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After analysis of recent data from the NEOWISE (Near-Earth Object WISE) space mission NASA announced that we are unlikely to be wiped out by a killer asteroid in the next few centuries. The new data suggests that there are fewer large near-Earth asteroids orbiting the Sun than previously thought but we are not completely out of the woods yet!

The new data reveals only a small decline from 1,000 to 981 in the estimated number of large near-Earth asteroids, which are at least 1 kilometre (0.62 miles) across. Asteroids of this type are of particular interest as they are about the size of a small mountain and if one were to strike the Earth the consequences would result in mass species extinction and large climate and atmospheric changes. For comparison it is thought that an asteroid approximately 10 kilometres (6 miles) across wiped out the dinosaurs. Importantly, of these 981 asteroids NASA has already found nearly 93% of them. This in total amounts to 911 asteroids and none of them pose a threat to the Earth in the foreseeable future.

An artist's conception of the WISE satellite in orbit around Earth (NASA/Caltech)

Tim Spahr, the director of the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts said "The risk of a really large asteroid impacting the Earth before we could find and warn of it has been substantially reduced". So for at least the next few hundred years we seem safe leaving plenty of time to plan an Earth saving Bruce Willis Hollywood style "Armageddon" mission if needed at some point in the distant future.

The news regarding large near-Earth asteroids is good but what about the smaller ones. In this case it's also looking much better for us. Astronomers have now reduced their estimate of the total number of near-Earth asteroids in the size range from 100 metres (330 feet) to 1 km (3,300 feet) by almost a half. Previous estimates of 35,000 have now been revised down to roughly 19,500. An asteroid of this size would still cause significant damage if it struck the Earth.

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. The infrared-sensing telescope performed the most accurate survey to date of a slice of this population as part of project called NEOWISE (NASA/Caltech)

Scientists say that the lower population of near-Earth asteroids may indicate that the hazard to Earth could be somewhat less than previously imagined. However, caution still remains as the majority of these mid-size asteroids remain to be discovered.

The NEOWISE mission was an extension to NASA's Wide-field Infrared Survey Explorer (WISE) mission. The WISE mission was an Earth-orbiting satellite launched on 14th December 2009 with a 40 cm (16 in) diameter infrared telescope. It performed an all-sky astronomical survey with images in 3, 5, 12 and 22 ┬Ám wavelength range bands over the next 10 months. By October 2010, WISE hydrogen coolant had ran out and rather than abandon the spacecraft, the NASA Planetary division stepped in with funding for a shorter fourth month mission extension called NEOWISE, to search for small solar system bodies close to Earth's orbit. The spacecraft is currently hibernating in a polar orbit around Earth. If needed, it could return service in the future, NASA said.

The findings were announced during a press conference on 29th September 2011.