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Episode
2: with guest Peter Jenniskens of the SETI Institute |
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In this episode, we explore those things that go "flash" in the night sky -- and often are romantically called "shooting stars". In reality, of course, they're not stars but "meteors". Now, meteors are not part of our weather, as people used to think, but are usually caused by pieces of rock that arrive from space at incredibly high speeds and collide violently with the air. These meteoroids can be as small as a grain of sand all the way up to a good-sized boulder and often come from streams of dust particles created by comets as they travel around the Sun. We'll also discuss other forms of cosmic debris, such as asteroids. |
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Listen (mp3, 10.9 MB) |
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Download Transcript (pdf) |
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Written and narrated by Carolyn Collins Petersen
Original music by Geodesium
Produced by the Astronomical Society of the Pacific
Web page materials by Andrew Fraknoi
Special thanks to Dr. Peter H. Jenniskens for his input on the script, and to Dr. Seth Shostak for audio recording assistance at SETI Institute.
Exploring
Cosmic Debris Further:
A Collection of Activities and Resources to Get Behind the Headlines
Andrew
Fraknoi (Foothill College & ASP)
June 2009
Here are some materials for informal science educators (and their audiences) to delve more deeply into the topics discussed in this month's "Astronomy Behind the Headlines" podcast. This month's topic concerns what astronomers like to call "cosmic debris" -- the smaller chunks of material in space left over from the formation of our solar system -- and how they interact with observers on Earth. We'll look at five topics inspired by Dr. Jenniskens' comments: meteors (shooting stars) and meteor showers; meteorites; comets, asteroids, and hybrid objects; and the discovery of the fragments of asteroid 2008TC3.
For more detailed information, see Dr. Jenniskens' recent book: Meteor Showers and Their Parent Comets (2008, Cambridge University Press) available in both hardcover and paperback. Here we will restrict ourselves to materials that are accessible on the Web with the click of a few keys.
C. Comets, Asteroids, and Hybrid Objects
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Painting
(with some artistic license) of a very strong meteor shower
in 1833. |
When a smaller chunk of cosmic material hits the Earth's atmosphere and burns up, the flash of light we see from it is called a meteor. When the Earth in its orbit encounters a stream of debris loosened by repeated passes of a returning comet, we get a good number of meteors at the same time and have a meteor shower.
Astronomy Magazine's Meteor and Meteor Shower Page: http://www.astronomy.com/asy/default.aspx?c=a&id=2109
Meteor
Background Information from NASA Ames' Leonids Site:
http://leonid.arc.nasa.gov/meteor.html
Meteor
Showers Online by Gary Kronk:
http://meteorshowersonline.com/
Sky
& Telescope magazine articles on meteor observing:
http://www.skyandtelescope.com/observing/objects/meteors
Space.com's
Meteor Top Page:
http://www.space.com/meteors/
The
American Meteor Society (for serious observers):
http://www.amsmeteors.org/index.html
The
International Meteor Organization (for serious observers):
http://www.imo.net/
Observing and Photographing Meteor Showers (Planetary Society): http://www.planetary.org/explore/kids/activities/meteor_showers.html
Topics for Classroom Discussion from the Kansas Meteorite Museum: http://www.wviz.org/cms_images/education/newsdepth/lessons/Kansas_Meteorite_Museum.pdf
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A
fragment of the 1969 Murchison Meteorite in a museum in Washington
DC (Art Bromage). |
When a chunk of cosmic material survives its fall through the Earth's atmosphere and lands on our planet's surface, scientists call it a meteorite. Unless a meteorite is found in an unusual location (for example in the middle of an ice field in the Antarctic), it can be hard to tell a cosmic piece of rock from one that belongs to the Earth. Many Earth rocks are brought to museums as possible meteorites, but turn out to be terrestrial -- scientists refer to these as meteor-wrongs instead of meteorites. But a real meteorite can be very valuable, since its composition can tell us more about the original chemical makeup of the "mother cloud" that gave birth to the solar system.
