ASTRONOMY 202 Spring 2007: Solar System Exploration Instructor: Dr. David Alexander Web-site: www.ruf.rice.edu/~dalex/astr202_s07 Class 34: Asteroids and Comets [4/13/07] Announcements Near-Earth Objects Mass Extinctions Chapter 12 Now Playing: Crash and Burn Blues Traveler
Announcements Homework HW9 online due Mon Apr 16 Extra-credit discussion paper is available due Apr 20 Web/Observing project due Apr 18 Observing???
The Origin of Comets
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.
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.
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 1994. Multiple impacts created ring of high clouds Impact scars lasted several months Chain of craters on Callisto provide evidence of similar collision in past
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
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.
Mass Extinctions Some of these impacts have had apparently catastrophic consequences. Energy in a Collision E = ½mv 2 Small meteor mass 10 12 kg Typical velocity 30 km/s Kinetic energy of meteor: 4.5 x 10 20 Joules
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
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
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.
Near Earth Objects NASA s Near Earth Object Program (http://neo.jpl.nasa.gov) 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-27 0.1017 39.6 200 m - 450 m 14.37 (2006 FU) 2006-Mar-28 0.0096 3.8 20 m - 45 m 12.31 (2003 FK1) 2006-Mar-29 0.1473 57.3 88 m - 200 m 13.61 (2006 FH36) 2006-Mar-30 0.0298 11.6 70 m - 160 m 5.64 (2000 WG10) 2006-Mar-30 0.1087 42.3 59 m - 130 m 3.78 (2006 DT14) 2006-Mar-31 0.1891 73.6 290 m - 660 m 17.80 (2006 GU2) 2006-Apr-01 0.0067 2.6 7.4 m - 17 m 7.46 (2003 BD44) 2006-Apr-02 0.1821 70.9 1.3 km - 2.8 km 21.10 (2006 EY) 2006-Apr-05 0.0498 19.4 25 m - 55 m 4.39 (2005 QE30) 2006-Apr-08 0.1101 42.9 950 m - 2.1 km 17.65 (2005 QY151) 2006-Apr-12 0.0890 34.7 790 m - 1.8 km 11.97 2002MN 2002-Jun-14 0.0008 0.31 100m 10.6km/s 1998 KJ9 1914-Dec-31 0.0016 0.6 330-750m 21.10 km/s 1 AU = ~150 million kilometers 1 LD = Lunar Distance = ~384,000 kilometers
Near Earth Objects NASA s Near Earth Object Program (http://neo.jpl.nasa.gov) 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-31 0.0226 8.8 1.2 km - 2.7 km 16.96 (2007 CQ5) 2007-Apr-02 0.1175 45.7 100 m - 230 m 3.08 (2007 FY20) 2007-Apr-02 0.0136 5.3 29 m - 65 m 9.32 (2007 EJ88) 2007-Apr-03 0.0791 30.8 56 m - 120 m 22.38 (2007 EK88) 2007-Apr-03 0.1705 66.3 120 m - 270 m 9.49 (2002 HQ11) 2007-Apr-05 0.1602 62.3 410 m - 920 m 19.65 (2007 FD3) 2007-Apr-05 0.1262 49.1 260 m - 570 m 19.62 (2001 HB) 2007-Apr-08 0.1580 61.5 220 m - 490 m 27.45 (2007 EL88) 2007-Apr-09 0.0697 27.1 430 m - 960 m 23.76 (2007 FO3) 2007-Apr-10 0.0526 20.5 33 m - 74 m 7.68 1 AU = ~150 million kilometers 1 LD = Lunar Distance = ~384,000 kilometers
Near Earth Objects