CNN: Doughnut found on the planet's surface. Rocks usually have the shape

  x = a sin(s) cos(t)
  y = b sin(s) sin(t)
  z = c cos(s)

where a,b,c are positive periodic functions in t and s Doughnut shapes have parametrizations

  x = (a + b cos(s)) cos(t) 
  y = (a + b cos(s)) sin(t) 
  z = c sin(s) 
 
where a,b,c are positive periodic functions in t and s.