N.a.s.a
Astronomers.
Scientists classify small objects in the solar system by size, shape, and composition
scientists can use them to study the early solar system
astronomers
astronomers
Scientists can use them to study the early solar system.
The best way to tell the difference is by tracking the object. If the object seems to move in an orbit around the Sun, then it is in the solar system. If not, it is outside it.
No one knows it. Scientists lie or exaggerate about knowing. Although the above is partially true, scientists do have theories about how the solar system was formed. If the entire solar system was formed at the same time then all objects in the solar system are the same age. Using radioactive dating of meteorites scientists calculate how long it has been since the meteorite solidified and go based on that date.
A solar system.
Kuiper Belt objects
Sirius is not part of our Solar System, so it is not appropriate to talk about "other objects in the solar system".
Astronomy is the study of the Solar System. Planetary Science, or a Planetologist, studies the planets.