When is the displacement measured by astrometry maximized for easier detection?
Answer
If the orbital plane is perfectly face-on relative to Earth
The effectiveness of astrometry is heavily dependent on the orientation of the exoplanet's orbit relative to our observation point on Earth. Astrometry measures the star's apparent positional shift, or wobble, caused by the planet's gravitational pull sideways across the sky. This sideways displacement is maximized when the entire orbital plane is perfectly face-on relative to Earth. Conversely, the radial velocity method, which measures movement along the line of sight (toward or away from Earth), works best when the orbit is edge-on. A face-on orbit minimizes the radial velocity signal but maximizes the astrometric signal.
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