What information does the Radial Velocity method primarily provide about an exoplanet, contrasted with Astrometry?
Answer
A lower limit on the planet's mass, dependent on inclination ($M \sin i$)
The Radial Velocity method measures the star’s color shift (Doppler effect), which reveals the component of the star's velocity directed toward or away from Earth (line-of-sight velocity). Because this measurement is highly dependent on the inclination ($i$) of the orbital plane relative to our line of sight, it only provides a lower limit on the planet's mass, expressed as $M \sin i$. If the orbit is face-on ($i o 0^ ext{o}$), the measured signal approaches zero, leading to severe underestimation of the true mass, a limitation astrometry overcomes by measuring the sky plane motion.
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