* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download ph507-16-1exo1
Discovery of Neptune wikipedia , lookup
Geocentric model wikipedia , lookup
History of astronomy wikipedia , lookup
Space Interferometry Mission wikipedia , lookup
Circumstellar habitable zone wikipedia , lookup
Nebular hypothesis wikipedia , lookup
Astrobiology wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Rare Earth hypothesis wikipedia , lookup
Kepler (spacecraft) wikipedia , lookup
Astronomical naming conventions wikipedia , lookup
Late Heavy Bombardment wikipedia , lookup
Formation and evolution of the Solar System wikipedia , lookup
History of Solar System formation and evolution hypotheses wikipedia , lookup
Satellite system (astronomy) wikipedia , lookup
Planets in astrology wikipedia , lookup
Planets beyond Neptune wikipedia , lookup
Extraterrestrial life wikipedia , lookup
Exoplanetology wikipedia , lookup
Definition of planet wikipedia , lookup
IAU definition of planet wikipedia , lookup
PH507 Astrophysics Prof M Smith 1 EXOPLANETS: Prof Michael SMITH TOPICS COVERED 1. 2. 3. 4. 5. Introduction: Review & Status Definitions, planets, disks. Discovery and detection methods Populations Properties: metallicity, eccentricity RESOURCES MOODLE + Module page: http://astro.kent.ac.uk/mds/Modules/modules.htm THE EXOPLANET NEWSLETTER: Past editions of the Newsletter http://exoplanet.open.ac.uk TABLES AND DATA http://exoplanetarchive.ipac.caltech.edu/cgi-bin/ExoTables/nphexotbls?dataset=planets see Table Plotter and http://exoplanets.org http://exoplanet.eu/ http://en.wikipedia.org/wiki/Extrasolar_planet Watch latest on discovery methods: http://www.youtube.com/watch?v=uicxfBcQIog See latest on discoveries: http://adsabs.harvard.edu/abs/2013arXiv1307.2944A http://exoplanetarchive.ipac.caltech.edu DESCRIPTION PH507 Astrophysics Prof M Smith 2 Definition of a Planet: • Discovery of large (bigger than Pluto) trans-Neptunian Objects (e.g. Eris, which has a mass that is over 25% bigger than Pluto) led to a problem – were these planets? Was Pluto not a planet? • International Astronomical Union ruled (in 2006) that a planet: Is in orbit around the Sun. Has sufficient mass to be in hydrostatic equilibrium and hence roughly spherical. Has “cleared the neighbourhood” of its orbit. • If only the first two criteria are fulfilled, the object is defined as a Dwarf Planet – e.g. Ceres (orbits Sun, is spherical, but lies in asteroid belt) and Pluto (orbits Sun, is spherical, but has not cleared orbital region). • What do you think? An extrasolar planet, or exoplanet, is a planet outside the Solar System. 1. Outside our solar system 2. Nuclear fusion not significant 3. Less than 13/1000 of our Suns mass = Less than 13 Jupiter masses Definition of a star/brown dwarf/planet • Stars: burn hydrogen (M > 0.075 Msun) • Brown dwarfs: burn deuterium • Planets: do not burn deuterium (M < 0.013 Msun) Deuterium burning limit occurs at around 13 Jupiter masses (1 MJ = 1.9 x 1027 kg ~ 0.001 Msun objects, there is no large change in properties at the deuterium burning limit. ALL young stars / brown dwarfs / planets liberate gravitational potential energy as they contract PH507 Astrophysics Prof M Smith 3 STATUS: Since the first exoplanet discoveries in the 1990s (Wolszczan & Frail 1992; Mayor & Queloz 1995) 1992: 1 discovered http://exoplanet.eu/catalog.php . Showing 661 planetary systems / 838 planets / 125 multiple planet systems as of 22/09/2012 Showing 750 planetary systems / 986 planets / 168 multiple planet systems as of 28/09/2013 Showing 1125 planetary systems / 1810 planets / 466 multiple planet systems as of 20/07/14 Showing 1160 planetary systems / 1849 planets / 471 multiple planet systems as of 01/11/14 Showing 1331 planetary systems / 2085 planets / 509 multiple planet systems as of 20/2/16 DETECTION: Although few of the planets have been directly imaged, the effects of the gravity tugging at the stars, as well as the way that gravitation affects can affect material close to the stars, has been clearly seen. PH507 Astrophysics Prof M Smith 4 Disc of material around the star Beta Pictoris – the image of the bright central star has been artificially blocked out by astronomers using a ‘Coronograph’ Types of planet Giant planets (gas giants, `massive’ planets) • Solar System prototypes: Jupiter, Saturn, Uranus... • Substantial gaseous envelopes • Masses of the order of Jupiter mass • In the Solar System, NOT same composition as Sun • Presence of gas implies formation while gas was still prevalent Cores: Gas giants may have a rocky or metallic core—in fact, such a core is thought to be required for a gas giant to form. H and He: The majority of its mass is in the form of the gaseous hydrogen and helium, with traces of water, methane, ammonia, and other hydrogen compounds. PH507 Astrophysics Prof M Smith 5 