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Comets-Meteor Copy • Comet – km-sized bodies with volatiles & refractories Definitions • Asteroid – small planetary bodies orbiting the Comets & Primitive Bodies sun (mostly refractory) • Meteoroid – small (<< km) extra-terrestrial body orbiting the sun Karen J. Meech, Astronomer • Meteor – meteoroid passing through Earth atm Institute for Astronomy • Meteorite/Fall – meteoroid which hits the ground • Fireball – very bright meteor • Find – meteorite found on ground, not associated with a fall • Parent body – comet or asteroid-like body in which the meteoroid formed Comets Inspire Terror Historical Highlights 1066 Halley Wm conqueror 1456 Halley Excommunicated 1531 Halley Observed by Kepler 1744 De Cheseaux 6 tails 1858 Donati Most beautiful 1811 Flaugergeus comet wine Dutch Woodcut (1668) – “Destruction by 4th century comet” 1861 Tebbutt Naked eye, aurorae 1901 Great S Daytime visibility ! Sudden appearance in sky ! Only a few bright naked-eye comets / century ! Tail physically large " millions of km ! Early composition: toxic chemicals Comet of 1577 McNaught 2007 Recent Historical Comet Halley Great Comets Ikeya-Seki, 1957 Hale Bopp 1995 Hayakutake, 1996 Top: Middle / Bottom: • Babylon 164 BC • Giotto Fresco 1301 • 1145 • Chinese 1378 (Halley - periodic) • Korea - 1222 at • 1531 - Peter Apian tail orientation Chomsongdae Obsty • 1759 - Korean observations Comet Halleys Perception: Science & Fear 1680 Alarm 1910 Alarm Historical The Modern Comet Understanding • Nucleus • Solid body, few km radius • H2O ice + dust + other volatiles: CO, CO2 + ! Tycho Brahe 1577 organics ! Parallax – outside atmosphere • Coma ! Edmund Halley • Gas & dust ! 1531, 1607, 1681 " Orbit • 106 km determination • Tails ! Newton – Principia • Ion tail (blue: CO, CN) ! 1950s – Models • Dust tail (yellow) ! F. L. Whipple " Dirty Snowball ! R. A. Lyttleton " Sandbank ! Resolution: 1986 Giotto Halley mission Phases of Water Phases of Water Freeze Melt Condense Vaporize Sublimate Condense 200 300 400 T [K] 200 300 400 T [K] Cold%Storage:%Oort%Cloud%&%Kuiper%Belt% Physical Processes ! Sublimation of gases – Energy Balance Sunlight " Scattered light + Heating + Sublimation + Conduction Usually very small Energy needed depends on ice Inverse square law: 1/r2 ! Drags dust from nucleus ! Gravity low ! Most dust escapes ! Solar radiation pressure " coma " dust tail ! Photodissociation " fluorescence ! Ionization " gas tail Comet Tail Formation • Dust Tail Comet Spectra • Reflected sunlight (yellow) • Follows orbit • Plasma Tail – ions • Caught by solar B field • Anti-solar • Fluorescing " blue (CO+) • Comet spectral components • Reflected sunlight from dust (blackbody radiation) • Emitted heat (blackbody) • Fluorescence (emission lines) • Spectra shown: C/1995 O1 Hale Bopp • Kohoutek from space (above), comet Tuttle Cometary Fates? Zodiacal Light • Physical Source • Dust throughout solar system • From comet outgassing • Asteroid collisions • Visible from Earth • In plane of solar system • Surface turns off (clogged) • Looks like bright glow after • Rocky body with no ice sunset and twilight has ended • Completely sublimates • Breaks up • Collision Ikeya Seki Meteor Showers Sungrazing%Comets% ! Earth passes thru dust along comet orbit ! Burns in Earth atmosphere ! Larger chunks result in meteorites from ! Defined%by%q%%<%0.005%AU%(50,000%km)% ! Moon ! No%special%composition%–%hard%to%observe% ! Mars ! Asteroids ! Daytime%obs:%%% ! atomic%lines%(Na,%Ca,%Cr,%Co,%Mn,%Ni,%Cu%.%.%.)% ! Breakup%of%a%large%comet% Lovejoy 12/22/11 From ISS ! Parent%–%seen%by%Aristotle%in%371%BC% ! Great%comets%1843,%1882,%Ikeya%Seki% ! Kreutz%Group% ! ~85%%of%SOHO%comets%belong%to%Kreutz%group%% ! As%of%mid%2011%–%the%count%was%2110% Sungrazers:%Comet%Lovejoy% Sungrazer – Comet ISON • Discovery%(9/2012,%6AU%Active)% – “fresh”%from%the%Oort%cloud% – “Prebdiscovery”%image%r%~%8.5%AU% – Bright%at%Discovery% • Bright%comets%enable%many%experiments% – 10%very%bright%comets%in%~270%years% 12/15/2011 – interaction with the sun’s corona – Brigther%than%0%mag%every%~15%years% – The%hope%that%this%would%be%“the%one”% SpaceExploration Why we Study Comets . Giotto Mission: Comet Halley – L: July 2, 1985; E: Mar 14, 1986 Comets are the most – First in-situ comet exploration – Science Results pristine things in the Solar • Proved solid nucleus System • Discovery: organic dust (CHON) • Gases: 80% H O, 10% CO 2 2 Comets tell us about the formation of the Solar Deep Space 1: 19P/Borrelly System – L: Oct. 4, 1998; E: Sep. 22, 2001 – Test 12 advanced space technologies – Science Results • First hint of smooth plateaus Making NASA willing to • No direct evidence of water ice spend $$ on missions NASA Discovery Simple but Challenging, 38 yrs ago It [an asteroid] was racing past them at almost thirty miles a second; they