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Radial-Velocity Exoplanet Detection

What you are seeing: a star and a planet orbiting their common center of mass. The star traces a small ellipse mirroring the planet's; the line-of-sight component of its velocity produces the radial velocity curve on the right. A horizontally-shifting spectral line below the curve illustrates the Doppler shift. This is how 51 Peg b was found

Figure 1. Top-down orbit of star + planet around the COM; radial velocity curve + Doppler-shifted spectral-line indicator. Method: Kepler solver + closed-form RV with K = (2πG/P)^(1/3) m_p sin(i) (M+m)^{-2/3} (1-e^2)^{-1/2}.
planet mass m_p0.010
period P1.6
eccentricity e0.20
inclination (°)80
animation speed2

WHAT TO TRY

  • Raise the planet mass: the star wobbles on a bigger mirror-image orbit, so the line-of-sight velocity swing K grows. The Doppler wobble is how the first exoplanets were found.
  • Add eccentricity: the radial-velocity curve skews from a clean sine into a lopsided shape, encoding the orbit shape.
  • Lower the inclination toward face-on: the line-of-sight velocity shrinks, so radial velocity only measures m sin i, the mass degeneracy that transits later break.