AST, METEORS, COMETS

1. AST, METEORS, COMETS

2. Small Bodies & the Origin of the Solar System 1

3. Unused Spare Parts • Comets, asteroids, and meteors are the unused leftovers from the formation of the solar system. • Their chemical compositions and distribution yield clues as to how the solar system formed. 2

4. Asteroids – rocky leftovers of the inner solar system • Location • Asteroid Belt • Trojan or Lagrange Asteroids • Random Orbits • Types of Asteroids • Minor planets • NEO’s 3

5. Asteroid belt • Generally, just outside Mars’ orbit • 2.7 A.U. average distance • Total mass of all asteroids is <5% of the earth’s mass (2 to 4 of our moons.) 4

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7. Lagrange Asteroids • Clusters of asteroids co-orbit with the gas giant planets, 60o ahead and 60o behind the positions of the planets. • The clusters are centered on the L4 and L5 Lagrange points (points in space where Jupiter’s gravitational influence equals the sun’s gravitation.) • Jupiter’s Lagrange asteroids are known as the Trojan asteroids. 6

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9. Types of Asteroids • S – Stony • C – Carbonaceous (modified stony asteroids with dark surfaces and interiors) • M – Metallic (comparatively rare) 8

10. Stony Asteroids Gaspra – a typical stony asteroid 9

11. Some asteroids are thought to be rubble piles held together by very low gravity. 10

12. Major Asteroids or Dwarf Planets? • Over 200 objects have diameters of >100 km. • Ceres – largest, the size of Texas (1030 km). Named after the Roman goddess of the harvest (cereal). Recently named a dwarf planet. 11

13. We don’t know what the white spot is yet. Rotation of Ceres Best Model 12

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15. Major Asteroids • Vesta – smaller (450 km diameter), but much brighter. Barely visible to naked eye. • Movie of Vesta’s rotation. http://atropos.as.arizona.edu/aiz/teaching/nats102/images/Vesta.mpg • Pallas • Juno 14

16. Vesta shows signs of having been molten at one point in its history. 15

17. NEO’s (Near Earth Objects)and PHA’s (Potentially Hazardous Asteroids) • Hundreds of asteroids cross earth’s orbit ! • Several have approached within 600,000 km of earth (2 times moon’s orbital distance) • Collisions with Earth have occurred in the past 16

18. Barringer Crater in Arizona – from an impact • within the last 50,000 to 100,000 years 17

19. This asteroid has its own little moon ! 18

20. Toutatis – one of the closest ! Toutatis spins on 2 axes. 5 km long. Passed just 29 lunar distancesfrom the earth in 2000. 19

21. Mission to Asteroids • Deep Space 1 flew by asteroid 1992 KD Braille in 1999. • N.E.A.R. took close-up photos of, then landed on asteroid Eros, Feb. 12, 2001. • JAXA Hayabusa visited asteroid Itokawa in 2005. It had a small lander which should have landed on the asteroid, but malfunctioned. 20

22. Asteroid 433 Eros 21

23. NEAR “landing” on Eros. 22

24. Hayabusa - ion propulsion - autonomous navigation - sample return 23

25. Comets – outer S.S. messengers • Structure • Orbits & Types • Oort Cloud vs. Kuiper Belt • Famous Comets • What message do they convey? 24

26. Structure • Nucleus • Water ice, frozen CO2, N2, methane, ammonia, HCN, (CN)2 (cyanogen), amino acids, sugars all detected. • Embedded with rocks and dust • Extremely dark, tarry surface. • Coma • Envelope of water vapor and H2 around nucleus 25

27. Structure (2) • Ion tail – ionized gas pushed directly away from the sun by solar wind. • Dust tail – heavier particles that follow along behind the path of the comet. • The dusty path of a comet lingers for decades, even centuries. When the earth passes through the dusty path again later, a meteor shower is produced. 26

28. Structure Dirty Snowballs 27

29. Nucleus of Halley’s Comet Sunlight causes jets of gas to spew from the comet’s nucleus. This creates the coma. Jets of gas Photo by Giotto spacecraft (ESA) • Dark, tarry organic coating 28

30. Nucleus of Borrelly 29

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33. Direction of comet’s movement • Dust tail • Ion or plasma tail 32

34. Comet Origins & Orbits • Kuiper Belt • Short period comets (return <200 yrs) • 50 to 200 A.U. • Several billion comets • Cometary orbits are more often near the ecliptic, but may be prograde or retrograde. 33

35. Comet Origins & Orbits (2) • Oort Cloud • Long period comets (return >200 years or may only pass by sun once) • Spherical shell of matter up to 2 light years (65,000 A.U.) in radius. • Trillions of comets • Comets may come in from any direction, with prograde or retrograde orbits. 34

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37. Halley (1984) Hale Bopp (’96) Hyakutake (’94) Shoemaker-Levy 9 (‘94) Kohoutek (’75) West (‘75) Famous Comets 36

38. Halley’s comet 1986 37

39. Halley’s Comet Orbit • Many comets have retrograde orbits 38

40. Comet Shoemaker-Levy 9 broke into a series of fragments before impacting Jupiter. The ‘fireball’ from each impact was larger than the earth. 39

41. An atmospheric “scar” left by the impact of Shoemaker-Levy 9. These faded after several weeks. 40

42. Comet Hale Bopp, 2002 41

43. Comet Swan has been visible in our sky the past few weeks. 42

44. Past Missions to Comets • There have been 11 past missions to comets, with 2 current missions. • Giotto – examined Halley’s comet in 1986. Photographed the nucleus from a distance of only 200 km, then continued on to comet Grigg-Skellerup in 1992. 43

45. Past Missions to Comets (2) • Deep Impact – launched a 350 kg copper impactor into the nucleus of comet 9P/Tempel 1, in July, 2005. • A 100 m x 25 m crater was created. • Visible and infrared spectrometers on the parent craft looked for the composition of the nucleus. • 250,000 kg of water vapor were detected. 44

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49. Current Missions to Comets • Stardust – sampled the coma of P Wild 2 from a distance of 236 km above the nucleus. • Returned comet particles back to the earth for microscopic examination and chemical testing. You can help with the microscopic work by signing up at the following website. http://stardust.jpl.nasa.gov/home/index.html 48

50. Stardust inside comet Wild’s coma. 49