Gravitational pull
The force of gravity causes orbits.
The Sun's gravitational force controls all the orbits of planets and other objects that orbit the Sun (dwarf planets, asteroids, comets, meteors).An object without a force acting on it travels in a straight line, But the Sun's gravity causes each object to accelerate towards the Sun, as described by Newton's second law: force = mass x acceleration.The acceleration causes any fast-moving object to curve towards the Sun, as Newton discovered using calculus. This is a permanent process with the object in a stable orbit unless disturbed by a collision of some sort.
They are held in place by the gravitational force of the sun.
The gravitational force of the Sun pulls objects, such as comets, towards itself and traps the object into an orbit if its velocity is not sufficient enough to escape the Suns pull.
Comets, like all objects in the solar system, are held together by their internal strength. The force of gravity can cause comets to rip apart.
Gravity. Specifically, the gravity of the Sun.
Unfortunately, you neglected to include the list of allowable choices that "follows" the question. Still, I know the answer. The force that keeps comets in closed orbits around the sun is the one that has the same effect on the planets; gravity. The only difference is that the orbits of the long-term comets are much more 'eccentric' (long and skinny) than those of the planets, so they have much shorter minimum distances from the sun, and much longer maximum distances, than planetary orbits have. So, the correct awnser is Gravity.
The gravitational force between planets supplies the centripetal force that causes them to orbit each other.
The orbit is not a perfect circle. Applies to all planets/asteroids/comets.
The force of gravity causes orbits.
That would be the gravitic force, or you could say 'the force of gravity'.
friction
The solar system's planets, planetesimals, asteroids, and comets are held in orbit by the force of gravity, the mutual attraction between these objects and the Sun.
Gravity is the force that connects the solar system to the sun.
The Sun's gravitational force controls all the orbits of planets and other objects that orbit the Sun (dwarf planets, asteroids, comets, meteors).An object without a force acting on it travels in a straight line, But the Sun's gravity causes each object to accelerate towards the Sun, as described by Newton's second law: force = mass x acceleration.The acceleration causes any fast-moving object to curve towards the Sun, as Newton discovered using calculus. This is a permanent process with the object in a stable orbit unless disturbed by a collision of some sort.
The Sun's gravitational force controls all the orbits of planets and other objects that orbit the Sun (dwarf planets, asteroids, comets, meteors). An object without a force acting on it travels in a straight line. The Sun's gravity causes each object to accelerate towards the Sun, as described by Newton's second law: force = mass x acceleration. The acceleration causes any fast-moving object to curve towards the Sun, as Newton discovered. This is a permanent process with the object in a stable orbit unless disturbed by a collision of some sort.
They are held in place by the gravitational force of the sun.