The tiny grains that make up most meteorites on Earth may have formed when ancient mini-moons smashed together billions of years ago. Scientists have always wondered how these round particles, called chondrules, came to be. Now, models suggest that chondrules originated during the final stages of planetary formation in the early Solar System.
A new study published in Science Advances has determined that chondrules were generated by planetary formation, which involved collisions between planetary embryos — moon- to Mars-sized bodies born within a ring of gas and dust. Some material from these collisions, packed together into chondrules, ended up in an orbit around the sun, becoming asteroids that still drift through space to this day.
“While several mechanisms may have created the chondrules themselves, I have always been surprised by how homogeneous the chondritic asteroids seem to be,” said the study’s first author, Hal Levison, a planetary scientist at the Southwest Research Institute, in a statement. “We were looking for a process that corrals these small droplets into asteroid-sized bodies”
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The Chaotic Origins of Chondrules
Chondrite meteorites are the most common meteorites found on Earth, representing around 86 percent of all meteorites recovered on the planet, according to Arizona State University’s Buseck Center for Meteorite Studies. Chondrites are like time capsules from the early Solar System; they emerged 2 million to 5 million years after the formation of calcium-aluminum-rich inclusions (CAIs), the oldest dated solid materials in the Solar System.
Chondrules serve as a window into this primordial era, yet exactly how they formed has been an ongoing mystery. Researchers involved with the new study aimed to uncover the particles’ origin using simulations of impact scenarios between planetary embryos.
These impacts ejected sheets of molten and solid material, and some of it remained gravitationally bound to one of the embryos. The debris then formed into a dense, rotating disk that eventually accumulated into larger, asteroid-sized bodies.
“The resulting asteroid-sized satellites are composed almost entirely of material from the original impact and are comparable in size and bulk composition to chondritic asteroids,” said Levison.
Orbiting Around the Sun
Many chondritic satellites didn't stay around their planetary embryos forever; occasionally, they were pushed away and entered orbits around the sun. This would've happened when planetary embryos had close encounters with each other, leading satellites to be stripped away from their parent embryo.
In the new study’s simulations, between 60 and 95 percent of the satellites end up in a heliocentric orbit. The rest eventually collide with their parent embryos. The satellites that do end up in orbit around the sun become the parent bodies of chondritic asteroids.
How Chondrites End Up on Earth
Chunks inevitably break off from some chondritic asteroids, and this can happen in a few different ways. One way is if they collide with another body in the asteroid belt, the region of space between the orbits of Mars and Jupiter that is home to an estimated 1.1 million to 1.9 million asteroids larger than 0.6 miles in diameter, according to NASA.
A more unusual scenario of asteroid breakup happens as a result of the YORP effect (short for the Yarkovsky-O'Keefe-Radzievskii-Paddack effect, named after the four scientists who first proposed its effects); the YORP effect occurs when sunlight hits an asteroid, causing it to release thermal energy, which can create a “windmill” effect that increases its rotation rate in a certain direction, according to The Planetary Society. An asteroid’s rotation can then get so fast that parts of it break off.
The pieces that break off the asteroids may then end up on Earth as chondrite meteorites. With the new explanation of how chondritic asteroids formed, researchers can now trace their origins back to a time when planetary embryos were embroiled in a chaotic stage of formation.
“They are escaped satellites — former moons-in-the-making — that carry within them a detailed record of the violent processes that built the terrestrial planets,” said second author Rogerio Deienno, also with the Southwest Research Institute, in the statement.
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from a study published in Science Advances: Chondrite parent bodies as escaped satellites of proto-planetary embryos
- This article references information from Arizona State University: Chondrites
- This article references information from NASA: Asteroid Facts
- This article references information from The Planetary Society: The YORP Effect and Bennu
