[meteorite-list] A Miss Is As Good As A Mile

[JoshuaTreeMuseum]

Or 9,000 miles as the case may be.

http://cosmiclog.msnbc.msn.com/archive/2009/11/11/2124702.aspx

Space Rock Buzzes Past Earth
Posted: Wednesday, November 11, 2009 1:55 PM by Alan Boyle

Asteroid-watchers say a space rock about as big as a garage came within 
9,000 miles (14,000 kilometers) of Earth last Friday, just 15 hours after it 
was detected.

Experts quickly determined that the asteroid 2009 VA would miss us - and 
even if it came directly at us, it wouldn't have caused a catastrophe. 
Nevertheless, the close encounter serves as a reminder that someday a much 
bigger rock may well hit us and that it's best to be prepared.

In this week's recap of the event, NASA's Near-Earth Object Program Office 
reported that 2009 VA came well within the moon's orbit - so close, in fact, 
that the asteroid's orbital path was bent by Earth's gravitational pull.

NASA and other space agencies around the world have been keeping 
increasingly close track of near-Earth asteroids and comets, with a strong 
assist from amateur astronomers. In this case, the object was first detected 
by the Catalina Sky Survey at the University of Arizona. It was quickly 
identified by the Minor Planet Center in Cambridge, Mass., as a 
close-approaching asteroid. Then NASA experts worked out its orbit and gave 
the all-clear.

Why wasn't the rock found sooner? Well, smaller objects are more difficult 
to detect in advance, and this one was estimated to be only 7 meters (23 
feet) wide. That's nowhere near as big as the 10-kilometer-wide 
(6-mile-wide) object that apparently did in the dinosaurs 65 million years 
ago - or even the 30-meter-wide (100-foot-wide) Tunguska object that was 
thought to have wreaked destruction in a Siberian forest in 1908.

For what it's worth, the Defense Department's Joint Space Operations Center 
tracks about 19,000 orbital objects down to the size of 10 centimeters (4 
inches), and NASA tracks bits of space junk that are even smaller. But 
incoming near-Earth objects are trickier to track until they're almost upon 
us.

In the close-but-no-collision category, this one was No. 3 on NASA's list 
for cataloged asteroids: A meter-wide (yard-wide) asteroid came within 6,150 
kilometers (3,821 miles) in October 2008, while another space rock about the 
size of 2009 VA passed within 6,535 kilometers (4,060 miles) in March 2004.

If 2009 VA had entered the atmosphere, it almost certainly would have blown 
itself up before hitting the ground - just as a larger asteroid did a month 
ago, without warning, in the skies over Indonesia. A somewhat smaller 
asteroid met a similar fate in the skies over Africa about 13 months ago. 
(Months later, students in Sudan found 4 kilograms (8.7 pounds) of 
meteorites that fell to Earth after last year's blast.)

Such atmospheric blow-ups release energy equivalent to about a kiloton of 
TNT. In comparison, the Hiroshima atomic bomb set off a roughly 15-kiloton 
blast.

So, for several reasons, we shouldn't hit the alarm button over 2009 VA. But 
that doesn't mean we should hit the snooze button, either: The Indonesia 
blast and the surprise pummeling that Jupiter took back in July are just 
foretastes of nasty surprises that could be waiting for us. The more we know 
about asteroids and how to fend them off, the better. Here are some reports 
that lay out the asteroid threat and what NASA has been doing about it:

  a.. How to track the 'wolves of the solar system'
  b.. NASA downgrades asteroid threat in 2036
  c.. Experts urge more action on asteroids
  d.. Interactive: Close encounters of the asteroid kind
  e.. Newsvine poll: What do you think of the asteroid threat?
Update for 3:35 p.m. ET: I've upped the estimate for the dino-killing 
asteroid to a whopping 10 kilometers (6 miles) across. Anything bigger than 
1 kilometer wide would be considered capable of causing a global 
catastrophe.