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January 4 2006 Summary

January 4 2006 Summary. Earth is a relatively large terrestrial planet with internal heat sources and active geological environment (eg volcanism, plate tectonics) The atmosphere acts as a thermal blanket for the biosphere and allows for the Greenhouse effect to occur.

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January 4 2006 Summary

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  1. January 4 2006 Summary Earth is a relatively large terrestrial planet with internal heat sources and active geological environment (eg volcanism, plate tectonics) The atmosphere acts as a thermal blanket for the biosphere and allows for the Greenhouse effect to occur. As a result of the atmosphere and our proximity to the Sun, water is able to exist in all three states of matter: solid (ice), liquid (water) and gas (vapour). The magnetic filed of the Earth deflects harmful particulate radiation from the Sun away from the planetary surface but does allow for some auroral activity to be visible. The Moon and the Earth orbit about their common centre of mass (baricentre) and it in turn traces out an orbital path about the Sun. The Moon is a relatively small world, devoid of active geology and has no atmosphere of magnetic field. The surface of the Moon is littered with craters, a testimony to the dangers posed by material impacting a planetary surface. The Moon generates tides on the Earth’s oceans (gravitational tidal force) which are strongest during full and new Moon phases. The Earth exists within the Habitable Zone of our Solar System (where water can exist in all three phases). Mars and Venus are on the edges of the Habitable Zone.

  2. Extra-solar planets January 9 + 11

  3. ExoPlanet Discovery techniques Direct Detection: • Message Detection (from a civilization) • Direct Observation (of planet) • Radial velocity (Doppler) observations In-direct Detection: • Gravitational Lensing • Transit • Astrometry

  4. Gravitational Lensing Magnification by planet Magnification by star Brightness Gravitational Lensing: Star and planet magnifies background starlight -20 0 +20 Time (days)

  5. Doppler Effect: the wavelength is affected by therelative motion between the source and the observer

  6. Doppler Shifts • Red Shift: The object is moving away from the observer • Blue Shift: The object is moving towards the observer Dl/lo = v/c Dl = wavelength shift lo = wavelength if source is not moving v = velocity of source c = speed of light

  7. Astronomers have discovered planets orbitingother stars • Geoff Marcy is using the 10-meter Keck telescope in Hawaii to measure the Doppler effect in stars that wobble because of planets orbiting around them • So far, he and other teams have found more than 170 extrasolar planets

  8. January 9 2006 Brief Summary • A number of Direct and In-Direct techniques exist for discovering Extrasolar Planets (also known as Exoplanets). • Direct techniques include receiving a message from another civilization or seeing an image of an extrasolar planet. • Remember that a planet shines by reflected light and is thus very faint compared to the star it is orbiting. The planet never strays very far from the star from our perspective here on Earth • In-direct techniques include radial velocity (wobble) techniques, gravitational lensing, transit method and astrometry. • By far the most successful discovery method is the radial velocity technique which relies on the Doppler effect. • The wobble technique assumes that a star will physically be perturbed by the orbit of a planet around it and the resulting motion of the star’s spectral lines can be observed. • The Doppler effect (applicable to all forms of wave motion) states that the apparent change in frequency (and wavelength) of a signal occurs because of the relative velocity between a source of waves (a star in this instance) and the receiver (you). • Red shifted spectra means the star is moving away f4om you: blue shifted spectra means the star is moving towards you. • Many techniques rely on repeat observation to substantiate a claim for a planet’s existence. Such observations though depend on the orbital period of a planet which can be very long.

  9. Stellar wobbles Planet Center of Mass Parent Star To Earth

  10. Finding Extrasolar Planets • The planets themselves are not visible; their presence is detected by the “wobble” of the stars around which they orbit

  11. Extrasolar Planets Most of the extrasolar planets discovered to date are quite massive and have orbits that are very different from planets in our solar system

  12. The results so far So-called “hot Jupiters” (or “roasters”) are relatively common – a few % of stars have them. Separations of 0.05-5 Astronomical Units (AU). (1 AU is the distance from the Earth to the Sun). Temperatures of 1000K Orbital periods of days.

  13. Other Detection Techniques • Pulsar Timing • Dust disk-warping • Optical Interferometry

  14. Future Space Missions • Terrestrial Planet Finder Mission (TPF) • Kepler • Space-based Interferometer Mission (SIM)

  15. Terrestrial Planet Finder

  16. TPF • A possible method - free-flying multiple mirrors in space. • A serious technological challenge: • Need to maintain path difference to within 20 nm (200 atoms) • 200m separation • Deep space (at Lagrange point)

  17. Kepler

  18. Planet Quest Overview • Intro and over-view

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