1. The Solar System CHAPTER 15 Vagabonds of the Solar System Asteroids and Comets

2. What led to the discovery of the asteroids Why the asteroids never formed into a planet What asteroids look like How an asteroid led to the demise of the dinosaurs What meteorites tell us about the nature of asteroids What meteorites may reveal about the origin of the solar system What comets are and why they have tails How comets originate from the outer solar system The connection between comets and meteor showers Coming up in this lecture …

3. Asteroids Orbit of Uranus fits the Titius-Bode Law 1800—Baron Xavier von Zach organizes the “Himmelspolizei” to find 2.8 AU planet 1/1/1801—Giuseppi Piazzi discovers the 1st asteroid—Ceres Four largest asteroids, Ceres, Vesta, Pallas, Hygieamake up 1/2 the mass of the belt.

4. Asteroid Belt about 1.5 AU wide with centroid at 2.8 AU!

5. Lagrange Points: L1–L5 • 3 Forces: • Gravitational • Centrifugal • Coriolis • ‘Equipotential’ contours • Gradients: • Away • Toward • Only L4 and L5 are ‘stable’

6. ‘Greeks’ ‘Trojans’

7. The Lagrangian points (L4 and L5) in the Jupiter-Sun planetary system are _____. positions in space at Jupiter's orbital distance from the Sun, where the combined forces of the Sun and Jupiter trap asteroids, called Trojans (and Greeks). points at high latitudes on Jupiter where auroras (called Lagrangian auroras) occur most frequently. areas in the asteroid belt where gravitational interaction of Jupiter with asteroids disturbs their orbits and causes a Kirkwood Gap. locations that would make excellent repositories for Earthling’s nuclear waste according to the French physicist, Joseph Louis de’Lagrange.

10. Asteroids Outside the Belt Notice ‘NEO’s’

11. Trail Accidentally Seen by HST

12. Finding an Asteroid

13. HST Image of Ceres

14. NEAR Spacecraft Image of 253 Mathilde

15. Gaspra First asteroid to be imaged— by Galileo spacecraft(1991)

16. ESO ‘Adaptive Optics’ Image

18. Stony Meteorite w/Fusion Crust

19. A piece of rock from outer space that reaches the Earth's surface after surviving a fiery passage through the Earth's atmosphere is known as a ____. Meteoroid Hemorrhoid Meteorite Deltoid Sigmoid

20. Stony Meteorite w/Iron Flecks

21. Stony Iron Meteorite

22. Iron Meteorite Surface covered w/depressions caused by ablation

23. Iron Meteorite • Cut & polished • Etched w/acid • Reveals ‘Widmanstätten’ pattern • Pattern forms as molten metal cools slowly over millions of years

24. Allende Meteorite • Chihuahua, Mexico 1969 • 4.56 billion yrs old • Carbonaceous chondrite • Contains Mg26

25. The Allende meteorite contained a large abundance of 26Mg, an isotope of magnesium. What is the significance of this? Magnesium has a high melting point, so Allende was a piece of asteroid that must have formed in the inner part of the solar system. The 26Mg in Allende probably became radioactive when it landed near a nuclear reactor in Chihuahua, Mexico. 26Mg is the stable product of the decay of radioactive 26Al. The 26Al parent of 26Mg was probably produced in a nearby supernova explosion whose shock wave might have triggered the formation of our solar system. This discovery suggests that elements such as 26Mg were more abundant in the early Kuiper Belt than we had originally thought.

26. Meteor Strike in NY—1992

28. Barringer(Meteor) Crater

29. The Tunguska Event—1908

30. Artist’s Impression of The Tunguska Event 15 km from Ground Zero—A few minutes after explosion 50 km South of Ground Zero • A 100 kiloton stony asteroid(or comet) entered atmosphere travelling at 22 km/s, or 50,000 mph! • It exploded above Ground Zero , releasing about 60 Hiroshima A-bomb equivalents—or 1 Megaton of TNT!

31. Tunguska Event Because the object exploded up in the atmosphere, instead of hitting the ground, it left no crater. The effect on the ground was limited to devastation of a large forest area. At ground zero, tree branches were stripped, leaving trunks standing up. But at distances from roughly 3 out to 10 miles, the trees were blown over, lying with tops pointed away from the blast. No one was known to have been this close to the blast. The closest humans were probably herders camped in tents roughly 30 km from ground zero. They related: "Early in the morning when everyone was asleep in the tent, it was blown up in the air along with its occupants. Some lost consciousness. When they regained consciousness, they heard a great deal of noise and saw the forest burning around them, much of it devastated." "The ground shook and incredibly prolonged roaring was heard. Everything round about was shrouded in smoke and fog from burning, falling trees. Eventually the noise died away and the wind dropped, but the forest went on burning. Many reindeer rushed away and were lost." One older man at about this distance was reportedly blown about forty feet into a tree, causing a compound fracture of his arm, and he soon died. Hundreds of the herders' reindeer, in the general area around ground zero, were killed. Many campsites and storage huts scattered in the area were destroyed.

32. Iridium-Rich Clay Layer at K-T Boundary

33. Blast Radius of K-T Impact

34. The Impact that Killed the Dinos

35. Chicxulub Crater—Yucatan Landsat radar image

36. Artist’s Impression • 10 km asteroid @ 22 km/sec • 100 million megatons TNT • 50 MT Largest man-made • 1000 MT combined US-Soviet arsenal

41. Frequency of Earth Impacts

42. Energy Released by Impact Russian Impact ~300 Ktons —Feb 15, 2013 A Tunguska Event takes place every several hundred or a thousand yrs ─ takes out New York! Every 100,000 yrs an impact of 8000 megatons causes a nuclear winter! Every 10’s of million years a >2-km global impactor hits releasing a million megatons!

43. Occurrences of Mass Extinctions Marks time of occurrence of major impact

44. Odds of Dying in the U.S. from Selected Causes … 90% of NEO’s have not been discovered!

45. Probability of Death… 1 in 195,249,054 Odds of Winning Powerball

46. Includes the infamous asteroid, 1997XF11, which made a major impact on the world's headlines in March 1997 when observations indicated that it had a good chance of colliding with the Earth in 2028! NEO’s An up to date map of the inner solar system displaying the orbits of the terrestrial planets and the estimated position of thousands of known asteroids. This diagram is missing comets, space probes and the undiscovered asteroids. It is estimated that there are perhaps 100,000 to 1,000,000 undiscovered asteroids on similar Earth crossing orbits. Have a Nice Day!

47. What is the likely connection between the metal iridium and the demise of the Earth's dinosaur population? Iridium, which is found in abundance on Earth's surface, is poisonous to reptiles. Radioactive iridium is found beneath Earth's crust. Meteor impacts during the dinosaur age probably exposed and uncovered enough of it to poison the dinosaurs. Iridium is highly radioactive. Its presence in a geologic layer dating to the dinosaur age suggests that natural radioactivity reached dangerous levels at that time, and the dinosaurs died from overexposure. Iridium is found in meteorites but is rare on the Earth. The existence of a world-wide layer of it suggests a large meteor impact during the dinosaur age. This impact probably triggered global volcanism, raised enough dust to block out sunlight and caused other catastrophes that killed the dinosaurs.

48. Oort Cloud—A Comet ‘Reservoir’

49. Comet Hyakutake 1996

50. Structure of a Comet • Dust tail blown by solar wind • Ion tail blown by solar radiation (sunlight)