Impact event

An impact event is a collision between astronomical objects causing measurable effects. These events happen regularly in planetary systems, with the most common involving asteroids, comets, or meteoroids. While many of these impacts have little effect, larger objects can cause significant damage when they hit terrestrial planets like Earth, traveling at speeds of several kilometres per second.

Impact events have played an important role in shaping the Solar System and Earth's history. They are believed to have helped form the Earth–Moon system and may have delivered the building blocks for life, as well as water, to our planet. Some scientists think that impacts were involved in causing mass extinctions, including the event that ended the age of dinosaurs around 66 million years ago, known as the Chicxulub impact.

Throughout history, many impacts have been recorded, with some causing damage or injuries. Famous examples include the Tunguska event in 1908 and the Chelyabinsk meteor in 2013. In 1994, the world watched as Comet Shoemaker–Levy 9 broke apart and crashed into Jupiter. Scientists are working hard to better predict and prepare for future impacts, as these events remain a real threat to our planet. Recent tests, like the Double Asteroid Redirection Test in 2022, show that we are developing ways to possibly deflect dangerous asteroids away from Earth.

Impacts and the Earth

Major impact events have played a significant role in shaping Earth's history. These events have been linked to the formation of the Earth–Moon system, the evolutionary history of life, the origin of water on Earth, and several mass extinctions. Impact structures serve as evidence of these prehistoric events, with notable examples including the hypothesized Late Heavy Bombardment and the confirmed Chicxulub impact 66 million years ago, which is believed to have caused the Cretaceous–Paleogene extinction event.

Small objects frequently collide with Earth, with the frequency of impacts decreasing as the size of the object increases. Asteroids with a 1 km diameter strike Earth every 500,000 years on average, while larger collisions with 5 km objects happen approximately once every twenty million years. The energy released by an impact depends on several factors, including the diameter, density, velocity, and angle of the impacting body. These factors determine the potential damage on the ground, which can include shock waves, heat radiation, crater formation, earthquakes, and tsunamis if water bodies are hit.

Elsewhere in the Solar System

Evidence of massive past impact events

Main article: List of largest craters in the Solar System

Impact craters show evidence of past collisions on planets and moons in our Solar System. Mars has large craters like Utopia Planitia and Hellas Planitia. The Moon has the huge South Pole–Aitken basin. Mercury’s Caloris Basin is another giant crater. These craters tell us about big impacts that happened long ago.

Observed events

Jupiter

See also: List of Jupiter events

Jupiter, the biggest planet in our Solar System, often catches comets and asteroids. In July 1994, Comet Shoemaker–Levy 9 broke apart and hit Jupiter, which was the first time we saw a space collision up close. Since then, we have watched many smaller impacts on Jupiter.

Other impacts

See also: Impact events on Mars

We have seen impacts on other planets too. In 2012, Mars had a big new crater. The Moon also gets hit sometimes, like in 2013 when a small space rock made a new crater. In 2021, Mars had several big new craters.

Human caused impacts

In the past, space probes have crashed on moons and planets. These crashes have left craters and changed the surface. Missions like Deep Impact in 2005 and Double Asteroid Redirection Test in 2022 were designed to study how these impacts work.

Extrasolar impacts

See also: List of extrasolar planetary collisions

Collisions between galaxies, such as galaxy mergers, have been seen by space telescopes like Hubble and Spitzer. Collisions within planetary systems, including stellar collisions, have long been guessed about but only recently observed directly.

In 2013, a crash between small planets around the star NGC 2547 ID 8 was found by Spitzer and confirmed from the ground. Computer modeling suggests this crash involved large asteroids or protoplanets, similar to events thought to have helped form planets like Earth.