Rotation and Interior Structure Experiment (RISE) is a radio science experiment onboard InSight Mars lander that will use the spacecraft communication system to provide precise measurements of Mars' rotation and wobble. RISE precisely tracks the location of the lander to measure how much Mars's axis wobbles as it orbits the Sun. These observations will provide new constraints on the core radius and help determine whether the core of Mars is mostly liquid, and which other elements, besides iron, may be present. This study will also help scientists understand why Mars's magnetic field is so weak, as compared to Earth's.