As an exoplanet orbits its parent star, it exerts a reflex motion on the star (caused by the gravitation pull of the planet on the star). This causes the position of the host star to oscillate with each orbital period of the planet. This movie is schematic, showing the reflex motion (red circle) of a star produced by the circular orbit of a planet (following blue circle). Both objects orbit the centre of mass of the system (at the centre of the frame). ESPRI will measure the reflex motion of the star in order to infer the presence of a planet.

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