Wednesday, 11 October 2017

Bright lights in the sky

The Chelyabinsk asteroid over Russia in February 2013.
THERE'S been significant worldwide media interest in tomorrow morning’s flyby of asteroid 2012 TC4, which will make an unusually close pass to Earth at a distance of just 43,780 km -  that’s well inside the orbit of the Moon and closer than some satellites.

"We know the orbit of TC4 well enough to be absolutely certain that it won't hit Earth," assures Paul Chodas, manager of the Center for Near-Earth Object Studies (CNEOS) at NASA’s Jet Propulsion Laboratory in California,"but we haven't established its exact path just yet."

The chunk of space rock is about as big (in the range of 10-20 m diameter) as the famous 2013 Chelyabinsk object which hit Earth without warning as the sun  rose over Russia’s Ural mountains on 15 February 2013.

As the space rock skimmed into the atmosphere the early morning sky lit up with a second ‘sun’ as shock waves shattered windows in hundreds of buildings around the wakening city.

It had impacted Earth literally ‘out of the blue’, flying in from the direction of the sun where no telescope could see it - and it took everyone by surprise.

Years later, meteorite hunters are still finding pieces of the ‘Chelyabinsk asteroid’ that rained down after its 17 m-wide body disintegrated in the atmosphere.

The difference with 2012 TC4, which could be up to 30 m wide, is that NASA knows it's coming. At 07:41 CEST (Central European Summer Time) tomorrow morning (12 October) it will pass 43,500 km above Earth’s surface, about 1/8th the distance to the Moon.

The flyby is so close, gravity will significantly alter the asteroid's trajectory before it exits the Earth-Moon system.

To get a better handle on the asteroid's orbit (and possible future encounters), an international network of telescopes will monitor 2012 TC4 as it speeds by.


Pinging the asteroid with its Goldstone telescope, NASA also hopes to learn much about the space rock's physical properties.

This asteroid is too small to see with the naked eye. However, skilled amateur astronomers using small telescopes will be able to observe it. At peak brightness, 2012 TC4 will shine like a 13th magnitude star as it zips through the constellations Capricornus and Sagittarius.

The house-sized space rock does afford space agencies across the globe an opportunity to test some of their planetary defence scenarios that might be needed if Earth was in the path of a more dangerous asteroid.

If an asteroid the size of TC4 or slightly bigger was on course to hit a populated area, agencies such as the ESA and NASA would look to warn people and work with relevant governments to potentially start an evacuation.

If anything signifcantly bigger the TC4 is ever detected, much more drastic action might be needed, including the possibility of trying to deflect any such asteroid before it collides with Earth.