Extra Solar Planets - Worlds around Other Stars Terry Evans 12th March 2014

Methods of Detecting Extra-Solar Planets Extra-solar planetary system types What Next?

Methods of Detecting Planets Radial Velocity Measurements Transits Timing Variations Microlensing Direct Observation Astrometry

Radial Velocity Measurement Uses Doppler Shift (Red/Blue shift)

Radial Velocity Measurement Uses Doppler Shift (Red/Blue shift) Detects the motion of the star caused by the orbiting planet

Radial Velocity Measurement Uses Doppler Shift (Red/Blue shift) Detects the motion of the star caused by the orbiting planet Detects more planets orbiting in line of sight

Radial Velocity Measurement Uses Doppler Shift (Red/Blue shift) Detects the motion of the star caused by the orbiting planet Detects more planets orbiting in line of sight Can provide minimum mass of a planet and/or inclination ( M sin(i) ) Can detect more than one planet by frequency analysis

51 Pegasi First extra-solar planetary system discovered around a normal star Announced 6th Oct 1995 by Mayor & Queloz Discovered by Radial Velocity measurements

51 Pegasi First extra-solar planetary system discovered around a normal star Announced 6th Oct 1995 by Swiss astronomers Mayor & Queloz Discovered by Radial Velocity measurements Probably orbits inclined by 79 degrees Period 4.23d Orbits 8 M miles from the star Minimum Mass 0.5 MJ (Jupiter Mass) “Hot Jupiter”

HARPS

HARPS High Accuracy Radial velocity Planet Searcher ESO La Silla 3.6m telescope Discovered more than 130 planets Can discover light planets (1.9 M) in “habitable” orbits Also used for “Astroseismology”

Transits Planet detected when it passes in front of its star

Transit of Venus 8th June 2004

Transits Planet detected when it passes in front of its star Low probability of detection 0.5% chance of detecting the Earth from another star! Good probability of finding more than one planet Allows measurement of size of planet

Transit Lightcurve – Kepler 6b

Transits Planet detected when it passes in front of its star Low probability of detection 0.5% chance of detecting the Earth from another star! Good probability of finding more than one planet Allows measurement of size of planet Transits can be measured with amateur equipment!

WASP-10 using 14” Meade

Kepler Launched 7th March 2009 Monitored 145,000 stars in Cygnus/Lyra 115 degree2 field of view (cf Hubble 10 min2) Detected nearly 1,000 planets (and another 3,000 candidate planets) Performance typically 30 parts per million Could detect planet phases Reaction wheels failed and now mothballed

Timing Measurements Pulsar Timing

PSR B1257+12 A First extra-solar planet, discovered 1992 4 planets in the system Only about 2 Lunar masses! 2nd Generation planet?

Timing Measurements Pulsar Timing Variable Star Timing

Variable Star Timing Uses pulsating or eclipsing variables Doppler shift determined photometrically without spectroscopy E.g. HW Virginis b 16 MJ Orbital period 16 years

Timing Measurements Pulsar Timing Variable Star Timing Transit Timing Variation

Transit Timing Variation Time and duration of a transit can be affected by perturbations by other planets in the system Needs a close-in transiting planet to be detected first Requires multiple transit observations Can determine maximum mass Again – can be done by amateurs

Kepler-19c Variations in transit times of Kepler-19b of up to 5 mins and period of about 300 days Orbit >160 days Mass <6 MJ

Microlensing Uses enhancement of light when one star passes nearly in front of another

Microlensing Uses enhancement of light when one star passes nearly in front of another Need to continually monitor the background star

Microlensing Uses enhancement of light when one star passes nearly in front of another Need to continually monitor the star A planet makes a contribution to the lensing, a small spike e.g. OGLE-2005-BLG-390Lb 5.5 M (Earth Mass) 2.6 AU orbit

Microlensing Main programmes are Optical Gravitational Lensing Experiment (OGLE) Microlensing Observations in Astrophysics (MAO) Both also looking for MACHOs and other lensing objects Potentially very sensitive detection method

Direct Observation A planet’s (reflected) light is usually swamped by its star’s light but could detect Large planet with faint star Young planets emitting IR Need to use a coronagraph to hide the star Sophisticated methods include: Angular Differential Imaging (ADI) Locally Optimized Combination of Images (LOCI)

Beta Pictoris b

HR 8799

Astrometry Measure variations to Proper Motion

Astrometry Measure variations to Proper Motion Companion (star) to Sirius detected in 1844 by Bessel Accuracy required not available from the ground No confirmed planets detected as yet Gaia will have the required accuracy and could potentially discover thousands

Types of Planetary Systems Very few systems are like our Solar System! Early discoveries were Hot Jupiters Single planet systems tend to have eccentric orbits Multi-planet systems have to have circular orbits (or they’d interact)

Numbers by Discovery Methods

Mass vs Period Note Log Scales

Note Log Scales

What Else can we See? Transits allow detection of Atmosphere composition (absorption)

Transiting Planet Absorption

What Else can we See? Transits allow detection of Atmosphere composition (absorption) Oblateness (from asymmetry of light curve) Temperature (using infra-red)

Types of Planets Vary in size Sub Earth Earth Sized Super Earth/Mini Neptune (2-10 M ) Neptune Sized (10-30 M) Jupiter Sized (>30 M ) Super Jupiters 3 MJ to >50 MJ (are these planets?)

Types of Planets Vary in Density Dense Iron Core Earth Like (Silicate with iron core) Super Earth Solid Giants Mini Neptunes Gas Giants

Habitable Planets? A habitable zone exists around most stars Goldilocks Zone (Not too hot – not too cold) Close in for small cool stars, far out for hotter stars Planet needs to be “Earth like”, not a gas giant It needs to be big enough to sustain an atmosphere So are there any?

Habitable Planets(?) About 16 Super-Earths in habitable zones

Habitable Planets(?) About 16 Super-Earths in habitable zones Another 30 or so candidates Earth like planets still difficult to detect Some estimates claim 1 in 5 Sun like stars will have Earth-like planets in the habitable zone

What Next? COROT & Kepler(?) are dead Lots of transit data to analyse GAIA for astrometry Improved ground based observations ESA’s PLATO mission

PLATO Planetary Transits and Oscillations of stars Selected by ESA for 2024 launch 34 small telescopes rather than Kepler’s 1 500,000 stars instead of 145,000 Orbit at L2 Complementary to Gaia

What Next COROT & Kepler(?) are dead Lots of transit data to analyse GAIA for astrometry Improved ground based observations ESA’s PLATO mission NASA’s WFIRST

WFIRST Wide-Field Infrared Survey Telescope 2.4M (Hubble sized) mirror Infra-Red large area survey Microlensing detection Direct imaging with a coronagraph

What Next COROT & Kepler(?) are dead Lots of transit data to analyse GAIA for astrometry Improved ground based observations ESA’s PLATO mission NASA’s WFIRST 30M class scopes (ELT, TMT, GMT)

Websites Exoplanet.eu kepler.nasa.gov (bit out of date!) Wikipedia (as ever) var2.astro.cz/ETD (Exoplanet Transit Datbase)