Astrometry

Astrometry ? consists in measuring the variations in the apparent position of the star against the background of the sky (in relation to the other stars). If the orbit is in the reference plane of the sky, the amplitude of the movement is:

$$ \delta(\theta)=\frac{a_{p} \times M_p}{M_{\text{star}} \times D} $$

where Mp and Mstar are the respective masses of the planet and the star, ap is the semi-major axis ? of the planet’s orbit and D is the distance of the exosystem from Earth.

Movement of the Sun in the reference plane of the sky as it would be seen at a distance of 10 parsecs ? perpendicular to the ecliptic. This movement is mainly dominated by the giant planets (Jupiter, Saturn, Uranus and Neptune).
(NASA)

So far 12/10/2026, the number of detections by astrometry ? is

. This will rapidly rise with the discoveries made by the Gaia satellite.

Advantages:

  • Can determine the mass of the planet.
  • Can be used to study planets far from their star.

Inconvénients :

  • Requires a very sensitive instrument that was for a long time unavailable before the arrival of the Gaia satellite ? .