Unit 8: Small Bodies around our Sun

1. Unit 8: Small Bodies around our Sun Mr. Ross Brown Brooklyn School for Law and Technology

2. In this unit we will learn about: • The different types of small bodies in our Solar System • Meteorites and their origins • Asteroids and dwarf planets • Comets, their orbits, and their structures • Results of collisions of these bodies with the Earth • The impact on Earth 65 millions years ago and how it led to the demise of the dinosaurs

3. What small objects also orbit our Sun? • 2 February 2016 • Do now: Why do we find so few meteorites here on Earth?

4. What happens when meteors approach the Earth? • Meteor: a streak in the night sky made by friction of a solid body passing through Earth’s atmosphere; a shooting star • Meteoroid: the solid body • Meteorite: if it reaches the Earth

5. What happens when meteors approach the Earth? • As meteoroids enter our atmosphere they encounter friction • 10-40 km/ second • Air resistance also slows them, so they can land

6. What types of meteorites are there? • Stony – silicates • Composed of grains of rock (chondrules) stuck together, thus called Chondrites • Carbonaceous chondrites: chondrites in carbon-rich substance, contains amino acids

7. What types of meteorites are there? • Achondrites(without chondrites) • Iron: show crystals, indicating they cooled over millions of years • Stony-iron: rare combination, perhaps from mantle-core boundary of exploding asteroid

8. What makes an asteroid “an asteroid?” • 3 February 2016 • Do now: Where did all those asteroids come from?

9. What makes an asteroid “an asteroid?” • Asteroids: small, rocky bodies 2-4 AU from the Sun • Aster: Greek for “star” • Bode’s Law predicted a planet at 2.8 AU • More than 100,000 found, but less than 1/1000 Earth’s mass • Ceres is largest

10. Bode’s Law

11. What makes an asteroid “an asteroid?”

12. What makes an asteroid “an asteroid?” • Ceres has enough mass to produce gravity to make it a sphere; considered a dwarf planet • Most are irregularly shaped Eros Itokawa Vesta compared to other asteroids

13. Ceres

14. What makes an asteroid “an asteroid?” • Many are iron or silicate but not all are solid • Loose rubble held together by gravity • Mathilde density 1.4, Itokawa 1.9

15. What makes an asteroid “an asteroid?” • Composition • Silicate, carbonaceous, or iron-nickel • Inner-belt are mostly silicate-rich • Outer-belt are mostly carbon-rich

16. What makes an asteroid “an asteroid?” • Origins • Solar Nebula Theory • Inner planets silicate based, thus inner asteroids…..

17. Homework #14 • 3 February 2016 • What is the difference between a meteor, a meteoroid, and a meteorite? • What shape are typical asteroids and how do we know? Why does Ceres not have this shape?

18. Aim: What lies beyond Neptune? • 4 February 2016 • Do now: Imagine you are in a rocket ship racing past Neptune. What objects might you encounter? What would these be made of?

19. What happened to Pluto? • Trans-Neptunian Objects (TNOs): very small objects orbiting our Sun beyond Neptune’s orbit • Pluto! • Discovered in 1930 by reviewing photos to identify objects whose position changed

20. Pluto • Named after the god of the underworld • Moon (Charon) discovered in 1978, named after boatman who ferries dead souls across the River Styx to the underworld

21. Pluto • Originally thought to be about Earth-sized • By studying Charon’s orbit  Pluto’s mass • .002 Earth mass, 1/20 Mercury • 1/5 Earth diameter • Density 2.1 • Orbit intersects Neptune’s  is it a planet?

22. What defines a “planet?” • International Astronomical Union (IAU) 2006 stated that a planet: • is in orbit around the Sun, • has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and • has "cleared the neighborhood" around its orbit.

23. Which criterion does Pluto miss?

24. Plutoids • Several hundred other objects kilometers in diameter orbit as far as Pluto • Sedna: 1000 km in diameter, well past Kuiper Belt • Eris: 38-97 AU from Sun, 2400 km in diameter, orbit inclined 44° • Because of these, and its own orbit and size, the International Astronomical Union defined Pluto and other like bodies as dwarf planets • Plutoids: dwarf planets that orbit our Sun

25. Plutoids

26. Plutoid Orbits

27. So, what are all the things in our Solar System?

28. Aim: What are comets? • 9 February 2016 • Do now: Of what are comets made? And from where do they come?

29. What are comets? • Once feared due to their mystery

30. What are comets? • 3 parts • Tail: long, narrow column of dust, can be 100 million km (almost 1 AU) • Coma: cloud of gas, can be 100,000 km diameter (10x Earth) but very little mass • Nucleus: block of frozen ice and gas, about 10 km

31. Comet Halley

32. How do comets’ tails form? • Comets aren’t visible unless within about 5 AU. Sun’s heat vaporizes ices into gases. • Gases blown into an ion tail by solar winds. This points away from the Sun.

33. How do comets’ tails form? • Dust tail: radiation pressure from the Sun pushes the dust coming off the comet.

34. Of what are comets made? • 10 February 2016 • Do now: From where do comets originate?

35. Of what are comets made? • How can we tell the composition of a comet? • Fluorescence: wavelength of reflected light • From dust from comets

36. Of what are comets made? • 2005, NASA Deep Impact mission • Smashed a probe (370 kg) into Comet Tempel 1 @ 10 km/ sec • Comet was made of water, silicates, clays

37. Of what are comets made? • If comets pass too close to the Sun…….? • SOHO Observatory shows dozens each year falling into the Sun

38. Of what are comets made? • Comet origins • Oort Cloud: trillions of icy bodies far beyond Neptune • Surrounds the Solar System

39. Oort Cloud

40. Oort Cloud

41. Of what are comets made? • Kuiper Belt • Begins about Neptune’s orbit, out to ~ 50 AU

42. Of what are comets made? • Oort Cloud comets may take millions of years to orbit the Sun. • Temperatures of 3°K or -454°F.

43. Of what are comets made? • Most comets take millions of years to return • Short-period comets • Less than 200 years • Kuiper Belt may contain more than 30,000 • Can they survive?

44. Homework #15 • 10 February 2016 • Explain the difference between the tail of a meteor and the tail of a comet. Are they made of the same things?

45. What have been the results of giant impacts? • 11 February 2016 • Do now: What would happen if a meteor 10 m in diameter hit the Earth? 100 m? 1 km? 10 km?

46. Meteor Showers • Asteroid fragments entering Earth atmosphere from the same orbit. Appear to come from constellation Perseus, hence Perseid Meteor Shower in mid-August.

47. What have been the results of giant impacts? • This happens every few thousand years! • 100 tons of meteoroids strike Earth every day • Most are smaller and our atmosphere slows them • However……

48. What have been the results of giant impacts? • Scars across our planet • Arizona: 50,000 years ago, 50 meters across • Impact crater 1.2 km across, 200 m deep

49. What have been the results of giant impacts? • 1908, north-central Siberia (Russia) • Trees leveled for 30 km

50. What have been the results of giant impacts? • 65,000,000 years ago • End of Cretaceous Period • Iridium found in sediments