Chapter 12. ASTRONOMY 202 Spring 2007: Solar System Exploration. Class 34: Asteroids and Comets [4/13/07] Announcements. Near-Earth Objects

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1 ASTRONOMY 202 Spring 2007: Solar System Exploration Instructor: Dr. David Alexander Web-site: Class 34: Asteroids and Comets [4/13/07] Announcements Near-Earth Objects Mass Extinctions Chapter 12 Now Playing: Crash and Burn Blues Traveler

2 Announcements Homework HW9 online due Mon Apr 16 Extra-credit discussion paper is available due Apr 20 Web/Observing project due Apr 18 Observing???

3 The Origin of Comets

4 Comets/Asteroids and Life on Earth Germs from Outer Space! Researchers Say Flu Bugs Rain Down from Beyond So say Sir Fred Hoyle and Chandra Wickramasinghe of the University of Cardiff. And while there is much doubt by many other scientists that the flu comes from space, Hoyle and Wickramasinghe are generating a lot of interest with their idea. Matthew Genge, of the Department of Mineralogy at the London Natural History Museum, has estimated that if you live to be 5,000 years old, you'll likely encounter one comet dust particle. Were it to harbor a virus, you would presumably have to inhale the particle, further reducing the odds of infection.

5 Interaction of small and large solar system bodies Over the history of the solar system impacts of small bodies (cometary fragments, asteroids, etc) on the planets and moons have played an important role in planetary geology, shaping the surfaces and providing an early source of internal heat. Collisions are still occurring and now we are more susceptible to their effects than ever.

6 Schoemaker-Levy 9 and Jupiter There is an estimated major impact with Jupiter about once every 1000 yrs. In 1992, Comet Shoemaker-Levy 9 interacted with Jupiter and broke up into several pieces. Astronomers calculated that it would actually hit Jupiter in July Multiple impacts created ring of high clouds Impact scars lasted several months Chain of craters on Callisto provide evidence of similar collision in past

7 Signs of impacts on Earth Barringer Crater, Arizona, 50,000 yrs ago Peekskill, NY, 1992 Tunguska, Siberia, 1908 Chicxulub Crater, Yucatan, 65 million yrs ago

8 Signs of impacts on Earth Manicouagan Lake, Canada, 214 million yrs ago Crater Lake, Oregon Geologists have identified more than 100 impact craters on our planet.

9 Mass Extinctions Some of these impacts have had apparently catastrophic consequences. Energy in a Collision E = ½mv 2 Small meteor mass kg Typical velocity 30 km/s Kinetic energy of meteor: 4.5 x Joules

10 Mass Extinctions While still contentious, it is becoming more and more accepted that the impact of a large meteor with the Earth some 65 million years ago was responsible for killing off 99% of all living organisms. EVIDENCE: Thin layer of dark sediments rich in iridium found around the world at a depth aged at 65 million years. High abundances of other rare metals, evidence for shocked quartz, spherical rock droplets, and soot also found in sedimentary layer. 200km crater of correct age found in Yucatan peninsula, Chicxulub crater. K-T Boundary Layer

11 Mass Extinctions IMPACT shower of hot molten rock Huge tidal wave Forest fires Toxic chemicals Acid rain Long global winter Decades of global warming MASS EXTINCTION There appear to have been at least four other mass extinctions during the past 500 million years

12 Probability of Impact The probability of a large meteor impacting the Earth is relatively small. We expect a 100m impact every 10,000 yrs or so with a mass extinction event every 100 million years. Smaller impacts occur all the time, most notable are the regular meteor showers which occur as Earth passes through cometary debris.

13 Near Earth Objects NASA s Near Earth Object Program ( monitors the skies for potential hazards RECENT CLOSE APPROACHES TO EARTH Object Name Close Approach Date Miss Distance (AU) Miss Distance (LD) Estimated Diameter* Relative Velocity (km/s) (2006 GX2) 2006-Mar m m (2006 FU) 2006-Mar m - 45 m (2003 FK1) 2006-Mar m m (2006 FH36) 2006-Mar m m 5.64 (2000 WG10) 2006-Mar m m 3.78 (2006 DT14) 2006-Mar m m (2006 GU2) 2006-Apr m - 17 m 7.46 (2003 BD44) 2006-Apr km km (2006 EY) 2006-Apr m - 55 m 4.39 (2005 QE30) 2006-Apr m km (2005 QY151) 2006-Apr m km MN 2002-Jun m 10.6km/s 1998 KJ Dec m km/s 1 AU = ~150 million kilometers 1 LD = Lunar Distance = ~384,000 kilometers

14 Near Earth Objects NASA s Near Earth Object Program ( monitors the skies for potential hazards RECENT CLOSE APPROACHES TO EARTH Object Name Close Approach Date Miss Distance (AU) Miss Distance (LD) Estimated Diameter* Relative Velocity (km/s) (2006 VV2) 2007-Mar km km (2007 CQ5) 2007-Apr m m 3.08 (2007 FY20) 2007-Apr m - 65 m 9.32 (2007 EJ88) 2007-Apr m m (2007 EK88) 2007-Apr m m 9.49 (2002 HQ11) 2007-Apr m m (2007 FD3) 2007-Apr m m (2001 HB) 2007-Apr m m (2007 EL88) 2007-Apr m m (2007 FO3) 2007-Apr m - 74 m AU = ~150 million kilometers 1 LD = Lunar Distance = ~384,000 kilometers

15 Near Earth Objects