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A
meteorite on exhibit in China. |
About
Meteorites (British and Irish Meteorite Society):
http://www.bimsociety.org/meteorites1.shtml
Meteorites
and their Properties (by David Kring, University of Arizona):
http://meteorites.lpl.arizona.edu/
Meteorites
that Have Struck Human Structures or People:
http://imca.repetti.net/metinfo/metstruck.html
Meteorites
from Mars (a listing and links from the Jet Propulsion Lab):
http://www2.jpl.nasa.gov/snc/
The
Meteoritical Society (more technical):
http://www.meteoriticalsociety.org/
Exploring
Meteorite Mysteries NASA Activity Guide:
http://ares.jsc.nasa.gov/Education/Activities/ExpMetMys/ExpmetMys.htm
Collecting
Micrometeorites (NASA):
http://education.jpl.nasa.gov/educators/micromet.html
C. Comets, Asteroids, and Hybrid Objects
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The
asteroid Ida with its moon Dactyl, as captured by the Galileo
spacecraft (NASA). |
Astronomers have divided the "debris" they find among the planets into two categories: the rocky pieces are called asteroids and the icy chunks are called comets. But more recently, it has become clear that asteroids can have ice on them and that comets can have quite a bit of rocky materials within. Objects that combine features of comets and asteroids (for example, having a comet-like orbit but being made mostly of rock) have been called Centaurs, after the mythological creatures who were half human and half horse. (Note that in this brief overview, we will not include web sites about asteroid and comet impacts on the Earth; those are likely to be a separate Astronomy Behind the Headlines feature in the future.)
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Painting
of Comet Donati in 1858. |
Dawn
Mission to the Largest Asteroids:
http://dawn.jpl.nasa.gov/
Introduction
to Comets (by Don Yeomans):
http://www.nasa.gov/worldbook/comet_worldbook.html
Missions
to Comets:
http://solarsystem.nasa.gov/missions/profile.cfm?Sort=Target&Target=Comets&Era=Past
Quick
Fact Sheet on Asteroids:
http://nssdc.gsfc.nasa.gov/planetary/text/asteroids.txt
Comet
Observing Articles from Sky & Telescope Magazine (for
serious observers):
http://www.skyandtelescope.com/observing/objects/comets
Cometography
(a site by Gary Kronk that list current and past comets of note
and has lots of detailed information):
http://cometography.com/
Centaurs
Wikipedia page:
http://en.wikipedia.org/wiki/Centaur_(planetoid)
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Comet
Hale-Bopp in 1996. |
Making
a Comet in the Classroom (by Dennis Schatz):
http://www.dennisschatz.org/activities/Make%20a%20Comet.pdf
Rocks
and Ice in the Solar System IYA Activities Kit (from the Night Sky
Network):
http://nightsky.jpl.nasa.gov/download-view.cfm?Doc_ID=307
Stardust
Mission (NASA) Comet Activities:
http://stardust.jpl.nasa.gov/classroom/guides.html
Vegetable
Light Curves (NASA Dawn Mission: making a graph of the brightness
of a potato to show how astronomers make light curves to explore
the surfaces of asteroids):
http://dawn.jpl.nasa.gov/DawnClassrooms/light_curves/TG_Vegetable.pdf
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The
discovery of fragments of 2008TC3 (SETI Institute). |
On October 6, 2008, astronomers found a small asteroid headed for the Earth, and it hit us the next day, exploding about 37 km above the ground. We were able to track it so well that the fragments were recovered in Sudan by a team led by Peter Jenniskens. 280 fragments were found after several trips into the Nubian Desert. This was the first example of a chunk of cosmic material that was both seen coming in and found on the ground after it crashed.
Kelly Beatty's March 2009 blog for Sky & Telescope: http://www.skyandtelescope.com/community/skyblog/newsblog/41873107.html
The
story by Seth Shostak (SETI Institute):
http://www.seti.org/Page.aspx?pid=1281
The
early story of 2008 TC3 as of October 2008 (by Emily Lakdawalla
of the Planetary Society):
http://www.planetary.org/blog/article/00001684/
NASA's
album of images:
http://www.nasa.gov/topics/solarsystem/tc3/index.html