A body in Solar orbit beyond the Kuiper belt exhibits an annual parallax that exceeds its apparent proper motion by up to many orders of magnitude .
Apparent motion of this body along the parallactic ellipse will deflect the angular position of background stars due to astrometric microlensing ( “ induced parallax ” ) .
By synoptically sampling the astrometric position of background stars over the entire sky , constraints on the existence ( and basic properties ) of a massive nearby body may be inferred .
With a simple simulation , we estimate the signal-to-noise ratio for detecting such a body – as function of mass , heliocentric distance , and ecliptic latitude – using the anticipated sensitivity and temporal cadences from Gaia ( launch 2011 ) .
A Jupiter-mass ( M _ { jup } ) object at 2000 AU is detectable by Gaia over the whole sky above 5 \sigma , with even stronger constraints if it lies near the ecliptic plane .
Hypotheses for the mass ( \sim 3 M _ { jup } ) , distance ( \sim 20 , 000 AU ) and location of the proposed perturber ( “ Planet X ” ) which gives rise to long-period comets may be testable .