Exoplanet Detection Lab: Transit & Radial Velocity
Tune a planet's size, mass and orbit and see whether the transit dip or the radial-velocity wobble is strong enough to detect above real instrument noise.
How to use: choose Transit or Radial Velocity mode, tune the planet and add instrument noise, and see whether the signal is strong enough to detect above the noise (signal-to-noise ratio, SNR).
Challenge 1: detect an Earth-sized planet
In Transit mode, set the planet radius near Earth's (about 1 R⊕) and lower the noise until SNR ≥ 3 (the standard detection threshold).
Challenge 2: detect with radial velocity
In Radial Velocity mode, tune planet mass and orbit so the RV semi-amplitude K clears the instrument noise with SNR ≥ 3.
About the Exoplanet Detection Lab: Transit & Radial Velocity
Free exoplanet detection lab: transit & radial velocity. Tune a planet's size, mass and orbit and see whether the transit dip or the radial-velocity wobble is strong enough to detect above real instrument noise. Drag, change the sliders and see the result live. No sign-up, works on phone and computer. Built for astronomy, the exoplanet detection lab: transit & radial velocity runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Tune a planet's size, mass and orbit and see whether the transit dip or the radial-velocity wobble is strong enough to detect above real instrument noise. Use it to explore astronomy ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Exoplanet Detection Lab: Transit & Radial Velocity
- Use the controls to change Planet radius (Earth radii), Planet mass (Earth masses), Orbital period (days), Star mass (solar masses), Instrument noise. The simulation reacts instantly.
- Press "Reset to defaults", "📄 Lab Report" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- In Transit mode, shrink the planet to Earth-size and watch the SNR readout fall.
- In Radial Velocity mode, shorten the orbital period and see the RV signal grow.
- Raise the noise slider until an easily-detectable planet becomes undetectable.
- Compare the same planet's detectability by both methods.
Key ideas you can learn
- The transit method measures a dip in starlight: depth = (R_planet / R_star)², so a Jupiter-sized planet blocks far more light than an Earth-sized one around the same star.
- The radial-velocity method measures the star's own tiny wobble caused by the planet's gravity, with amplitude K depending on planet mass, orbital period and star mass.
- A signal only counts as a real detection when it clears the noise by enough - astronomers typically require a signal-to-noise ratio (SNR) of at least 3.
- The two methods are complementary: transit gives a planet's radius, radial velocity gives its mass, and together they reveal its density and likely composition.
Where this is used in the real world
Missions like Kepler and TESS use the transit method to find thousands of candidate planets, while ground-based spectrographs use the radial-velocity method to confirm planet masses - exactly the two techniques modeled here.
Who is this simulation for?
Students, teachers and curious learners of all ages.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
Why is Earth-sized planet harder to detect than a Jupiter-sized one by transit?
Transit depth scales with the square of the radius ratio, so a Jupiter-sized planet (about 11 Earth radii) produces a dip over 100 times deeper than an Earth-sized planet around the same star, far easier to spot above instrument noise.
Why do 'hot Jupiters' dominate early radial-velocity discoveries?
RV semi-amplitude grows with planet mass and shrinks with orbital period, so a massive planet in a very short, close orbit around its star produces the largest, easiest-to-detect stellar wobble.
Is the Exoplanet Detection Lab: Transit & Radial Velocity free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Exoplanet Detection Lab: Transit & Radial Velocity work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.