Afireball over Utah overnight Tuesday was the talk of the state. And an asteroidthat could have delivered nearly half the energy of the Hiroshima atom bombwhizzed past Earth earlier this month, NASA reported recently. Meanwhile, ameteor shower dazzled skywatchers around the globe early Tuesday morning.
What'sgoing on? Nothing all that unusual, astronomers say.
Thefireball over Utah ? said to have turnednight briefly into day ? was the sort of event that happens more than mostpeople realize. Space rocks disintegrate as they crash through Earth'satmosphere. Those the size of a softball up to perhaps a small car can createdramatic fireballs. We don't see most of these fireballs because they occurover unpopulated land areas or over the oceans. Earth is two-thirds ocean. Afireball during daytime could also go largely unnoticed.
Thefireball was notable for occurring near the peak of the annual Leonidsmeteor shower, but early reports suggest the events were unrelated. TheLeonid "shooting stars" are created by tiny bits of comet debris,mostly no larger than a pea. This year's shower was better than average,skywatchers reported.
Meanwhile,asteroid 2009 VA flew past Earth Nov. 6 at about 4:30 p.m. EST. It didn'tdisintegrate, but boy was it a close call. The space rock was discovered by theCatalina Sky Survey only some 15 hours before it approached us. It passed just8,700 miles (14,000 km) from our planet's surface ? slightly less than Earth'sdiameter.
Theasteroid was just about 23 feet wide (7 meters). Still, had its path collidedwith Earth, it would have packed the energy of "about six kilotons ofTNT," explained astronomer Donald Yeomans, manager of NASA's Near-EarthObject program office at the Jet Propulsion Laboratory in Pasadena, Calif.
This nearmiss makes is the third-closest known asteroid to squeak past Earth. The otherclose approaches include the yard-wide (1 meter) asteroid 2008 TS26, which camewithin 3,820 miles (6,150 km) of the Earth's surface on October 9, 2008, andthe 23-feet-wide (7 meter) asteroid 2004 FU162 that passed within 4,060 miles(6,535 km) on March 31, 2004.
"Fouror five objects in the several tens of meters to 100 meters in size have agreater than a 1 in a million chance of hitting us ? the odds are in our favor,but people win the lottery every day, too," Johnson said. "We'recertainly trying to keep an eye on those."
"We'reprobably within a year of achieving that goal ? we're at about 85 percent rightnow," Johnson said. The program has a current annual budget of about $4.2 million.
Congresshas asked NASA to extend the search to objects "that are 140 meters in size (460feet) or larger," Yeomans said. Altogether, there are roughly 100,000 ofthese, Johnson explained, of which 20,000 might potentially be hazardous. Sofar scientists have detected about 5 percent of these 100,000 objects, "including about2,250 objects from 300 meters (985 feet) to one kilometer in size and 1,500 to1,600 objects 100 meters (330 feet) to 300 meters in size," Johnson added.
"We'retrying to do what we can with the same telescopes used for large NEO search ?we find them all the time, but we don't have the capability need to achievethat 90 percent goal for 140-meter-sized objects by 2020," Johnson said.
"It'snot something that we should worry about on a daily basis, but it is a naturalhazard that can cause levels of devastation greater than anything we know aboutor have experienced, more than any earthquake or hurricane," Johnson said."So it's certainly worth the effort to at least find out if there is anynear-term hazard."
"AndNEOs represent more than just a hazard to us," he noted. "They'repotentially a source of resources and destinations as well, as we explore thesolar system."
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