dozen comets
that were too dark to find using visible light.
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