[meteorite-list] Spring is Fireball Season

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 31 Mar 2011 11:56:33 -0700 (PDT)
Message-ID: <201103311856.p2VIuXki022276_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/science-news/science-at-nasa/2011/31mar_springfireballs/

Spring is Fireball Season
NASA Science News
March 31, 2011

What are the signs of spring? They are as familiar as
a blooming Daffodil, a songbird at dawn, a surprising shaft of warmth
from the afternoon sun.

And, oh yes, don't forget the meteors.

"Spring is fireball season," says Bill Cooke of NASA's Meteoroid
Environment Center. "For reasons we don't fully understand, the rate of
bright meteors climbs during the weeks around the vernal equinox."

In other seasons, a person willing to watch the sky from dusk to dawn
could expect to see around 10 random or "sporadic" fireballs. A fireball
is a meteor brighter than the planet Venus. Earth is bombarded by them
as our planet plows through the jetsam and flotsam of space--i.e.,
fragments of broken asteroids and decaying comets that litter the inner
solar system.

In spring, fireballs are more abundant. Their nightly rate mysteriously
climbs 10% to 30%.

"We've known about this phenomenon for more than 30 years," says Cooke.
"It's not only fireballs that are affected. Meteorite falls--space rocks
that actually hit the ground--are more common in spring as well^1 ."

Researchers who study Earth's meteoroid environment have never come up
with a satisfactory explanation for the extra fireballs. In fact, the
more they think about it, the stranger it gets.

Consider the following:

There is a point in the heavens called the "apex of Earth's way." It is,
simply, the direction our planet is traveling. As Earth circles the sun,
the apex circles the heavens, completing one trip through the Zodiac
every year.

The apex is significant because it is where sporadic meteors are
supposed to come from. If Earth were a car, the apex would be the front
windshield. When a car drives down a country road, insects accumulate on
the glass up front. Ditto for meteoroids swept up by Earth.

Every autumn, the apex climbs to its highest point in the night sky. At
that time, sporadic meteors of ordinary brightness are seen in
abundance, sometimes dozens per night.

Read that again: Every autumn.

"Autumn is the season for sporadic meteors," says Cooke. "So why are the
sporadic fireballs peaking in spring? That is the mystery."

Meteoroid expert Peter Brown of the University of Western Ontario notes
that "some researchers think there might be an intrinsic variation in
the meteoroid population along Earth's orbit, with a peak in big
fireball-producing debris around spring and early summer. We probably
won't know the answer until we learn more about their orbits^2 ."

To solve this and other puzzles, Cooke is setting up a network of smart
meteor cameras around the country to photograph fireballs and
triangulate their orbits. As explained in the Science at NASA story What's
Hitting Earth?
<http://science.nasa.gov/science-news/science-at-nasa/2011/01mar_meteornetwork/>,
he's looking for places to put his cameras; educators are encouraged to
get involved. Networked observations of spring fireballs could
ultimately reveal their origin.

"It might take a few years to collect enough data," he cautions.

Until then, it's a beautiful mystery. Go out and enjoy the night sky. It
/is/ spring, after all.


Author: Dr. Tony Phillips
Credit: Science at NASA
Received on Thu 31 Mar 2011 02:56:33 PM PDT