New research shows that most of the space rocks that hit Earth come from a single source

The sight of a fireball streaking across the sky brings wonder and excitement to children and adults alike. It reminds us that the Earth is part of a much larger and incredibly dynamic system.
Each year, approximately 17,000 of these fireballs not only enter the Earth’s atmosphere, but also survive the perilous journey to the surface. This gives scientists a rare opportunity to study rocky visitors from space.
Scientists know that some of these meteorites come from the Moon or Mars, but the majority come from asteroids. But two separate studies published today in the journal Nature go a step further. The research was led by Miroslav Brož from Charles University in the Czech Republic and Mikael Marcet from the European Southern Observatory in Chile.
These papers trace the origin of most meteorites back to fragmentation events of just a handful of asteroids, and in some cases to individual asteroids. In turn, they build our understanding of the events that shaped the history of Earth, and the history of the entire solar system.
What is a meteorite?
Only if a fireball reaches the surface of the Earth is it called a meteorite. They are generally classified into three types: stony meteorites, iron meteorites, and stony iron meteorites.
There are two types of stony meteorites.
The most common are chondrites, which have round objects that appear to have formed as molten droplets inside. These make up 85% of all meteorites found on Earth.
Most are known as “ordinary chondrites”. They are then divided into three broad classes: H, L, and LL, based on the iron content of the meteorites and the distribution of iron and magnesium in the main minerals olivine and pyroxene. These silicate minerals are the mineral building blocks of the solar system, occur in basalts, and are common on Earth.
“Carbonaceous chondrites” are a separate group. Clay minerals contain a lot of water and also contain organic substances such as amino acids. Chondrites have never melted and are direct samples of the dust that originally formed the solar system.
The less common of the two types of stony meteorites are the so-called “achondrites.” These have undergone dissolution in planetary bodies and therefore do not have the characteristic round grains of chondrites.
asteroid belt
Asteroids are the main source of meteorites.
Artist’s graphic of the asteroid belt between Mars and Jupiter. Credit: NASA/McREL
Most asteroids exist in the dense belt between Mars and Jupiter. The asteroid belt itself is made up of millions of asteroids that are swept around and organized by Jupiter’s gravity.
Interactions with Jupiter can disrupt the asteroid’s orbit and cause a collision. This generates debris that can aggregate to form a rubble pile asteroid. These then take on a life of their own.
It is this type of asteroid that the recent Hayabusa and Osiris-Rex missions visited and brought back samples. These missions established connections between different types of asteroids and meteorites that fall to Earth.
S-class asteroids (similar to stony meteorites) are found in the inner regions of the belt, while C-class carbonaceous asteroids (similar to carbonaceous chondrites) are more commonly found in the outer regions of the belt. .
But as two Nature studies show, certain types of meteorites can be linked to specific source asteroids in the main belt.
one family of asteroids
Two new studies place the origin of common chondrite types into specific asteroid families, and possibly specific asteroids. This research requires painstaking tracking of meteoroid trajectories, observations of individual asteroids, and detailed modeling of the parent body’s orbital evolution.
The study, led by Miroslav Broz, reports that ordinary chondrites originate from collisions between asteroids more than 30 kilometers in diameter that occurred less than 30 million years ago.
The Coronis and Massalia asteroid families provide suitable celestial sizes and positions for material to fall to Earth, based on detailed computer modeling. Among these families, the asteroids Coronis and Karin may be the main sources of H chondrites. The Massalia (L) and Flora (LL) families are the main sources of L- and LL-type meteorites.
Research led by Michael Marcet further documents the origin of L-chondrite meteorites from Massalia.
It collected spectroscopic data of asteroids in the belt between Mars and Jupiter – characteristic light intensities that can be fingerprints of different molecules. This showed that the composition of L-chondrite meteorites on Earth is very similar to that of Massalia family asteroids.
Scientists then used computer modeling to show that an asteroid impact that occurred approximately 470 million years ago formed the Massalia family. Coincidentally, this impact led to the discovery of large amounts of meteorite fossils in the Ordovician limestone of Sweden.
In determining the source asteroid body, these reports provide the basis for missions to visit asteroids, which are the most common source of space visitors to Earth. Understanding these origin asteroids allows us to see the events that shaped our planetary system.
Provided by The Conversation
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