November 9th, 2009
Surprise! Unknown Asteroid Buzzed Earth
Written by Nancy Atkinson
Trajectory of Asteroid 2009 VA Past Earth on November 6, 2009. Credit: NASA/JPL
A previously undiscovered asteroid came within 14,000 km (8,700 miles) of Earth last week, and astronomers noticed it only 15 hours before closest approach. On Nov. 6 at around 16:30 EST a 7 meter asteroid, now called 2009 VA, came only about 2 Earth radii from impacting our home planet. This is the third-closest known non-impacting Earth approach on record for a cataloged asteroid.
Early on Nov. 6 the asteroid was discovered by the Catalina Sky Survey and was quickly identified by the Minor Planet Center in Cambridge MA as an object that would soon pass very close to the Earth. JPL's Near-Earth Object Program Office also computed an orbit solution for this object, and determined that it was not headed for an impact.
The two closer approaches include the 1-meter sized asteroid 2008 TS26, which passed within 6,150 km (3,800 miles) of the Earth's surface on October 9, 2008, and the 7-meter sized asteroid 2004 FU162 that passed within 6,535 km (4,060 miles) on March 31, 2004. On average, objects the size of 2009 VA pass this close about twice per year and impact Earth about once every 5 years.
Only thirteen months ago, another asteroid, 2008 TC3 was discovered under similar circumstances, but that one was found to be on a trajectory headed for the Earth, with impact only about 11 hours away. It impacted in a remote area of Africa; no one was injured and fragments have since been recovered for study.
Source: JPL NEO office
Filed under: Asteroids
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November 9th, 2009 at 3:23 pm
Did this close approach negate the possibility of this asteroid being a future threat or was its orbit sufficiently changed to make this body no longer a probabilistic threat?
November 9th, 2009 at 3:37 pm
No word, Jon, on that from NASA yet. I'm sure they're still figuring out the trajectory of this thing since they've just discovered it. If the image they provided is accurate (top), it appears its pass by Earth had a definite effect on the object's future trajectory.
November 9th, 2009 at 4:07 pm
Well we dodged a bullet there!
If you have privy to the ephemeris of the asteroid you can numerically figure this out. The problem is that it might have either gravitationally put the object on an orbit that removes it, or it could be a hunter-chaser resonance that will eventually bring it in.
My hunch is that the asteroid gained some energy from the Earth in the same way that we use planets as gravitational "slingshots" to hurl spacecraft into different orbits. More than likely that would put it out of harms way.
On the other hand there can be resonance conditions set up. The periodicity of close interaction enhances the resonance — BOOM! This is less likely though.
LC
November 9th, 2009 at 4:50 pm
Nothing but a bit of Planet X. Nothing to worry about. For a couple years…..ok sorry just had to say it . Someone will hear about this and use it as "proof" of our impending doom.
November 9th, 2009 at 5:07 pm
Looking at the trajectory, that one will never come back!
November 9th, 2009 at 7:47 pm
Thanks to Nancy and LC for their response to my query
November 9th, 2009 at 9:38 pm
What was the size of the thing?
November 10th, 2009 at 12:56 am
7m
November 10th, 2009 at 1:55 am
What sort of damage could we expect from a 1m – 10m piece of rock? I can't remember the numbers off-hand.
November 10th, 2009 at 2:59 am
What sort of damage to expect is hard to say. Sufficiently large ones seem to make craters between 7 and 10 times their width. Rocks of a few meters across often break up and do very little damage – like the one which recently came down in Africa. Asteroids of about 30 meters across are supposed to have the potential of being "City Wreckers" – thanks be to Goodness, no proof has been provided…
November 10th, 2009 at 3:13 am
The impact simulator says a 7 m asteroid is unlikely to hit ground in one piece.
Here are the details:
http://www.lpl.arizona.edu/impacteffects/cgi-bin/crater.cgi?dist=2000&distanceUnits=1&diam=7&diameterUnits=1&pdens=&pdens_select=3000&vel=17&velocityUnits=1&theta=45&wdepth=&wdepthUnits=1&tdens=2500
November 10th, 2009 at 6:02 am
The atmosphere does a pretty good job of protecting us. A 25-50m asteroid is about where you start getting nuclear attack energy levels deposited on an area of land.
LC
November 10th, 2009 at 6:03 am
Early estimates show this object will have an orbital period of about 20 months, and be back at this same spot around Jul 2011. Although, Earth will not be anywhere near this spot at this time.
The orbit seems to take it out past Mars to a distance of approximately 1.94 AU (from the Sun), then comes back in as close as .92 AU (from the Sun), and tilts at about 7 degrees from the ecliptic.
It will swing back out and be at 1 AU in Jan 2010, however it will be out ahead of and below Earth's orbital plane then.
So, preliminarily it has a orbital period of 623 days (1.71 year).
I'll let you do your own math on the next meeting and probability!
November 10th, 2009 at 8:42 am
Aodhhan: Where did you get this information?
LC
November 10th, 2009 at 10:49 am
@Aodhhan Have you got a Celestia data file for this object with it's new orbit? If not, can you fill in the blanks?:
"2007 VA" "Sol"
{
Class "asteroid"
Mesh "asteroid.cms"
Texture "asteroid.jpg"
Radius ?
EllipticalOrbit
{
Period ?
SemiMajorAxis ?
Eccentricity ?
Inclination ?
AscendingNode ?
ArgOfPericenter ?
MeanAnomaly ?
}
Albedo ?
RotationPeriod ?
}
November 10th, 2009 at 2:27 pm
How many miles away was it?
November 10th, 2009 at 3:32 pm
You just can't win, can you?
But I, for one, thank you for having switched to SI in your posts.
(Father Google sez: 14 000 kilometers = 8 699.19669 miles)
November 10th, 2009 at 4:24 pm
Am I reading this incorrectly?
"This is the third-closest known non-impacting Earth approach on record for a cataloged asteroid."
"came only about 2 Earth radii from impacting our home planet."
"On average, objects the size of 2009 VA pass this close about twice per year and impact Earth about once every 5 years."
So, if this happens every 6 months, and 1 asteroid of this size actually hits the earth every 5 years, isn't it odd that this is the 3rd closest non-impacting object ever observed?
We must be overestimating the frequency of these impacts or be quite bad at observing near-flying asteroids.
On average, an asteroid of this size passes through the gap between the earths surface and a circle of radius 3 earth radii, so a disc of area 8 pi earth r squared. Yet, only 2 of those have been observed to have been closer in the last 5 1/2 years? A total of 3 of 11 detected?
November 13th, 2009 at 9:17 am
We don't use SI mesurements here in America. So, if the article is meant to be read by a US audience, the article should use terms we are familiar with. After all, one wouldn't write a paper in Japanese if it was meant for an English speaking audience. How hard is it to post US labels as well? Like,
xxx KM (xxx miles)