The gravity of other planets is typically measured using spacecraft or satellite missions. Here are some common methods used to measure planetary gravity:
Orbital Mechanics: By studying the motion of spacecraft in orbit around a planet, scientists can calculate the gravitational force exerted by the planet. The spacecraft's trajectory, speed, and acceleration provide valuable information about the planet's gravitational field.
Doppler Shift: The Doppler shift in radio signals transmitted to and received from a spacecraft can be used to measure the spacecraft's velocity with respect to the planet. Variations in this velocity reveal the gravitational effects of the planet, allowing scientists to determine the planet's gravity.
Radio Tracking: By precisely tracking the radio signals emitted by a spacecraft in orbit around a planet, scientists can measure the changes in distance between the spacecraft and Earth. These measurements help determine the planet's gravitational field and can provide insights into its internal structure.
Gravitational Assist: In some cases, spacecraft can use the gravity of a planet to alter their trajectory and gain speed or change direction. By carefully analyzing the spacecraft's path before and after the gravitational assist, scientists can infer the planet's gravitational characteristics.
Spaceborne Gravimetry: Dedicated gravity-measuring satellites, such as the Gravity Recovery and Climate Experiment (GRACE), use sensitive instruments to measure tiny variations in the planet's gravitational field. These satellites precisely measure the distance between each other and detect gravitational anomalies, which contribute to mapping the planet's gravity field.
By employing these methods, scientists can gather data and construct models that describe the gravitational field of other planets, providing valuable insights into their internal structure, mass distribution, and geophysical properties.