Earth-impact events

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 information on this page and visit the links, and then join the discussion.

The science of Near-Earth objects

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

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

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

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

Fictional impact events
Fictional asteroid collisions with Earth
Off on a comet (Jules Verne novel)
Meteor (1979 film)
Armageddon (1998 film)
Deep Impact (1998 film)

In the news

Near-Earth Asteroid 2007 TU24 to Pass Close to Earth on Jan. 29 - Should be Observable with Modest Sized Telescopes - January 22, 2008
Asteroid to narrowly miss Earth - January 24, 2008
Small Asteroid Predicted to Cause Brilliant Fireball over Northern Sudan - October 6, 2008
Boulder-Size Asteroid to Be Fireball Over Earth Monday - October 6, 2008
Impact of Asteroid 2008 TC3 Confirmed - October 7, 2008
Incoming Asteroid Burned Up in Earth's Atmosphere Right on Time - October 8, 2008
Little Asteroid Makes a Big Splash - October 9, 2008
For first time, scientists predict arrival of asteroid - October 11, 2008
Who's watching our skies? - October 12, 2008
Asteroid 2008 TC3 Strikes Earth: Predictions and Observations Agree - November 4, 2008

Commentary

Asteroids ahead - don't panic - June 6, 1998
Asteroid False Alarm Shows Limits of Alert Systems - March 8, 2004
Impact! - March 7, 2007
The Sky Is Falling. Really. - March 16, 2007
The Sky Is Falling - June 2008
What 'Deep Impact' might an asteroid make on Earth, astronauts ask - September 25, 2008
Will an asteroid destroy Earth? Time for U.N. to keep tabs, say experts - September 25, 2008
Death by meteorite - October 13, 2008