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PH709 Extrasolar Planets - 1 Professor Michael Smith 1 EXOPLANETS: Prof Michael SMITH TOPICS COVERED 1. 2. 3. 4. 5. 6. Introduction: Review & Status Measurement : Dynamics, Binaries 2-component systems Definitions, planets, disks; Detection methods Populations Theory of formation Theory of evolution, Migration/eccentricity RESOURCES MOODLE + Module page: http://astro.kent.ac.uk/mds/Modules/modules.htm THE EXOPLANET NEWSLETTER: Past editions of the Newsletter may be 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 1 PH709 Extrasolar Planets - 1 Professor Michael Smith 2 DESCRIPTION We are still in the early days of a revolution in the field of planetary sciences that was triggered by the discovery of planets around other stars. 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 Since the first exoplanet discoveries in the 1990s (Wolszczan & Frail 1992; Mayor & Queloz 1995) 1992: 1 discovered Now: 1160 planetary systems 1849 planets 471 multiple planet systems 3,359 to be confirmed (Kepler) 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 2 PH709 Extrasolar Planets - 1 Professor Michael Smith 3 Showing 1241 planetary systems / 1958 planets / 488 multiple planet systems as of 27/9/15 Types: Hot Jupiters – 300 earths Neptune-Twins – 17 earths Super-Earths Earth-Twins (since 2011) Mercury? – 1/19 earths 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', etc TRANSITS: KEPLER MISSION SURVEY Observational surveys for extrasolar planets probe the diverse outcomes of planet formation and evolution. These surveys measure the frequency of planets with different masses, sizes, orbital characteristics, and host star properties. Observations of exoplanets have entered a new age with the advent of the Kepler mission, see: http://kepler.nasa.gov/ Currently the most important class of exoplanets are those that transit the disk of their parent stars, allowing for a determination of planetary radii. Kepler was launched in 2009 and obtained precise photometric measurements with nearly continuous coverage for four years. 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/ 3 PH709 Extrasolar Planets - 1 Professor Michael Smith 4 Search of Kepler stellar light curves for the characteristic dips in flux indicative of a planet. Small planets between the sizes of Earth and Neptune substantially outnumber Jupiter-sized planets. Super-Earths with orbital periods less than 100 days are extremely abundant around Sun-like stars. It is unlikely that these planets formed at their current locations. Rather, they likely formed at large distances from the star and subsequently migrated inward. Kepler-10b is the first confirmed terrestrial planet to have been discovered outside the Solar System.[3] Discovered after several months of data collection during the course of the NASA-directed Kepler Mission, which aims to discover Earth-like planets crossing in front of their host stars, the planet's discovery was announced on January 10, 2011. Kepler-10b has a mass between 3.3 and 5.7 Earth masses and a radius of 1.4 Earth radii. However, it lies extremely close to its star, Kepler-10, and as a result is too hot to support life. Read this paper on the remarkable Kepler 11: http://adsabs.harvard.edu/abs/2013ApJ...770..131L 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 4 PH709 Extrasolar Planets - 1 Professor Michael Smith Intensity of starlight from Kepler 11 Kepler 11 b c d e f g 5 5 PH709 Extrasolar Planets - 1 Professor Michael Smith 6 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. Kepler-47, a system consisting of two planets orbiting around an eclipsing pair of stars. The inner and outer planets have radii 3.0 and 4.6 times that of Earth, respectively. The binary star consists of a Sun-like star and a companion roughly one-third its size, orbiting each other every 7.45 days. With an orbital period of 49.5 days for the inner planet. http://adsabs.harvard.edu/abs/2012Sci...337.1511O 6 PH709 Extrasolar Planets - 1 Professor Michael Smith 7 Comparative planetology, which once included only our Solar System's planets and moons, now includes Earth-twins, subNeptunes to super-Jupiter-mass planets in other solar systems. Overview of units: mass, distance and constitution Mass: Sun Jupiter 's mass Earth's mass Sun 1.989 10 30 kg MJ = 1.898 1027 kg ME = 5.974 1024 kg = 300,000 Jupiter = Neptune = Mercury = ME 300 ME 17.1 ME 0.0553 ME. Orbit/Distance: 1 astronomical units (AU) = 1.496 108 km, distance between Earth and Sun Planet Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Distance from Sun in AU 0.39 0.72 1.0 1.5 5.2 9.5 19.2 30.1 7 PH709 Extrasolar Planets - 1 Pluto Professor