The plan includes a dedicated 200‑day astrometry survey during HWO’s five‑year primary mission, aiming for roughly 100 observations per target to determine masses of about 40 habitable‑zone Earth‑like planets within 10% precision.

The Habitable Worlds Observatory aims to directly image Earth-like exoplanets and analyze atmospheric chemistry, but requires precise planetary mass measurements to resolve atmospheric degeneracies and assess habitability.

Astrometry’s effectiveness is limited by photon-noise from background stars, with the density of reference stars depending on the observing direction relative to the galactic plane.

Astrometry offers a complementary method by detecting the star’s side‑to‑side wobble caused by an orbiting planet, providing a path forward especially for active stars where radial velocity struggles.

Simulations indicate the Gaia G-band as the optimal filter, balancing star density against the diffraction limit of the Habitable Worlds Observatory.

Detecting an Earth-like planet at about 10 parsecs via astrometry would require around 0.3 microarcseconds of precision, a demanding specification that also relies on background stars for reference.

Radial velocity, the current standard for mass measurements, is often inadequate for Earth-like planets and for targets dominated by hot, rapidly rotating stars among HWO targets.

Though HWO isn’t expected to launch until the early 2040s, integrating precise photometry with astrometry could enable confirmation of truly habitable worlds beyond our solar system.