Lecture 16: Exoplanets, Brown Dwarfs, This class Exoplanets Chapt 15 brown dwarfs Read before coming to class The Sun Chapt 16 Stars Chapt 17 flux, luminosity, magnitudes, spectra Hertzsprung-Russell Diagram Full Moon by Michael Light negatives by astronauts. ALL NOTES COPYRIGHT JAYANNE ENGLISH

dist < 1/2 dist between Earth & Luna News! Oct 19th dist == distance Discovered by:Robert H. McNaught at Siding Spring Observatory in Australia Comet Siding Spring, will pass within ~139,500 kilometers of the Red Planet dist < 1/2 dist between Earth & Luna dist < 1/10 dist of any known comet flyby of Earth. Named after Siding Spring Observatory

Exoplanets and their planetary systems: David Lafreniere, Ray Jayawardhana, Marten H. van Kerkwijk (University of Toronto, Gemini Observatory) This image could be the first direct image of a planet (upper left) around another Sun-like star (center). Extra-solar planets == exoplanets How different from those in our SS (Solar System)? Are our theories about SS formation applicable to other systems? We’ve described our solar system in general.

Atacama Larger Millimeter/submillimeter Array (ALMA) 64 antennas 22 countries (incl. Canada) molecular emission lines  Molecular gas distribution, T, density & motions.

“hybrid disk”  both planetesimals (dust) and gas dust more extended Proplyd disk around HD 21997 DUST RING (Hershel Space Obs. & ALMA) CO gas (ALMA) Gas rotating around host star (ALMA) If it had T Tauri stage at a few million years the gas would have been cleared by now but nuclear fusion doesn’t turn on until 10 million years so perhaps this is ok. ~10 million years old “hybrid disk”  both planetesimals (dust) and gas dust more extended

Exoplanets: Characteristics MASSES Roughly 1822 planets detected (this week). Interactive catalogue at http://exoplanet.eu/ # of planets Mass Uranus Mass Earth Super-Earths Mj == Jupiter Masses. Earth is 0.003 Mj. SuperEarths are 5- 10 mass of Earth last year’s histograms on this page This is quite different from the solar system! When have a mass orbiting a central mass, we can determine the central mass. Mass Uranus masses in Jupiter’s mass (Mjup: 318 x Mearth). maximum mass ~ 50 x Mjup  gas giants

Exoplanets: Characteristics DISTANCES Roughly 1822 planets detected. Interactive catalogue at http://exoplanet.eu/ # of planets This year’s histogram Mj == Jupiter Masses. Earth is 0.003 Mj. This is quite different from the solar system! Can get radius of orbit from Kepler’s 3rd law. Distance Earth Distance Neptune distance from host star in AU maximum distance a few thousand AU  most are closer than Earth

Exoplanets: Characteristics Note that by 2009 only 23 planets found with masses less than Jupiter. small mass planets rare? or was our observational method biased?

Exoplanets: Radial Velocity Method Radial Velocity == velocity along our line of sight. Fgrav between star + planet causes star to be pulled towards planet.  star wobbles  Star’s motion is Doppler Shifted. shift correlates with Fgrav See our class’s public website for animations. Movie

Exoplanets: Radial Velocity Method If m (==planet mass) large, then F large  radial velocity large. If r (== star – planet distance) small, then F large  radial velocity large.  Easier to detect massive planet close to star. See the class’s public website for animations.

Review Most exoplanets detected to ~2013 had masses similar to Jovians & orbit closer to their star than Jupiter does to ours.

Exoplanets: Doppler Shift Method Period Jupiter (5 AU) = 12 yrs. long time for one person to observe one star! note Saturn’s Period vs career length.  Easier to detect planets close to star. Currently team work  longer time.

most low-mass candidates in multi-planet systems. Artist’s impression: The star Gliese 667 C, which belongs to a triple system – 2 of the stars seen in the background. The 6 Earth-mass exoplanet circulates around its low-mass host star at a distance equal to only 1/20th of the Earth-Sun distance. Exoplanets Planet around alpha Centauri B! Sun-like star. 4.3 ly distant, 3 stars. Earth mass planet P~3 days closer than Mercury High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph, on ESO's 3.6-metre telescope, discovery of 150 exoplanets Sept 12/11. at that time HARPS helped discover most of the planets of mass < 20 Earth masses -> super-Earths and small gas giants. (About 40). most low-mass candidates in multi-planet systems.

r = 1.2 x Earth & M = 1.7 x Earth  density ~ Earth => same density Exoplanets -- Kepler 78b r = 1.2 x Earth & M = 1.7 x Earth  density ~ Earth => same density orbit’s every 8.5 hrs => 2000K hotter tidal forces will break it apart HARPS & HIRES spectrograph on Keck I

Exoplanets CoRoT- 7b (HARPS on ESO 3.6m) 5 earth-masses Density Earth-like  rocky. 23 * closer to star than Mercury to Sun Gliese 581g ((aka Zaramina’s World) (HIRES on Keck) red dwarf star in habitable zone (.15 AU) – distance for liquid H2O 3* earth-mass; 1.5* earth-diameter Could just do Gliese 581g

Exoplanets: Transit Method method for Canada's space telescope called MOST Produces a light curve (Intensity vs Time) as the planet orbits. larger planets  larger dips in light curve. closer planets  shorter time between dips (e.g. within career).  Easier to detect large planets close to their star. movie Now there are1147 planets discovered by this method (i.e. Kepler Mission) There are earth-sized planets but harder to detect.

