[meteorite-list] The 2011 Geminid Meteor Shower

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 13 Dec 2011 09:16:05 -0800 (PST)
Message-ID: <201112131716.pBDHG5GX023330_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/science-news/science-at-nasa/2011/13dec_geminids/

The 2011 Geminid Meteor Shower
NASA Science News
December 13, 2011

The 2011 Geminid meteor shower peaks on the night of Dec. 13-14, and
despite the glare of a nearly-full Moon, it might be a good show.

"Observers with clear skies could see as many as 40 Geminids per hour,"
predicts Bill Cooke of the NASA Meteoroid Environment Office. "Our
all-sky network of meteor cameras has captured several early Geminid
fireballs. They were so bright, we could see them despite the moonlight."

The best time to look is between 10 pm local time on Tuesday, Dec. 13,
and sunrise on Wednesday, Dec. 14th. Geminids, which spray out of the
constellation Gemini, can appear anywhere in the sky. "Dress warmly and
look up," says Cooke. "It's that simple."

The source of the Geminids is near-Earth asteroid 3200 Phaethon. Most
meteor showers come from comets, so having an asteroid as a parent makes
the Geminids a bit of an oddball.

"This is the thing I love most about Geminids," says Cooke. "They're so
strange."

Every year in mid-December, Earth runs through a trail of dusty debris
that litters the orbit of 3200 Phaethon. Comets vaporizing in hot
sunlight naturally produce such debris trails, but rocky asteroids like
3200 Phaethon do not. At least they're not supposed to. The incongruity
has baffled researchers since 1983 when 3200 Phaethon was discovered by
NASA's IRAS satellite.

One clue: 3200 Phaethon travels unusually close to the sun. The
asteroid's eccentric orbit brings it well inside the orbit of Mercury
every 1.4 years. The rocky body thus receives a regular blast of solar
heating that might somehow boil jets of dust into the Geminid debris
stream.

In 2009, NASA's STEREO-A spacecraft saw this process at work.
Coronagraphs onboard the solar observatory watched 3200 Phaethon as it
was swinging by the sun. Sure enough, the asteroid doubled in
brightness, probably because it was spewing jets of dust.

"The most likely explanation is that Phaethon ejected dust, perhaps in
response to a break-down of surface rocks (through thermal fracture and
decomposition cracking of hydrated minerals) in the intense heat of the
Sun," wrote UCLA planetary scientists David Jewitt and Jing Li, who
analyzed the data.

Jewett and Li's "rock comet" hypothesis is compelling, but they point
out a problem: The amount of dust 3200 Phaethon ejected during its 2009
sun-encounter added a mere 0.01% to the mass of the Geminid debris
stream--not nearly enough to keep the stream replenished over time.
Perhaps the rock comet was more active in the past ????

"We just don't know," says Cooke. "Every new thing we learn about the
Geminids seems to deepen the mystery."

Led by Cooke, the Meteoroid Environment Office has just released an app
for iPhones and iPads to help citizen scientists count meteors and
report their observations to NASA. The "Meteor Counter" is available for
free from Apple's app store:

http://itunes.apple.com/us/app/meteor-counter/id466896415

Cooke hopes sky watchers everywhere will use it to monitor the
mysterious Geminids.


Author:Dr. Tony Phillips
Production editor: Dr. Tony Phillips
Credit: Science at NASA
Received on Tue 13 Dec 2011 12:16:05 PM PST