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(meteorobs) Excerpts from "CCNet 114/2001 - 6 November 2001" [Leonids are coming!]
Is anyone familiar with the ASP Director Jane Houston Jones,
mentioned in item #1 below as an experienced meteor observer?
Clear skies!
Lew Gramer
------- Forwarded Message
From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet 114/2001 - 6 November 2001
Date: Tue, 6 Nov 2001 11:57:03 -0000
CCNet 114/2001 - 6 November 2001
(1) LEONID METEOR SHOWER COULD BE ONE OF BEST IN HISTORY
SpaceDaily, 6 November 2001
(2) SUBARU APPROACHES ORIGIN OF COMETS
Ron Baalke <baalke@zagami.jpl.nasadot gov>
[...]
======================================================================
(1) LEONID METEOR SHOWER COULD BE ONE OF BEST IN HISTORY
>From SpaceDaily, 6 November 2001
http://www.spacer.com/news/leonid-01b.html
San Francisco - Nov 6, 2001
In the wee morning hours of Sunday, November 18, the Leonid meteor shower
might intensify into a dazzling meteor storm, with "shooting stars"
continuously blazing trails across the night sky.
Viewers across the United States are perfectly positioned to take advantage
of the storm, which could be among the most spectacular sky events of the
21st century according to the latest scientific predictions.
The peak in shower activity will occur between 4:00 and 6:00 a.m. EST, or
1:00 and 3:00 a.m. PST on Sunday morning, November 18. "During the peak,
people viewing under clear and dark skies could see meteors shooting across
the sky at a rate of 1,000 to 2,000 per hour, with flurries of one meteor
per second at the peak of the storm," says Robert Naeye, Editor of Mercury
magazine, which is published in San Francisco by the Astronomical Society of
the Pacific (ASP).
During the predicted storm, Earth will plow through a trail of tiny dust
particles left behind by Comet Tempel- Tuttle during its passage through the
inner solar system in the year 1767.
This comet rounds the Sun every 33.25 years, shedding dust particles as it
is warmed by sunlight. Meteor showers occur when Earth passes through debris
left behind by comets. But meteor storms occur when Earth passes through
particularly dense ribbons of comet debris.
"During a typical Leonid meteor shower, an experienced observer might see
about 10 to 15 meteors per hour. But during a storm, that rate climbs to
1,000 or more meteors per hour," says Naeye.
"This year's Leonid storm might peak at a rate of up to 2,000 per hour,
although it's difficult to pin down a precise number. The rates will rise
and fall over a period of two hours."
"Of course, these numbers depend on the accuracy of our predictions. But the
predictions have been remarkably accurate in recent years," says ASP member
Dr. Peter Jenniskens, an astronomer and meteor researcher at the SETI
Institute in Mountain View, California, and author of an in-depth article
about meteor science in the November/December 2001 issue of Mercury
magazine.
This year's Leonid display has two added bonuses. The Moon will rise during
daylight and set six hours before the peak, so the Moon's glare will not
obscure fainter meteors. In addition, the peak will occur on a Sunday
morning, so many people can sleep in after a long night of skygazing.
If one mentally traces back the trajectory of Leonid meteors, they appear to
originate in the constellation Leo (the Lion). Leo rises around midnight, so
the shower will be minimal in the hours immediately after sunset. But it
will pick up considerably as the night progresses.
The entire United States should enjoy a good shower. Peak meteor rates
should occur around 5:00 a.m. EST, 4:00 a.m. CST, 3:00 a.m. MST, and 2:00
a.m. PST. Observers in eastern Asia and the Western Pacific will also enjoy
a storm approximately 8 hours later (in the morning hours of November 19,
local time), according to the forecasts. For the latest predictions for your
local area, visit this website from NASA's Ames Research Center.
Earth will encounter another dense ribbon of Comet Tempel-Tuttle debris in
2002, but under a full Moon. After that, it's over for nearly a century.
"It's now or never," stresses Naeye.
"People should take advantage of this year's Leonid storm, because
astronomers don't think we'll see another storm like this one until the
year 2099. We will probably never see a better meteor shower in our
lifetimes."
When you see meteors, popularly known as "shooting stars," you're seeing
interplanetary dust particles burning up in the atmosphere at altitudes of
about 60 to 70 miles. A typical comet dust particle --known as a meteoroid--
is only about the size of a grain of sand or a pebble when it enters the
atmosphere.
Larger chunks of comet debris, perhaps up to the sizes of basketballs,
sometimes light up the sky as they burn up, which are events called
fireballs or bolides. Leonids enter the atmosphere at 160,000 miles per
hour, making them the fastest meteors of the year.
