1. Meteorites, Asteroids, and Comets
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2. Meteorites Meteoroid = small body in space Distinguish between:
Meteoroid = small body in space
Distinguish between:
Meteor = meteoroid colliding with Earth and producing a visible light trace in the sky
Meteorite = meteor that survives the plunge through the atmosphere to strike the ground
The small pieces from the comet’s nucleus spread out into a loose group within the original orbit of the comer. These pieces of dust and rock, along with those derived from other sources are called meteoroids.
A meteoroid that burns up in Earth’s atmosphere is called a meteor. A meteoroid that doesn’t burn up and strikes the earth is a meteorite.

3. Meteoroids, Meteors and Meteorites
Meteoroids are small rocky bodies that travel through space.
A meteor is a bright streak that results from a meteoroid burns up in Earth’s atmosphere, what we call shooting stars.
A meteorite is a meteoroid that reaches the Earth’s surface without burning up.

4. Three Types of Meteorites
Stony- Rocky material
Metallic- Iron and Nickel
Stony Metallic- Rocky material, iron and nickel
Just for their information

5. Stony Meteorites
Rocky material

6. Metallic Meteorite
iron and nickel

7. Stony-Iron Meteorite
rocky material, iron and nickel

8. A fragment of the meteorite that created Meteorite Crater.
Metallic Meteorite

9. Sizes from microscopic dust to a few centimeters.
Meteorites
Sizes from microscopic dust to a few centimeters.
About 2 meteorites large enough to produce visible impacts strike the Earth every day.
Statistically, one meteorite is expected to strike a building somewhere on Earth every 16 months.
Typically impact onto the atmosphere with 10 – 30 km/s (≈ 30 times faster than a rifle bullet).

10. Meteor Showers
Most meteors appear in showers, peaking periodically at specific dates of the year.

11. Meteoroid Orbits
Meteoroids contributing to a meteor shower are debris particles, orbiting in the path of a comet.
Spread out all along the orbit of the comet.
Comet may still exist or have been destroyed.
Only few sporadic meteors are not associated with comet orbits.

12. Radiants of Meteor Showers
Tracing the tracks of meteors in a shower backwards, they appear to come from a common origin, the radiant.
↔ Common direction of motion through space.
The Perseid Meteor Shower

13. The Leonid Meteor Shower in 2002
The Leonid Meteor Shower in 2002

14. Meteorite Crater-Winslow, Arizona
This crater was formed approximately 50,000 years ago when an iron mass, estimated to be about 80 feet in diameter and weighing over 60,000 tons entered the Earth's atmosphere over the American Southwest. The resulting formation is about 4,000 feet (1,200 meters) wide and 570 feet (175 meters) deep.

15. Meteorite Impacts on Earth
Over 150 impact craters found on Earth.
Famous example: Barringer Crater near Flagstaff, AZ:
Formed ~ 50,000 years ago by a meteorite of ~ 80 – 100 m diameter

16. Weird Science!
In 1954, Mrs. Hodge, of Alabama was struck by a meteorite as she was taking
her afternoon nap. Bruised , but not badly injured, she is one of only two people known to have been struck by a meteorite.

17. Asteroids
Asteroids are small rocky bodies that revolve around the sun.
They range in size from a few meters to more than 900 kilometers in diameter.
Asteroids have irregular shapes, but some are spherical, or round.
Most asteroids orbit the sun in asteroid belt.
The asteroid belt orbits between Mars and Jupiter.
Asteroids are thought to be left over from the formation of the solar system.
Why located in asteroid belt? The gravity of Jupiter might have kept a planet from forming in the area where the asteroid belt is located now.

18. Asteroids
Last remains of planetesimals that built the planets 4.6 billion years ago!

19. The Asteroid Belt
Most asteroids orbit the sun in a wide zone between the orbits of Mars and Jupiter.
Mars
Jupiter
Pluto
Uranus
Saturn
Neptune
(Distances and times reproduced to scale)

21. Sizes and shapes of the largest asteroids, compared to the moon
The Asteroid Belt
Small, irregular objects, mostly in the apparent gap between the orbits of Mars and Jupiter.
Thousands of asteroids with accurately determined orbits are known today.
Sizes and shapes of the largest asteroids, compared to the moon

22. There are several gaps where no asteroids are found:
Kirkwood Gaps
The asteroid orbits are not evenly distributed throughout the asteroid belt between Mars and Jupiter.
There are several gaps where no asteroids are found:
Kirkwood gaps
These correspond to resonances of the orbits with the orbit of Jupiter.
Example:
2:3 resonance

23. Non-Belt Asteroids Not all asteroids orbit within the asteroid belt.
Not all asteroids orbit within the asteroid belt.
Apollo-Amor Objects:
Trojans: Sharing stable orbits along the orbit of Jupiter.
Asteroids with elliptical orbits, reaching into the inner solar system.
Some potentially colliding with Mars or Earth.

