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

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

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

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

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

9. 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

12. 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

14. 51 Pegasi
First extra-solar planetary system discovered around a normal star
Announced 6th Oct 1995 by Mayor & Queloz
Discovered by Radial Velocity measurements

16. 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”

17. HARPS

18. 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”

19. Transits
Planet detected when it passes in front of its star

20. Transit of Venus 8th June 2004

22. 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

23. Transit Lightcurve – Kepler 6b

24. 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!

25. WASP-10 using 14” Meade

26. 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

27. Timing Measurements
Pulsar Timing

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

29. Timing Measurements
Pulsar Timing
Variable Star Timing

30. 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

31. Timing Measurements Pulsar Timing Variable Star Timing
Transit Timing Variation

32. 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

33. 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

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

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

38. 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

39. 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

40. 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)

41. Beta Pictoris b

42. HR 8799

43. Astrometry
Measure variations to Proper Motion

45. 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

46. 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)

47. Numbers by Discovery Methods

48. Mass vs Period
Note Log Scales

49. Note Log Scales

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

51. Transiting Planet Absorption

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

53. 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?)

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

56. 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?

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

59. 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

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

61. 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

62. 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

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

64. 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)

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