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Transcript
Objective
Describe the characteristics of comets, asteroids, and meteors.
The Adventure Is Waiting
(modified from a NASA Activity)
Background Information
Most meteorites are thought to be broken fragments of asteroids — small “planets” or
bodies of rock or ice orbiting around the Sun. The largest asteroid is Vesta, almost 330
miles in diameter, much smaller than our Moon (2,200 miles). The distance from the
Sun ranges from 204,600,000 to 297,600,000 miles.
Ceres was the first asteroid (now dwarf planet) discovered (in 1801), and about 6,000
have been discovered since then. Asteroids are so small that telescopes on Earth can
see them only as points of light.
The Galileo spacecraft passed close to the asteroids Gaspra and Ida and sent us
pictures of them. Both are irregular masses of rock, seemingly broken and covered
with impact craters. As indicated by their colors (reflectance spectra), most asteroids
are mixtures of metal and silicate minerals, possibly like chondrite meteorites. A few
are made of basalt rock, just like the basalt meteorites (example: 1983RD in this
lesson).
Most asteroids orbit in the asteroid belt between 2.2 and 3.2 times the Earth’s distance
from the Sun; their orbits are ellipses, oval-shaped curves that carry them nearer and
farther from the Sun. Only a few asteroids follow orbits that get near the Earth, and
these asteroids are probably the sources of some meteorites. An asteroid that crosses
the Earth’s orbit could collide with the Earth and cause a devastating impact explosion.
About 200 of these Earth-crossing asteroids are known, and it is estimated that 20–40
percent of them will collide with the Earth over the next million years. No known
asteroid will hit the Earth for at least 200 years. We will likely have many years of
warning before an asteroid collision like this. The Earth is really a very small target. But
when there are a million shots, over a long time, one is likely to hit.
To hunt for asteroids, astronomers photograph the night sky and look for “stars” that
move, compared to real stars. A long exposure photograph would show a background
of stars as spots, with a streak from an asteroid, due to the asteroid’s motion across the
sky. To discover the orbit of an asteroid, it is not necessary to observe the asteroid as it
1
Objective
Describe the characteristics of comets, asteroids, and meteors.
follows its whole orbit; knowing its location a few times, over several weeks or
months, is sufficient.
Asteroid Facts
The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo,
the first asteroid of this group to be discovered by Karl Wilhelm Reinmuth. They are
Earth-crosser asteroids. The Apollo asteroids travel just inside Earth’s orbit to 2/3rd
of the way to Mars. Some can get very close to the Earth, making them a potential
threat to our planet.
1862 Apollo was discovered by Karl Reinmuth in 1932, but lost and not recovered
until 1973. It is named after the Greek god Apollo. It is the namesake of the Apollo
asteroids. It was the first asteroid recognized to cross Earth's orbit. It is also a Venusand Mars-crosser asteroid.
Centaurs - The centaurs are an unstable orbital class of minor planets named after
the mythological race of centaurs. The name was chosen because they behave as half
asteroid and half comet. Centaurs have transient orbits that cross or have crossed the
orbits of one or more of the giant planets, and have dynamical lifetimes of a few
million years.
The first centaur-like object to be discovered was 944 Hidalgo in 1920. However, they
were not recognized as a distinct population until the discovery of 2060 Chiron in
1977. The largest known centaur is 10199 Chariklo, discovered in 1997, which at 160
miles in diameter is as big as a mid-sized main-belt asteroid.
Ceres, formal designation 1 Ceres, is the smallest dwarf planet in the Solar System
(since 2006) and the only one in the asteroid belt. It was the first asteroid discovered
on 1 January 1801, by Giuseppe Piazzi, and is named after the Roman goddess Ceres
— the goddess of growing plants, the harvest, and motherly love.
2060 Chiron (keye-ron) is a planetoid in the outer Solar System. Discovered in 1977
by Charles T. Kowal (precovery images have been found as far back as 1895), it was
the first known member of a new class of objects now known as centaurs, with an
orbit between those of Saturn and Uranus.
2
Objective
Describe the characteristics of comets, asteroids, and meteors.
Although it was initially classified as an asteroid, it was later found to exhibit behavior
typical of a comet. Today it is classified as both, and accordingly it is also known by the
cometary designation 95P/Chiron.
Chiron is named after the centaur Chiron in Greek mythology.
433 Eros is the first discovered Near-Earth asteroid (NEA), named after the Greek
god of love, Eros. It is a stony approximately 21 x 7 x 7 miles size, the second-largest
(NEA) after 1036 Ganymed. It is a Mars-crosser asteroid and was the first asteroid that
was known to come within the orbit of Mars.
944 Hidalgo (hi-DAL-goh) is an unusual asteroid, and has the longest orbital period
(13.77 years) of any asteroid in the traditional asteroid belt. It is a Centaur-like
asteroid. (This designation is given to those objects that have orbits between Jupiter
and Neptune.)
It travels from the inner edge of the asteroid belt (251,100,000 miles) out to Saturn's
orbit (887,220,000 miles). Some astronomers suspect that it was once a comet. Its
diameter is estimated to be 24 miles.
3352 McAuliffe is a near Earth asteroid and a Mars-crosser asteroid (asteroid crosses
the orbit of Mars) which was discovered by Norman G. Thomas on February 6, 1981.
It is named in memory of Christa McAuliffe, the civilian teacher astronaut who died in
the 1986 Challenger space shuttle disaster.