Michael Smith 8 39.5 Constitution Sun + MVEM gas rock + asteroids (Ceres) + JSUN rock gas + P rock/ice SUN: 99.85% of SS mass, 92% H, 8% He Density kg/m3 Earth is most dense, Saturn is much lower density…..: 1 Earth 5515 2 Mercury 5427 3 Venus 5243 4 Mars 3933 5 Moon 3350 6 Pluto 1750 7 Neptune 1638 8 Sun 1408 9 Jupiter 1326 10 Uranus 1270 11 Saturn 687 + moons, comets, asteroids, Kuiper belt, Oort cloud, debris, dust DOPPLER METHOD DOPPLER SPECTROSCOPY: METHOD RADIAL VELOCITY Radial velocity method permits a minimum planet mass to be determined. HARPS is a vacuum spectrograph designed to measure precise radial velocities, with the specific goal of searching for exoplanets in the Southern hemisphere. This high-resolution Echelle spectrograph (R=115000) is fiber-fed by the ESO 3.6-meter telescope at La Silla Observatory. R is the spectral Resolution: R = c / v. 8 PH709 Extrasolar Planets - 1 Professor Michael Smith 9 So R=15,000 is not itself very good. HOT JUPITERS Began earnestly in 1995 by definite discovering hot jupiters through Radial Velocity method; had to be close to satr in order to be detectable! . SUPER-EARTHS Thanks to remarkable progress, radial velocity surveys are now able to detect terrestrial planets at habitable distance from low-mass stars. The unexpected diversity of exoplanets includes a growing number of superEarth planets, i.e., exoplanets with masses smaller than 10 Earth masses. Unlike the larger exoplanets previously found, these smaller planets are more likely to have similar chemical and mineralogical composition to the Earth. EARTHS-TWINS And since 2011 we discuss earth twins ……. The most common class of planetary system detectable today consists of one or more planets approximately one to three times Earth’s size orbiting within a fraction of the Earth-Sun distance. In April 2013, using observations by NASA's Kepler Mission, a team led by William Borucki, of the agency's Ames Research Center, found five planets orbiting in the habitable zone of a Sun-like star, Kepler-62, 1,200 light years from Earth. These new super-Earths have radii of 1.3, 1.4, 1.6, and 1.9 times that of Earth. Theoretical modelling of two of these superEarths, Kepler-62e and Kepler-62f, suggests both could be solid, either rocky or rocky with frozen water. On June 25, 2013 Three “super Earth” planets have been found orbiting a nearby star at a distance where life in theory could exist, according to a record-breaking tally announced on Tuesday by the European Southern Observatory. They are part of a cluster of as many as seven planets that circle Gliese 667C, one of three stars located a relatively close 22 light years from Earth in the constellation of Scorpio, it said. The planets orbit Gliese 667C in the so-called Goldilocks Zone — a distance from the star at which the temperature is just right for water to exist in liquid form rather than being stripped away by stellar radiation or locked permanently in ice. Gliese 581d & Goldilocks. 9 PH709 Extrasolar Planets - 1 Professor Michael Smith 10 In April 2007, a team of 11 European scientists announced the discovery of a planet outside our solar system that is potentially habitable, with Earth-like temperatures. The planet was discovered by the European Southern Observatory's telescope in La Silla, Chile, which has a special instrument that splits light to find wobbles in different wave lengths, HARPS. Those wobbles can reveal the existence of other worlds. Gliese 581c. What they revealed is a planet circling the red dwarf star, Gliese 581. The discovery of the new planet, named Gliese 581c, is sure to fuel studies of planets circling similar dim stars. About 80 percent of the stars near Earth are red dwarfs. Super-earth. The new planet is about five times heavier than Earth, classifying it as a superearth. SIZE: Its discoverers aren't certain if it is rocky, like Earth, or if it is a frozen ice ball with liquid water on the surface. If it is rocky like Earth, which is what the prevailing theory proposes, it has a diameter about 1 1/2 times bigger than our planet. If it is an iceball, it would be even bigger. Gliese 581: M star: 3480K, mass: 0.31 solar masses; 0.29 solar radii, red dwarf star (approximately 6.12 parsecs from Earth) Luminosity: 0.013 solar Hot Neptune Gl 581b 15.7 ME Super-earth Gl 581c 5.06ME Super-earth Gl 581d 8.3 ME 0.041 AU 0.073 AU 0.22 AU Gl 581c: a pleasant 20C (albedo = 0.5 assumed) Greenhouse? Tidal locking? Extremophiles. An extremophile is an organism that thrives in and may even require physically or geochemically extreme conditions that are detrimental to the majority of life on Earth. Most known extremophiles are microbes. HZ – Habitable