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AST 248, Lecture 22 AST 248, Lecture 22 James Lattimer Department of Physics & Astronomy 449 ESS Bldg. Stony Brook University April 27, 2020 The Search for Life in the Universe [email protected] James Lattimer AST 248, Lecture 22 Uniqueness of Earth? I Sun has sufficient Main Sequence lifetime for life to develop and evolve. I Sun is a single star. I Earth has the right distance from the Sun, i.e., is in \Habitable Zone". Limits determined by runaway greenhouse and refrigerator effects. I Mass of Earth enough to retain large but not too large atmosphere, the greenhouse effect compensates for increasing solar luminosity. I Has large moon, producing tides and stabilizing Earth's spin axis. I Jupiter, giant planets removed minor planets and comets from Earth-crossing trajectories, reducing impact rate. I Jupiter also prevented a planet from forming, resulting in asteroids. I Solar composition has C/O<1 (0.55), so free oxygen is available. I The Earth has sufficient Fe to generate sufficient magnetic field to prevent loss of atmosphere, and also prevent oxygen catastrophe. I The Earth has sufficient water so that upper-mantle convection can lead to plate tectonics, which contribute to climate stability, being an important part of the CO2 cycle. James Lattimer AST 248, Lecture 22 Future Habitability of Earth I The Sun brightens as it ages, due to accumulation of He ash in Sun's core. Also, number of pressure-producing particles decreases (4H!He). The Sun's core temperature and density must increase to compensate, resulting in an increase in luminosity. I Since the Sun was born, its luminosity has increased about 30%. James Lattimer AST 248, Lecture 22 Search Techniques for Other Solar Systems I Satellite and space telescope infrared observations (IRAS, HST), of dust emission from protosolar disks. I Radio telescope searches for Jupiter-like bursts of radio waves. I Gravitational effects on motion of star due to planets I \wobbling" (astrometry) I Doppler shifts I Ground and space-based continuous monitoring of millions of stars (Kepler) I Planetary transits I Gravitational lensing (microlensing) I Imaging I Speckle imaging especially in infrared with adaptive optics I Nulling with interferometry and coronographs I Large space-based infrared interferometers (Ex-NPS) for direct imaging James Lattimer AST 248, Lecture 22 Disks James Lattimer AST 248, Lecture 22 Gravitational Effects I \wobbling" I Doppler shifts James Lattimer AST 248, Lecture 22 Limits of Doppler Technique Jupiter r Neptune r Earth r James Lattimer AST 248, Lecture 22 Transits Brief, periodic dimming of star James Lattimer AST 248, Lecture 22 HD 209458 H2O also identified James Lattimer AST 248, Lecture 22 Atmosphere James Lattimer AST 248, Lecture 22 Occultations James Lattimer AST 248, Lecture 22 James Lattimer AST 248, Lecture 22 Thermal Brightness Map James Lattimer AST 248, Lecture 22 Spectrography During Transits James Lattimer AST 248, Lecture 22 James Lattimer AST 248, Lecture 22 SWEEPS James Lattimer AST 248, Lecture 22 James Lattimer AST 248, Lecture 22 Gravitational Lensing Brief, one-time brightening of star James Lattimer AST 248, Lecture 22 Gravitational Lensing James Lattimer AST 248, Lecture 22 Direct Imaging I Existing methods have inherent limitations I Doppler method requires large orbital velocity; small period or orbital radius (a < 5 AU) I Transit method requires smaller orbit still (a < 1 AU) I Extracting atmospheric information is indirect and quite difficult James Lattimer AST 248, Lecture 22 Direct Imaging I Existing methods have inherent limitations I Doppler method requires large orbital velocity; small period or orbital radius (a < 5 AU) I Transit method requires smaller orbit still (a < 1 AU) I Extracting atmospheric information is indirect and quite difficult I Direct Detection I Permits direct atmosphere studies with spectroscopy I Very difficult: planets are intrinsically faint and very close (in angle) to bright star I Detectability greater if in larger orbits (a > 5 AU) I Brightness of planet increases with mass (> 5 MJup) I Brightness of Jovian planet greater if very young (< 10 Myr) James Lattimer AST 248, Lecture 22 James Lattimer AST 248, Lecture 22 James Lattimer AST 248, Lecture 22 Technical Challenge Diffraction from telescope aperture Currently not a limitation Could be reduced with coronagraphy Scattering from atmosphere Can be compensated by adaptive optics Scattering from optics Small defects on optical surfaces Speckles produced are problematic James Lattimer AST 248, Lecture 22 What's Been Found James Lattimer AST 248, Lecture 22 What's Been Found James Lattimer AST 248, Lecture 22 What's Been Found James Lattimer AST 248, Lecture 22 What's Been Found James Lattimer AST 248, Lecture 22 Hot Jupiters Hot Jupiters cannot have formed in their present locations. I No massive planets can form inside the ice-line, since the amount of heavy elements is too small. I Not enough material available there to form a massive planet. Inward migration due to I Slow migration due to momentum transfer from asteroid/comet/dust gravitational scattering, (slingshot or gravity-assist effect). I Fast migration due to planet-planet gravitational scattering, perhaps ejecting or relocating small planets. I Kozai cycles: interactions due to an outer massive companion (stellar binary companion), \cold friends". Could distinguish these: I Slow migration dampens inclination I Planet-planet scattering gives wide range of inclinations I Outer massive companion also gives wide range of inclination. About 10% of hot Jupiters have \cold friends" from observations. Hot stars with hot Jupiters have high obliquities. James Lattimer AST 248, Lecture 22 Overall, Hot Jupiters are Rare James Lattimer AST 248, Lecture 22 James Lattimer AST 248, Lecture 22 James Lattimer AST 248, Lecture 22 James Lattimer AST 248, Lecture 22 James Lattimer AST 248, Lecture 22 James Lattimer AST 248, Lecture 22 Exoplanet Radii Many planets have too-large radii to explain with cold substances. Heating could be due to tidal dissipation from I orbital eccentricity or obliquity (inclination between rotation and spin axes) I thermal tides I ohmic dissipation of electrical currents, or I high atmospheric opacity. James Lattimer AST 248, Lecture 22 Gliese 581 James Lattimer AST 248, Lecture 22 Kepler's Planets James Lattimer AST 248, Lecture 22 Kepler-11 System James Lattimer AST 248, Lecture 22 James Lattimer AST 248, Lecture 22 James Lattimer AST 248, Lecture 22 Recent Successes of Direct Imaging I GQ Lupi b I AB Pic A b I CT Cha b I DH Tau b I CHXR 73 (Cha I) b I 1RXJS J1609-2104 b: A giant planet candidate around a young solar analogue I HR 8799 bcd: A system of three giant planets I Fomalhaut b: Opticatl detection of a giant planet inside a dusty disc I β Pic b: A giant planet at only 8 AU James Lattimer AST 248, Lecture 22 James Lattimer AST 248, Lecture 22 Multi-Planet Detection: HR 8799 James Lattimer AST 248, Lecture 22 Fomalhaut James Lattimer AST 248, Lecture 22 β Pictoris James Lattimer AST 248, Lecture 22 Planetary Spectra James Lattimer AST 248, Lecture 22 Terrestrial Planet Finder James Lattimer AST 248, Lecture 22 The Future James Lattimer AST 248, Lecture 22 James Lattimer AST 248, Lecture 22.
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