What we can't see can kill us. We need bigger telescopes!

Editor's Note: We're keeping an eye out for asteroids that can wipe out most of Earth's extant species. Good. But a special panel tells us that smaller (less than 1 km across) asteroids, which we're not able to spot with the currently assigned telescopes, if they strike us, won't be a picnic either.

New Scientist - August 12, 2009, by David Shiga

Asteroid Eros, seen here by NASA's NEAR spacecraft, is 33 kilometres wide, making it the second largest near-Earth asteroid (Image: NEAR Project/NLR/JHUAPL/Goddard SVS/NASA)

Existing sky surveys miss many asteroids smaller than 1 kilometre across, leaving the door open to damaging impacts on Earth with little or no warning, a panel of scientists reports. Doing better will require devoting more powerful telescopes to asteroid hunting, but no one has committed the funds needed to do so, it says.

Near-Earth asteroids larger than 1 kilometre across could blast huge amounts of sunlight-blocking dust into Earth's atmosphere in an impact, causing devastating climate change. The US Congress asked NASA in 1998 to find 90 per cent of those in this size range within 10 years, a goal that has now nearly been reached.

Astronomers have now found 784 of them, mostly using telescopes funded by NASA. That works out to 83 per cent of the 940 estimated to be out there by astronomer Alan Harris of the Space Science Institute in Boulder, Colorado.

But asteroids below 1 kilometre in size can cause serious harm, too, and they hit Earth more frequently because they are more numerous. To address the small-asteroid threat, Congress told NASA in 2005 to find 90 per cent of the near-Earth asteroids larger than 140 metres across by 2020.

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