"Shooting stars are for every man, woman, and child to see, and it doesn't
take any special equipment to see them," says Jane Houston Jones, a member
of the ASP Board of Directors and an experienced meteor observer. "Most
Leonid meteors are faint, so you'll see more of them if you are far away
from city light pollution.
"If you can't get to a dark site, then control your own light pollution by
turning out as many lights as you can control. Then sit back in a lawn
chair, bundle up in a blanket, and at a little before midnight local time,
face east. You'll see the backwards question-mark shape of Leo's mane
rising, and that's where the meteors will appear to radiate over the next
few hours."
Meteors are beautiful sky events for skygazers. But for scientists, meteors
are fascinating in their own right. "Meteor science involves more than just
predicting storms. We also want to learn about the meteoroids themselves,
which in turn tell us a great deal about the parent comet," says Jenniskens.
"We also want to learn more how meteors may have brought critical organic
material to Earth, perhaps leading to the origin and prevalence of life on
our planet."
Copyright 2001, SpaceDaily
======================================================================
(2) SUBARU APPROACHES ORIGIN OF COMETS
>From Ron Baalke <baalke@zagami.jpl.nasadot gov>
http://www.subaru.naoj.org/Science/press_release/2001/11/index.html
Subaru Approaches Origin of Comets ---
First Estimate of the Formation Temperature of Ammonia Ice in a Comet
National Astronomical Observatory Of Japan
November 1, 2001
Observations made with the High-Dispersion Spectrograph (HDS) of Subaru
Telescope have, for the first time, allowed astronomers to measure the
formation temperature of ammonia ice in a comet. The temperature of 28 +/- 2
Kelvin (about -245oC or -410oF) suggests that this comet, Comet LINEAR
(C/1999 S4), was formed between the orbits of Saturn and Uranus. These
observations provide us with not only direct evidence of the environment in
which the comet was born, but also establish brand new methods for probing
the origin of comets.
Comet LINEAR was discovered in 1999 by the Lincoln Near Earth Asteroid
Research project (LINEAR), operated by the MIT Lincoln Laboratory. Figure 1
shows two images of Comet LINEAR obtained by
Subaru Telescope in 2000 (see Latest News on July 24th, 2000). A team of
researchers from the National Astronomical Observatory of Japan, the HDS
group, and the Gunma Astronomical Observatory made spectroscopic
observations of Comet LINEAR on July 5th, 2000, during the commissioning
phase of HDS, when the comet was bright.
The team concentrated on the emission lines produced when NH2 molecules
which have been previously excited, lose some energy and emit light at a
series of characteristic wavelengths (Figure 2). Previous studies indicate
that NH2, which consists of one nitrogen and two hydrogen atoms, is produced
when the powerful Solar UV rays free a hydrogen atom from the ammonia (NH3)
gas which is constantly boiling off the comet. The emission lines of the NH2
molecules should therefore contain information on their parent ammonia
molecules.
Molecules like NH2 and NH3 which contain two or three hydrogen atoms are
classified as either "ortho" or "para", depending on whether the quantum
mechanical spins of the hydrogen atoms are aligned or not. The ortho-to-para
ratio strongly depends on the physical environment, and would have been
preserved when the molecules were confined into the icy cometary nuclei. The
observed ratio can therefore reveal the temperature at the time the ice was
formed.
Molecules in the ortho and para states emit radiation at wavelengths which
are very close together, but subtly different due to the differences in
alignment between the spins of the hydrogen atoms. The resolving power of
HDS is high enough to separate these lines and determine how much light is
being emitted by molecules in the ortho and para states. Using code written
by Mr. Hideyo Kawakita of the Gunma Astronomical Observatory, the strengths
of the emission lines from NH2 could be modeled and compared with the
observations to determine the ratio of ortho to para molecules in Comet
LINEAR. Furthermore, the team investigated the ortho-to-para ratio of the
parent NH3 molecules and estimated that the formation temperature of the
ammonia ice to be 28 +/- 2 Kelvin, which suggests that Comet LINEAR was
formed between the orbits of Saturn and Uranus in the primordial Solar
System nebula.
Until now, the formation temperature had only been determined for water ice
in comets, and this is the first time that it has been measured for another
molecule. Dr. Jun-ichi Watanabe of the National Astronomical Observatory of
Japan, and a member of the team who performed this research, says "The brand
new methods using NH2 molecules have great potential for studying the origin
of comets. I have a high expectation for future results obtained by these
methods, especially for short-period comets which are thought to have a
different origin from long-period comets such as Comet LINEAR."
This result has been published in Science, November 2nd, 2001 Issue.
* Figure 1: Two images of Comet LINEAR observed in 2000 with Subaru
Telescope (Latest News on July 24th, 2000)
* Figure 2: A Comparison between the spectrum observed with HDS and the
spectrum simulated with the model calculations.
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