Why do the planets orbit the sun?

 Reason behind planets not falling into the stars they orbit?               

The planets are moving fast enough and at a great enough distance that the Sun will never intersect with their orbital path. Actually, planets orbit the Sun due to the force of gravity. The Sun's gravity is not stronger than that of any planet; rather, its mass is significantly larger, allowing it to exert a stronger gravitational pull. When planets formed, they had initial velocities that, combined with the Sun's gravitational pull, resulted in elliptical orbits in accordance with Kepler's laws of planetary motion. They don't fall into the Sun because their velocity is high enough to continually "miss" it.

In space mysteries, this is a brilliant question because the notion of an orbit is counterintuitive. We know that massive objects (really, any objects with mass) gravitationally attract other massive objects; Newton’s law of universal gravitation is firmly established on this point. For instance, throw a baseball horizontally at about shoulder height and it will follow a curved path until it strikes the ground because Earth quickly draws the ball back to its surface. (Technically, Earth and the ball move toward each other and collide, but Earth is so much more massive than the ball that the former’s motion is practically zero.) A star and attendant planet, both being massive, should also come together rapidly. Instead, planets tend to maintain orbits around stars without actually crashing into them. When you throw a rock from a tower, it starts with an initial forward velocity which propels it horizontally, while Earth's gravity pulls it downward. If thrown at a sufficient speed, the rock's forward momentum will balance out the gravitational pull. Following are the important points here:-

Gravity continuously pulls the rock towards the Earth's center, curving its path downward.

The rock's initial velocity propels it forward. This forward motion tries to move the rock in a straight line.

Earth's surface curves away beneath the rock as it moves forward. So while gravity pulls it down, the ground is also "falling away" from it.

The result is that the rock is in a perpetual state of "freefall" around Earth. It never hits the ground because its forward speed ensures that as it falls, Earth's surface curves away at the same rate.

This balancing act between gravitational attraction and forward momentum is what keeps the rock (or a satellite, or a planet) in orbit. It's always being pulled toward Earth, but its horizontal speed prevents it from ever actually reaching Earth. It's like the rock is constantly "missing" the Earth as it falls, creating a stable orbit.

To understand how planets are able to maintain a respectful distance from their parent stars, let’s return to the aforementioned baseball. Earlier, we imagined throwing it at normal human strength. Now, imagine you throw it again, but at a much higher velocity. The baseball still falls to the ground, but it takes longer, the parabolic path it follows is longer, due to its increased horizontal speed. Continue throwing the ball at ever-increasing velocities and the descending path the ball follows becomes increasingly longer. Finally, imagine that you are able to throw the ball so fast that the surface of Earth curves away from the ball’s path faster than the ball can fall. As a result, the ball’s curved path carries it around Earth. The ball wouldn’t ever strike the ground but would constantly miss it altogether and continue falling, and end up orbiting the planet. The problem here is apart from the fact that nobody can throw a ball that fast, is that atmospheric drag would quickly reduce the ball’s speed and cause it to strike the ground. Many artificial satellites moving around Earth, including the International Space Station, experience this atmospheric drag, albeit to a lesser extent due to the reduced particle density at such high altitudes. (As a result, these objects all eventually crash back to Earth unless they are boosted up again.) 

The speeds that allow planets to orbit the Sun stem from the formation of the Solar System. During this time, material with lower angular momentum became part of the Sun, while faster-spinning material escaped. The remaining material coalesced into planets, retaining enough velocity to maintain stable orbits. The Sun and planets share the same direction of rotation because they originated from the same spinning nebular cloud. As it contracted under gravity, it spun faster due to angular momentum conservation. This led to a flattened disk, which is why planets orbit in a relatively flat plane called the ecliptic. A planet is essentially moving through a vacuum, and so no reduction of its velocity will occur. The planets are moving fast enough and at a great enough distance that as they “fall toward” the Sun, the Sun will never actually intersect with their orbital path. To paraphrase the late Douglas Adams, “The knack of flying is learning how to throw yourself at the ground and miss.” Orbits operate on essentially the same principle. In a simple system without other major celestial bodies, a planet would have a circular orbit. However, the gravitational effects from other planets, especially gas giants like Jupiter, cause orbits to deviate into elliptical shapes in our universe.