PHYSICS AND CHEMISTRY OF COMETS
CONTENTS 1 GENERAL INTRODUCTION 1 1 HISTORICAL PERSPECTIVE 1 2 DISCOVERY 1 3 APPEARANCE 1 4 STATISTICS 1 5 IMPORTANCE 1 6 BRIGHTNESS 1 7 MAIN CHARACTERISTICS 1 8 SPACECRAFT ENCOUNTERS WITH COMETS 1 9 AN OVERALL VIEW PROBLEMS REFERENCES 2 DYNAMICS 2 1 ORBITAL ELEMENTS 2 2 ORBIT IN SPACE 2 2 1 RELEVANT EQUATIONS 2 2 2 ORBITAL ELEMENTS FROM POSITION AND VELOCITY 2 2 3 ORBITAL ELEMENTS FROM OBSERVATIONS 3 PHYSICAL ASPECTS 3 1 BLACK BODY RADIATION 3 2 PERFECT GAS LAW 3 3 DISSOCIATIVE EQUILIBRIUM 3 4 DOPPLER SHIFT 3 5 SPECTROSCOPY 3 5 1 ATOMIC SPECTROSCOPY 3 5 2 MOLECULAR SPECTROSCOPY 3 5 3 CHEMICAL SUBGROUPS 3 6 ISOTOPIC E?ECT 3 7 FRANCK-CONDON FACTORS 3 8 INTENSITY OF EMITTED LINES 3 9 BOLTZMANN DISTRIBUTION 3 10 ?-DOUBLING 3 11 PHOTOCHEMISTRY OF WATER 3 12 SILICATE 3 13 ANNEALING 3 14 CARBON 3 15 SOLAR RADIATION 3 16 SOLAR WIND 4 SPECTRA 4 1 MAIN CHARACTERISTICS 4 2 FORBIDDEN TRANSITIONS 4 3 LINE–TO–CONTINUUM RATIO 5 SPECTRA OF COMA 5 1 FLUORESCENCE PROCESS 5 1 1 ROTATIONAL STRUCTURE 5 1 2 VIBRATIONAL STRUCTURE 5 1 3 COMPARISON WITH OBSERVATIONS 5 1 4 CASE OF C2 MOLECULE 5 1 5 PROMPT EMISSION LINES OF OH 5 1 6 MOLECULES OTHER THAN DIATOMIC CONTENTS 5 1 7 OH RADIO LINES 5 1 8 OXYGEN LINES 5 1 9 FORBIDDEN TRANSITIONS 5 1 10 MOLECULAR BAND POLARIZATION 5 2 EXCITATION TEMPERATURE 5 2 1 ROTATIONAL TEMPERATURE 5 2 2 VIBRATIONAL TEMPERATURE 5 3 ABUNDANCES OF HEAVY ELEMENTS 5 4 ISOTOPIC ABUNDANCES 5 5 SUMMARY 6 GAS PRODUCTION RATES IN COMA 6 1 THEORETICAL MODELS 6 1 1 FROM THE TOTAL LUMINOSITY 6 1 2 FROM SURFACE BRIGHTNESS DISTRIBUTION 6 1 3 FROM NUMBER DENSITIES 6 1 4 SEMI-EMPIRICAL PHOTOMETRIC THEORY 6 2 RESULTS 6 2 1 OH AND H 6 2 3 CN, C2, C3, NH 6 2 4 CH, NH2 6 2 5 CO, CO2 6 2 7 IONS 6 2 8 COMPLEX MOLECULES 6 2 9 O, C, N, S 6 3 ANALYSIS OF HYDROGEN OBSERVATIONS 6 3 1 ANALYSIS OF LYMAN ? MEASUREMENTS 6 3 2 ANALYSIS OF H? OBSERVATIONS 6 4 RELATED STUDIES 6 4 1 GAS-PHASE CHEMISTRY IN THE COMA 6 4 2 IN SITU MASS SPECTROMETER FOR IONS 6 4 3 TEMPERATURE AND VELOCITY OF THE COMA GAS 6 5 PARENT MOLECULES 6 6 CHEMICAL DIVERSITY 6 7 SUMMARY 7 DUST TAILS 7 1 DYNAMICS 7 2 ANTI-TAIL 7 3 DUST TRAILS 7 4 SODIUM GAS TAILS 7 5 DUST FEATURES 8 LIGHT SCATTERING THEORY 8 1 MIE SCATTERING THEORY 8 1 1 E?CIENCY FACTORS 8 1 2 ALBEDO 8 1 3 SCATTERED INTENSITY 8 1 4 POLARIZATION 8 2 APPROXIMATE EXPRESSIONS 8 3 COMPUTATION OF CROSS SECTIONS 8 4 RESULTS 8 5 PARTICLES OF OTHER TYPES 8 6 OPTICAL CONSTANTS 9 THE NATURE OF DUST PARTICLES 9 1 VISIBLE CONTINUUM 9 1 1 ALBEDO 9 1 2 PHASE FUNCTION 9 1 3 DUST PRODUCTION RATE FROM CONTINUUM 9 1 4 DUST PRODUCTION FROM A(?)F? 9 2 POLARIZATION 9 2 1 LINEAR POLARIZATION 9 2 2 CIRCULAR POLARIZATION 9 3 GRAIN SIZES 9 4 INFRARED MEASUREMENTS 9 4 1 DUST PRODUCTION FROM INFRARED OBSERVATIONS CONTENTS 9 4 2 ANTI-TAIL 9 5 SPECTRAL FEATURE 9 5 1 SILICATE SIGNATURE 9 5 2 MINERALOGY OF DUST PARTICLES 9 5 3 THE C-H STRETCH FEATURE 9 5 4 ICE SIGNATURE 9 6 PROPERTIES DERIVED FROM DIRECT MEASUREMENTS 9 7 RADIATION PRESSURE E?ECTS 9 8 SUMMARY 10 ION