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Exoplanets: the Search for Another Earth

Exoplanets: the Search for Another Earth. By Ben Waxer. Habitable Zone. Aka Goldilocks' Zone The range of a planet’s orbit around its star that allows the existence of liquid water Liquid water is a requirement of life Too close to the sun = too hot Too far from the sun = too cold.

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Exoplanets: the Search for Another Earth

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  1. Exoplanets: the Search for Another Earth By Ben Waxer

  2. Habitable Zone • Aka Goldilocks' Zone • The range of a planet’s orbit around its star that allows the existence of liquid water • Liquid water is a requirement of life • Too close to the sun = too hot • Too far from the sun = too cold

  3. Types of Exoplanets • Gas Giant • Hot Jupiter • Super Earth • Terrestrial • Unknown

  4. Gas Giants • Very massive • Thick atmosphere of hydrogen and helium • Core of rocky elements • Hydrogen and helium constitutes most of the planet or only an outer envelope

  5. Hot Jupiters • Subset of gas giants • Similar characteristics to Jupiter • Orbits very close to their stars • Incredibly high surface temperatures • Most common known form of extrasolar planet • Easy to detect

  6. Super Earths • Defined by mass only • 1.9 – 10 Earth masses • Debate over how to further classify them

  7. Terrestial • Aka rocky planet • Composition of silicate rocks or metals • Solid planetary surface • Central iron metallic core • Silicate mantle • Generally smaller and harder to detect • Many more detected with Kepler

  8. Needle in a Haystack • Radial Velocity variations 10 cm/s • Transit depths 10^-4 • Astrometric variations 0.1 microarcseconds • Contrast ratios of 10^-10 and 10^-7

  9. Search for Exoplanets • 1706 planets around 1036 stars • 442 systems with multiple planets • 415 Gas Giants • 1008 Hot Jupiters • 193 Super Earths • 80 Terrestrial Planets • 10 Unknown Planets

  10. Kepler • space telescope • March 2009 – August 2013 • surveyed 100,000 stars in constellation Cygnus • used transit method to detect planets • could detect planets 30-600 times less massive than Jupiter • has confirmed 942 exoplanets and 2903 candidates

  11. Methods of Detection • Doppler Effect • Transit • Gravitational Microlensing • Many others to a lesser extent

  12. Doppler Shift • Radial Velocity Method • Measures velocity changes • Star and planet orbit center of mass • Easier to detect close, massive planets • Hard to detect Earth-sized planets • Has found 499 planets

  13. Transit • Planet transits in between star and observer • Small dip in star brightness • Period of dip gives planet orbit • Depth of dip gives planet size • Method used by Kepler and CoRoT spacecraft • Has found 1126 planets

  14. Gravitational Microlensing • Light from Source star gets amplified as it is bent around the lens star • Amount of amplification grows with degree of alignment • Planet forms a binary lens with lens star • Causes caustics -> lightcurve variations

  15. Average fraction of microlensing source stars • LMC = 1.2*10^-7 • Bulge = 2.43*10^-6 • Einstein radius • Amplification Factor • Better detects low mass planets • Must monitor millions of stars • Only have one (short) try and can easily miss it if your timings off u= Lens-source angular separation / Einstein Radius

  16. Searching for Life • Mass and Radius -> Density • Compare to Models -> Planet Structure • Alternatively observe spectra and search for biosignatures • Planned for James Webb Space Telescope

  17. Interesting Exoplanets • Tau Bootis b • KOI-314c • Messier 67 • Kepler 186 f

  18. Tau Bootis b • Hot Jupiter • Water vapor found in atmosphere • 51 light years away • Analyzed faint spectra emitted by planet • Found unique signature of water

  19. KOI-314c • Approximately the mass of Earth • Orbits a red dwarf star • Large, ‘puffed-up’ atmosphere • 1.6 times the radius of Earth • Blurs the line between rocky planets and gas giants

  20. Messier 67 • Three planets in star cluster • 2600 light years away • Detected ‘wobble’ using radial velocity method • Two hot jupiters and one gas giant • One hot jupiter orbits a star nearly identical to the sun

  21. Kepler 186 f • 500 light years away • Most promising candidate • In Habitable Zone of its M type star • 1.1 times the size of Earth • Orbits every 130 days • Detected by Kepler using transit method

