What is the escape velocity from the Sun's surface in km/s?

The escape velocity from the Sun’s surface is about 617.7 km/s. An object leaving the Sun at this speed, without further propulsion or atmospheric drag, would have enough kinetic energy to escape the Sun’s gravitational field.

Escape velocity depends on an object’s mass and radius, following the relationship v = √(2GM/r). The Sun is vastly more massive than Earth, so its surface escape velocity is far higher. For comparison, Earth’s escape velocity at the surface is about 11.2 km/s, while the Moon’s is only about 2.4 km/s.

This does not mean the Sun launches material at exactly 617.7 km/s whenever it erupts. Solar flares and coronal mass ejections can accelerate particles and plasma to a wide range of speeds. Some material remains gravitationally bound, while especially fast solar-wind streams and eruptions can travel through the heliosphere.

The value also changes with distance from the Sun: farther away, the required escape speed is lower. At the Sun’s photosphere, the commonly quoted value is approximately 618 km/s. The photosphere is called the surface for convenience, although the Sun is a ball of plasma with no solid boundary.