As an astronaut, you observe a small planet to be spherical. After landing on the planet, you set off, walking always straight ahead, and find yourself returning to your spacecraft from the opposite side after completing a lap of 25.9 km. You hold a hammer and a falcon feather at a height of 1.35 m, release them, and observe that they fall together to the surface in 25.7 s. Determine the mass of the planet.
2. The attempt at a solution
I don't even know where to start. Any pointers?