The Space.com article How NASA Mars Lander's 'Steampunk' Claw Will Work (Video) says:
InSight's mission aims to provide a detailed look at Mars' interior structure and composition. The lander carries two primary science instruments — a burrowing heat probe called the Heat Flow and Physical Properties Package (HP3) and the Seismic Experiment for Interior Structure (SEIS), a suite of super-precise seismometers. (InSight will also use its onboard communications gear to perform a radio-science experiment that should shed further light on Mars' innards.)
Question: Just how exactly will InSight's onboard communications gear perform a radio-science experiment to shed further light on Mars' innards?
A few GHz won't penetrate very far into the planet at all, so the experiment must be quite subtle, and therefore pretty cool, and use some planetary effects on upwards-propagating signals from the lander to a passing orbiter, or to Earth, or so I suppose. Is the effect related to some plasma, or is it inertial perhaps (tiny displacements or rotation shifts)?