[meteorite-list] The Fireballs of February

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 23 Feb 2012 13:15:29 -0800 (PST)
Message-ID: <201202232115.q1NLFToR007518_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/science-news/science-at-nasa/2012/22feb_februaryfireballs/

The Fireballs of February

Feb. 22, 2012: In the middle of the night on February 13th, something
disturbed the animal population of rural Portal, Georgia. Cows started
mooing anxiously and local dogs howled at the sky. The cause of the
commotion was a rock from space.

"At 1:43 AM Eastern, I witnessed an amazing fireball," reports Portal
resident Henry Strickland. "It was very large and lit up half the sky as
it fragmented. The event set dogs barking and upset cattle, which began
to make excited sounds. I regret I didn't have a camera; it lasted
nearly 6 seconds."

Strickland witnessed one of the unusual "Fireballs of February."

"This month, some big space rocks have been hitting Earth's atmosphere,"
says Bill Cooke of NASA's Meteoroid Environment Office. "There have been
five or six notable fireballs that might have dropped meteorites around
the United States."

It's not the number of fireballs that has researchers puzzled. So far,
fireball counts in February 2012 are about normal. Instead, it's the
appearance and trajectory of the fireballs that sets them apart.

"These fireballs are particularly slow and penetrating," explains meteor
expert Peter Brown, a physics professor at the University of Western
Ontario. "They hit the top of the atmosphere moving slower than 15 km/s,
decelerate rapidly, and make it to within 50 km of Earth???s surface."

The action began on the evening of February 1st when a fireball over
central Texas wowed thousands of onlookers in the Dallas-Fort Worth area.

"It was brighter and long-lasting than anything I've seen before,"
reports eye-witness Daryn Morran. "The fireball took about 8 seconds to
cross the sky. I could see the fireball start to slow down; then it
exploded like a firecracker artillery shell into several pieces,
flickered a few more times and then slowly burned out." Another observer
in Coppell, Texas, reported a loud double boom as "the object broke into
two major chunks with many smaller pieces."

The fireball was bright enough to be seen on NASA cameras located in New
Mexico more than 500 miles away. "It was about as bright as the full
Moon," says Cooke. Based on the NASA imagery and other observations,
Cooke estimates that the object was 1 to 2 meters in diameter.

So far in February, NASA's All-Sky Fireball Network has photographed
about a half a dozen bright meteors that belong to this oddball
category. They range in size from basketballs to buses, and all share
the same slow entry speed and deep atmospheric penetration. Cooke has
analyzed their orbits and come to a surprising conclusion:

February Fireballs (meteorcam, 200px) <http://fireballs.ndc.nasa.gov/>
This camera is part of NASA's All-Sky Fireball Network. [more
<http://fireballs.ndc.nasa.gov/>]

"They all hail from the asteroid belt - but not from a single location in
the asteroid belt," he says. "There is no common source for these
fireballs, which is puzzling."

This isn't the first time sky watchers have noticed odd fireballs in
February. In fact, the "Fireballs of February" are a bit of a legend in
meteor circles.

Brown explains: "Back in the 1960s and 70s, amateur astronomers noticed
an increase in the number of bright, sound-producing deep-penetrating
fireballs during the month of February. The numbers seemed significant,
especially when you consider that there are few people outside at night
in winter. Follow-up studies in the late 1980s suggested no big increase
in the rate of February fireballs. Nevertheless, we've always wondered
if something was going on."

Indeed, a 1990 study by astronomer Ian Holliday suggests that the
'February Fireballs' are real. He analyzed photographic records of about
a thousand fireballs from the 1970s and 80s and found evidence for a
fireball stream intersecting Earth's orbit in February. He also found
signs of fireball streams in late summer and fall. The results are
controversial, however. Even Halliday recognized some big statistical
uncertainties in his results.

NASA's growing All-Sky Fireball Network could end up solving the
mystery. Cooke and colleagues are adding cameras all the time, spreading
the network's coverage across North America for a dense, uninterrupted
sampling of the night sky.

"The beauty of our smart multi-camera system," notes Cooke, "is that it
measures orbits almost instantly. We know right away when a fireball
flurry is underway???and we can tell where the meteoroids came from." This
kind of instant data is almost unprecedented in meteor science, and
promises new insights into the origin of February???s fireballs.

Meanwhile, the month isn't over yet. "If the cows and dogs start raising
a ruckus tonight," advises Cooke, "go out and take a look."


Author:Dr. Tony Phillips
Production editor: Dr. Tony Phillips
Credit: Science at NASA
Received on Thu 23 Feb 2012 04:15:29 PM PST