# Is it easy for a spacecraft to hit celestial bodies in the asteroid belt?

A child is operating a spacecraft on the screen. The spacecraft can freely change directions up, down, left, or right, and it can also accelerate and decelerate instantly. Many fallen asteroids on the screen smashed into the spacecraft, and there were also flying saucers that fired at the spacecraft. Children need to quickly operate the buttons to drive the spacecraft to avoid danger and fire and destroy the asteroids and flying saucers that hinder its progress. When the spacecraft completes its mission, it will clear the customs. At this time, the children will dance happily. Maybe at night they will dream of driving a spaceship galloping in space and swiftly avoiding the impact of a flying asteroid!
The question is, when you drive a spacecraft through the planetary belt, will you really encounter such a dangerous situation? Will asteroids really be as dense as in the game? From the viewing experience of many movies, it seems that this is indeed the case-in the movie “Star Wars V: The Empire Strikes Back” such a scene: due to the failure of the hyperspace thruster of the “Millennium Falcon” , And the enemy’s imperial fighters and star cruisers are in hot pursuit. In order to escape the danger, the protagonist Solow plans to fly into the asteroid belt. But the intelligent robot “C3PO” told Solow that the survival probability of entering the asteroid belt is only 1/3720. The following plot shows that this danger comes from the impact of a large number of asteroids.
But the fact is that the planetary belt has a very low density of planets. Even if you fall asleep while driving the spacecraft through the asteroid belt, it is much safer than driving on Earth with your eyes open. Why do you say that? Taking the asteroid belt between the orbits of Mars and Jupiter as an example, the International Astronomical Union’s astronomer Garache calculated that the space occupied by each planet in the belt reached 1.36 billion cubic kilometers. what is this concept? 1.36 billion cubic kilometers is roughly equivalent to the volume of 120,000 earths, that is to say, in a space the size of about 120,000 earths, you can only encounter one planet. From this perspective, you want to hit a planet, it is difficult to reach the sky!