Washington: In order to defend Earth from asteroids, the trick is to spot the near-Earth objects first, according to NASA researchers.

A mere 17-20 metres across, the Chelyabinsk meteor caused extensive ground damage and numerous injuries when it exploded on impact with the Earth’s atmosphere in February 2013.

To prevent another such impact, Amy Mainzer, principal investigator of NASA’s asteroid-hunting mission at the Jet Propulsion Laboratory in Pasadena, California, and colleagues have devised a new way to spot tiny near-Earth objects (NEOs) as they hurtle toward the planet.

“If we find an object only a few days from impact, it greatly limits our choices, so in our search efforts, we’ve focused on finding NEOs when they are further away from Earth, providing the maximum amount of time and opening up a wider range of mitigation possibilities,” Mainzer explained.

NEOs are intrinsically faint because they are mostly really small and far away from us in space.

“Add to this the fact that some of them are as dark as printer toner, and trying to spot them against the black of space is very hard,” she added.

Instead of using visible light to spot incoming objects, Mainzer’s team has leveraged a characteristic signature of NEOs — heat.

Asteroids and comets are warmed by the sun and so glow brightly at thermal wavelengths (infrared), making them easier to spot with the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) telescope.

“With the NEOWISE mission, we can spot objects regardless of their surface colour and use it to measure their sizes and other surface properties,” Mainzer said.

Astronomers think that examining the composition of asteroids will help understand how the solar system was formed.