'All-clear' asteroid will miss Earth in 2040

December 21, 2012
'All-clear' asteroid will miss Earth in 2040
Gemini Multi-Object Spectrograph image of 2011 AG5. The asteroid is the point at the center of the image (circled) with background stars trailing because the telescope tracked on 2011 AG5. This single 300 second exposure is oriented with north up and east left - each background star streak is about 15 arcseconds in length. 2011 AG5 is highly variable in brightness and other Gemini observations on October 27th required longer exposures than the one shown here.

(Phys.org)—Using the Gemini North telescope on Mauna Kea, Hawai'i a team of astronomers from the University of Hawaii's Institute for Astronomy (IfA) have confirmed that the chance of asteroid 2011 AG5 impacting Earth in 2040 is no longer a significant risk – prompting a collective sigh-of-relief. Previously, scientists estimated that the risk of this 140-meter-diameter (about the length of two American football fields) asteroid colliding with the Earth was as high as one in 500.

If this object were to collide with the Earth it would have released about 100 megatons of energy, several thousand times more powerful than the atomic bombs that ended World-War II. Statistically, a body of this size could impact the Earth on average every 10,000 years.

The observations, using the Gemini Multi-Object Spectrograph (and imager), were especially challenging said team-member Richard Wainscoat. "These were extremely difficult observations of a very faint object," he said. "We were surprised by how easily the was able to recover such a faint asteroid so low in the sky." The Gemini observations were made on October 20, 21, and 27, 2012.

In addition to multiple observations since the asteroid's discovery, the team had also acquired images about two weeks earlier with the University of Hawai'i 2.2-meter telescope also on Mauna Kea – however, these data were all less conclusive and required confirmation. Gemini was able to make the follow-up observations rapidly due to the observatory's scheduling flexibility and availability of several instruments at a moment's notice.

IfA astronomers David Tholen, Richard Wainscoat, Marco Micheli, and Garrett Elliott conducted the original observations and analysis of the data. Further analysis was performed at NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory (JPL) in Pasadena, California. The updated trajectory of 2011 AG5, based on the Gemini data, has a factor of 60 less uncertainty than the previous due in part to the increase in sampling points in the 's orbit. The original discovery was made from images obtained with the NASA-sponsored Catalina Sky Survey on Mt. Lemmon in Arizona.

According to a press release issued by JPL, while this new result has reduced the interest in 2011 AG5, the experience gained by studying this object and conducting a contingency deflection analysis has demonstrated that astronomers, using NSF and NASA facilities, are well poised to detect and predict the trajectories of -threatening asteroids in the future.

The data for this study are being published by the Minor Planet Center in Cambridge, Massachusetts.

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1 / 5 (5) Dec 21, 2012
Theres lots 100 meter asteroids out there headed towards earth prbit that we cannot see.
2 / 5 (1) Dec 21, 2012
Theres lots 100 meter asteroids out there headed towards earth prbit that we cannot see.

They track hundreds if not thousands. But if we cannot see them yet and they are coming to earth they must be alot smaller or even further away.....if we can see the 140m asteroid... and obviously (to some extent) the smaller they are the less we have to worry.

Naturally that ain't 100% correct, they don't even have to hit the earth surface to cause destruction on earth.

I wonder if they have a set size an asteroid has to be before they consider it "potential" to cause damage if there was a collision with earth but then I guess we don't always know the composition of them.... any one know much on that?
not rated yet Dec 21, 2012
I wonder if they have a set size an asteroid has to be before they consider it "potential" to cause damage if there was a collision with earth but then I guess we don't always know the composition of them.... any one know much on that?

Formula for a Sphere(oid) shows this object is 2.75 times more massive than the Tunguska event object, which is currently believed to be only 100m diameter. Advanced computer modeling, with some new theories and applying all known physics, has shown that it takes far less to be destructive than was once thought.

If I remember correctly, It is currently believed that a 30 meter diameter object can destroy an entire metropolis in an "airburst" scenario.

The number of objects of a particular size increases exponentially as the size you are investigating decreases. Based on volume and mass, we would expect a 30m diameter object to be about 37 times as common as a 100m diameter object, if the distributions are inversely proportional to mass.
4.2 / 5 (5) Dec 21, 2012
sirchick: Any asteroid bigger than about 10 meters across can cause major regional damage.

At ~10 meters an asteroid can destroy a city.
At ~30 meters, it can destroy a small country (equivalent to a 15 megaton nuke or so).
At ~100 meters, it can cause low to moderate planet-wide damage.
At ~1000 meters, it can cause severe planet wide damage.
At ~5000 meters, mass extinction occurs.
At ~50000 meters, not much but bacteria survive.
At ~500000 meters the entire crust of the planet and upper mantel liquifies, extinguishing all life.
5 / 5 (3) Dec 21, 2012
...the Tunguska event object, which is currently believed to be only 100m diameter.

The most recent simulations indicate that it was between 30 and 50 meters in diameter, depending on the composition.
3.7 / 5 (3) Dec 22, 2012
gopher65 - you have to specify your density/velocity assumptions to make your table valid.

The amount of energy in a strike is mass X velocity squared. The mass of an asteroid of a specific size is determined by its density, which can vary all over the map. Even more important is its velocity, which is essentially determined by its orbit. A slow moving quite massive object could do considerably less damage than a much smaller, more dense, fast moving object. The impact velocities are incredibly variable. A hyperbolic orbit moving in the opposite direction of the earths orbit could impact as fast as 20K kilo/sec. A co-orbital object could hit us at a few hundred kilo/sec or even slower.

So unless you are talking absolute worse case, iron-nickel asteroids traveling at 20,000 kilo/sec, your table is misleading.
1 / 5 (3) Dec 22, 2012
Unless the orbit changes by 0.00000001% in the next 28 years, then it's headed for New York!
1 / 5 (3) Dec 22, 2012
astroid apophis would have already shattered earth by 2029
5 / 5 (3) Dec 23, 2012
For those who want to play around, here's am interesting site:


It let's you choose the diameter, density, impact velocity, angle, and target material, then calculates the results.
1 / 5 (3) Dec 24, 2012
angle, and target material

In addition to all the other factors mentioned by others, I was going to add these. Whether it lands over land or water is a significant factor, as well as desert, mountain, etc.

Taking all things into account, the odds of a significant impact happenning in our lifetime are slim. Furthermore, the odds of one that does more damage than an average landfalling hurricane are exceptionally slim. And finally, it's likely that any event like Tunguska would happen in an area uninhabited by people. As with Tunguska, there might not even be anyone to witness it. However, an ocean impact might be amplified by secondary effects, such as land slides along the contintinental shelves, which could cause much more damage through tsunami than the impact would.
not rated yet Dec 24, 2012
gopher65 - you have to specify your density/velocity assumptions to make your table valid.

Those are for dead average velocity and composition.

When you get to the larger ones (10 kilometers) it stops mattering too much, since the damage at that point is already going to cause a near total extinction of life even under the best circumstances.

But for the smaller ones, speed is the big variable (though the other stuff you all listed matters too). Speed varies from a slow 10km/s (if they're in a similar orbit to Earth and catching up from behind when they hit) to a staggering 70km/s if they're coming in from the Oort cloud. 20-40 is normal.

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