Large Asteroid Barely Misses Earth—Can We Prevent Future Collisions?

March 04, 2009 10:29 AM
by Haley A. Lovett
Asteroid 2009 DD45 missed Earth by only twice the distance of Earth-orbiting satellites. Could early detection save the planet from future asteroids?

Asteroid 2009 DD45 a Very Close Call

On March 2, 2009, an asteroid approximately 115 feet across flew very close to Earth.  According to, astronomers knew that the asteroid was coming and that it was not going to collide with Earth. At its closest point to Earth, it was only twice the distance of a geostationary communications satellite.

It isn’t uncommon for space objects to come close to Earth, but asteroid 2009 DD45 was much closer than usual. NASA has a schedule of upcoming close encounters that details the size of each asteroid and the distance from Earth that each will pass.

Background: Earth’s collisions with space objects

Asteroid 2009 DD45’s estimated size makes it about the same size as the Tunguska asteroid that leveled 2,000 kilometers of forest in Siberia in 1908, reports NewScientist. The incident at Tunguska is thought to have been caused by an explosion by a comet or asteroid 6–8 kilometers above the surface of the Earth, as no crater or meteorite fragments were ever found at the site, according to findingDulcinea.

Earth takes on about 10,000 tons of space debris each year, mostly from dust from comets or asteroid pieces. It is not uncommon for small bits of rock to fall to Earth, however a recent prediction of a collision with a space rock was a first for scientists. According to NewScientist, in October 2008 the Mt. Lemmon Observatory near Tucson, Ariz., discovered that a rock about five meters across would hit the earth near Sudan about 24 hours later. The prediction turned out to be right.

The rock, owing to its small size, did not cause any damage. But it did offer hope that scientists might detect large asteroids on a collision course with Earth early enough to prevent disaster.

Opinion & Analysis: Can NASA prevent asteroid collisions?

In 2004, scientists discovered that asteroid Apophis has the potential to collide with Earth in 2036. Apophis is about 1,000 meters wide. Although the chance of it hitting Earth is small (about one in 44,000 according to it was chance enough for Congress to create the Shapiro panel, which is dedicated to detecting and deflecting potentially harmful asteroids.

Although it is believed that we have identified most of the very large asteroids (those with diameters of more than 200 km), it is thought that we are only aware of a small fraction of the asteroids with 1-km diameters.

NASA has created a Near Earth Object Program to detect Potentially Hazardous Asteroids (PHAs) as they approach Earth. So far there are 1,034 known PHAs. Even before asteroid Apophis, NASA was studying asteroids. In 1996 NASA launched the NEAR (Near Earth Asteriod Rendezvous) probe to observe asteroids at close range. In 2001, NEAR landed on an asteroid.

The next step given to the Shapiro panel is to identify ways to deflect or destroy asteroids. Some ideas include using nuclear weapons, painting an asteroid to change how it is heated and eventually its direction, and a “gravity tractor.”

Reference: Asteroids, comets and meteorites

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