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Galaxy Forum India 11 - goswami


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Galaxy Forum India 11 - goswami

  1. 1. Planetary Science and Astronomy J. N. Goswami Physical Research Laboratory, Ahmedabad, India
  2. 2. Gravitational collapse of an interstellar molecular gas clloud led to the formation of the Proto-Sun surrounded by a rotating gas and dust disk A stellar event most probably triggered the cloud collapse A human quest lasting three thousand years: Let us start at the beginning Formation of the Solar System: A very concise Resume’ Eight planets in equatorial circular orbits with one habitable planet ( Earth ) Gradual formation of grain, grain aggregates, cm-meter-km-sized objects, planetesimals and planets Planetary Science & Astronomy Asteroids & Comets
  3. 3. A Historical Perspective In the beginning: Observation & studies of motion of heavenly bodies Pythagoras (c. 624-547 BC) Earth is a sphere, and All other heavenly bodies are perfect sphere Plato (428-347 BC) All heavenly bodies appear to move in circles around earth Aristotle (384-322 BC) : Earth-centric Universe Universe is finite and has Two parts The immobile, imperfect and changing earth; Perfect and immutable heavenly bodies moving westward around the Earth The fixed stars define the edge of the Universe Moon Fire Air Water Planetary Science & Astronomy
  4. 4. Ptolemy’s Universe The fixed star and the “wanderers” (Planets) Consolidated the idea of an Earth-centric Universe. Introduced Epicycle, Deferent ……. to explain the motion of planets Claudius Ptolemy (c. 90-168 AD) The Earth-centric system of Ptolemy ( 2 nd to 15 th century) Planetary Science & Astronomy
  5. 5. Nicholas Copernicus (1473-1543) The Copernican Revolution: The Sun-centric solution Sun-centric system: A new idea proposed purely on aesthetic and intuitive intellectual ground as an alternate to the earth-centric system with the extremely complex system of epicycles …… Planetary Science & Astronomy Retrograde movement of Mars resolved without epicycles
  6. 6. Precise determination of Planetary Motion Tycho Brahe (1546-1601) Observational Support for Copernican System Tychos’ Model of Solar System I. Sun and Moon circling the Earth II. Other planets moving around the Sun Still has Earth-centric elements III. The fixed stars are at the boundary of a finite universe Planetary Science & Astronomy
  7. 7. The Laws of Planetary Motions inferred from observation of Tycho Brahe Planetary orbits are ellipses with the Sun at one focus. Johannes Kepler (1571-1630): The Solar system as we know it A planet’s orbital period : [P year ] 2 = [a AU ] 3 A line from a planet to the Sun sweeps over equal areas in equal interval of time. Planetary Science & Astronomy
  8. 8.  Moon: The heavenly bodies are not perfect and immutable as perceived Telescopic observations: Confirmation of Sun-centric system The conflict with Church : A new way of finding truth; the scientific method Galileo Galilei (1564- 1642)  Milky way: Full of stars; the universe may not be finite Jupiter: Has satellite rotating around it (a mini Solar System) Venus: Shows phase just like the Moon; goes behind the Sun Ptolemaic Universe Copernican Universe Planetary Science & Astronomy
  9. 9. Isaac Newton: 1643-1727 The Theory of Gravitation: F = G M m / r 2 Provide a natural explanation for the Kepler’s empirical Laws of Planetary motion The next Question: The origin of the Solar System The basic properties of the Solar system, with the Sun at the center and the Planets, satellites and minor objects, such as Asteroids and comets, orbiting around it in well defined orbit, is established for good Circle Parabola HyPerbola Planetary Science & Astronomy
  10. 10. Estimated distance of the Moon and the Sun from Earth Proposed a Sun-centric system A bit of Historical Note Aristarchus(c. 310-230 BC) The Indian Scene: Aryabhatta (AD 476-550) Proposed that Earth rotates & revolves around the Sun Suggested Sun as the source of Moonlight Wrote about eclipses and gravitational attraction Work translated to Latin in the 13 th century It is not clear if he has explicitly proposed a Sun-centric system (1000 year before Copernicus!!) Mentioned in “Sand-Reckoner” by Archimedes (287 BC-212 BC) Planetary Science & Astronomy
  11. 11. Immanuel Kant (1724-1804) The “Solar Nebula” Hypothesis Chaotic distribution of matter with density variation Accretion of matter; formation of flattened disks Sun formed at the center and planets at secondary condensates The Solar Nebula concept remains central to Origin of the Solar System Kant: Natural History & Theory of the Heavens (1755) Pierre-Simon de Laplace (1749-1827) Combined Vortex theory with Newtons gravity Formation of the solar system through gradual evolution of a primitive rotating gas and dust cloud, the “SOLAR NEBULA” Laplace: Systems of the World (1796) Planetary Science & Astronomy
  12. 12. Initial collapse; proto-Sun surrounded by rotating solar nebula An active early Sun; Energy release from Sun along the poles in the form of Jets Formation of a gas and dust disk in the central plane Formation of the Sun and the Solar Nebula is a coupled process: Non-homologous collapse (Larson R. B., 1968) Advances in Astrophysics and Observational Astronomy Formation of Sun-like stars: The various stages Theoretical estimate of Formation time scale of single Sun-like star (1995) Planetary Science & Astronomy
  13. 13. Closure Home: Formation of Stars & Planets A very concise Resume Gravitational collapse of an interstellar molecular gas cloud led to the formation of the Proto-Sun surrounded by a rotating gas and dust disk Death of a star most probably triggered the cloud collapse Gradual formation of grain, grain aggregates, cm-meter-km-sized objects, planetesimals and planets There are observational and experimental evidence supporting such a scenario Planetary Science & Astronomy
