|There will not be an asteroid impact in 2012|
|Will an asteroid hit the Earth in 2012?|
|Artist's depiction of an asteroid impact|
Table of Contents
Many sites are claiming that in 2012 an asteroid (or several) will either impact the earth, or make a close pass causing a disruption. Despite these claims, we will show that we are in no immediate danger of an impact, especially not within the next 20 years.
December 2012 close approaches
There are in fact several asteroids that will make close passes to the earth in December of 2012. We present a partial table below1:
|Object (and name)||Date of encounter (TT)||Distance|
|2009 BS5||2456273.14||2012 Dec. 11.64||0.02141|
|(4179) Toutatis||2456273.78||2012 Dec. 12.28||0.04633|
|(88213) 2001 AF2||2456277.21||2012 Dec. 15.71||0.1812|
|1999 NW2||2456280.98||2012 Dec. 19.48||0.1695|
|(33342) 1998 WT24||2456284.82||2012 Dec. 23.32||0.1779|
|2000 WL63||2456288.18||2012 Dec. 26.68||0.1772|
|2003 UC20||2456291.31||2012 Dec. 29.81||0.06593|
The most noteworthy of these is (4179) Toutatis, which is fairly large2.
(4179) Toutatis has a very eccentric, four-year orbit3 which extends from just inside the Earth's orbit to the main asteroid belt between Mars and Jupiter. The plane of Toutatis's orbit is closer to the plane of the Earth's orbit than any other known several-kilometer Earth-orbit-crossing asteroid, or ECA. As a result Toutatis makes frequent close approaches to the Earth.
However, if you note the distance above, you see that the distance is indicated as 0.04633. That number is given in Astronomical Units (AU). 1 AU = 149,598,000 km (92,955,887.6 miles). This number is derived from the average distance between the Sun and the Earth4. Multiplying 0.04633 the distances above we derive the distance as 6,931,000 km (4,307,000 miles). The average distance to the moon is 384,403 km (238,857 miles) miles. In other words this "close approach" is 180 times as far away as the moon!
Toutatis is not going to come anywhere near hitting us in 2012.
Asteroid (99942) Apophis5 was recently predicted to pass by Earth in April 2013 and 2021, and an extremely close to Earth in April 2029, (within approximately 15,000 miles), and possibly impact Earth in April 2036. However, the most recent estimates at a 2036 impact are 1:250,0006
Due to its "smaller" size7 and current extreme distance from Earth, it is not possible at this time to determine exactly what Apophis looks like, what it is made of and what its precise orbital course will be by 2029 and later years. It could be a single object of solid rock or metal, or loose rock, or several objects of solid or loose material. The serious concern is that if Apophis passes through a resonance (gravitational) "keyhole" close to Earth in 2029, which is an area approximately 2,000 feet across and about 18,700 miles from Earth, its orbit could be affected just enough (tugged) by Earth's gravity to change its course for a possible impact with Earth in 2036. At the moment, the keyhole is just within but close to the limits of its possible range of trajectories in 2029. New and better measurements in 2011 or 2013 should reduce this range of possible trajectories so that the keyhole lies outside its limits. So we don't have to wait until 2029 - we should have the answer (almost certainly that it will miss) in the next couple of years.
To most scientists, it is not a matter of if we will be struck by an asteroid in the future as it is to when we will be struck again. There are many variables to analyze when attempting to address this issue. As with anything, time is crucial. We can't rally an effort to deflect an asteroid if we only see it a few hours ahead of impact.
Who is looking?
Since 1995 there has been a concerted effort to discover potentially hazardous asteroids. There are several teams of astronomers worldwide are surveying the sky with electronic cameras to find these objects. Some of the groups are: The LINEAR search program of the MIT Lincoln Lab; The NEAT search program in Hawaii; The Spacewatch survey at the University of Arizona; The LONEOS survey at Lowell Observatory in Flagstaff Arizona, and the Catalina Sky Survey in Tucson Arizona. Other astronomers (many of them amateurs) follow up the discoveries with supporting observations.
What are they finding?
New observations by NASA's Wide-field Infrared Survey Explorer, or WISE, show there are significantly fewer near-Earth asteroids in the mid-size range than previously thought. The findings also indicate NASA has found more than 90 percent of the largest near-Earth asteroids, meeting a goal agreed to with Congress in 1998.
