Simplify the following text for a Grade 7 native English-speaking person.
Original: Siarnaq is thought to be about 40 kilometres in diameter and orbits Saturn at an average distance of 17,500,000 km in 895 days .
Simplified: Siarnaq is thought to be about 40 kilometres in diameter and orbits Saturn at an average distance of 17.5 Gm in 895 days .