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How we think the planets were born Oliver Gressel (NBIA) Folkeuniversitetet i København I. Solar system inventory Print: Verónica Olivera Gómez Folkeuniversitetet i København Origin of the word “planet” ● ● ● ● ἀστέρες πλανῆται (asteres planetai) “wandering stars” objects which apparently move across the sky eight “modern” planets: Image: NASA Folkeuniversitetet i København Ages of discoveries ● ● ● ● ● Mercury, Venus, Mars, Jupiter & Saturn known by Babylonian times (2000 BC) 1577: Tycho Brahe showed that comets were not atmospheric phenomena 1608: Invention of the telescope in Holland Galileo discovers Jupiter's (inner) moons in 1650s, Cassini Saturn's in 1670/80s Uranus (the 7th planet) found by William Herschel in 1781 Folkeuniversitetet i København Planet discoveries ● ● ● Ceres (the “8th” planet) first announced by Piazzi in 1801 Galle & LeVerrier 1846: Neptune (8th planet since 1851) Clyde Tombaugh, Pluto, discovered 1930 in search for “Planet X” Folkeuniversitetet i København Our solar-system planets Folkeuniversitetet i København Our solar-system planets Folkeuniversitetet i København Trans-Neptunian objects Folkeuniversitetet i København Asteroid belt Asteroids are minor planets, especially those of the inner Solar System. The main Asteroid Belt lies between the orbits of Mars and Jupiter. Folkeuniversitetet i København Asteroid belt Asteroids are minor planets, especially those of the inner Solar System. The main Asteroid Belt lies between the orbits of Mars and Jupiter. Folkeuniversitetet i København Kuiper belt The Kuiper belt lies outside the orbit of Neptune (~30au) and extends out to a distance of 50au from the Sun. Objects composed of frozen volatiles. Folkeuniversitetet i København Extrasolar debris discs Images: NASA, Hubble Space Telescope Folkeuniversitetet i København II. Meteorites: cosmic heralds Folkeuniversitetet i København Comets Icy-rocky bodies originating from the outer solar system. Heating produces coma and tails when passing near the sun. 67P/Churyumov–Gerasimenko as seen September 2014 by esa Rosetta mission Comet Hale-Bopp. Image: NASA Folkeuniversitetet i København Geminids meteor shower The Geminids can be annually observed in the first half of December, with its peak activity being around December 14. The shower owes its name to the constellation Gemini from where the meteors appear to emerge from in the sky (the so-called “radiant”). Unlike most other meteor showers, the Geminids are associated not with a comet but with an asteroid - the 3200 Phaethon, which was discovered in 1983 by NASA's IRAS. It resembles main belt asteroid Pallas so much, it might be a 5-kilometer chip off that 544 km block. An artist's concept of an impact event on Pallas. Credit: B. Schmidt and S. Radcliffe of UCLA. Folkeuniversitetet i København Meteoritics ● ● Radiometric dating Mineralogy – – Pristine meteorites Chondrites/Achondrites Iron meteorites (from ~50 differentiated bodies) Agpalilik (“the man”) outside the Geological Museum in Copenhagen Agpalilik, when transported from its original location in Greenland in 1963 Folkeuniversitetet i København Chondrules Pinhead-sized grains formed from (partly) molten droplets, then accreted onto the surface of larger bodies. From Greek “χόνδρος” (chondros), grain. The individual chondrules are from 1-4mm across. Photo: Bob King Folkeuniversitetet i København Centre for Star and Planet formation Multidisciplinary research center for cosmochemistry, astrophysics and astronomy funded by the DNRF and located at the Natural History Museum of Denmark, University of Copenhagen. Folkeuniversitetet i København Chondrule chonology Folkeuniversitetet i København III. New horizons: extrasolar planets Folkeuniversitetet i København The ancient view "There cannot be more worlds than one.” - Aristotle (384-332 BC) "There are innumerable worlds which differ in size. In some worlds there is no sun and moon, in others they are larger than in our world, and in others more numerous. They are destroyed by colliding with each other. There are some worlds without any living creatures, plants, or moisture.” - Hippolytus of Rome (c. 170 - 236) on Democritus (460-370 BC) “There is an infinite number of worlds, some like this world, some unlike it… For the atoms out of which a world might arise, or by which a world might be formed, have not all been expended on one world or a finite number of worlds, whether like or unlike this one. Hence there will be nothing to hinder an infinity of worlds." - Epicurus of Samos (342-270 BC) “Now since there is illimitable space empty in every direction, and since seeds innumerable in number in the unfathomable universe are flying about in many ways driven by everlasting movement it cannot by any means be thought likely that this is the only round earth and sky that has been made…” - Lucretius (99-55 BC) “And if their force and nature abide the same, Able to throw the seeds of things together Into their places, even as here are thrown The seeds together in this world of ours, 'Tmust be confessed in other realms there are Still other worlds, still other breeds of men, And other generations of the wild.” - Lucretius (99-55 BC) Folkeuniversitetet i København Image: xkcd.com/1298 Census Folkeuniversitetet i København Image: xkcd.com/1298 Census Folkeuniversitetet i København The radial velocity method Image: esa Image: esa Folkeuniversitetet i København The transit method planethunters.org The transit method is a powerful tool for detecting planets with low enough orbital inclination so that they pass in front of their host star. Folkeuniversitetet i København Planet microlensing Planet microlensing captures the gravitational deflection of light, or “lensing”, for extremely rare events where a star with a planet passes right in front of a background star. Has been described as the task of “detecting a planet we cannot see, orbiting a star we cannot see either...” Images: OGLE website Folkeuniversitetet i København Direct imaging of planets Gemini Planet