Zone: life zone", "Comfort Zone", "Green Belt" or "Goldilocks Zone" (because it's neither too hot nor too cold, but "just right") However, further research on the potential effects of the planetary atmosphere casts doubt upon the (extremophile life form) habitability of Gliese 581c: Planet “c” receives 30% more energy from its star than Venus from the Sun, 10 PH709 Extrasolar Planets - 1 Professor Michael Smith 11 with an increased radiative forcing caused by the spectral energy distribution of Gl 581. This planet is thus unlikely to host liquid water, although its habitability cannot be positively ruled out by theoretical models due to uncertainties affecting cloud properties and cloud cover. Gl 581d: , Gliese 581d, is a better candidate for habitability. Currently, Gliese 581d, the third planet of the, appears to be the best example yet discovered of a possible terrestrial exoplanet which orbits close to the habitable zone of space surrounding its star. Although Gliese 581 d orbits outside the theoretical habitable zone of its star, conditions on the planet may be conducive to supporting life. Scientists originally believed that Gliese 581 d would be too cold for liquid water to exist, and therefore could not support life in forms as existing on Earth. Going by strict terms, it appears to reside outside the "Goldilocks Zone", but the greenhouse effect may raise the planet's surface temperature to that which would support liquid water. Highly reflective clouds covering at least 75% of the day side of the planet could indeed prevent the water reservoir from being entirely vaporized. Planet “d”. Irradiation conditions of planet “d” are comparable to those of early Mars, which is known to have hosted surface liquid water. Thanks to the greenhouse effect of CO2-ice clouds, also invoked to explain the early Martian climate, planet “d” might be a better candidate for the first exoplanet known to be potentially habitable. Sources and sinks of atmospheric carbon dioxide. The photosynthesis11 PH709 Extrasolar Planets - 1 Professor Michael Smith 12 sustaining habitable zone (pHZ) is determined by the limits of biological productivity on the planetary surface. List of Habitable Planets: Kepler -62 Gliese 667c Gliese 581d etc…………. http://phl.upr.edu/projects/habitable-exoplanetscatalog . The Earth's temperature would be about -19°C without any greenhouse gases, and due to a theorized greenhouse effect of Gliese 581 d, research now suggests that atmospheric conditions on the planet could create temperatures at which liquid water can exist, and therefore the planet may be capable of supporting life. Now: f and g have been discovered but NOT confirmed. Gliese 581 g has attracted attention because it is near the middle of the habitable zone of its parent star. That means it could sustain liquid water on its surface and could potentially host life similar to that on Earth. 12 PH709 Extrasolar Planets - 1 Professor Michael Smith 13 Top view of the GJ 581 system. For reference, the orbits of Earth, Venus, and Mercury are overlaid as dashed blue, green, and red lines, respectively. NUMBERS 13 PH709 Extrasolar Planets - 1 Professor Michael Smith 14 Showing 1160 planetary systems / 1849 planets / 471 multiple planet systems as of 01/11/14 http://exoplanets.org/ 1492 planets with good orbits, 1,516 confirmed 3359 unconfirmed Kepler candidates Exoplamets are associated with: Fusing stars, Pulsars, Brown dwarfs. There is currently at least one known planet orbiting a brown dwarf. Exoplanets.eu Showing 1959 planets / 1241 planetary systems / 489 multiple planet systems RADIAL VELOCITY: Showing 612 planets / 458 planetary systems / 109 multiple planet systems TRANSITS: Showing 1221 planets / 689 planetary systems / 359 multiple planet systems Candidates detected by microlensing Showing 40 planets / 38 planetary systems / 2 multiple planet systems Candidates detected by imaging Showing 61 planets / 56 planetary systems / 3 multiple planet systems Candidates detected by timing Showing 19 planets / 14 planetary systems / 4 multiple planet systems + some cluster and free floating?, plenty of candidates, retractions, …… 14 PH709 Extrasolar Planets - 1 Professor Michael Smith 15 15 PH709 Extrasolar Planets - 1 Professor Michael Smith 16 16 PH709 Extrasolar Planets - 1 Professor Michael Smith 17 17 PH709 Extrasolar Planets - 1 Professor Michael Smith 18 18 PH709 Extrasolar Planets - 1 Professor Michael Smith 19 19 PH709 Extrasolar Planets - 1 Professor Michael Smith 20 20 PH709 Extrasolar Planets - 1 Professor Michael Smith Log scale: 21 21 PH709 Extrasolar Planets - 1 Professor Michael Smith 22 22 PH709 Extrasolar Planets - 1 Professor Michael Smith 23 23