As an astronaut, you observe a small planet to be spherical. After landing on thte planet you set off, walking always straight ahead, and find yourself returning to your spacecraft from the opposite side after completing a lap of 26.5 km. You hold a hammer at a height of 1.31 m, release it, and observe that it falls to the surface in 25.4 s. Determine the mass of the planet (in Tkg; 1 Tkg = 1012 kg)