The closest distance an object can approach Earth without entering its atmosphere and causing an impact depends on various factors, including the object’s size, speed, and trajectory. This distance is not fixed and can vary widely.
Objects in space, such as satellites, the International Space Station, and other spacecraft, have different orbits and altitudes. The International Space Station (ISS), for example, orbits at an altitude of approximately 420 kilometers (about 260 miles) above the Earth’s surface, whereas many satellites in geostationary orbit are located at an altitude of about 35,786 kilometers (about 22,236 miles).
However, for objects that are not in orbit and are on a collision course with Earth, they need to pass through the Earth’s atmosphere before reaching the surface. The specific altitude at which an object would start to encounter the Earth’s atmosphere and experience significant atmospheric drag can vary depending on its size, composition, and speed.
In general, objects that approach the Earth from space would typically begin to interact with the atmosphere and experience significant heating and deceleration at altitudes of around 100 kilometers (62 miles) above the Earth’s surface. This region is often referred to as the Kármán line, and it’s considered the boundary between Earth’s atmosphere and outer space.
Objects entering the atmosphere at higher speeds and steeper angles may interact with the atmosphere at slightly higher altitudes, while those with lower speeds and shallower angles may interact with the atmosphere at lower altitudes.
Keep in mind that the exact altitude and conditions vary based on the specific circumstances, and experts in orbital mechanics and atmospheric science calculate these parameters to predict reentry trajectories for objects entering Earth’s atmosphere from space.