Transcript 951 Gaspra
Asteroids, Comets and Meteorites Important Points 1. Small objects in the solar system are leftovers that never accreted into planets 2. Minor planets mostly orbit between Mars and Jupiter 3. Comets formed in the outer solar system and were flung outward by close encounters with other planets 4. Comets can be trapped in the inner solar system by planetary encounters 5. The head and tail of a comet glow from sunlight shining on gases evaporated from the comet 6. Meteors and meteorites are pieces broken off larger bodies by collisions, or dust shed by comets 7. Occasionally comets or minor planets collide with larger objects like the earth Small Bodies of the Solar System • • • • • • Asteroids: within the orbit of Jupiter Centaurs: Between Jupiter and Neptune Kuiper Belt Objects (KBO’s): Beyond Neptune Scattered Disk: Extreme KBO’s Comets: Icy bodies with elongated orbits Meteoroids: Small objects – Meteors: vaporize in Earth’s atmosphere – Meteorites: survive to reach surface 1. Small objects in the solar system are leftovers that never accreted into planets The Bode-Titius Law • • • • • • • The planets have fairly regular spacings Start with 0, 3, 6, 12, 24, 48, 96, 192, 384, 788 Add 4: 4, 7, 10, 16, 28, 52, 100, 196, 388, 792 Divide by 10: 0.4, 0.7, 1.0, 1.6, 2.8, 5.2, 10 … Matches distances of planets in A.U. What’s at 2.8? First Asteroid Discovered, 1801 2. Minor planets mostly orbit between Mars and Jupiter The Bode-Titius Law • Neptune,discovered in 1846, matched the predicted 38.8 value poorly (30.1) • Pluto didn’t match at all (39.5 versus 79.2) • Coincidence? • Or is the Bode-Titius pattern due to the influence of Jupiter and planetary clearing? 2. Minor planets mostly orbit between Mars and Jupiter Other Hypothetical Planets • Vulcan – Hypothetical planet within the orbit of Mercury – Some asteroids and many comets cross the orbit of Mercury, but nothing is known to orbit entirely within the orbit of Mercury • Planet X – Hypothetical massive outer planet beyond Neptune • Nemesis – Hypothetical dwarf star companion to Sun The Asteroid Belt, 2001 The Asteroid Belt, 2010 Asteroid Discoveries Asteroids Year 1 1801 100 1867 500 1902 1,000 1921 2,000 1942 5,000 1972 10,000 1981 20,000 1993 50,000 1999 100,000 2000 200,000 2003 2. Minor planets mostly orbit between Mars and Jupiter 2010 SEPT. 2 • 535789 Minor planets catalogued • 251651 Officially numbered • 16154 Named 2. Minor planets mostly orbit between Mars and Jupiter How We Study Them • Spacecraft • Ground-Based and Hubble Imaging • Radar Imaging 2. Minor planets mostly orbit between Mars and Jupiter Spacecraft Images 2. Minor planets mostly orbit between Mars and Jupiter 951 Gaspra (15 km) 243 Ida (40 km) and Dactyl 253 Mathilde (50 km) Three Asteroids Compared 433 Eros (20 km) Eros Eros 2. Minor planets mostly orbit between Mars and Jupiter Asteroid Itokawa 2. Minor planets mostly orbit between Mars and Jupiter Spacecraft Shadow Earth-Based Optical Imaging 2. Minor planets mostly orbit between Mars and Jupiter 4 Vesta (500 km) Ceres and Vesta Radar Imaging 2. Minor planets mostly orbit between Mars and Jupiter Double Asteroids Comets 3. Comets formed in the outer solar system and were flung outward by close encounters with other planets Types of Comets • Short Period (<200 years) – Record reobserved comet is Comet Ikeya-Zhang (1661-2002) • Long Period (>200 years) – Hale-Bopp (2400 years) – Need a source very far away – Oort Cloud – Too little material very far from the Sun – Flung out by planetary encounters 3. Comets formed in the outer solar system and were flung outward by close encounters with other planets Where Comets Come From • Ice and Frozen Gases – Outer Solar System (Kuiper Belt) • Planetary Encounters perturb Orbits – Diverted inward to become short-period – Diverted outward to Oort Cloud 3. Comets formed in the outer solar system and were flung outward by close encounters with other planets Creation of Long Period Comet 3. Comets formed in the outer solar system and were flung outward by close encounters with other planets Capture of Short Period Comet 4. Comets can be trapped in the inner solar system by planetary encounters Anatomy of a Comet Comet McNaught 2008 Comet McNaught 2008 Record-Breaking Hale-Bopp • • • • Most-observed comet in history Discovered the furthest from the Sun Largest cometary nucleus known Visible to the naked eye for 18 months – twice the previous record • Brighter than magnitude 0 for eight weeks, longer than any other comet in the last thousand years. 