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Transcript
Let’s explore the mysterious universe
Are you ready?
Comets
Candy Long
Have you seen the comets with your friends before?
Let’s talk about our experience!
Does everyone know
Comets?
Do you know what is
Comet?
Let’s get start it!
Composition
Comets contain dust, ice, carbon dioxide, ammonia,
methane and more.
Some researchers think comets might have originally
brought some of the water and organic molecules to
Earth that now make up lift here.
When they are near the Sun and active,
comets have several distinct parts: nucleus,
coma, hydrogen cloud, dust tail and ion tail.
Comet Life Cycle
-Departure
Some comets are not bound to the sun, on orbits that take them out of the
solar system.
-Extinction
Comets lose ice and dust each time they come near the sun, leaving behind
trails of debris. Eventually, they can lose all their ices, with some turning into
fragile, inactive objects similar to asteroids.
-Breakup
Other comets, upon losing all their ices, break up and dissipate into clouds of
dust.
-Collisions
The orbits comets take sometimes end with them colliding with planets and
their moons. Many impact craters seen in the solar system were caused by such
collisions.
Physical Characteristics
The solid nucleus or core of a comet consists
mostly of ice and dust coated with dark organic
material, with the ice composed mainly of frozen
water but perhaps other frozen substances as
well, such as ammonia, carbon dioxide, carbon
monoxide and methane. The nucleus might have a
small rocky core.
Orbital Characteristics
Asteroids classify comets based on the durations of their
orbits around the sun. Short-period comets need roughly 200
years or less to complete one orbit, long-period comets take
more than 200 years, and single-apparition comets are not
bound to the sun, on orbits that take them out of the solar
system. Recently, scientist have also discovered comets in the
main asteroid belt — these main-belt comets might be a key
source of water for the inner terrestrial planets.
History
In antiquity, comets inspired both
awe and alarm, "hairy stars" resembling
fiery swords that appeared unpredictably
in the sky. Often, comets seemed to be
omens of doom — the most ancient
known mythology, the Babylonian "Epic
of Gilgamesh," described fire, brimstone,
and flood with the arrival of a comet,
and Emperor Nero of Rome saved
himself from the "curse of the comet" by
having all possible successors to his
throne executed. This fear was not just
limited to the distant past — in 1910,
people in Chicago sealed their windows
to protect themselves from what they
thought was the comet’s poisonous tail.
For centuries, scientists thought comets
traveled in the Earth's atmosphere, but
in 1577, observations made by Danish
astronomer Tycho Brahe revealed they
actually traveled far beyond the moon.
Isaac Newton later discovered that
comets move in elliptical, oval-shaped
orbits around the Sun, and correctly
predicted that they could return again
and again.
A number of recent missions have
ventured to comets. NASA's Deep
Impact collided an impactor into Comet
Tempel 1 in 2005 and recorded the
dramatic explosion that revealed the
interior composition and structure of
the nucleus. In 2009, NASA announced
samples the Stardust mission returned
from Comet Wild 2 revealed a building
block of life. The European Space
Agency's Rosetta is scheduled to orbit
Comet Churyumov-Gerasimenko in
2014 and deploy a probe to make the
first landing on a comet.
If you want to learn more,
you can go to this
website:
http://www.space.com/5
3-comets-formationdiscovery-andexploration.html
10 Need-to-Know Things About Comets:
1. If the sun were as tall as a typical front door, Earth would be the size of a nickel, dwarf planet Pluto would
be the size of a head of a pin and the largest Kuiper Belt comet (about 100 km across, which is about one
twentieth the size of Pluto) would only be about the size of a grain of dust.
• Short-period comets (comets that orbit the sun in less than 200 years) reside in the icy region known as the
Kuiper Belt beyond the orbit of Neptune from about 30 to 55 AU. Long-period comets (comets with long,
unpredictable orbits) originate in the far-off reaches of the Oort Cloud, which is five thousand to 100 thousand
AUs from the sun.
• Days on comets vary. One day on comet Halley varies between 2.2 to 7.4 Earth days (the time it takes for
comet Halley to rotate or spin once). Comet Halley makes a complete orbit around the sun (a year in this
comet's time) in 76 Earth years.
• Comets are cosmic snowballs of frozen gases, rock and dust.
• A comet warms up as it nears the sun and develops an atmosphere, or coma. The coma may be hundreds
of thousands of kilometers in diameter.
• Comets do not have moons.
• Comets do not have rings.
• More than 20 missions have explored comets from a variety of viewpoints.
• Comets may not be able to support life themselves, but they may have brought water and organic
compounds -- the building blocks of life -- through collisions with Earth and other bodies in our solar system.
Comet Halley makes an appearance in the Bayeux Tapestry from the year 1066, which chronicles the overthrow
of King Harold by William the Conqueror at the Battle of Hastings.
Famous Comets
Halley's Comet is likely the most famous comet in the world, even
depicted in the Bayeux Tapestry that chronicled the Battle of Hastings of 1066.
It becomes visible to the naked eye every 76 years when it nears the sun.
When Halley's Comet zoomed near Earth in 1986, five spacecraft flew past it
and gathered unprecedented details, coming close enough to study
its nucleus, which is normally concealed by the comet's coma. The roughly
potato-shaped, nine-mile-long (15 km) contains equal part ice and dust, with
some 80 percent of the ice made of water and about 15 percent of it consisting
of frozen carbon monoxide. Researchers believe other comets are chemically
similar to Halley's Comet. The nucleus of Halley's Comet was unexpectedly
extremely dark black — its surface, and perhaps those of most others, is
apparently covered with a black crust of dust over most of the ice, and it only
releases gas when holes in this crust expose ice to the sun.
Learn more
RELATED: See Asteroid Facts our overview of
Solar System Facts or learn more about the
Solar System Planets.
Video
http://www.space.com/17980-cometsfrozen-seeds-of-life-from-beyond-thesolar-system-video.html