We measured the spin state of Mercury with radar speckle tracking to probe the interior of the planet. In 2007, we found that Mercury has a molten core. Links and illustrations related to our Science paper can be found here.

We used Earth-based observations over a period of 10 years to characterize the spin state of Mercury in great detail, which enabled a measurement of the moment of inertia of Mercury and the size of its core. A 2012 JGR paper summarizes our findings.

We combined gravity information from MESSENGER with our spin state measurements to characterize the interior of Mercury.

We also modeled the response of a planet to the influence of solar tides, and we found that one can place additional constraints on the nature of the interior by measuring the tidal amplitude.