3677 Life in the Universe: Extra-solar planets

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3677 Life in the UniverseExtra-solar planets

• Dr. Matt Burleigh
• www.star.le.ac.uk/mrb1/lectures.html

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Course outline

• Lecture 1
• Definition of a planet
• A little history
• Pulsar planets
• Doppler wobble (radial velocity) technique
• Lecture 2
• Transiting planets
• Transit search projects
• Detecting the atmospheres of transiting planets

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Course outline

• Lecture 3
• Microlensing
• Direct Imaging
• Planets around evolved stars
• Lecture 4
• Statistics mass and orbital distributions,
  incidence of solar systems, etc.
• Hot Jupiters
• Super-Earths
• Planetary formation
• The host stars

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Course outline

• Lecture 5
• The quest for an Earth-like planet
• Results from the Kepler mission
• Habitable zones
• Biomarkers
• Future telescopes and space missions

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Useful numbers

• RSun 6.995x108m
• Rjup 6.9961x107m 0.1RSun
• Rnep 2.4622x107m 4Rearth
• Rearth 6.371x106m 0.1Rjup 0.01RSun
• MSun 1.989x1030kg
• Mjup 1.898x1027kg 0.001MSun 317.8Mearth
• Mnep 1.02x1026kg 5x10-5MSun 0.05Mjup
  17.15Mearth
• Mearth 5.97x1024kg 3x10-6MSun 3.14x10-3Mjup
• 1AU 1.496x1011m
• 1 day 86400s

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Towards other Earths
Telescope Method Date
Corot (Fr) Transits 2007
Kepler (NASA) Transits 2009
GAIA (ESA) Astrometry 2013
SIM (NASA) Astrometry 2015 (?)
CHEOPS (ESA) Transits 2017
TESS (NASA) Transits 2017
Plato (ESA) Transits 2024
Darwin (ESA) Imaging 2030 (?)
39m E-ELT Imaging 2021
JWST Imaging 2018
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Towards Other Earths Habitable Zones

• Habitable zone defined as where liquid water
  exists
• Changes in extent and distance from star
  according to stars spectral type (ie temperature)

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Kepler

• Searching for Earths by transit method
• Launched 2009 by NASA
• 0.95m schmidt telescope, FOV 105 square deg.
• 150,000 MS stars, with V10 - gt14 mag
• Aim find an Earth around a Sun-like star in a
  one year orbit
• Need three transits
• So mission lasts at least three years

Jupiter
Earth
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Kepler results
By Nov 2014 Kepler had identified 4,173 candidate
planets (most unconfirmed)
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Kepler results

• Petigura et al. 2013
• 114 of sun-like stars have an Earth-sized
  planet receiving 1 to 4 times the stellar
  intensity that Earth receives
• define Earth-sized as 1-2REarth
• 5.7 (1.7 - 2.2) of Sun-like stars have an
  Earth-sized planet with orbital periods between
  200 400 days
• 22 of Sun-like stars have Earth-sized planets
  orbiting within their habitable zones
• (generous definition of HZ includes Venus
  Mars!)
• Implies gt10 billion Earths in milky way galaxy!
• suggests that the nearest such planet could be
  within 12 light years

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Keplers limitations

• Kepler observes probable transit events
• Validates these
• with 3 transits
• tries to rule out background binaries/triple star
  systems
• Statistical likelihood planet is real
• But transit only gives radius
• To confirm its a planet, need mass, and hence
  density
• Confirm structure gas giant or terrestrial
• Although we dont know where boundary lies
  Super-Earths

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Keplers limitations

• Mass comes from two sources
• Radial velocity observations
• But most Kepler stars are too faint for Doppler
  Wobble measurements with current telescopes
• Transit timing variations
• Kepler media confuse planet status
• Earth-sized?
• Earth-like?
• Earth-mass?

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Earth-like planet detected!

• Astronomers Find First Habitable Earth-Like
  Planet
• Science Daily, 24 April 2007
• Gliese 581g the most Earth like planet yet
  discovered
• Daily Telegraph, 29 Sep 2010
• Super-earth exoplanet found that could support
  life
• The Guardian, 13 Sep 2011

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Kepler-22b

• Kepler has observed 3 transits
• Lies within its stars habitable zone
• 290 day orbit
• The radius is 2.4x Earth
• NO mass measurement
• Upper limit of 38x Earth
• Could be rocky, or gaseous
• Host star too faint (gt11th) for RV

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• Ranked by Earth Similarity Index where Earth
  1.00
• See http//phl.upr.edu/projects/earth-similarity-i
  ndex-esi
• Define Earth-like as ESIgt0.9 none meet this
  criterion

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Tatooine-like planet Kepler-16-b
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Kepler-11

• Multiple system of 6 planets
• Masses measured through transit timing variations
• Effect of gravity on time of centre of successive
  transits

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Alpha Cen Bb

• Alpha Cen system is the nearest star system to us
• Alpha Cen B has been monitored by radial velocity
  method
• Very recent discovery of a rocky planet
• Minimum mass 1.1xEarth
• Period 3.2 days
• Dumusque et al. 2012, Nature
• Thought if Alpha Cen B has a rocky planet, do
  most stars have rocky planets?

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Towards Other Earths Biomarkers

• So we find a planet with the same mass as Earth,
  and in the habitable zone
• How can we tell it harbours life?
• Search for biomarkers
• Water
• Ozone
• Albedo