10/05/2011 01:19 pm ET | Updated Dec 05, 2011

Large, Near-Earth Asteroids Less Numerous Than Previously Thought, NASA Says

In a time of budget woes and falling satellites, it's nice to get a little good news from NASA.

A NASA orbiter has found that there are fewer big asteroids passing close to our planet than we thought. Specifically, there are only about 20,500 near-Earth asteroids larger than 100 meters. That sounds like a lot, but previous estimates were about 75 percent higher.

The new, lower figures come from the WISE spacecraft, which surveyed the skies with an infrared camera. WISE only spotted a few hundred nearby asteroids, but that was enough to extrapolate how many are out there. The findings will appear in the Astrophysical Journal. [Amy Mainzer et al., "NEOWISE Observations of Near-Earth Objects: Preliminary Results"]

If a 100-meter asteroid hit Earth, it would be equivalent to exploding an 80-megaton H-bomb. A larger asteroid could stir up huge tsunami waves if it hit the ocean. Luckily no known asteroids pose a real threat to Earth.

But there could still be some out there that are menacing. Astronomers estimate that they have identified only a quarter of near-Earth asteroids 100 meters and up. They still need to find the rest and show that they're not a threat before we're sure to avoid the fate of the dinosaurs.

[The above text is a transcript of this podcast.]