Planet Hunter

When a planet passes in front of its star, it blocks a small part of the starlight. The fraction blocked is the share of the star's disk the planet covers, so the depth of the dip is about (planet radius / star radius)². A Jupiter-size planet dims a Sun-like star by about 1%, an Earth-size planet by less than 0.01%. The dips repeat once per orbit, which gives the planet's year. This is how HD 209458 b was caught in 1999, and how NASA's Kepler and TESS found most known exoplanets.

The light curves in the game are simulated, not real telescope data. Each one is built from the published period, size ratio, orbit size and tilt of a real system in the NASA Exoplanet Archive (Kepler-16 from Doyle et al. 2011, Science), with random noise added from a fixed seed so everyone sees the same curve. The noise levels are chosen for each level, not copied from the missions. The star's edge is darker than its center (limb darkening), which the model includes with one generic setting for every star instead of values fitted to each one.

Other simplifications: orbits are circular except Kepler-16's, the planets' own glow is ignored, and only two of the seven TRAPPIST-1 planets are included in level 5. Candidate C in level 6 is a made-up grazing binary, typical of the false alarms survey teams have to weed out. The fold in level 4 is a tiny version of box least squares (BLS), the search real surveys run over many trial periods.