posttrib
PICTURESQUE 
Weather Updates

Today’s asteroid not a surprise like meteorite, Adler astronomer says

Updated: February 15, 2013 11:20AM



The meteorite that hit Russia and injured nearly 1,000 people caught astronomers by surprise, but scientists have a good handle on the path of the asteroid that will buzz past Earth on Friday, an Adler Planetarium astronomer said.

“We know the asteroid’s orbit very, very well. We know that it poses zero chance of hitting the Earth. Not even just a tiny chance. No chance. We know its position plus or minus two miles,” said Mark Hammergren, an astronomer at the Adler Planetarium.

Asteroid 2012 DA14 will come within 17,200 miles of Earth Friday, passing over the Indian ocean near Indonesia.

It won’t be visible to anyone in Chicago, and even those near Indonesia will need big binoculars and precise timing to see it, Hammergren said.

Though the asteroid and meteorite are close in time, the two are unrelated, Hammergren said.

The 10-ton meteorite that streaked the skies of Chelyabinsk, Russia, Friday wasn’t on astronomers’ radars because it was too faint for large telescopes to pick up, Hammergren said.

The large telescopes used to track meteorites have a field of view the size of a postage stamp.

“These things can’t be seen until they come very close to Earth,” Hammergren said. “I don’t think anybody had an awareness of it until it hit the atmosphere and started glowing as brightly as it did.

While Hammergren said meteorites are fairly small, he called Friday’s “fairly large.” A fireball of its size — approximately 30 feet across — would have been visible for hundreds of miles. Its sonic boom could’ve been heard dozens of miles from its path.

Unlike a meteor — the flash of light seen in the sky when a chunk of an asteroid hits the atmosphere — a meteorite is the chunk of rock or metal that hits ground, Hammergren said.

A meteorite’s force can shatter windows and damage buildings, but few of its fragments are left behind. Meteorites travel, on average, between eight and 20 miles per second, so most of the material gets vaporized and “blasted off” by the atmosphere, Hammergren said.

What should sky aficionados keep their eyes out for next?

Hammergren noted two comets coming this year that could “be nice sights in the sky,” specifically comet ISON, set to come close to the sun in late November or early December.

Yet the nature of this, like Russia’s meteorite, is tough to predict.

“Comets are fickle beasts. This one is on its first pass close to the sun, so sometimes comets like this don’t brighten as much as we predict them to.”

Hammergren believes these meteorites, asteroids and comets are all subtle hints for land-dwellers.

“They highlight that we here on the Earth are part of a dynamic solar system, that part of our planet is part of a large universe. And every now and then, nature feels the need to remind us of this fact.”



© 2014 Sun-Times Media, LLC. All rights reserved. This material may not be copied or distributed without permission. For more information about reprints and permissions, visit www.suntimesreprints.com. To order a reprint of this article, click here.