Escape Velocity

Escape Velocity in the Solar System

Gravitas (depth of personality) was one of the Roman virtues, along with Pietas (duty, devotion), Dignitas (charisma, self-esteem), and Virtus (moral excellence); the opposite of virtue is vice.

In astronomy, gravity is a term dating back to the Middle Ages and used by Isaac Newton (1643-1727) to speak of the terrestrial attraction exerted on any mass in its vicinity. It is the force of the gravitational field that keeps us on the surface of the Earth. In reality, it makes us constantly fall towards the center of the Earth, but we are held back by the solid surface of our planet.

Gravitation acts at very great distances in all directions, on all objects endowed with mass; in other words, it is an invisible and universal attractive force of matter directly linked to its mass. Gravitation is non-shieldable, meaning it cannot be escaped. This concept is fundamental in astronomy, as it explains all the trajectories of spatial orbits.

How can a body disconnect and escape the attraction of another body?

The escape velocity allows a body to permanently escape the gravitational attraction of another body; this velocity depends on the mass and radius of the celestial body.

On a very small body like Deimos (Mars' moon) with dimensions of ≈8×6×5 km, it would be enough to run at 20 km/h (5.556 m/s) to leave the ground and escape Deimos permanently. But for Earth, which has a mass of 5.972E24 kg and a radius of 6371 km, this escape velocity is more difficult to achieve; it is 11.186 km/s or 40,270 km/h. On a celestial body more massive than Earth, the escape velocity will be even more difficult to achieve. This is the case with the Sun, which is 333,000 times more massive and 109 times larger than Earth. The escape velocity of the Sun is approximately 617 km/s.

Examples of Escape Velocities

Escape Velocity of Stars

A large part of the stars in the Galaxy have an escape velocity of a few hundred km/s. To measure much higher escape velocities, one must observe white dwarfs, as a white dwarf with 1 solar mass has a radius on the order of that of Earth. Thus, an object close to its surface will have great difficulty escaping; the escape velocity at the surface of white dwarfs is a few thousand km/s.

In neutron stars, the escape velocities are even higher. Indeed, neutron stars are very small and very dense. They concentrate the mass of a star like the Sun within a radius of about 10 km. Since the radius is very small, the gravitational field at the surface is even higher, and it is even more difficult to escape. The escape velocity can reach 200,000 km/s, or 66% of the speed of light.

Escape Velocity of Black Holes

It is with black holes that we reach the limit of escape velocity, which is the speed of light. Black holes are massive objects whose gravitational field is so intense that it prevents any form of matter or radiation from escaping. The theory of black holes states that they are objects so dense that their escape velocity exceeds the speed of light (300,000 km/s).