5. The head and tail of a comet glow from sunlight shining on gases evaporated from the comet Comet Hale-Bopp 1997 5. The head and tail of a comet glow from sunlight shining on gases evaporated from the comet Halley’s Comet 5. The head and tail of a comet glow from sunlight shining on gases evaporated from the comet Comet Holmes 2007 Comet Borelly Comet Tempel I The Deep Impact Mission A Comet Hits The Sun Meteoroids • Meteoroid – Small object orbiting Sun • Meteor – Meteoroid that becomes incandescent from friction with atmosphere • Bolide or Fireball – Exceptionally brilliant meteor – In impact studies, “bolide” often used for an impacting meteoroid prior to impact • Meteorite – A meteoroid that reaches the surface • Micrometeorite – microscopic meteoroid 6. Meteors and meteorites are pieces broken off larger bodies by collisions, or dust shed by comets Bolide Meteor Showers • Earth passes through streams of orbiting debris • Many linked to orbits of known comets • Occur predictably – Perseids: August – Orionids: October (Halley’s Comet) – Leonids, November • No known falls • Generally 20 or so per hour, rarely 1000’s • Appear to radiate from one point in sky 6. Meteors and meteorites are pieces broken off larger bodies by collisions, or dust shed by comets A Meteor Shower Radiant Meteorites • Stony (95%) – Chondrites: Pellet-like texture – Carbonaceous Chondrites: Most similar to the Sun (minus gases), planetary raw material – Achondrites: Basalt • Stony-Iron (1%) • Nickel-Iron (4%) – Kamacite (>6% Ni) and Taenite (>25% Ni) – Texture revealed by etching 6. Meteors and meteorites are pieces broken off larger bodies by collisions, or dust shed by comets Finding Meteorites • Finds versus Falls – Fall: Observed to fall, then recovered – Find: Identified long after fall – Stony Meteorites weather and are hard to tell from natural rocks – Iron meteorites are more easily recognized • Prime Scientific Collecting Localities – Antarctica – Deserts 6. Meteors and meteorites are pieces broken off larger bodies by collisions, or dust shed by comets Meteorite Peekskill, NY 1992 Chondrite Stony-Iron Meteorite Iron Meteorite Meteo-Wrongs • Meteorites Never: – Have internal cavities – Have layers – Have veins – Flatten on impact – Mold around objects – Almost never light in color outside • If you “think” it’s magnetic, it’s not magnetic 6. Meteors and meteorites are pieces broken off larger bodies by collisions, or dust shed by comets Nope Nope Nope Nope Nope Nope Nope Tektites • • • • Very silica-rich, water poor glassy rocks Terrestrial vs. Extraterrestrial origin? Volcanic vs. Impact origin? Problems: – Odd chemistry – If terrestrial, why are they spread so widely? – If extraterrestrial, why are they so localized? • Now considered impact glass – Atmospheric shock wave evacuates atmosphere 7. Occasionally comets or minor planets collide with larger objects like the earth Tektites Zodiacal Dust Speaking of Zodiacal Bands…. Chancellor Brian May, CBE (Liverpool John Moores University) Take-Away Points 1. Small objects in the solar system are leftovers that never accreted into planets 2. Minor planets mostly orbit between Mars and Jupiter 3. Comets formed in the outer solar system and were flung outward by close encounters with other planets 4. Comets can be trapped in the inner solar system by planetary encounters 5. The head and tail of a comet glow from sunlight shining on gases evaporated from the comet 6. Meteors and meteorites are pieces broken off larger bodies by collisions, or dust shed by comets 7. Occasionally comets or minor planets collide with larger objects like the earth