24. Please pick up your transmitter and swipe your ID

25. SPI:
Use data to draw conclusions about the major components of the universe.
Turn in textbook to page 216

26. I Can: Describe how comets change as they approach the Sun.
Explain that objects from space sometimes impact Earth.

27. Comet Ikeya-Seki in the dawn sky in 1965
Comets
Comet Ikeya-Seki in the dawn sky in 1965

28. Weird Science
In 1908, an object thought to be a comet about 60 m in diameter exploded less than 10 km above a remote part of Siberia. The blast flattened trees in an area greater than 2,000km2 and left no crater.

29. Throughout history, comets have been considered as portants of doom, even until very recently:
Appearances of comet Kohoutek (1973), Halley (1986), and Hale-Bopp (1997) caused great concern among superstitious.
Comet Hyakutake in 1996

30. Comets
A comet is a small body of ice, rock and cosmic dust loosely packed together.
Scientists refer to them as dirty snowballs.

31. Gas and Dust Tails of Comet Mrkos in 1957

33. Comet Hale-Bopp in 1997

34. Fragmentation of Comet Nuclei
Comet nuclei are very fragile and are easily fragmented.
Animation 1
Animation 2
Comet Shoemaker-Levy was disrupted by tidal forces of Jupiter
Two chains of impact craters on Earth’s moon and on Jupiter’s moon Callisto may have been caused by fragments of a comet.

35. Only small rocky fragments remained.
Fragmenting Comets
Comet Linear apparently completely vaporized during its sun passage in 2000.
Only small rocky fragments remained.

36. The comet's tail gets bigger as it gets closer to the sun and then decreases as it moves away from the sun.

37. Parts of a Comet
When they are near the Sun and active, comets have several distinct parts:
Nucleus: relatively solid and stable, mostly ice and gas with a small amount of dust and other solids;
Coma: dense cloud of water, carbon dioxide and other neutral gases
Hydrogen cloud: huge (millions of km in diameter) but very sparse envelope of neutral hydrogen;
Dust tail: up to 10 million km long composed of smoke-sized dust particles driven off the nucleus by escaping gases; this is the most prominent part of a comet to the unaided eye;
Ion tail: consists of electrically charged particles called ions. It produces rays and streamers caused by interactions with the solar wind.
They do not have a tail until they get near the Sun when they warm up.

38. Two Types of Tails
Ion tail: Ionized gas pushed away from the comet by the solar wind. Pointing straight away from the sun.
Dust tail: Dust set free from vaporizing ice in the comet; carried away from the comet by the sun’s radiation pressure. Lagging behind the comet along its trajectory

39. Comets Facts A comets ion tail always points away from the sun.
Solar winds blow the ion tail away from the sun.
The dust tail follows the comet’s orbit and do not always point away from the sun.
Scientists believe that comets come from the Oort Cloud, a region that surrounds the solar system.
Comets can also come from the Kuiper Belt which exists outside of Neptune’s orbit.

40. Comet’s Orbit Comets orbit the Sun in highly elliptical orbits.
Their velocity increases greatly when they are near the Sun and slows down at the far reaches of the orbit.
Since the comet is light only when it is near the Sun (and is it vaporizing), comets are dark (virtually invisible) throughout most of their orbit.
The solar wind pushes the tail away from the Sun.

41. Comet facts continue:
A comet develops a coma because of heat from the sun.
The comet develops a tail because of the solar wind.
After a comet has made several trips around the Sun-the heat from the Sun vaporizes most of the frozen ice and the remaining small particles spread out in the orbit of the comet.

42. The Geology of Comet Nuclei
Comet nuclei contain ices of water, carbon dioxide, methane, ammonia, etc.
(Materials that should have condensed from the outer solar nebula).
Not solid ice balls, but fluffy material with significant amounts of empty space.
“Dirty snowballs”

43. Shoemaker-Levy Comet
On 1994 July 16-22, over twenty fragments of comet Shoemaker-Levy 9 collided with the planet Jupiter.
The comet, discovered the previous year by astronomers Carolyn and Eugene Shoemaker and David Levy, was observed by astronomers at hundreds of observatories around the world as it crashed into Jupiter's southern hemisphere.

45. The Deep Impact Mission
Video 1
Video 2
Placing a probe into the path of Comet Tempel 1 and documenting the result of the impact
Impact: July 4, 2005

46. Comets are believed to originate in the Oort cloud:
The Origin of Comets
Comets are believed to originate in the Oort cloud:
Spherical cloud of several trillion icy bodies, ~ 10,000 – 100,000 AU from the sun.
Gravitational influence of occasional passing stars may perturb some orbits and draw them towards the inner solar system.
40,000 – 100,000 AU
Interactions with planets may perturb orbits further, capturing comets in short-period orbits.
Oort Cloud

47. The Kuiper Belt
Second source of small, icy bodies in the outer solar system:
Kuiper Belt, at ~ 30 – 100 AU from the sun.
Pluto and Charon may be captured Kuiper-Belt objects.

48. Beyond the Solar System