  14. 14. Formation of the Solar System: Observational Evidence Gravitational collapse of an interstellar molecular gas cloud led to the formation of the Proto-Sun surrounded by a rotating gas and dust disk Planetary Science & Astronomy
  15. 15. Our Solar system have planetary objects up to +40 AU from the Sun Jet Star Disk Jet and Disk around young Sun-like stars Disk and Reflection Nebula around young stars The observed Disks are few hundred Astronomical Unit (AU) (Sun-Earth distance) Planetary Science & Astronomy
  16. 16. Origin and Early Evolution of the Sun and the Solar system Questions we would like to answer: 1. What caused the collapse of the protosolar cloud ? 2. Time-scale of collapse of the protosolar cloud to form the Sun and some of the first solar system grains. Need to identify solar system objects that formed at different stages of solar system evolution and retain pristine records from that era 3. Processes and time-scales governing the formation and differentiation of planetesimals and planets Establishing these “timescales” is the key to identify the most plausible pathway leading to the Origin and Evolution of the Solar System Planetary Science & Astronomy: Origin of the Solar System
  17. 17. First Solar System Solids: Refractory Oxides and Silicates Silicate Spherules: Product of transient high temperature events in the Nebula Early Solar System solids present in primitive Meteorites 0.1mm mm mm Planetary Science & Astronomy: Origin of the Solar System
  18. 18. BPMG (present) (-11.5 Ma) LCC UCL (present)  Pictoris moving group (BPMG); Lower Centaurus Crux (LCC); Upper Centaurus Lupus (UCL) Carbon-rich gaseous nebula (Nature, June 8, 2006) A Sun-like young (15 Ma) star with a disk and planetary objects Beta Pictoris Sun: A lonely star? Or it had company
  19. 19. Planetary Materials: Probing Beyond the Solar System Meteorites and Comets host Interstellar grains formed in stellar atmosphere of evolving or exploding stars How we know this for sure ? Isotopic composition of C, O, N, Si provide the clue Physical processes (e.g. heating) can change Elemental abundance in an open system BUT NOT ISOTOPIC COMPOSITION ; [Minor changes depends on masses of the isotopes and can be predicted] Interstellar Silicon Carbide Grains in Meteorites Stardust Mission 0.1micron
  20. 20. Planetary Materials: Probing Beyond the Solar System Identification of Interstellar (Presolar) silicates: Anomalous Carbon and Oxygen Isotope composition SS Value The Grains marked differ from solar composition And are of presolar/stellar origin and Represent three possible types of distinct stellar environment where they could have formed
  21. 21. Are we alone; The other Solar systems Discovery of exo-planets: 1995 Several Methods: Most pursued : Wobble of the star due to Planets around it Number of Planetary Systems Identified ~ 500 And ONLY A HANDFUL OF THEM LOOK LIKE OUR SOLAR SYSTEM The Kepler is a space craft launched on 2009 to look for probable candidate (using transit method) has identified about 1200 prospective candidate that need further study, We shall soon initiate studies of Exo-Planets; PRL has fabricated a system and test observations are progressing at Mt. Abu Observatory Planetary Science & Astronomy
  22. 22. Gravitational tug between the unseen planet and the star, lead the star to wobble like a “toy top” recorded using precision spectrographs attached to ground based telescopes one can estimate the unseen planet’s mass and radius of orbit Observer on Earth using a spectrograph can observe the star’s wobble Star Unseen planet Astronomy: Other Solar System
  23. 23. The main Optics are expected to arrive from SESO (France) sometime in Nov. The spectrograph layout inside the Vacuum Chamber Chamber Inside view CCD dewar Camera Optics Prism Echelle Off-axis Parabolas Slit position & Fiber optics ) Search for Exo-Planet: Indian Effort Planetary Science & Astronomy
  24. 24. “ Our idea of origin of the Solar system is about as secure as that of a BOTANIST who would infer the life history from one blossom the only FLOWER he has seen” Philip Morrison (in early eighties) Let us hope that with more exploration and newer discoveries we shall be able to learn more about the origins of solar systems Thanks to Astronomical Observations, With the discovery of other Solar Systems, we have now remote experience of possible fragrance of other flowers of the family Planetary Science & Astronomy
  25. 25. Thank you for your Kind Attention
  26. 27. Temperature Control environment: about one hundredth of a degree at 27C Pressure Control environment: about one-tenth million of the atmosphere over the night (10 – 12hrs) Optical fiber-fed; that is star-light from the 1.2m telescope focal plane is carried to the entrance of the spectrograph (slit) using optical fibers PARAS (PRL Advanced Radial-velocity All-sky Search): The PRL spectrograph to measure the star’s wobble due to the gravitational tug with the unseen planet The PRL 1.2m telescope, Mt. Abu Observatory The star-light is fed to the spectrograph thru Optical fiber Spectrograph installed inside the Vacuum Chamber at Mt. Abu Observatory
  27. 28. The Star spectra and Thorium-Argon calibration spectra recorded simultaneously for precision radial velocity measurements. The continuous lines with absorption features is the star spectra coming from the star fiber and the bright dots represent the Thorium-Argon spectra Star’s “wobble” can be detected by taking many spectra of the star at time intervals (time series) and the shift seen in absorption features in the star’s spectra against the reference calibration spectra t1 t2 t3 Time series time Planet Mass: 4 Jupiter Mass, Period : ~3.6days Time in Days in April
  28. 29. Radial Velocity precision of 2.5m/s have now been achieved with PARAS, the star is 47 Uma This means that the PARAS spectrograph is now capable of detecting short period planets of down to 15 to 20Earth mass sizes around Sun-like stars If PARAS is attached to a larger aperture telescope of 2.5m then it may be possible to detect planets to the size of 5 Earth masses How precise is the PRL spectrograph (PARAS) ?