- Using 19 objects, Oort concluded that the Sun was surrounded by a cloud of comets.
- This structure is large.
- radius ~ 50,000 AU or 0.25 pc or 20% to the nearest star.
- Estimated 1011 comets.
- From dynamical calculation of rate in which stars feed comets into inner Solar System.
- Need so many because from 20,000AU the planetary system is a small target.
- Current: ~4x1011. (Francis 2008)
- Still see it in modern data.