  Radio wavelength astrometry of stars and other objects has a long and
productive history. The use of that technique to determine whether stars have
planets around them would cover a nearly unique part of the parameter space for
detection of those systems. Namely, astrometric observations are most sensitive
to systems with large planets in moderately wide orbits (a few to ~10 AU),
because it is those systems that produce large reflex motion of the star, in a
short enough measurement period (years to tens of years). In addition,
astrometric observations are most sensitive to systems which are nearly
face-on. Other techniques (radial velocity, or the photometric method of
Kepler) are more sensitive to systems with planets in close orbits (less than
$\sim$1 AU), which are nearly edge-on. We describe here, using the Hipparcos
and Gaia star catalogs, how ngVLA could use this technique on hundreds of
stars, some tens of which are solar analogs, to determine whether these stars
have planets orbiting them.
