Our Solar System can a chaotic place, and you can see just how vulnerable many of its planets and moons are by studying the many impact craters that have been formed throughout its 4.5 billion-year history.
Here we'll take a look at some of the best-known and biggest craters in the Solar System, with a special focus on Earth and how likely it is that our planet could suffer a sizeable impact.
Jupiter
Perhaps the most famous is the tale of comet Shoemaker–Levy 9, which broke up and impacted Jupiter in July 1994.
But even that was not the first known object to strike the planet.
Jupiter experiences the largest number of impacts of any planet and is often referred to as the ‘cosmic vacuum-cleaner’, hoovering up passing objects that could be a threat to the inner Solar System.
With a diameter of around 140,000km (87,000 miles), 11 times bigger than Earth’s, the giant planet is the largest in the Solar System and plays a key role in safeguarding Earth.
Its proximity to the inner Solar System, combined with its mass and enormous sphere of gravitational influence, has a huge effect on the distribution of smaller bodies orbiting the Sun, which are frequently captured by Jupiter.
Some of these comets escape the grasp of the gas giant and regain an orbit of the Sun, while others smash into the planet or, on rarer occasions, become one of its satellites.
In recent years, several impacts have been observed on Jupiter by amateur astronomers.
A bright flash caused by an object colliding with the planet was recorded by José Luis Pereira of Brazil in September 2021, and in August 2023 a collision was observed and recorded by an observer in China.
Recent research questions how much of a protector Jupiter may be.
The colossal planet certainly deflects comets and asteroids away from Earth, but there’s evidence it may increase the frequency of short-period comets and asteroids that head our way.
Not all objects are redirected and consumed by the gas giant, and the ones that have got away have inevitably impacted on other bodies within the Solar System.
There is evidence of these impact events all around us, with some of the largest collisions occurring uncomfortably close to home.
It’s important to remember, though, that not all impacts are of significant size.
Earth
According to NASA, 90 tonnes of material from outer space, ranging in size from tiny grains of cosmic dust to rocks, bombard Earth every day.
On a clear night, you may see some of this material zipping through Earth’s atmosphere as a meteor or ‘shooting star’.
Some of these meteors may land on Earth’s surface.
These meteorites are a reminder of how exposed we are to potential larger impacts from near-Earth objects (NEO), asteroids or comets passing within 45 million kilometres of Earth’s orbit.
One of Earth’s most significant impact craters is Chicxulub, located beneath the Yucatán Peninsula, Mexico, which formed around 66 million years ago.
The 200km-diameter (125-mile) crater was created when an asteroid 10km (6 miles) in diameter tore through Earth’s atmosphere and smashed into the surface.
An impact of this size caused a mass extinction event, wiping out three-quarters of life on Earth, including dinosaurs.
But Chicxulub is not Earth’s largest crater.
Earth's largest verified impact crater is Vredefort near Johannesburg in South Africa, with a whopping diameter of 300km (185 miles), having formed two billion years ago.
The Moon
There are an estimated one million craters on the Moon with a diameter of more than a kilometre (0.6 miles), each one a perfect example of past impact events.
Unlike Earth, the Moon does not have a protective atmosphere, which makes it extremely vulnerable to incoming material hurtling towards its surface.
Consequently, the largest crater on the Moon is the South Pole–Aitken Basin, a massive 2,500km (1,550 miles) in diameter and between 6.2km and 8.2km (3.8–5 miles) deep.
It is the second-largest crater in the Solar System and is thought to have been caused by a low-velocity impact from an object 200km (125 miles) in diameter.
Thankfully, humans weren’t around to witness these colossal impact events.
But today we can observe and record impacts across the Solar System thanks to powerful Earth- and space-based telescopes, and advances in space technology.
Mars
Since the late 1990s, spacecraft and landers visiting Mars have detected a whole host of new impact craters.
The Mars Global Surveyor orbited the Red Planet for 10 years and was the first spacecraft to map the surface in a resolution high enough to identify new impacts.
The craft detected its first impact between 2000 and 2001, and more than 1,200 impacts have been discovered by Martian orbiters and landers since then.
10 biggest impact craters in the Solar System
Utopia
- Body: Mars
- Diameter: 3,300km / 2,050 miles
The largest confirmed impact basin in the Solar System contains large quantities of underground ice
South Pole–Aitken Basin
- Body: The Moon
- Diameter: 2,500km / 1,550 miles
The largest and deepest basin on the Moon, formed on the lunar far side 4.2 billion years ago
Hellas
- Body: Mars
- Diameter: 2,300km / 1,430 miles
Formed 3–4 billion years ago, Hellas crater was the first Martian feature to be discovered by telescope from Earth
Isidis
- Body: Mars
- Diameter: 1,900km / 1,200 miles
Likely to be the youngest impact basin to be created on Mars. Isidis Planitia lies within a basin
Argyre
- Body: Mars
- Diameter: 1,700km / 1,060 miles
Argyre crater was formed during the Late Heavy Bombardment 3.9 billion years ago
Caloris
- Body: Mercury
- Diameter: 1,550km / 960 miles
Discovered on images taken by Mariner 10 in 1974, it is one of the largest impact basins in the Solar System
Sputnik Planitia Basin
- Body: Pluto
- Diameter: 1,300km / 800 miles
The basin forms the western lobe of the heart-shaped Tombaugh Regio on Pluto
Imbrium
- Body: The Moon
- Diameter: 1,145km / 710 miles
This impact crater formed on the Moon after a collision with a protoplanet 3.9 billion years ago
Rembrandt
- Body: Mercury
- Diameter: 715km / 415 miles
The second-largest impact basin on Mercury. Discovered by the MESSENGER spacecraft in 2008
Rheasilvia
- Body: Vesta (asteroid)
- Diameter: 505km / 315 miles
Created 1 billion years ago, the crater floor lies 13km (8 miles) below the surrounding surface
This article appeared in the July 2024 issue of BBC Sky at Night Magazine
