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17/08/2014 The Perseid Radiant The Annual Perseid Meteor Shower Professor Michael D Smith University of Kent 2014 Acknowledge: many colleagues, International Meteor Organisation, ESA, NASA The annual Perseid Meteor Shower • Looking north ………. The Perseid Meteor Shower: Fact Sheet Runs annually from July 17 to August 24. • The Perseid Meteor Shower: Fact Sheet Runs annually from July 17 to August 24. • The Perseid Meteor Shower: Fact Sheet Runs annually from July 17 to August 24. Peaks this year on the night of August 12 and the morning of August 13. 1 17/08/2014 • The Perseid Meteor Shower: Fact Sheet Expect to see around 60 -‐ 100 meteors per hour this year. The best viewing will be between the hours of 11pm and 3am. But the peak is between 19:00 on the 12th until 08:00 on the 13th. No guarantee (UT – Universal Time = GMT, BST: +1h) The waning gibbous moon will block out some of the meteors this year, but the Perseids are so bright and numerous that it should still be a good show. Try looking in the opposite direction of sky from the Moon. Meteors will radiate from the constellation Perseus, but can appear anywhere in the sky…….. The Origin Perseids have been observed for at least 2000 years. The first information on them came from the Far East . In the period 1864-1866, Schiaparelli (1871) proved by calculations of the Perseid orbit that this stream shared the orbit of Comet 1862 III (109P/Swift-Tuttle). This was the first proven association between a meteor shower and a comet. It is produced by comet Swift-Tuttle. It is periodic, period 133 years Solid nucleus is about 26 kilometers Currently, orbit is locked into 1:11 resonance with Jupiter Returned in 1737, 1862, 1992 ….. So what are Meteoroids? Meteors? Meteorites? • Small pieces of space debris (usually parts of comets or asteroids) that are on a collision course with the Earth are called meteoroids. • When meteoroids enter the Earth's atmosphere they are called meteors. They are travelling at speeds of up to 60-70 km per second. • If they survive and strike the surface of the Earth they are called meteorites. Meteors – as Shooting Stars • Meteoroids range in size from grains to metre-sized rocks. • Enter Earth’s atmosphere and become meteors or “shooting stars”. • Most meteors are tiny specks of dust. • Larger meteors produce fireballs. Hannover, 1995! Several hundred tons of meteoroids enter the Earth's atmosphere each day (100 million kg/year ). Most are very small pieces (milligrams) that burn up quickly in the atmosphere and never reach the surface. Perseid Shower, 1996! Peekskill, 1992! So what are Meteoroids? Meteors? Meteorites? • The typical size of a meteor that produces a visible streak of light ranges from about the size of a grain of sand to the size of a small pebble. • Average weight is only around 1 gram! • Metre –sized rocks occasionally • Fireballs (large, brilliant meteors) are periodically seen. These may weigh up to several undred kilograms or more. 2 17/08/2014 Meteor Shower Designations • Meteor showers are usually named for the constellation in which their radiant lies at the peak of the shower… Ex.: Perseid shower = Perseus Ex.: Leonid shower = Leo Ex.: Geminid shower = Gemini The Physics. Why do meteors generate a streak of light?? • As they travel through our atmosphere, meteors collide with air molecules. • This knocks away materials and strips electrons from the meteor. • When the stripped atoms recapture electrons, light is emitted. • The colour of the light depends on the temperature and the material being “excited.” 3 Questions… 1. True/False: The material or element that makes up a meteor is the main factor that determines the colour of the glowing trail left behind True 2. This major meteor shower has a peak time around early/mid August: a. Geminids b. Leonids c. Orionids d. Perseids d. Perseids 3. What is the point in the sky from which all of the meteors seem to come during a shower called? Radiant Meteor Showers and Comets • Occur on a regular schedule Some Meteor Showers Name Parent Date of Meteors / Hour Maximum at Max Quadrantids Jan. 4 110 - Perseids Aug. 12 68 Comet 1862 III Orionids Oct. 21 30 Comet Halley Leonids Nov. 17 10 Comet P/Tempel-Tuttle Geminids Dec. 14 58 3200 Phaethon Are all meteors the same colour?? Iron Sodium Calcium The material or element that makes up a meteor is the main factor that determines the color of its glowing trail. -‐ Magnesium Silicon Impact Hazard: Barringer Crater in Arizona Size: 1.2 kilometers across and 200 meters deep Age: formed about 49,000 years ago Cause: impact of a 50 meter nickel/iron meteorite. Speed: traveling at a speed of 11 kilometers per second. 