Stuart Gary
ABC
http://www.abc.net.au/science/articles/2013/02/08/3686287.htm
People living in the west of Australia are well placed to see a space rock half the size of a football field skim past Earth next weekend.
Discovered last year, the asteroid called 2012 DA14 is described by NASA as ‘the biggest asteroid they’ve ever seen passing so close to Earth”.
The asteroid will make its nearest approach to Earth at 6.24 am AEDT* on the 16 February (19.24 UTC 15 February), when it will be less than 27,700 kilometres above the ground.
From its brightness, scientists estimate it’s between fifty and eighty metres wide and weighs about 130,000 tonnes.
“The asteroid will approach the planet over Antarctica, crossing the Indian Ocean west of Perth, with the closest approach being near the Indonesian island of Sumatra,” says astronomer Craig O’Neill from Macquarie University.
“The western portions of Australia from Adelaide to Perth should be able to see it, but you’ll still need a small telescope or a solid pair of binoculars.”
“At its closest, it will have an apparent magnitude (level of brightness) of about 7.4, so you won’t be able to see it with the naked eye,” says O’Neill.
“And it is going to be coming in the morning so the sky will be lightning up which will affect its visibility as well.”
About four minutes after its close approach, the asteroid should pass into Earth’s shadow for about 18 minutes before reappearing only to quickly fade in brightness as it moves away.
Unstable orbit
Although the asteroid will not hit Earth, scientists are watching its orbit.
2012 DA14 circles the Sun in an orbit almost identical to Earth’s, but tipped by about 12 degrees and slightly more elongated.
“This isn’t typical for an asteroid population, it’s been perturbed at some point and it’s not particularly stable where it is,” says O’Neill.
“At the moment it has an orbital period (the time it takes to go around the Sun) of about 368 days, a bit more than an Earth year.”
“But that’s going to change as it flies by the Earth.”
According to O’Neill the encounter will slow the asteroid down, dropping its orbital period to about 317 days.
NASA’s Goldstone radar in the Mojave Desert will track the asteroid, which O’Neill says will help refine its trajectory after its Earth encounter.
“That will give us a much better idea of what its future orbit is going to be,” says O’Neill.
“In terms of tracking Near Earth Asteroids and assessing the risk of these things hitting Earth, that’s really important.”
“We’ve got to understand where they are and how they’re moving in order to understand what the odds are of one of these things actually crashing into us.”
ANIMATION LINK
http://www.youtube.com/watch?feature=player_embedded&v=ISSArm_yvtQ
It’s happened before
Don Yeomans from NASA’s Near Earth Object SENTRY program at the Jet Propulsion Laboratory in Pasadena California, says an asteroid like 2012 DA14 flies close to Earth every 40 years, on average.
“But only hits the planet once every 1200 years,” says Yeomans.
“If it were to hit the Earth, it would impact with the force of a 2.4 megaton bomb.”
“A similar-sized object formed the 1.6 kilometre wide Meteor Crater in Arizona when it struck about 50,000 years ago.”
In 1908, a space rock about the size of 2012 DA14 exploded in the skies above Tunguska Siberia, flattening over 2000 square kilometres of forest.
Since that was just over a hundred years ago, statistically speaking it means we’re probably safe for a while.
*4.24 am Perth local time *5.54 am Adelaide local time