New research shows most space rocks crashing into Earth come from a single source

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The sight of a fireball zipin' across the sky gives kids and adults a real buzz. It's a reminder that Earth's part of a way bigger and pretty wild system.

Not only do some of these fireballs make it into Earth's atmosphere, but they also manage to survive the treacherous trip to the surface. This provides scientists with a fantastic opportunity to study these space rocks up close.

From the European Southern Observatory in Chile.

The papers look at the source of most meteorites originating from few asteroids, if not individual ones, breaking apart – and the events that led to that shattering. In doing so, they create a picture of the major events that changed the history of the Earth and the whole solar system.

What is a meteorite?

A fireball is only referred to as a meteorite after it hits Earth's surface. They're frequently categorised as three types: stony meteorites, iron meteorites, and stony-iron meteorites.

Stony meteorites come in two basic types.

The most common types are chondrites, which have rounded objects inside that seem to have formed as molten droplets. They make up approximately 85% of all meteorites discovered on the planet.

Most chondrites are known as "ordinary chondrites". They're broken up into three main types – H, L and LL – based on the amount of iron in the meteorites and how the iron and magnesium are spread out in the minerals olivine and pyroxene. These silicate minerals are the building blocks of the material that makes up our Solar System and are also common on Earth, found in basalt.

“Carbonaceous chondrites” are a specific type. They've got high amounts of water locked up in clay minerals and carbon-based compounds like amino acids. These chondrites haven't been melted, so they're direct samples of the dust that made up the solar system right from the start.

The less common of the two types of stony meteorites are the so-called “achondrites”. These don't have the characteristic spherical particles of chondrites, because they experienced heat-melt conditions on planetary bodies.

JPL/Smithsonian Institution

The asteroid belt

Asteroids are the main supply of meteorites.

Most asteroids are found in a thick belt between Mars and Jupiter. This asteroid belt is made up of millions of asteroids being kept in motion by Jupiter's gravitational pull.

The interactions with Jupiter can mess up the orbits of asteroids, which can lead to collisions and debris. This debris can build up to form rubble pile asteroids that start operating independently.

Missions to space visited certain asteroids and brought back samples from them. These spaceships made a connection between different kinds of asteroids and the meteorites that land on Earth.

In Oz, you can find S-class asteroids that are like meteorites from rocks in the inner parts of the asteroid belt, while C-class carbonaceous asteroids – which are similar to carbon-rich chondrites – are more commonly found out in the outer bits of the belt.

But, as the two Nature studies show, we can track a particular type of meteorite back to its corresponding origin asteroid in the main asteroid belt.

NASA/McREL

One family of asteroids

The two new studies pinpoint the sources of regular chondrite types to specific asteroid families – and most likely specific asteroids. This work demands meticulous tracing of meteoroid trajectories, observations of individual asteroids, and detailed modelling of the orbital evolution of parent bodies.

Miroslav Brož's research states that normal chondrites result from collisions between asteroids over 30 kilometres in diameter that occurred less than 30 million years ago.

The Koronis and Massalia asteroid groups have the right size and position, according to computer simulations, and their meteorites are likely to fall to Earth. Specifically, the Koronis and Karin groups are probably the main sources of H chondrite meteorites. On the other hand, the Massalia (L) and Flora (LL) groups are the main sources of L- and LL-like meteorites, respectively.

Led by Michaël Marsset further investigates the source of L chondrite meteorites from Massalia.

It compiled spectroscopic data – that is, characteristic light intensities which can be fingerprints of different molecules – of asteroids in the region between Mars and Jupiter. This showed that the chemical composition of L chondrite meteorites on Earth is quite similar to that of the Massalia family of asteroids.

The scientists then used computer modelling to show that a asteroid collision that happened around 470 million years ago started the Massalia family. By good luck, this collision also produced a large number of meteorite fossils in Ordovician limestones in Sweden.

In workin' out where the asteroids that come to Earth come from, these reports give us the groundwork for missions to check out the asteroids that make the most common visitors to our space. By findin' these source asteroids, we can take a look at how our planetary system formed.

Lecturer, Faculty of the Environment

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