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The Open University

An introduction to exoplanets

The Open University via OpenLearn

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Overview

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This introductory course explains how exoplanets are discovered and characterized using stellar wobbles, transits, spectra, and measurements of planetary size and mass. It places these methods in the context of planetary habitability, atmospheres, and the search for life.

Syllabus

  • Introduction and guidance
  • Introduction and guidance
  • Maths help
  • What is a badged course?
  • How to get a badge
  • Acknowledgements
  • Week1Week 1: Planets and the Solar System
  • Introduction
  • 1  What is a planet?
  • 1.1  Phases
  • 1.2  Two characteristics of planets
  • 1.3  Planets and dwarf planets
  • 1.4  What defines a planet?
  • 1.5  Other objects in the Solar System
  • 2  Stars and galaxies
  • 2.1  Exoplanets
  • 2.2  The Milky Way and other galaxies
  • 3  The sky
  • 4  This week’s quiz
  • 5  Summary of Week 1
  • Acknowledgements
  • Week2Week 2: Planets, large and small
  • Introduction
  • 1  Terrestrial and giant planets
  • 2  The scale of the Solar System: everything is big!
  • 2.1  Sizes of the Solar System planets
  • 2.2  Distances between the Solar System planets
  • 2.3  The astronomical unit: a convenient way to measure distances in the Solar System
  • 3  Gas giants and ice giants
  • 4  Planet vital statistics
  • 4.1  Planet sizes
  • 4.2  Planet volumes
  • 4.3  Scaling radii and volumes
  • 4.4  Mass and density
  • 4.5  Floating, sinking and planetary structure
  • 4.6  Average densities
  • 4.7  Densities of Solar System planets
  • 5  Simplifying the numbers
  • 6  Gallery of planet portraits
  • 6.1  Terrestrial planets
  • 6.2  Giant planets
  • 7  This week’s quiz
  • 8  Summary of Week 2
  • Acknowledgements
  • Week3Week 3: Dawn of the exoplanet era
  • Introduction
  • 1  Exoplanet names
  • 2  The first exoplanet: 51 Pegasi b
  • 3  Wobbling stars
  • 3.1  Gravity, orbits and see-saws
  • 3.2  Getting a feel for the common centre of mass
  • Centre of mass interactive activity part 1
  • Centre of mass interactive activity part 2
  • 3.3  The common centre of mass of our Solar System
  • 3.4  Down to Earth: a practical exploration of planet and star orbits
  • 3.5  Interactive orbits
  • 4  Measuring the movement of stars
  • 4.1  Velocity and speed
  • 4.2  Light as a wave and the Doppler effect
  • 4.3  Chemical fingerprints in starlight
  • 4.4  Spectra, the Doppler effect and radial velocities
  • 4.5  Interpreting the radial velocity curve
  • Interactive orbits
  • The orbital inclination
  • The star’s motion
  • Orbital motion and radial velocity
  • Radial velocity
  • 4.6  DIY chemical fingerprints
  • 5  The exoplanet collection
  • 6  This week’s quiz
  • 7  Summary of Week 3
  • Acknowledgements
  • Week4Week 4: You’re in my light – transits
  • Introduction
  • 1  Transits in the Solar System
  • 2  Size matters
  • 2.1  Transits of Mercury and Venus
  • 2.2  Transits of exoplanets
  • 2.3  Stars, colour and size
  • 2.4  Circles and spheres
  • 2.5  Circles, radii and area
  • The equation for the area of a circle
  • Comparing areas for circles of differing size
  • 2.6  Remember, stars are big!
  • 3  Putting the ingredients together
  • 3.1  Measuring a transit
  • 3.2  An introduction to professional transit searches
  • 3.3  From dips to planet size measurement
  • 3.4  Do it yourself: planet size measurement
  • 3.5  Planet size and transit depth
  • 3.6  Star size and transit depth
  • 4  This week’s quiz
  • 5  Summary of Week 4
  • Acknowledgements
  • Week5Week 5: How to measure your exoplanet
  • Introduction