Launched March 2009 - now finished. This is a test on a known planet. Exoplanets Kepler made it easier to detect smaller planets. NASA’s Kepler Mission Launched March 2009 - now finished. This is a test on a known planet.

r = 1.2 x Earth & M = 1.7 x Earth  density ~ Earth => same density Exoplanets -- Kepler 78b The equations for the derivation of a planet’s mass, radius, and density were given in lecture. How do we get planet radius for density? Transit method. r = 1.2 x Earth & M = 1.7 x Earth  density ~ Earth => same density

Combine Spectroscopy and Transit method  Temperature Maps http://www.nasa.gov/press/2014/october/nasas-hubble-maps-the-temperature-and-water-vapor-on-an-extreme-exoplanet/#.VDc8VUuAbGs WASP-43b is too distant to be photographed, but because its orbit is observed edge-on to Earth, astronomers detected it by observing regular dips in the light of its parent star as the planet passes in front of it.The planet is about the same size as Jupiter, but is nearly twice as massive. The planet is so close to its orange dwarf host star that it completes an orbit in just 19 hours. The planet is also gravitationally locked so that it keeps one hemisphere facing the star, just as our moon keeps one face toward Earth.The scientists combined two previous methods of analyzing exoplanets and put them together in one for the first time to study the atmosphere of WASP-43b. Spectroscopy allowed them to determine the water abundance and temperature structure of the atmosphere. By observing the planet’s rotation, the astronomers were also able to measure the water abundances and temperatures at different longitudes. Tidally locked Hot Jupiter WASP-43b too distant to be photographed T and H2O abundance at different longitudes

Exoplanets: Imaging Technique low resolution high resolution Recall resolution.

Resolved and Unresolved: These are generalizations. Some galaxies are so far away that they are unresolved. Some stars are becoming resolved using new technologies and observing techniques. We will talk more about this in the section on stars later in the term. Resolved galaxies in background. Generally structure of stars cannot be distinguished  unresolved.

Exoplanets: Imaging Technique David Lafreniere, Ray Jayawardhana, Marten H. van Kerkwijk (University of Toronto, Gemini Observatory) This image could be the first direct image of a planet (upper left) around another Sun-like star (center). Resolve the planet from its host star. Do not resolve surface of either star or planet.

Imaging Technique  birth of a giant planet! http://www.eso.org/public/news/eso1310/ This composite image shows a view from the NASA/ESA Hubble Space Telescope (left) and from the NACO system on ESO’s Very Large Telescope (right) of the gas and dust around the young star HD 100546. The Hubble visible-light image shows the outer disc of gas and dust around the star. The new infrared VLT picture of a small part of the disc shows a candidate protoplanet. Both pictures were taken with a special coronagraph that suppresses the light from the brilliant star. The position of the star is marked with a red cross in both panels. HST: protoplanetary disk ESO: protoplanet candidate ESO’s Very Large Telescope on right with adaptive optics and coronograph.

Exoplanets: Imaging Technique Other techniques are microlensing and pulsar timing. Found 51 planets, all but 2 have M >= 3*Mjup, up to 32*Mjup Fomalhaut planet < 3 Earth masses.

Review There was an observational bias systems with Hot Jupiters mass  stronger Doppler Shift in radial velocity method  larger light dip in transit method proximity  shorter time in radial velocity method shorter time in transit method but there are super-Earths.

There are planets smaller than Jupiter Harder to detect them. Summary There are planets smaller than Jupiter Harder to detect them. Now have 405 planetary systems with planets M<10*M_Earth. (333 multiple planet systems) 885 planets Other planetary systems are different than ours massive planets close to star but both condensation and instabilty theories predict gas giants in outer solar system

Exoplanets: planets close to host stars Migration while there is still the gas disk: E.g. friction between the gas disk and the protoplanets cause the protoplanets to lose energy and spiral inwards. Gap blown by proto-star’s wind. Particularly effective for “Hot Jupiters”. Hot Jupiters are planets close to their host star. Perhaps even Jupiter formed out in the Kuiper Belt and migrated in.

Later Migration: The Nice Model Got to here. In the era of planetesimal ejection Neptune moves outside orbit of Uranus.