  22. The Con • More radiation • Life has to evolve to deal with this

  23. Just the Beginning • Reaching the point where we’re just starting to be able to detect Earth-sized planets. • Starting to see Earth Lookalikes such as Kepler 186f • Habitable planets around M-type stars

  24. Easier to Detect • Doppler Variations K ~ M*^(-3/2) • Transit Depth ~ M^-2 • M type stars ~ ¼ as massive as our sun -> Variations ~ 10 * larger

  25. Planets are Everywhere • We’ve seen planets around many types of stars. • In Binary Systems • In Star Clusters • For every star in the Milky Way, there is an estimated 1.6 planets. • Countless Galaxies and Stars in this Universe • The odds are that Earth 2.0 is out there somewhere • All we need to do is look for it

  26. References • Deep Astronomy. “Kepler’s New Universe.” Youtube. 19th February, 2014. 24th April 2014, https://www.youtube.com/watch?v=YmB-MYH3_1Q&feature=player_detailpage#t=18 . • Gannon, Megan. “Water Found in Atmosphere of Nearby Alien Planet.” Discovery. Discovery Communication, LLC. 26th February 2014. 26th April 2014. http://news.discovery.com/space/alien-life-exoplanets/water-found-in-atmosphere-of-nearby-alien-planet-140226.htm. • “Gas Giant.” Wikipedia. Wikimedia Foundation Inc. 24th April 2014. 1st May 2014. http://en.wikipedia.org/wiki/Gas_giant#Extrasolar_gas_giants. • Gens, Henry. “Professor Discovers New Exoplanet.” The Observer. The Observer. 28th April, 2014. 1st May, 2014. http://ndsmcobserver.com/2014/04/professor-discovers-new-exoplanet/. • “Gravitational Microlensing.” Wikipedia. Wikimedia Foundation Inc. 1st April 2014. 17th May 2014. http://en.wikipedia.org/wiki/Gravitational_microlensing. • Johnson, John. “International Year of Astronomy Invited Review on Exoplanets.” Caltech. 17th March, 2009. • Kane, Stephen. “Kepler 186 System” Habitable Zone Gallery. 25th April 2014, http://physics.sfsu.edu/~skane/hzgallery/493_2.png.

  27. “Kepler 186f.” Jet Propulsion Laboratory. NASA. 23rd April 2014, http://planetquest.jpl.nasa.gov/exoplanet/1789. • “Methods.” Jet Propulsion Laboratory. NASA. 23rd April 2014, http://planetquest.jpl.nasa.gov/page/methods. • O’neill, Ian. “Rare Exoplanet Found in Cluster, Orbits Sun’s Twin.” Discovery. Discovery Communication, LLC. 15th January 2014. 26th April 2014. http://news.discovery.com/space/alien-life-exoplanets/rare-exoplanet- found-in-star-cluster-orbits-suns-twin-140115.htm. • O’neill, Ian. “Weird Small ‘Puffed-Up’ Exoplanet Discovered.” Discovery. Discovery Communication, LLC. 6th January 2014. 26th April 2014. http://news.discovery.com/space/alien-life-exoplanets/weird-puffed-up-earth-mass-exoplanet-discovered-140106.htm. • Pheonixpics. “Exoplanets – What’s All the Fuss About.” Cumbrian Sky. WordPress. 29th March, 2009. http://cumbriansky.wordpress.com/2009/03/29/exploanets-whats-all-the-fuss-about/. • “Planet Counts.” NASA Exoplanet Archive. NASA. 24th April, 2014. http://exoplanetarchive.ipac.caltech.edu/docs/counts_detail.html. • Sackett, Penny. “Microlensing Exoplanets.” Scholarpedia. 2010. 17th May, 2014. http://www.scholarpedia.org/article/Microlensing_exoplanets. • “Super Earth.” Wikipedia. Wikimedia Foundation Inc. 22nd April 2014. 1st May 2014. http://en.wikipedia.org/wiki/Super-Earth. • “Terrestrial Planet.” Wikipedia. Wikimedia Foundation Inc. 21st March 2014. 1st May 2014. http://en.wikipedia.org/wiki/Terrestrial_planet.

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