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Physics · Astronomy

Exoplanet Hunter

Find hidden worlds from a star’s dip and wobble, read an alien atmosphere, visit TRAPPIST-1 and design a habitable planet.

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First lesson01 · A faint world next to a blinding starSee all 30 lessons →

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The course

7 worlds · 30 lessons

World 1 · Planets Around Other Stars

FREEWhat an exoplanet is, how we find them, and why the first count is biased
  1. 01A faint world next to a blinding starWhy almost no exoplanet is photographed · 10 min
  2. 02Five ways to find a hidden worldTransit, wobble, imaging, lensing, astrometry · 11 min
  3. 03The first discoveriesPulsar planets and 51 Pegasi b · 10 min
  4. 04How many planets are out there?The census and its blind spots · 11 min

World 2 · The Transit Dip

PRORead a light curve: depth, radius, period, orbit size and false alarms
  1. 01The shadow of a planetLight curves and depth · 10 minPRO
  2. 02Reading a planet’s sizeFrom dip to radius · 10 minPRO
  3. 03Period, orbit and KeplerHow far out is it? · 11 minPRO
  4. 04Tilt and luckTransit probability · 10 minPRO
  5. 05Is it really a planet?False alarms and vetting · 11 minPRO

World 3 · The Wobbling Star

PROGravity works both ways: finding planets from a star’s tiny motion
  1. 01Planets tug backThe barycentre · 10 minPRO
  2. 02Light that stretches and squeezesThe Doppler shift · 11 minPRO
  3. 03Reading the velocity curvePeriod, amplitude, minimum mass · 12 minPRO
  4. 04Mass plus radius gives densityWhat is it made of? · 11 minPRO

World 4 · The Goldilocks Zone

PROStarlight, temperature and the range of orbits where water could be liquid
  1. 01How much light does a planet get?Luminosity and the inverse square · 10 minPRO
  2. 02Stars come in many sizesWhere the zone sits around G, K and M stars · 11 minPRO
  3. 03The temperature of a bare rockEquilibrium temperature, albedo and greenhouse · 12 minPRO
  4. 04What the zone does not promiseLimits of “habitable” · 11 minPRO

World 5 · Reading an Alien Sky

PROWhat starlight filtered through a planet’s air can tell us
  1. 01A thin ring of air in the dipTransmission spectroscopy · 11 minPRO
  2. 02Fingerprints in the spectrumWhich gas absorbs where · 11 minPRO
  3. 03Catching a planet’s heatSecondary eclipse and phase curves · 12 minPRO
  4. 04Signs of life? Handle with careBiosignatures and false positives · 12 minPRO

World 6 · Visit TRAPPIST-1

PROSeven planets around one tiny red star, 40 light years away
  1. 01A tiny star with seven worldsMeet the system · 10 minPRO
  2. 02A system inside Mercury’s orbitPeriods, Kepler and resonance · 11 minPRO
  3. 03Which worlds are in the zone?Insolation on seven planets · 11 minPRO
  4. 04Seven dips in one light curveTelling the planets apart · 11 minPRO
  5. 05Life under a red sunThe sky, the flares and what JWST found · 12 minPRO

World 7 · Design a Habitable World

PROPick a star, an orbit, a size and an atmosphere, then see what telescopes would see
  1. 01Step 1: choose your starTrade-offs of G, K and M · 10 minPRO
  2. 02Step 2: pick an orbit and a sizeGravity and holding on to air · 11 minPRO
  3. 03Step 3: air and oceansPressure, greenhouse and liquid water · 12 minPRO
  4. 04Step 4: what would we see?Signals from your world · 12 minPRO
Exoplanet Hunter — interactive 3D lab · Novareka