The lowest theoretical impact speed at which a meteorite could collide with Earth depends on various factors, including the relative velocities of the meteorite and Earth, the gravitational influence between them, and the orbital dynamics involved. However, there are a few considerations to keep in mind:
Escape Velocity: The minimum speed at which an object needs to travel to escape the gravitational pull of Earth is known as the escape velocity. On Earth's surface, the escape velocity is approximately 11.2 kilometers per second (6.95 miles per second). If a meteorite were to impact Earth, it would generally need to have a speed higher than the escape velocity.
Atmospheric Entry: When a meteorite enters Earth's atmosphere, it experiences atmospheric drag, which causes it to slow down due to air resistance. As the meteorite slows down, its speed decreases further before it potentially impacts the surface. The precise speed at which a meteorite impacts the Earth depends on various factors, including its initial velocity, mass, shape, composition, and angle of entry.
Terminal Velocity: Terminal velocity is the constant speed at which an object falls through a fluid (in this case, the Earth's atmosphere) when the drag force equals the force of gravity. For smaller meteorites, typically in the range of a few meters to tens of meters in diameter, their terminal velocities are relatively low due to their small mass-to-surface area ratio. These meteorites tend to burn up and disintegrate in the atmosphere before reaching the Earth's surface.
In summary, while it is challenging to provide an exact numerical value for the lowest theoretical impact speed of a meteorite on Earth, it would need to exceed the escape velocity and overcome atmospheric drag to reach the surface. The specifics of a meteorite's entry angle, mass, composition, and other factors significantly influence its actual impact speed.