Image 1 - Earth Safer Than Previously Thought From Mid-Size Asteroids
September 29, 2011

Mid-size Asteroids Not As Big Of A Threat

[ Watch the Video ]

New asteroid population numbers given by NASA shows that Earth isn't as threatened as previously thought by the space rocks.

NASA announced on Thursday that its Wide-field Infrared Survey Explore (WISE) has found that there are significantly less near-Earth asteroids in the mid-size range than previously thought.

Astronomers believe there are about 19,500 mid-size near-Earth asteroids, which is over 15,000 less than previously thought.

Scientists say this improved understanding of the population may help indicate the hazard to Earth could be less than what would be assumed with 35,000 mid-size near-Earth asteroids.
The space agency said the new findings indicate that it has found over 90 percent of the largest near-Earth asteroids, which is a goal Congress made for NASA back in 1998.

"The results come from the most accurate census to date of near-Earth asteroids, the space rocks that orbit within 120 million miles (195 million kilometers) of the sun into Earth's orbital vicinity," NASA said in a press release.

The survey project known as NEOWISE is the asteroid-hunting portion of the WISE mission.

"NEOWISE allowed us to take a look at a more representative slice of the near-Earth asteroid numbers and make better estimates about the whole population," Amy Mainzer, lead author of the new study and principal investigator for the NEOWISE project at NASA's Jet Propulsion Laboratory in Pasadena, California, said in a press release. "It's like a population census, where you poll a small group of people to draw conclusions about the entire country."

The new study did not change the population of the largest near-Earth asteroids too much.  The population of these 3,300 feet and up asteroids dropped just 19, according to the study.

However, the study did confirm that it has found 911, or 93 percent, of the estimated population of these large asteroids.

"The risk of a really large asteroid impacting the Earth before we could find and warn of it has been substantially reduced," Tim Spahr, the director of the Minor Planet Center at the Harvard Smithsonian Center for Astrophysics in Cambridge, Massachusetts, said in a press release.

The study was published in the Astrophysical Journal.


Image 1: NEOWISE observations indicate that there are about 20,500 near-Earth asteroids in total that are larger than 330 feet -- 43 percent less than previous estimates of 36,000. Image credit: NASA/JPL-Caltech

Image 2: This chart shows how data from NASA's Wide-field Infrared Survey Explorer, or WISE, has led to revisions in the estimated population of near-Earth asteroids. Image credit: NASA/JPL-Caltech

Image 3: This chart illustrates how infrared is used to more accurately determine an asteroid's size. Image credit: NASA/JPL-Caltech

Image 4: This chart illustrates why infrared-sensing telescopes are more suited to finding small, dark asteroids than telescopes that detect visible light. Image credit: NASA/JPL-Caltech


On the Net: