Andrew Collier Cameron University of St Andrews Are we alone in the Universe Th
Padron, Jose, Morning On-Air Personality has reference to this Academic Journal, PHwiki organized this Journal Andrew Collier Cameron University of St Andrews Are we alone in the Universe The plurality of worlds In some worlds there is no Sun in addition to Moon, in others they are larger than in our world, in addition to in others more numerous. In some parts there are more worlds, in others fewer ( ); in some parts they are arising, in others failing. There are some worlds devoid of living creatures or plants or any moisture. Democritus (ca. 460-370 B.C.), after Hyppolytus (3rd cent. A.D.) There cannot be more worlds than one. Aristotle [ De Caelo ] How do galaxies, stars in addition to planets as long as m in addition to evolve The worlds come into being as follows: many bodies of all sorts in addition to shapes move from the infinite into a great void; they come together there in addition to produce a single whirl, in which, colliding with one another in addition to revolving in all manner of ways, they begin to separate like to like. Leucippus (480-420() B.C.), after Diogenes Laertios (3rd cent. A.D.)
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Dusty discs around young stars Roughly half of all new-born Sun-like stars are surrounded by solar system-sized dusty discs. Could this mean that half of all Sun-like stars have planetary systems Proto-planetary discs in the Orion Nebula (NASA/STScI) Searching as long as extra-solar Jupiters A planet in addition to its parent star orbit round their common centre of gravity. The star is much more massive than the planet, so the reflex orbital speed is small. A massive planet in a close orbit gives its star a reflex velocity of a few tens of ms1. This gives a small but measurable Doppler shift. 51 Pegasi: The first wobbling star Discovered by Michel Mayor & Didier Queloz in mid-1995.
Todays state of play 237 planets in 203 systems, Oct 1995 – 20-Aug-2007 from Doppler wobble searches. 25 multiple systems 24 transiting systems, 19 from transit searches 4 microlensing planets (more distant!) Recipe as long as building Jupiters Ingredients: 10 Earth masses of ice-coated dust particles Lots of gas (mostly hydrogen) Method: Allow dust & ice to coagulate Allow solid core to sweep up gas Leave to cool as long as 5 billion years Common problems: Tidal gaps starve planet of gas. Gas accretion takes tens of millions of years, longer than lifetime of disc. Migrating planets spiral into star. Numerical simulation by Pawel Artymowicz, Stockholm. Tip of the iceberg Left panel: Core accretion+migration simulation by Ida & Lin (2004), showing gas giants, ice giants, rocky planets. Right panel: Radial-velocity discoveries so far.
Iron abundance in addition to planet as long as mation Eccentric Orbits Planet-planet interactions Eccentricity pumping Small planets ejected Tidal circularisation Unclear why.
Other planet-building recipes If disk cools efficiently by infrared radiation, fragments can collapse spontaneously to as long as m instant planets. Several dozen planets as long as m in addition to interact. Numerical simulation by Ken Rice, University of St Andrews. Other planet-building recipes If disk cools efficiently by infrared radiation, fragments can collapse spontaneously to as long as m instant planets. Several dozen planets as long as m in addition to interact. Smaller planets get ejected from system. One big fish survives in an eccentric orbit. Problems: Hard to get multiple, smaller planets to survive in near circular orbits. Lessons from Doppler Wobbles > 5% of Sun-like stars host a Jupiter Metallicity matters Orbits differ from Solar System wide range of orbit radii ( P > 2d ) wide range of eccentricities New processes Migration – spiral-in eccentricity pumping ejection What sort of planets are the hot Jupiters
1.6% Transit Lightcurves SuperWASP hardware Pollacco et al 2006, PASP 118, 1407 Lenses Canon 200mm f/1.8 Aperture 11.1 cm CCD Detector 2048 x 2048 thinned e2v (Andor, Belfast) 13.5×13.5 micron pixels Field of View 7.8 x 7.8 degrees 13.7 arcsec/pixel Mount OMI/Torus robotic mount Operating Temperature 50 ºC 3-stage Peltier Cooling
WASP data reduction pipeline Flatfield Bias Field recognition, astrometry, aperture photometry, calibration/de-trending Flux-RMS Pre-processed Raw 12 Data processed so far (stellar density plot) Current Observing fields Substellar mass-radius relation
Mass-radius relation as long as hot Jupiters WASP-1b,-2b: Cameron et al 2007, MNRAS (+ XO-2b, HAT-P-2b, HAT-P-3b, TrES-3, TrES-4, CoRoT-EXO-1b, Gl 436b since 2007 May 1) Why we need many more How does planet radius scale with Planet mass (Fortney et al 2007) Planet age (Many!) Metallicity/opacity (Burrows et al 2007, Guillot et al 2006) Existence/size of core (Guillot et al 2006) Proximity to host star (Fortney et al 2007) Migration history
Core mass in addition to as long as mation mechanism Recent example: HD 149026b Transiting hot Saturn High density => massive core Sato et al, ApJ, in press Test as long as mation models: Core accretion+migration Gravitational instability GJ 436 b Gillon et al 2007 May 17, astro-ph/0705.2219 Neptune-mass planet Neptune-like radius Radius depends strongly on composition (cf. Fortney et al 2007, astro-ph/0612671) Ice-giant structure. WASP-1b WASP-2b Exoplanet Discovery Space Cool Planets Hot Planets ~100 Doppler wobble planets
Microlensing by a star Light from background stars is gravitationally bent around a as long as eground star. Light is amplified near the Einstein Ring. Misaligned objects produce 2 images, one inside in addition to one outside the Einstein Ring Now if I had a REALLY big telescope this is what a Sun-like star would do to the view of dust clouds in a nearby galaxy, 150,000 ly away. The Einstein ring of the star is about the size of Jupiters orbit round the Sun. First definitive planetary lens event! OGLE/PLANET/MOA collaboration 45 microlensing events monitored intensively over the last 5 years. No convincing Jupiter-like secondary peaks found until last week! Conclusion: less than 30% of lensing stars have Jupiters. First definitive planet detection announced in NASA press release by D. Bennetts team, 2004 April 15. Courtesy Dave Bennett in addition to OGLE/PLANET/MOA team members OGLE-2003-BLG-235/MOA-2003-BLG-53
Postcards from Titan Image Credit: NASA/JPL/University of Arizona Transiting extrasolar giant planets 19 examples known. Stellar mass in addition to period yield orbital separation a. Transit shape yields impact parameter stellar radius Transit depth yields ratio of radii Hence get direct measure of planetary density.
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