Gravitational waves in the microhertz regime represent an unexplored window into slow dynamical processes in planetary interiors and the longu2011period tidal interactions within the Solar System. Jupiter, whose rotation period of 9.925 h is known with high precision, should generate a gravitational wave near 55.97 $mu$Hz if its mass distribution departs from perfect axial symmetry. Such a signal is far below the sensitivity of existing gravitationalu2011wave detectors and is strongly Doppleru2011shifted by the synodic Earth—Jupiter motion, making direct detection challenging.Using 20 years of barometric pressure data from DWD stations, we extract Jupiter’s gravitational wave through coherent demodulation of the phase modulations induced by Earth’s orbit and by the four Galilean moons. The recovered carrier frequency exhibits SNR $approx100$ and reveals a previously unknown longu2011term frequency drift associated with Jupiter’s deep interior. The modulation indices and phases of Io, Europa, Ganymede, and Callisto are stable across 752 independent realizations, demonstrating that Earth’s atmosphere responds coherently to microhertz gravitational forcing.The measured modulation indices exceed linearized Doppler predictions by a factor of 12.7, implying a propagation speed of $vapprox 0.08 c$ for the wave along the Jupiter—Earth path. Because this path lies entirely within the Sun’s gravitational potential, our results suggest that microhertz gravitational waves may experience dispersive propagation in strongly curved spacetime. No additional longu2011term phase modulations were detected. These findings open a new observational channel for studying gravitational phenomena in the Solar System at ultrau2011low frequencies.