Terrestrial planets Mercury: 75% iron/nickel : • Prototypes: Earth, Venus, Mars • Primarily composed of silicate rocks (carbon/diamond planets?) • In the Solar System (ONLY) orbital radii less than giant planets PH507 Astrophysics Prof M Smith 6 Much more massive terrestrial planets could exist (>10 Earth masses), though none are present in the Solar System. The Solar system also has asteroids, comets, planetary satellites and rings we won’t discuss those in this course. Core: A central metallic core, mostly iron with a surrounding silicate mantle. The Moon is similar, but lacks an iron core. Terrestrial planets have canyons, craters, mountains, and volcanoes. Types of EXOplanet Hot Jupiters – 300 earths Neptune-Twins – 17 earths Super-Earths Earth-Twins (since 2011) Mercury? Small planets between the sizes of Earth and Neptune substantially outnumber Jupiter-sized planets. NAMING CONVENTION Names: According to astronomical naming conventions, the official designation for a body orbiting a star is the star's catalogue number followed by a letter. The star itself is designated with the letter 'a', and orbiting bodies by 'b', 'c', et Currently the most important class of exoplanets are those that transit the disk of their parent stars, allowing for a determination of planetary radii. TRANSITS: KEPLER MISSION SURVEY Kepler was launched in 2009 and obtained precise photometric measurements with nearly continuous coverage for four years. PH507 Astrophysics Prof M Smith 7 The Kepler mission (Transit Method) continuously monitored one patch of sky in the Cygnus region, monitoring 160,000 mainsequence stars. Detection of sub-Earth size planets was the mission's goal, with detection of planets with radii as small at 1 Mercury radius possible around M stars. http://kepler.nasa.gov/ Search of Kepler stellar light curves for the characteristic dips in flux indicative of a planet Kepler-10b is the first confirmed terrestrial planet to have been discovered outside the Solar System The Kepler mission has recently discovered a number of exoplanetary systems, such as Kepler-11 and Kepler-32, in which ensembles of several planets are found in very closely packed orbits (often within a few per cent of an AU of one another). The Kepler-11 planetary system contains six transiting planets ranging in size from 1.8 to 4.2 times the radius of Earth. Five of these planets orbit in a tightly packed configuration with periods between 10 and 47 days. CIRCUMBINARY & CIRCUMPRIMARY PLANETS Kepler-16: We report the detection of a planet whose orbit surrounds a pair of low-mass stars. http://adsabs.harvard.edu/abs/2011Sci...333.1602D PH507 Astrophysics Prof M Smith Intensity of starlight from Kepler 11 Kepler 11 b c d e f g 8 PH507 Astrophysics Prof M Smith 9 TOP: Geometry of the Kepler 16b stellar system. Two stars move about their center of mass, while Kepler 16b orbits both stars. LOWER: Kepler 16b is Saturn-like, but the view from its cloud tops could be similar to the view imagined from the planet Tatooine in the movie Star Wars. Atmosphere of Planet Gas giants possess primary atmospheres — atmospheres captured directly from the originalsolar nebula. Terrestrial planets possess secondary atmospheres — atmospheres generated through internal vulcanism and comet impacts. Temperature of Planet Estimate the temperature of an exoplanet based on the intensity of the light it receives from its parent star. PH507 Astrophysics Prof M Smith 10 We calculate the equilibrium blackbody temperature of a planet. We assume that thermal equilibirium (i.e., constant temperature) applies, and consequently that the power ( = energy/time) emitted by the planet is the power absorbed from its parent star: Pabsorbed = Pemitted The left hand side is found from geometry, corrected by a coefficient that takes into account reflected light; the right hand side is given by the Stefan-Boltzmann law: Lstar (1 - A) ( Rp/4 dp)2 = 4 p 2 Tp4 Lstar = luminosity (power) of the parent star A = planet's albedo = (light reflected)/(light incident) Rp = planet's radius Tp = planet's temperature dp = distance of planet from parent star = Stefan-Boltzmann constant Solving for Tp gives Tp4 = Lstar(1 - A)/(16 p 2 ) Albedo? Notice that the equilibrium temperature depends on the "guessed" albedo of the planet; This calculation doesn't take into account the thermal energy released from the planet's interior, tidal energy released via a starplanet interaction, the greenhouse effect in the atmosphere, etc. DISTRIBUTIONS: MASS, log(MASS), log(number)-log(MASS) PH507 Astrophysics Prof M Smith 11 PH507 Astrophysics Prof M Smith 12 PH507 Astrophysics Prof M Smith 13 PH507 Astrophysics Prof M Smith 14 PH507 Astrophysics Prof M Smith 15 PH507 Astrophysics Prof M Smith 16 PH507 Astrophysics ECCENTRICITY Prof M Smith 17 PH507 Astrophysics METALLICITY Prof M Smith 18