"The risk of a really large asteroid impacting the Earth before we could find and warn of it has been substantially reduced," said Tim Spahr, the director of the Minor Planet Center at the Harvard Smithsonian Center for Astrophysics in Cambridge, Mass.8
Mankind has never attempted to deflect an asteroid or comet, so a great deal of design and possible advance demonstration missions will be required. A serious recommendation was recently submitted to the U.S. government to send a spacecraft to Apophis by 2013 to land a transponder on it to be used to monitor its precise path, providing much needed time to evaluate its course, perform risk assessments and develop protection plans. NASA already has some experience, having orbited and landed on asteroid Eros with the NEAR mission, and impacted on comet Tempel 1 with the Deep Impact mission. We now have, or are close to having, the necessary technology and ability to slightly
deflect (or nudge) an object from its present course, but since we have never done it, we must learn by doing.
What have we found?
The following video shows asteroid discoveries since 1980, colour coded according to whereabouts they travel within the solar system. As time goes on, more and more detailed surveys are taken and more and more asteroids are found. We know of over half a million objects already, and we know that none of these are heading for us in 2012.
NASA's Jet Propulsion Lab in Pasadena maintains a NEO Risks page at http://neo.jpl.nasa.gov/risk/.
The highest risk I could find on that page is for asteroid 2006 JY26, with an Impact Probability of 5.8e-03, or a 0.580000000% chance or 1 in 172 chance. In other words, a 99.42000000% chance the asteroid will miss the Earth. All of this for an object that is approximately 7 meters!
You are far more likely to die from walking down the street, or from eating too many doughnuts, than you are from any kind of an impact event.
Categorizing objects by type
Meteorites are categorized by their physical properties, which is done for meteorites which have been retrieved from the Earth's surface. We list the most common types of meteorites below.
These are the most common type of meteorite. These are stony meteorites that are characterized by chondrules — small spheres of minerals that were melted, but have come together with other mineral matter to form a solid rock. Chondrites are believed to be among the oldest rocks in the solar system. 82 percent of meteorites are chondrites.
These are stony meteorites without chondrules, and some of them may have originated on the surface of the Moon, or Mars. These represent about 7.8 percent of meteorites.
These meteorites are made of a crystalline iron-nickel alloy, and represent about 4.8 percent of meteorites.
These meteorites are mixtures of iron-nickel alloy and non-metallic mineral matter, and represent about 1.2 percent of meteorites.
Why type is important
The types of meteorites represent vastly different structural strength. The strongest types are the iron and stony iron meteorites. The weakest are the chondrites and achondrites. The strength of the material plays a role in whether the object will disintegrate or explode in the atmosphere, or if it will hold together make it through to the surface.
Categorizing objects by size
The size of an object determines whether we refer to it as a planet, an asteroid, or a meteoroid.
Asteroids are objects that are smaller than planets, but larger than meteoroids.
Meteoroids are objects that are smaller than asteroids.
The current official definition of a meteoroid from the International Astronomical Union is "a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom."9 The Royal Astronomical Society has proposed a new definition where a meteoroid is between 100 µm and 10 m across10. The NEO definition includes larger objects, up to 50 m in diameter, in this category. Very small meteoroids are known as micrometeoroids or interplanetary dust.
We will roughly categorize these objects into three groups by size.
Every day the Earth's mass is increased by about 100 tons as small meteoroids burn up in the atmosphere. These are generally very small, sand-sized, rice-sized or gravel-sized, but range upward in size to about a meter. This is the threshold between when an object is not likely make it through the atmosphere and when it has a possibility of making it down in one piece. None of these "small" objects will ever make it to the ground except in the form of dust.
Objects that are large enough and strong enough may survive to reach the ground. These are usually very rare. The exact size required to make it all the way down depends on the composition of the object, and the speed and angle that it enters the atmosphere with. Generally an object would have to be at least a meter across before it has a chance of making it down to the ground, and the resulting meteorite would be considerably reduced in size and mass. NASA's NEO site apparently marks the upper end of this range at 50 meters.
"Larger" objects (larger than 50 meters) have a good chance of making it down through the atmosphere. From this size up to about 1 km diameter, an impacting NEO can do tremendous damage on a local scale. Above an energy of a million megatons (diameter about 2 km), an impact will produce severe environmental damage on a global scale. The probable consequence would be an "impact winter" with loss of crops worldwide and subsequent starvation and disease. Still larger impacts can cause mass extinctions, like the one that ended the age of the dinosaurs 65 million years ago (15 km diameter and about 100 million megatons).
The exact effects of any impact would vary based on the object's composition, and the location and angle of impact, and of course its size.
The good news is that the larger objects are easier to find. We're currently tracking objects that are very small (down to a few meters), and finding more all the time. The big ones that are capable of causing major damage are found easier, and hopefully this means that we will find any potential impactors well ahead of their rendezvous with Earth.
There is no known object that is going to impact Earth in 2012. Small to medium objects impact Earth every day with no damage. Large objects are more likely to be found than small objects, and so we are confident that we are safe from large objects for the next several decades.