Impact event

An impact event is when astronomical objects crash into each other and cause changes. These crashes happen often in planetary systems, usually with asteroids, comets, or meteoroids. Most of these crashes do not do much, but bigger objects can cause big problems when they hit terrestrial planets like Earth. They move very fast, at speeds of several kilometres per second.

Impact events have helped shape the Solar System and Earth's history. They may have helped create the Earth–Moon system and might have brought the basic parts for life and water to our planet. Some scientists think that impacts helped cause big changes in life on Earth, like the event that ended the age of dinosaurs a very long time ago, known as the Chicxulub impact.

People have seen many impacts over time, and some have caused damage. Well-known examples include the Tunguska event in 1908 and the Chelyabinsk meteor in 2013. In 1994, everyone watched as Comet Shoemaker–Levy 9 broke apart and crashed into Jupiter. Scientists are working to better predict and prepare for future impacts, because these events can still be a danger to our planet. Tests like the Double Asteroid Redirection Test in 2022 show that we are finding ways to possibly move dangerous asteroids away from Earth.

Impacts and the Earth

Major impact events have helped shape Earth's history. These events may have played a role in forming the Earth–Moon system, affecting the evolutionary history of life, and bringing water to Earth. Impact structures show evidence of these ancient events. Famous examples include the Late Heavy Bombardment and the Chicxulub impact that happened 66 million years ago. This impact is thought to have caused big changes in life on Earth.

Small objects hit Earth often. Bigger objects crash less often. The damage from an impact depends on the size, speed, and angle of the object. This can cause shock waves, heat, craters, earthquakes, and tsunamis if water is 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 us that planets and moons in our Solar System have had big collisions in the past. 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 help us learn about big impacts from long ago.

Observed events

Jupiter

See also: List of Jupiter events

Jupiter, the largest planet in our Solar System, often catches comets and asteroids. In July 1994, Comet Shoemaker–Levy 9 broke apart and hit Jupiter. This 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 also seen impacts on other planets. In 2012, Mars had a big new crater. The Moon 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 left craters and changed the surface. Missions like Deep Impact in 2005 and Double Asteroid Redirection Test in 2022 were meant 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. Collisions within planetary systems, including stellar collisions, have been guessed about for a long time but only recently seen.

In 2013, a crash between small planets around the star NGC 2547 ID 8 was found. Computer modeling suggests this crash involved large asteroids or protoplanets, like events that may have helped form planets such as Earth.