Yes, comets are bound by gravity, and their orbits are influenced primarily by the gravitational forces of the Sun and other celestial bodies in the solar system.
### Key Points About Cometary Orbits and Gravity
1. **Solar Gravity**:
- The primary gravitational influence on a comet is the Sun. Comets orbit the Sun in elliptical, parabolic, or hyperbolic paths.
- Most comets have highly elongated elliptical orbits, bringing them close to the Sun (perihelion) and then taking them far into the outer regions of the solar system (aphelion).
2. **Jupiter Family Comets and Oort Cloud Comets**:
- **Jupiter Family Comets**: These comets have shorter orbital periods (less than 20 years) and are influenced by the gravity of Jupiter, which can alter their orbits.
- **Oort Cloud Comets**: These comets originate from the Oort Cloud, a distant spherical shell of icy bodies surrounding the solar system. Their orbits are influenced mainly by the Sun's gravity, but they can also be perturbed by the gravitational influence of passing stars and the galactic tide.
3. **Kuiper Belt Comets**:
- Comets originating from the Kuiper Belt, a region beyond Neptune filled with icy bodies, have intermediate orbital periods and are influenced by the gravity of the Sun and the outer planets (mainly Neptune).
4. **Gravitational Perturbations**:
- Comets can experience gravitational perturbations from planets, particularly the giant planets like Jupiter and Saturn. These perturbations can alter the comet's orbit, potentially capturing it into a shorter-period orbit or ejecting it from the solar system.
- The gravitational influence of passing stars and the galactic tide (the gravitational effect of the Milky Way) can also perturb the orbits of comets, especially those in the distant Oort Cloud.
5. **Interstellar Comets**:
- Interstellar comets, like ‘Oumuamua and 2I/Borisov, are not bound by the Sun's gravity. They enter the solar system from interstellar space, influenced by the gravitational forces of their original star systems and the galactic environment.
### Summary
- **Bound by Solar Gravity**: The primary force binding most comets is the gravity of the Sun, determining their orbits within the solar system.
- **Influence of Planets**: The orbits of comets, particularly those of the Jupiter family, are significantly influenced by the gravity of planets, especially the giant planets.
- **Oort Cloud and Kuiper Belt**: Comets from the Oort Cloud and Kuiper Belt are influenced by the Sun's gravity and can be perturbed by the gravitational effects of other stars and the galactic tide.
- **Interstellar Comets**: These comets are not bound by the Sun's gravity and are influenced by the gravitational forces of their original star systems and the Milky Way.
Overall, the gravitational forces of the Sun, planets, and other celestial bodies within and beyond the solar system play crucial roles in determining the orbits and behavior of comets.