  • 1  The first transiting planet – HD 209458 b
  • 2  Hot Jupiter transits are easy to measure
  • 2.1  HD 209458 b transit: discovered in a car park
  • 2.2  WASP: Wide area search for planets
  • 3  The names of transiting planets
  • 4  How to measure an exoplanet’s size and mass
  • 4.1  Transit depth gives size
  • 4.2  Planet sizes with a pocket calculator
  • 4.3  The radial velocity see-saw gives mass
  • 4.4  Applying this to HD 209458 b
  • 5  Transits from space
  • 5.1  Continuous observations
  • 5.2  Prevent the stars from twinkling
  • 5.3  Small rocky planets
  • 5.4  CoRoT and Kepler: into space for planets galore
  • 5.5  Mass measurements for Kepler planets
  • 5.6  The population of known transiting planets
  • 6  Close-in planets
  • 6.1  Close-in planets are easiest to find
  • 6.2  Close-in planets are hot, hot, hot!
  • 6.3  How hot?!
  • 7  Density is key
  • 8  This week’s quiz
  • 9  Summary of Week 5
  • Acknowledgements
  • Week6Week 6: Planets galore: the contents of the Milky Way
  • Introduction
  • 1  Learning about the whole Galaxy
  • 2  How many planets?
  • 2.1  Not all planets transit!
  • 2.2  Selection effects – transits
  • 2.3  How many are there really?
  • How it’s done
  • The Kepler results
  • Selection effects for the radial velocity method
  • 3  The Milky Way variety pack
  • 4  The light year
  • 5  The habitable zone
  • 5.1  The Goldilocks effect
  • 5.2  The perfect distance depends on the star’s type
  • 5.3  Why isn’t the Earth frozen?
  • 5.4  Fighting climate change with paint
  • 5.5  Lots of habitable planets!
  • 6  Where are the aliens? The Drake equation
  • 7  Kepler’s small planets
  • 8  The search for Earth’s first cousins
  • 8.1  The MEarth survey
  • 8.2  TRAPPIST planets
  • 8.3  Radial velocity searches for small worlds
  • 8.4  Habitable planets around M dwarfs
  • 9  This week’s quiz
  • 10  Summary of Week 6
  • Acknowledgements
  • Week7Week 7: The Special Ones
  • Introduction
  • 1  Spectra: how we learned what stars are made of
  • 1.1  The electromagnetic spectrum
  • 2  Atmospheres of planets and their climates
  • 2.1  Why are atmospheres important?
  • 2.2  The greenhouse effect
  • 2.3  Atmospheres and transits
  • 2.4  Being an atmosphere detective
  • 3  Measurements and uncertainty: why great distances are bad news
  • 4  Special planets
  • 4.1  The hot ones: HD 189733 b, HD 209458 b and WASP-12 b
  • 4.2 The small ones: GJ 1214 b and GJ 1132 b
  • 4.3  The disintegrating one: Kepler-1520 b
  • 4.4  The habitable ones? TRAPPIST-1 planets
  • 5  This week’s quiz
  • 6  Summary of Week 7
  • Acknowledgements
  • Week8Week 8: Where do we go from here?
  • Introduction
  • 1  Welcome to the neighbourhood
  • 2  The Pale Red Dot search: a planet around our closest neighbour?
  • 2.1  Our closest stellar neighbour
  • 2.2  Our closest exoplanetary neighbour!
  • 2.3  Consequences of being so close to a star
  • 2.4  But what is it really like?
  • 2.5  Exploring the Galaxy’s rocky planets
  • 2.6  Barnard’s Star b
  • 2.7  LHS 1140 system
  • 3  The history of rocky planet formation
  • 3.1  Stars, planets and chemical elements
  • 3.2  The Kepler-444 planetary system
  • 4  Prospects for extraterrestrial life
  • 4.1  Biosignatures
  • 4.2  Life on strange worlds
  • 5  The future of exoplanet exploration
  • 5.1  Planet finders: Gaia, TESS and PLATO
  • The Gaia mission
  • The Transiting Exoplanet Survey Satellite – TESS
  • 5.2  PLAnetary Transits and Oscillations of stars – the PLATO mission
  • 5.3  Studying new worlds: JWST, Twinkle and ARIEL
  • 5.4  Seeing exoplanets directly
  • 6  This week’s quiz
  • 7  Summary of Week 8
  • Take the next step
  • Tell us what you think
  • Acknowledgements

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