Earth-impact events

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Is this artist's impression of an asteroid colliding with Earth too sensationalistic? (See Impact!, and discuss)

What objects exist in space near the Earth? How often do they collide with our planet? What are the risks of such an impact? Is this something that we should be worried about? Have scientists and journalists done a good job of informing the public? Please read the infomation on this page and visit the links, and then join the discussion.

The science of Near-Earth objects[edit]

Meteor Crater is the result of an Earth impact 50,000 years ago.

The Solar System consists of the Sun, the planets and their moons, and many smaller objects. These smaller objects include asteroids, comets and large meteoroids. Most of these objects are distant from the Earth and never pass close to our planet. For example, the vast majority of asteroids orbit within the main asteroid belt. But there are objects that are known to approach the Earth very closely, and many have collided with our planet thoughout its history. These Near-Earth objects include some that are potentially hazardous.

Near-Earth objects[edit]

Near-Earth objects (NEO) are asteroids, comets and large meteoroids whose orbits bring them close to Earth's orbit, and which may therefore pose a collision danger.

  • On October 7, 2008 a meteoroid called 2008 TC3 which was 2 - 5 meters (7 - 16 ft) in diameter entered Earth's atmosphere and burned up before it reached the ground. The object had just been discovered about a day before the impact. It exploded tens of kilometers above the ground with the energy of around 1 - 2 kiloton of TNT, causing a large fireball in the early morning sky over northern Sudan. An impact like this happens 2 - 4 times per year, but this is the first time that such an object has been observed and tracked before entering the atmosphere.

Potentially Hazardous Asteroids[edit]

Potentially Hazardous Asteroids (PHA) are Near-Earth asteroids that are big enough to cause unprecedented regional devastation if they were to hit the Earth.

Radar image of 4179 Toutatis
  • On September 29, 2004 the asteroid 4179 Toutatis made a particularly close approach (within 4 LD, or lunar distances) from Earth. The next close approach is November 9, 2008, but it will be five times more distant. It is about 4.6 km by 2.4 km in size.
  • The asteroid 2007 CN26 passed within 0.6 LD of the Earth on September 2, 1985. The size of this object is in the range of 170 - 380 meters in diameter. It was not discovered until February 2007, more than 20 years after the close approach to the Earth.
  • There is some concern that the asteroid 99942 Apophis could impact earth on April 13, 2036. It is about 210 - 330 meters in size. The probability of a collision is currently esitmated to be 1 in 45,000. These calculations are uncertain due to another close encounter in 2029 which will modify the orbit of the asteroid, making a collision either more or less likely. New measurements possible in 2011-2013 will likely confirm that the asteroid will miss the earth.
  • The asteroid 2007 VK184 is currently estimated to have a probability of 1 in 3,030 of impacting Earth on June 3, 2048. This 130 meter object has the potential of releasing 150 megatons of energy if it were to collide.

Close-Approaches[edit]

The close approach of 99942 Apophis to the Earth and Moon on April 13, 2029 will alter the orbit of the asteroid.
NEO Earth Close-Approaches
Close-Approach Date Object Name Estimated Size Miss Distance
2008-Oct-03 2008 TN9 9 - 19 m 0.6 LD
2008-Oct-07 2008 TC3 2 - 5 m impact
2008-Oct-09 2008 TS26 about 1 m 0.03 LD
2008-Oct-16 2008 UB95 35 - 75 m 4.4 LD
2008-Oct-18 2008 UA202 3 - 7 m 0.9 LD
2008-Oct-19 2008 UR2 11 - 24 m 1.5 LD
2008-Oct-19 2008 UF1 17 - 37 m 3.8 LD
2008-Oct-20 2008 US 1.3 - 2.9 m 0.08 LD
2008-Oct-22 2008 UM1 1 - 2.2 m 0.2 LD
2008-Oct-23 2008 TT26 51 - 120 m 3.6 LD
2008-Oct-28 2008 UW99 35 - 78 m 3.4 LD
2008-Oct-29 2005 VL 8 - 19 m 2.5 LD
2008-Oct-29 2005 VN 72 - 160 m 4.1 LD
2008-Oct-30 2005 VU3 65 - 150 m 3.7 LD
2008-Nov-02 2008 UT95 8.9 - 20 m 1.5 LD
2008-Nov-02 2008 UC7 11 - 24 m 4.5 LD
2008-Nov-03 2008 VM 2.5 - 5.5 m 0.1 LD
2008-Nov-04 2008 VB4 5.8 - 13 m 1.3 LD
2008-Nov-04 2008 VC 11 - 25 m 4.4 LD
2008-Nov-16 2008 WO2 3.0 - 6.7 m 1.0 LD
2008-Nov-18 2004 XK3 36 - 80 m 1.8 LD


PHA Earth Close-Approaches
Close-Approach Date Object Name Estimated Size Miss Distance
2008-Jan-29 2007 TU24 210 - 470 m 1.4 LD
2008-Jul-14 2008 BT18 670 - 1500 m 5.9 LD
2008-Dec-23 2008 EV5 270 - 600 m 8.4 LD
2009-Feb-10 2006 AS2 230 - 520 m 9.2 LD
2009-Feb-18 1999 AQ10 240 - 540 m 4.4 LD


1 LD = Lunar Distance = ~384,000 kilometers

See the NASA/JPL Near Earth Object Program for up-to-date information.

In fiction[edit]

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