had only a few frantic minutes in which to observe it closely. The Stardust - 1st sample return automatic cameras took dozens of photographs, the navigation radar's returning echoes were – L: Feb. 7, 1999, E: Jan. 2, 2004, R: Jan. 15, 2006 carefully recorded for future analysis - and there – 1st US comet mission was just time for a single impact probe. The – Science Results probe carried no instruments; none could survive a collision at such cosmic speeds. It was merely • Comets form from stuff that went all over the solar system! a small slug of metal, shot out from Discovery on a course which should intersect that of the asteroid. Deep Impact – L: Jan. 12, 2005, E: Jul. 4, 2005 .....They were aiming at a hundred-foot-diameter – 1st Active experiment target, from a distance of thousands of miles... Against the darkened portion of the asteroid there – Science Results was a sudden, dazzling explosion of light. ... • Comets are good insulators! • Little surface ice Arthur C. Clarke, 1968. In 2001: A Space Odyssey. • New ideas about formation Chapter 18 • Can study geology! • Launch January 12, 2005 Mission Profile • Encounter July 4, 2005 Approach & Encounter Impactor Release! AutoNav Enabled! E-24 hours! E-2 hr! ITM-1 Start! ITM-2! ITM-3! E-88 min! E-48 min! E-15 min! Tempel-1! Nucleus" 64! 2-way! kbps! S-band ! Crosslink! 500 km" Flyby S/C! Deflection Maneuver! Science and ! E-23.5 hr! Autonav Imaging to! Impact + 800 sec! Flyby S/C Science Shield Mode! And Impactor Data Attitude through! Inner Coma at 175 kbps* Flyby Science " ! Realtime Data TCA +! TBD sec! at 175 kbps*! Flyby S/C Science Data Playback at 175 kbps* • Geocentric Dist 0.89 AU to 70-meter DSS! • Heliocentric Dist 1.49 AU (q) 24 hrs before – spacecraft separate o • Approach phase 63 • 364 kg impactor Main s/c diverts for flyby • Solar Elong 104o • 10.2 km/s Deep Impact Encounter Deep Impact Encounter ! At Jet Propulsion lab • Earth Based Program ! At Jet Propulsion lab • Earth Based Program ! Science team – real time data – 50 observatories, 130 people ! Science team – real time data – 50 observatories, 130 people ! Immediate analysis – Pre 2005 229 obs nts ! Immediate analysis – Pre 2005 229 obs nts ! Followed by workshop in Hilo – 2005: 550 nts, 73 telescopes ! Followed by workshop in Hilo – 2005: 550 nts, 73 telescopes Deep%Impact% Impact Site ! ITS (impactor) images – impact site indicated by arrows (ecliptic N: upper right quadrant, sun to right) ! Sense of rotation – top is approaching ! Oblique impact – 20-45° from horizontal Comets,%PrebePOXI%&%NexT% RebUseable%Missions% Comets as icy primordial left-overs of planet formation – key for delivery of volatiles & organics. 2004 " 2011 ! Comets are a mixture of dust (organics) & volatiles ! Primary volatile is H2O – but mostly not on surface ! Comets are physically very diverse ! New ideas about formation ! Excellent insulators ! Comets are a mixture of high and low-T solar system materials. 2005 " 2010 ! DI " EPOXI ! Explore 103P/Hartley 2 ! Stardust " Stardust-NExT Giotto Halley-1986 DS1 Borrelley-2001 Stardust Wild 2-2004 Deep Impact Tempel 1-2005 ! Return to 9P/Tempel 1 StardustNexT% ! Encounter%2/14/2011% ! Close%approach%178%km%(10.9%km/s)% ! Goals% ! Look%for%changes%since%2005%passage% ! extend%coverage%of%surface,%image%DI%impact%site% ! Science%experiments% ! 72%NAVCAM%images%(±4%min%of%close%approach;%11b12%m/pix)% ! Dust%data%from%2%instruments% Deep Impact StardustNExT ! Major%Challenge% ! Time%of%Arrival% Key%Mission%Results% Team%Consensus% ! Nucleus%is%globally%layered% ! Rapid%geological%evolution% ! What%is%source%of%jets?%% Central%crater% ! Surface%material%is%loose%and%porous% Possible%% outer%rim% Prebexisting% New%depressed% ridge% area%(downrange%% “scoured”%zone?)%% P. Schultz 2012 Unknowns% • Pitted%terrain%–%related%to%outbursts?% • We%still%don’t%know%what%a%fresh%crater%looks%like% • What%is%the%deep%structure?% • What%is%a%“typical”%comet?% Thomas et al. 2013 ePOXI%Mission% ! Nov%4,%2010%encounter% ! 12.3%km/sec;%700%km%flyby% ! 2m%/%pix%best%resolution% % ! Instruments% ! Medium%Resolution%Camera%(MRI)% Spacecraft ! High%res%Camera%(HRIV)% Ball – JPL mission ! IR%spectrometer%(HRII;%1.0%–%4.8%µm)% Still operational ! impactor% Activity%Drivers% ePOXI%–%Close%Approach% A’Hearn et al. 2011, Science 332, 1396 • HRI%b%High%resolution%Camera%–%% • Jets%from%dark%side,%“snow”,%interesting%surface%features% • HRI%b%High%resolution%camera%b%deconvolved% • Dust,%CO %and%waterbice%grains%flow%together% – Jets%from%dark%side,%“snow”,%interesting%surface% 2 – New%discovery:%%CO2%drives%jets%&%activity% features% – H2O,%CO%and%CO2%most%abundant%in%early%SS% – Mass%loss%>>%1%%/%orbit% • Water%vapor%originates%from%waist% – Water%vapor%is%everywhere%–%%just%faint% – This%was%the%behavior%seen%by%Tempel%1%
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