Simplify the following text for a Grade 5 native English-speaking person.
Original: They estimated that the two components orbit around their center of mass in 4.283 Â 0.004 d at a distance of 680 Â 20 km , describing a roughly circular orbit .
Simplified: They thought that the two asteroids orbit around their center of mass in 4.283 Â 0.004 d at a distance of 680 Â 20 km , describing a close to circular orbit .