TAILS 10 1 EVIDENCE FOR THE SOLAR WIND 10 2 DYNAMICAL ABERRATION 10 3 THEORETICAL CONSIDERATIONS 10 3 1 COMPARISON WITH OBSERVATIONS 10 4 INSTABILITIES AND WAVES 10 5 ACCELERATION OF COMETARY IONS 10 6 LARGE SCALE STRUCTURES 10 6 1 TAIL RAYS OR STREAMERS 10 6 2 KNOTS OR CONDENSATIONS 10 6 3 OSCILLATORY STRUCTURE 10 6 4 “SWAN-LIKE” FEATURE 10 6 5 BEND IN THE TAIL 10 6 6 DISCONNECTION EVENTS 10 7 X-RAYS 10 8 SUMMARY 11 NUCLEUS 11 1 MORPHOLOGY 11 2 THEORY OF VAPOURIZATION 11 3 OUTBURSTS 11 4 ALBEDO AND RADIUS 11 5 MASS, DENSITY AND SURFACE GRAVITY 11 6 ROTATION 11 7 NUCLEUS COMPOSITION 11 8 MASS LOSS 11 9 STRUCTURE 11 10 NON-GRAVITATIONAL FORCES 11 11 ORTHO TO PARA RATIO OF MOLECULES 11 12 BINARY SYSTEMS 11 13 SUMMARY 12 ORIGIN 12 1 EVIDENCE FOR THE OORT CLOUD 12 2 EVOLUTION AND PROPERTIES OF OORT CLOUD 12 2 1 SHORT PERIOD COMETS 12 3 ORIGIN OF THE OORT CLOUD 12 4 TAXONOMY 12 5 SUMMARY 13 RELATION TO OTHER SOLAR SYSTEM STUDIES 13 1 ASTEROIDS 13 2 METEORITES 13 3 METEOR STREAMS 13 4 PARTICLES COLLECTED AT HIGH ALTITUDES 13 5 PRIMORDIAL MATERIAL 13 6 CHEMICAL EVOLUTION 13 7 TERRESTRIAL WATER 13 8 IMPACT OF OUTSIDE BODIES 13 9 OVERVIEW 14 PROBLEMS AND PROSPECTS 14 1 EPILOGUE 14 2 FUTURE STUDIES CHAPTER GENERAL INTRODUCTION 1 1 HISTORICAL PERSPECTIVE AMONG THE VARIOUS OBJECTS OF THE SOLAR SYSTEM, COMETS HAVE ATTRACTED AND FASCINATED THE COMMON MAN TO A LARGE EXTENT FOR THE LAST TWO THOUSAND YEARS OR SO THIS INFORMATION COMES FROM THE ANCIENT RECORDS OF PAINTINGS OR DRAWINGS OF COMETS ON CAVES, CLOTHES, ETC AS WELL AS FROM THE OBSERVATIONS OF EARLY WRITERS IT WAS NOT UNTIL THE SIXTEENTH CENTURY THAT COMETS WERE DEMONSTRATED TO BE CELESTIAL OBJECTS THIS CAME FROM THE WORK OF TYCHO BRAHE WHO OBSERVED THE BRIGHT COMET OF 1577 AD WITH ACCURATE INSTRUMENTS AND FROM VARIOUS LOCATIONS IN EUROPE THIS REALLY REVOLUTIONIZED THE IDEAS ABOUT COMETS AND FROM THEN ON, OBSERVERS TOOK A SERIOUS VIEW OF COMETS AND STARTED MAKING POSITION MEASUREMENTS THE COMPLETE CREDIT FOR THE DISCOVERY THAT COMETS ARE PART OF THE SO- LAR SYSTEM GOES TO EDMOND HALLEY HALLEY, USING NEWTONIAN MECHANICS, SHOWED THAT THE COMETS WHICH HAD APPEARED IN 1531, 1607 AND 1682 ARE THE ONE AND THE SAME WITH A PERIOD OF ABOUT 75 2 YEARS HE ALSO NOTICED THAT THE TIME INTERVAL BETWEEN THE SUCCESSIVE PERIHELION PASSAGES WAS NOT THE SAME HE CONCLUDED RIGHTLY THAT THIS COULD BE DUE TO THE PERTURBATION OF THE COMETARY ORBIT PRODUCED BY THE PLANETS JUPITER AND SATURN FOL- LOWING THESE SUCCESSES, HE PREDICTED THAT THE SAME COMET WOULD RETURN IN 1758 AS PREDICTED, THE COMET DID APPEAR IN 1758, THOUGH HALLEY, DEAD BY THEN, WAS NOT THERE TO WITNESS THE GLORIOUS TRIUMPH OF HIS PREDICTION THIS COMET IS THEREFORE NAMED AFTER HIM IN RECENT YEARS THIS COMET HAS BEEN TRACED BACKWARDS THROUGH MANY CENTURIES BY SEVERAL INVESTIGATORS THROUGH ORBIT CALCULATIONS THROUGH THIS WORK, IT HAS BEEN POSSIBLE TO IDENTIFY EVERY APPEARANCE OF THE COMET AS SHOWN BY ANCIENT RECORDS UNTIL ABOUT 240 BC SO FAR, IT SEEMS TO HAVE MADE ABOUT TWENTY-EIGHT APPEARANCES