3 17/08/2014 The Asteroid and the Dinosaur WHEN: 65 million years WHERE: what is now Yucatan WHAT: a 10-‐kilometer wide asteroid at an impact speed of 11 km/second RESULTS: (1) threw huge amounts of matter into the atmosphere (2) created the 180 km Chicxulub Crater (3) generating 600 meter waves (emptied the Gulf of Mexico!?). (4) months of darkness interfering with photosynthesis and climate. Stones: Chondrite Meteorites" Contain round grains of minerals." By far the largest number of meteorites - 85% " Similar in composition to asteroids, mantles and crusts of the terrestrial planets." Formed: accretion, thermal processing by a shock wave" (5) extinction of many species, including the last of the dinosaurs. Chondrites: variety Achondrites – Stoney No round chondrules Pallasites and mesosiderites Fe-‐Ni and rock fragments Igneous: core/mantle boundary and mixing of different material Achondrites pes Iron Meteorites" Primarily iron and nickel alloy: easily recognised -‐ Represents the cores of differenCated asteroids -‐ Formed by melCng/crystalizaCon Originate in planetary cores of planetesimals (large ancient asteroids). 4 17/08/2014 Meteorite finds Carbonaceous Chondrites" Desert Finds May contain organic compounds (e.g. amino-‐acids) that EETA79001-Martian may hold keys to how life developed in the Solar System. Antarctic finds ALHA81005 – Martian METEORITES FROM MARS Meteorites and Meteorwrongs • Only 132 found on Earth! Ejected from Mars surface during mega-impact • Trapped gases are identical to those measured by Viking 1 & 2 missions • Fusion crust Magnetism Regmaglypts (ablation dents) Viking missions carried gas chromatography mass spectrometers to analyse soil • Magnetism Chondrules Density Mars to Morocco:Tissint • Fell 18th July 2011 in Morocco pristine! Moon Meteorite ALH84001 • 7kg found after the fall • 1kg is now in London Natural History Museum • Offers a unique insight into the Red Planet 5 17/08/2014 Lunar Meteorites • Discovered in Antarctica 1984 • About 40 found on Earth • Dislodged from Mars about 16 million years ago • All found in hot or cold deserts • Ejected from moon during • Fell to Earth 13,000 years ago • May contain fossil evidence that may indicate that primitive life existed on Mars more than 3.6 billion years ago. Formation of the the Moon • Has less iron than the Earth • Lacks many "volatile elements" • Resemble Earth's mantle • Oxygen isotopes are identical to Earth’s • Moon is made of “earth-‐like” material Several otheheories: – • formation) • Theory: Collision with Mars-‐size body – Theia Binary system (co- – Capture – Fission Comets Dirty snowballs -‐ small objects of ice, gas, impact up to 20 million years ago. • Go into orbit Chemistry and mineralogy identical to Apollo samples • What are meteor showers??? - result when the Earth encounters cometary orbits The annual nature of meteor showers hints to the nature of the orbits of meteoroids. Comet Swift Tuttle goes out to 52 AU and swings in to 0.96 AU, just inside earth’s orbit. Comet Parts dust, tiny traces of organic material Image from http://hubblesite.org/newscenter/archive/releases/2004/52/image/a/ Image credit: K. Jobse, P. Jenniskens and NASA Ames Research http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=9 Image from: http://antwrp.gsfc.nasa.gov/apod/ap000805.html Nucleus, Coma Dust tail – white “smoke” reflects sun. 600,000 to 6 million miles long Ion tail – Solar UV breaks down CO gas, glow blue. 10’s of millions of miles 6 17/08/2014 So why study meteorites? • Unique insights into how the planets formed • Develop theories about the formation of the solar system • Develops the understanding of neighbouring planets • Search for extraterrestial life Rosetta’s 6th August appointment On March 2, 2004, ESA’s Rosetta’s 6th August rendezvous Objectives. Rosetta was launched. It sent footage of Main-‐ Belt asteroid (21) Lutetia on 10 July 2010 h To catch comet 67P/Churyumov-Gerasimenko in 2014 and accompany it into the interior solar system. To deploy Philae in November to make first controlled landing on a comet. Philae will use harpoons to anchor itself to the come New problem: the rubber duck Peekskill, 1992 7