  The data recently released by the North American Nanohertz Observatory for
Gravitational Waves (NANOGrav) provides compelling evidence supporting the
existence of a stochastic signal that aligns with a gravitational-wave
background. We show that the scalar-induced gravitational waves from the Higgs
inflation model with the parametric amplification mechanism can explain this
signal. Such a gravitational-wave background naturally predicts the substantial
existence of planet-mass primordial black holes, which can be planet 9 in our
solar system and the lensing objects for the ultrashort-timescale microlensing
events observed by the Optical Gravitational Lensing Experiment. Therefore, the
NANOGrav signal, the potential Planet 9 in our solar system, and the Optical
Gravitational Lensing Experiment can be explained within the framework of Higgs
inflation.