Imager’s first light image of the light scattered by a disk of dust orbiting the young star HR4796A The challenge in imaging planets directly lies in their extreme faintness compared to their much brighter host stars. Coronagraphs are used to block the light from the star. HR8799 direct imaging planet detections Credit: Marois et al (2010) Folkeuniversitetet i København The Kepler mission launched in March 2009 earth-trailing helioc. orbit photometric monitoring of 150,000 stars 3277 planetary candidates announced so far Kepler spacecraft. Image: NASA Folkeuniversitetet i København The harvest... Folkeuniversitetet i København The harvest... Folkeuniversitetet i København The Kepler 11 system Folkeuniversitetet i København The Kepler 11 system Folkeuniversitetet i København The “habitable” zone Folkeuniversitetet i København The “habitable” zone Folkeuniversitetet i København Exoplanet atmospheres Transmission spectroscopy of planetary atmosphere allows to get information about planet's “weather”. Image: NASA, JPL/CalTech Folkeuniversitetet i København “Weather” forecasting Cho, J. et al. (2003), Astrophysical Journal, 587, 117, The changing face of the extrasolar planet HD 209458b Time-dependent temperature distribution on hemisphere facing star for a model hot Jupiter Simulated flows and vortices on an irradiated hot Jupiter Harrington, J. et al, (2005), Science, “The Phase-Dependent Infrared Brightness of the Extrasolar Planet ʊ Andromedae b” Varying infrared luminosity of Upsilon Andromeda b as a function of orbital phase Folkeuniversitetet i København Small fraction of starlight passes through planet atmosphere during transit Absorption features due to sodium observed in the spectrum - in agreement with theoretical predictions… Using a similar techniques H2O, CH4, CO and CO2 have been detected in atmospheres of the planet HD 189733b Recent observations using the Hubble Space Telescope suggest that the atmosphere of HD 209568b is boiling off - producing a long ‘cometary tail’ Folkeuniversitetet i København HD 209458b Originally discovered using radial velocity technique in 1996 ● Found to transit in front of its star in 1999 – the first transiting planet ● Combining transit data and radial velocity measurements gives the planet mass and radius: ● mass=0.69 Jupiter masses radius=1.347 Jupiter radii gas giant planet with mean density of about 1 g/cm3 Folkeuniversitetet i København IV. Planetary birthplaces Folkeuniversitetet i København The nebular hypothesis The Nebula Hypothesis for the formation of the Solar System was developed in the 18th century by Emanuel Swedenborg (1734), Immanuel Kant (1755) and Pierre-Simon Laplace (1796). Hypothesis: “The Sun and planets formed from a rotating and flattened rotating cloud of gas and dust - the Solar Nebula” Folkeuniversitetet i København dusty protoplanetary disc Image: Hubble Space Telescope Star formation regions Folkeuniversitetet i København The ALMA revolution The ALMA site at the Atacama desert of northern Chile ● ● ● ● radio telescope array, sub-mm wavelength unprecedented sensitivity and resolution spirals or gaps associated with hidden planets kinematic information via spectral lines ALMA (ESO/NAOJ/NRAO), S. Casassus et al. HD 142527 lies in the constellation Lupus, about 450 light years away NASA/JPL-Caltech/T. Pyle (SSC) Folkeuniversitetet i København ALMA “first light” long-baseline New high-resolution capabilities achieved by spacing the antennas up to 15km apart. Most detailed image of the disc around HL Tau, a million-year-old Sun-like star 450 light-years from Earth in the constellation of Taurus. Folkeuniversitetet i København Gap formation Simulation of a planet opening a gap in a protoplanetary disc. Video: Richard P. Nelson, QMUL Folkeuniversitetet i København A Saturn-mass planet opening a gap Folkeuniversitetet i København Gas giant formation magnetic field lines magneticallycollimated jet horseshoe region Synthetic image of disc/gap/planet. streamlines Folkeuniversitetet i København How to build a planetary system... Take a disc of well mixed gas + dust, make a snowline beyond 3au where temperature falls below -100oC, dust + ice grains collide and stick, forming kilometre-sized planetesimals Giant planets: outside snowline, growth occurs until massive planetary core forms gaseous envelope settles onto core after few million years Terrestrial planets: smaller rocky planets form nearer the Sun Folkeuniversitetet i København Lab experiments on dust growth Levitation of ice aggregates via the Knudsen “compressor” effect. Study growth of dusty/icy aggregates into larger agglomerates. Video: AG Wurm, Uni Duisburg Folkeuniversitetet i København Dust collision experiments Collision of two dust agglomerates at a few tens of cm/s. The volume filling factor is higher on the hanging agglomerate, the "target", while the more porous agglomerate, the "impactor", is destroyed completely in this collision (catastrophic disruption). The overall result is a slight growth of the target while a lot of small particles are produced. Video: AG Wurm, Uni Duisburg Folkeuniversitetet i København Jumping the metre-sized barrier Folkeuniversitetet i København The role of magnetic fields Image: R. Moll, Garching HH30, Image:NASA HST Folkeuniversitetet i København Defining the environment... Scenario A: “Viscous” transport – – – – Turbulent flow Strong particle stirring Puffed-up dust disc Broadened spectral lines Scenario B: Magneto-centrifugal wind – – – – Laminar flow Quiescent environment Dust settled into thin disc Double-peaked lines Folkeuniversitetet i København Defining the environment... Scenario A: “Viscous” transport – – – – Turbulent flow Strong particle stirring Puffed-up dust disc Broadened spectral lines Scenario B: Magneto-centrifugal wind – – – – Laminar flow Quiescent environment Dust settled into thin disc Double-peaked lines Folkeuniversitetet i København Effect of turbulence on particle collisions Folkeuniversitetet i København Back to the big picture... The pale blue dot. Folkeuniversitetet i København