{"id":795366,"date":"2025-04-17T06:14:06","date_gmt":"2025-04-17T11:14:06","guid":{"rendered":"http:\/\/spaceweekly.com\/?p=795366"},"modified":"2025-04-17T06:14:06","modified_gmt":"2025-04-17T11:14:06","slug":"most-meteorites-that-hit-earth-arent-typical-why","status":"publish","type":"post","link":"https:\/\/spaceweekly.com\/?p=795366","title":{"rendered":"Most meteorites that hit Earth aren\u2019t typical. Why?"},"content":{"rendered":"


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View at EarthSky Community Photos. | Doug Ingram from Bodalla, Australia, captured this fireball on September 1, 2024. Studies of meteorites that have landed on Earth show most are not made of carbon, even though observations with telescopes show a majority of space rocks are<\/em> made of carbon. So why are the samples on Earth outliers?<\/figcaption><\/figure>\n

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  • Observations and sample-return missions<\/strong> show us that space rocks tend to be rich in water, carbon and organic compounds. Yet most meteorites that have made it to Earth are not. Why?<\/li>\n
  • Astronomers long thought the space rock\u2019s journey through our atmosphere<\/strong> filtered out these materials. But a new study published April 14, 2025, found something else.<\/li>\n
  • The temperature changes from space rocks traveling back and forth near the sun<\/strong> formed cracks in the rocks. So space rocks lose much of their carbon material before they even make it to Earth.<\/li>\n

    By Patrick M. Shober, NASA<\/span><\/p>\n

    Meteorites that hit Earth<\/h3>\n

    Much of what scientists know about the early solar system comes from meteorites. They are ancient rocks that travel through space and survive a fiery plunge through Earth\u2019s atmosphere. Among meteorites, one type \u2013 carbonaceous chondrites \u2013 stands out as the most primitive. They provide a unique glimpse into the solar system\u2019s infancy.<\/p>\n

    The carbonaceous chondrites are rich in water, carbon and organic compounds. They\u2019re hydrated<\/em>, which means they contain water bound within minerals in the rock. The components of the water are locked into crystal structures. Many researchers believe these ancient rocks played a crucial role in delivering water to early Earth. <\/p>\n

    Before hitting Earth, rocks traveling through space are generally referred to as asteroids, meteoroids or comets, depending on their size and composition. If a piece of one of these objects makes it all the way to Earth, it becomes a meteorite<\/em>. <\/p>\n

    From observing asteroids with telescopes, scientists know that most asteroids have water-rich, carbonaceous compositions. Models predict that most meteorites \u2013 over half \u2013 should also be carbonaceous. But less than 4% of all the meteorites found on Earth are carbonaceous. So why is there such a mismatch?<\/p>\n

    In a study published in the journal Nature Astronomy<\/em> on April 14, 2025, my planetary scientist colleagues and I tried to answer an age-old question: Where are all the carbonaceous chondrites? <\/p>\n

    Sample-return missions<\/h3>\n

    Scientists\u2019 desire to study these ancient rocks has driven recent sample-return space missions. NASA\u2019s OSIRIS-REx and JAXA\u2019s Hayabusa2 missions have transformed what researchers know about primitive, carbon-rich asteroids. <\/p>\n

    Meteorites found sitting on the ground are exposed to rain, snow and plants. This can significantly change them and make analysis more difficult. So, the OSIRIS-REx mission ventured to the asteroid Bennu to retrieve an unaltered sample. Retrieving this sample allowed scientists to examine the asteroid\u2019s composition in detail. <\/p>\n

    Similarly, Hayabusa2\u2019s journey to the asteroid Ryugu provided pristine samples of another, similarly water-rich asteroid. <\/p>\n

    Together these missions have let planetary scientists like me study pristine, fragile carbonaceous material from asteroids. These asteroids are a direct window into the building blocks of our solar system and the origins of life.<\/p>\n

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    NASA\u2019s OSIRIS-REx sample-return spacecraft captured this image of the carbonaceous near-Earth asteroid Bennu. Image via NASA.
    <\/figcaption><\/figure>\n

    The carbonaceous chondrite puzzle<\/h3>\n

    For a long time, scientists assumed Earth\u2019s atmosphere filtered out carbonaceous debris. <\/p>\n

    When an object hits Earth\u2019s atmosphere, it has to survive significant pressures and high temperatures. Carbonaceous chondrites tend to be weaker and more crumbly than other meteorites. So these objects just don\u2019t stand as much of a chance. <\/p>\n

    Meteorites usually start their journey when two asteroids collide. These collisions create a bunch of centimeter- to meter-size rock fragments. These cosmic crumbs streak through the solar system and can, eventually, fall to Earth. When they\u2019re smaller than a meter, scientists call them meteoroids. <\/p>\n

    Meteoroids are far too small for researchers to see with a telescope. That\u2019s unless they\u2019re about to hit the Earth, and astronomers get lucky.<\/p>\n

    But there is another way scientists can study this population, and, in turn, understand why meteorites have such different compositions.<\/p>\n

    Meteor and fireball observation networks<\/h3>\n

    Our research team used the Earth\u2019s atmosphere as our detector. <\/p>\n

    Most of the meteoroids that reach Earth are tiny, sand-sized particles. But occasionally, bodies up to a couple of meters in diameter hit. Researchers estimate that about 5,000 metric tons of micrometeorites land on Earth annually. And, each year, between 4,000 and 10,000 large meteorites \u2013 golf ball-sized or larger \u2013 land on Earth. That\u2019s more than 20 each day. <\/p>\n

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