發信人: harry901.bbs@ptt.cc (哈利) 看板: astronomy
標  題: [新聞] Comet ISON Meteor Shower
發信站: 批踢踢實業 (2013/07/06 Sat 23:35:42)

http://science.nasa.gov/science-news/science-at-nasa/2013/19apr_isonids/
(大意:C/2012 S1 ISON彗星將有可能帶來2014年01月12日流星雨)

April 19, 2013: Anticipation is building as Comet ISON plunges into the inner
solar system for a close encounter with the sun in November 2013. Blasted at
point-blank range by solar radiation, the sungrazer will likely become one of
the finest comets in many years.

When NASA's Swift spacecraft observed the comet in January 2013, it was still
near the orbit of Jupiter, but already very active. More than 112,000 pounds
of dust were spewing from the comet's nucleus every minute.

It turns out, some of that dust might end up on Earth.

Veteran meteor researcher Paul Wiegert of the University of Western Ontario 
has been using a computer to model the trajectory of dust ejected by Comet 
ISON, and his findings suggest that an unusual meteor shower could be in the 
offing.

"For several days around January 12, 2014, Earth will pass through a stream 
of fine-grained debris from Comet ISON," says Wiegert. "The resulting shower 
could have some interesting properties. 

Auroras Underfoot (signup)According to Wiegert's computer models, the debris
stream is populated with extremely tiny grains of dust, no more than a few
microns wide, pushed toward Earth by the gentle radiation pressure of the
sun. They will be hitting at a speed of 56 km/s or 125,000 mph. Because the
particles are so small, Earth’s upper atmosphere will rapidly slow them to a
stop.

"Instead of burning up in a flash of light, they will drift gently down to
the Earth below," he says.

Don’t expect to notice. The invisible rain of comet dust, if it occurs,
would be very slow. It can take months or even years for fine dust to settle
out of the high atmosphere.

While the dust is “up there,” it could produce noctilucent clouds (NLCs).

ISONids (model, 200px)
Paul Wiegert's model of the Comet ISON debris stream: AVI movieNLCs are icy
clouds that glow electric-blue as they float more than 80 km above Earth's
poles. Recent data from NASA's AIM spacecraft suggests that NLCs are seeded
by space dust. Tiny meteoroids act as nucleating points where water molecules
gather; the resulting ice crystals assemble into clouds at the edge of space
itself.

This is still speculative, but Comet ISON could provide the seeds for a
noctilucent display. Electric-blue ripples over Earth's polar regions might
be the only visible sign that a shower is underway.

Wiegert notes another curiosity: "The shower is going to hit our planet from
two directions at once."

When Earth passes through the debris stream, we will encounter two
populations of comet dust. One swarm of dust will be following the Comet ISON
into the sun. Another swarm will be moving in the opposite direction, pushed
away from the sun by solar radiation pressure. The streams will pepper
opposite sides of Earth simultaneously.

"In my experience, this kind of double whammy is unprecedented," says Wiegert.

Bill Cooke, lead scientist at NASA's Meteoroid Environment Office, says
there's little danger to Earth-orbiting spacecraft. "These particles are just
too small to penetrate the walls of our satellites, and they don't stand a
chance against the heavy shielding of the ISS." However, he adds, mission
operators will be alert around January 12th for possible anomalies.

Sky watchers should probably be alert, too. The odds of seeing anything are
low, but Comet ISON could prove full of surprises.


--
因為好奇也順便問一下好了
有那麼剛好的事情嗎?  大彗星+流星雨?

--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 111.243.222.107
※ 編輯: harry901        來自: 111.243.222.107      (07/06 23:19)
推 jses1:原文推論雖然ISON會帶來許多塵埃 但它們的大小都小如米粒     07/06 23:33
→ jses1:因此在剛進入大氣層就燃燒殆盡 發出的光在地表應該看不太到   07/06 23:34
→ jses1:所以不大可能造成流星雨的現象                              07/06 23:35