Some asteroids have intersecting orbits with that of Earth due to gravitational interactions with other celestial bodies in our solar system, which can alter their trajectory and bring them closer to our planet.
Asteroids quietly follow their orbit until a planet, especially Jupiter, passes close to them. The massive gas giant, with its powerful gravity, seriously disrupts the trajectories of these space rocks. These gravitational perturbations can alter the speed and direction of an asteroid, pushing it to adopt a completely different orbit. As a result, some objects end up crossing the orbits of other planets, like that of Earth, thereby increasing the potential risk of collision. Even weak but repeated interactions with the planets can accumulate their effects and eventually bring these asteroids closer to intersecting trajectories with our beloved blue planet.
The Yarkovsky effect is a rather subtle phenomenon that, simply due to sunlight, gradually changes the orbits of asteroids. Essentially, the asteroid spins on its axis, absorbing heat from the sunlit side, and then gently releasing this thermal energy into space when it is turned elsewhere. This tiny shift gently nudges the object, but over millions of years, these small pushes can significantly alter a trajectory. Another force at play is the tidal forces, caused by the uneven gravitational pull of a planet or another massive body. Imagine a big rock passing near a planet; the planet will exert a different pull on each end of the asteroid, slowly stretching its path, which can strongly alter its orbit and sometimes even send it crossing Earth's orbit.
In our Solar System, asteroids jostle with one another: sometimes lightly, sometimes quite violently. When a collision occurs, the initial trajectory of these rocky objects completely changes direction. Imagine it like billiards: a head-on or side impact, and voila, the asteroid is propelled into a totally different orbit. These impacts significantly disrupt their paths and can send them crossing the orbits of planets, including that of Earth. Over time, these accumulated collisions permanently alter the dynamics of the Solar System, thereby creating new unforeseen trajectories that make some of these asteroids potentially hazardous to us.
Orbital resonance occurs when two celestial bodies orbit the Sun with orbital periods related by a simple ratio like 2:1 or 3:2. In this case, certain areas become particularly unstable: the asteroids located there experience a sort of "kick" effect each time they pass near large planets like Jupiter. This eventually disrupts their trajectories and pushes these asteroids inward toward the solar system. As a result, they can cross Earth's orbit, becoming what are known as Earth-crossing asteroids, with a potential risk of collision. These phenomena of regular attraction create "empty" zones of asteroids called Kirkwood gaps, which clearly demonstrate how a small orbital resonance can completely disrupt the apparent calm of space.
The famous Meteor Crater in Arizona, visible from space, was caused about 50,000 years ago by a celestial body estimated to be just 50 meters in diameter!
NASA considers an asteroid to be potentially hazardous to Earth if its orbit brings it within 7.5 million kilometers and if it is more than 140 meters in diameter.
About once a year, an asteroid the size of a small car enters our atmosphere and disintegrates in a spectacular fireball visible to the naked eye.
The Yarkovsky effect, caused by the heat emitted by an asteroid heated by the Sun, can subtly alter its trajectory over the years, potentially leading to a crossing of Earth's orbit!
Asteroids are generally observed using ground-based or space telescopes. Once detected, their position and speed are tracked precisely to calculate and predict their future orbits.
Space missions like NASA's DART are currently exploring this scenario. The idea is to intentionally crash a spacecraft into an asteroid to slightly alter its trajectory and reduce the risk of a potential collision.
The Yarkovsky effect is a phenomenon by which asteroids receive a slight but constant push caused by thermal emissions due to absorbed and re-emitted solar radiation. This leads to slow but significant changes in their orbits over long periods.
A comet is primarily composed of ice and dust and often comes from the cold outskirts of the solar system. An asteroid, on the other hand, is mainly made up of rock and metal and primarily orbits between Mars and Jupiter. Finally, a meteorite is a small rocky body that passes through the Earth's atmosphere and reaches the ground.
Even though several asteroids cross Earth's orbit, the probability of a collision remains extremely low. Space agencies constantly monitor these objects to accurately assess any potential risk.
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