Satellites orbiting the earth have finite life and sometimes debris of satellites fall to the earth. This is because,

As observed from earth, the sun appears to move in an approximate circular orbit. For the motion of another planet like mercury as observed from earth, this would

Different points in earth are at slightly different distances from the sun and hence experience different forces due to gravitation. For a rigid body, we know that if various forces act at various points in it, the resultant motion is as if a net force acts on the c.m. (centre of mass) causing translation and a net torque at the c.m. causing rotation around an axis through the c.m. For the earth - sun system (approximating the earth as a uniform density sphere)

Both earth and moon are subject to the gravitational force of the sun. As observed from the sun, the orbit of the moon

In our solar system, the inter - planetary region has chunks of matter (much smaller in size compared to planets) called asteroids. They