2578 Saint-Exupéry is a small main belt asteroid, which was discovered by Tamara M.
Smirnova on November 2, 1975. It is named after Antoine de Saint-Exupéry, the
French aviator and writer. The name is appropriate, as Saint-Exupéry's best-known
character, The Little Prince, lives on an asteroid.
In the book, the little prince's asteroid also has a unique code: B612. 2578 SaintExupéry's provisional designation was 1975 VW3, which is not a match. However,
there is another asteroid called 46610 Bésixdouze, which is French for "B-six-twelve"
(B612 in hexadecimal notation equals 46610).
2266 Tchaikovsky (cheye-cough-ski) (1974 VK) is a main belt asteroid discovered on
November 12, 1974 by L. Chernykh at Nauchnyj. Tchaikovsky wrote pieces like the
1812 Overture, The Nutcracker, and Swan Lake.
3
Objective
Describe the characteristics of comets, asteroids, and meteors.
The Adventure Is Waiting
(modified from a NASA Activity)
Do not write on this sheet of paper!
1. What are most meteorites thought to be?
a. Rocks blown off the Moon.
b. Leftovers in the Kuiper Belt.
c. Broken fragments of asteroids.
d. Leftovers in the Oort Cloud.
2. In what year was Ceres discovered?
a. 1701
b. 1801
c. 1901
d. 2001
3. You can see asteroids without a telescope.
a. True
b. False
4. The asteroids are what shape?
a. Round
b. Irregular
5. The asteroids are between _________________ and _________________ miles
from the Sun. (There are two answers to this question.)
a. 93,000,000 miles
b. 204,600,000 miles
c. 297,600,000 miles
d. 404,200,000 miles
You should not be writing on this sheet of paper!
6. Asteroids that get near the Earth are not sources of some meteorites.
a. True
b. False
7. There are _________ Earth-crossing asteroids.
a. 50
b. 100
c. 150
d. 200
4
Objective
Describe the characteristics of comets, asteroids, and meteors.
8. How do astronomers hunt for asteroids?
a. Space probes are sent to look for them.
b. They look at the same area of the sky every night for a month.
c. They photograph the night sky and look for “stars” that move.
d. They watch one spot of the sky all night.
You still shouldn’t be writing on this sheet of paper!
_____9. 1862 Apollo
_____10. 2060 Chiron
_____11. 2266 Tchaikovsky
A. A group of near-Earth asteroids. These asteroids
are Earth-crossers. Some get very close to Earth.
B. A small main belt asteroid. Named after the
French aviator and writer of the book, The Little
Prince.
_____12. 2578 Saint-Exupèry C. It has the longest orbital period (13.77 years) of
any asteroid in the traditional Asteroid Belt.
_____13. 3352 McAuliffe
D. Main belt asteroid. Named after the composer of
the 1812 Overture, The Nutcracker, and Swan Lake.
_____14.433 Eros
_____15. 944 Hidalgo
_____16. Apollo asteroids
E. Near Earth and a Mars-crosser asteroid. Named
after the civilian teacher astronaut who died in the
Challenger space shuttle disaster.
_____17. Centaurs
F. These asteroids behave as half asteroid and half
comet.
_____18. Ceres
G. This asteroid orbits between Saturn and Uranus.
They are in an unstable orbit.
H. This is the first asteroid discovered on 1 January
1801.
I. This is the first asteroid recognized to cross
Earth’s orbit; it also crosses the orbits of Venus and
Mars.
5
Objective
Describe the characteristics of comets, asteroids, and meteors.
J. This is the first discovered Near-Earth asteroid
(NEA). It is named after the Greek god of love.
The Adventure Is Waiting – Key
(modified from a NASA Activity)
1. What are most meteorites thought to be?
c. Broken fragments of asteroids.
2. In what year was Ceres discovered?
b. 1801
3. You can see asteroids without a telescope.
b. False
4. The asteroids are what shape?
b. Irregular
5. The asteroids are between _________________ and _________________ miles
from the Sun. (There are two answers to this question.)
b. 204,600,000 miles; c. 297,600,000 miles
6. Asteroids that get near the Earth are not sources of some meteorites.
b. False
7. There are _________ Earth-crossing asteroids.
d. 200
6
Objective
Describe the characteristics of comets, asteroids, and meteors.
8. How do astronomers hunt for asteroids?
c. They photograph the night sky and look for “stars” that move.
I 9. 1862 Apollo
G 10. 2060 Chiron
D 11. 2266 Tchaikovsky
B 12. 2578 Saint-Exupèry
E 13. 3352 McAuliffe
J 14.433 Eros
C 15. 944 Hidalgo
A 16. Apollo asteroids
F 17. Centaurs
I 18. Ceres
7
Objective
Describe the characteristics of comets, asteroids, and meteors.
The Adventure Is Waiting – Scoring Guide
1. c
2. b
3. b (2 choices)
4. b (2 choices)
5. b, c
6. b (2 choices)
7. d
8. c
9. I (10 choices)
10. G (10 choices)
11. D (10 choices)
12. B (10 choices)
13. E (10 choices)
14. J (10 choices)
15. C (10 choices)
16. A (10 choices)
17. F (10 choices)
18 I (10 choices)
Scoring
Guide
18 – 4
15-17 – 3
11-14 – 2.5
8-10 – 2
5-7 – 1.5
4–1
1-3 – .5
0–0
8
Objective
Describe the characteristics of comets, asteroids, and meteors.
9