Figure 4-20 Detecting an Exoplanet Through Doppler Shift of Its Star The radial velocity method indirectly detects a tiny and nonvisible exoplanet gravitationally pulling on its host star during its orbit. When the star moves toward us because its planet is moving away from us, its spectrum is blueshifted, while it is alternatively redshifted when the star moves away from us as its planet moves toward us.