Thursday, May 9, 2024

4461 - METEORITES - messages from space?

 

-    4461  -  METEORITES  -  messages from space?  -    Meteorites provide our best information about how the solar system formed and evolved. This includes planet formation. We also obtain information on astrophysics (stellar processes) through studies of pre-solar grains.



-----------------------------  4461    -   METEORITES  -  messages from space?

-    Meteorites: What can they teach us about finding life beyond Earth?  Studying impact craters, planetary surfaces, exoplanets, astrobiology, solar physics, comets, planetary atmospheres, planetary geophysics, and cosmo-chemistry, and how this myriad of intricately linked scientific disciplines can assist us in better understanding our place in the cosmos and searching for life beyond Earth.

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-    There is often confusion regarding the differences between an asteroid, meteor, and meteorite.   An asteroid is a physical, orbiting planetary body that is primarily comprised of rock, but can sometimes be comprised of additional water ice, with most asteroids orbiting in the Main Asteroid Belt between Mars and Jupiter and the remaining orbiting as Trojan Asteroids in the orbit of Jupiter or in the Kuiper Belt with Pluto.

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-    A meteor is the visual phenomena that an asteroid produces as it burns up in a planet’s atmosphere, often seen as varying colors from the minerals within the asteroid when heated up.

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-    The pieces of the asteroid that survive the fiery entry and hit the ground are called meteorites, which scientists’ study to try and learn about the larger asteroid body it came from, and where that asteroid could have come from, as well.

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-    Benefits: scientific knowledge, information on potential resources (e.g., metals, water) for humans to utilize, information on how to link meteorites and asteroids, which can provide information on space collision hazards for Earth.

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-    Challenges: compared to Earth rocks, we lack field evidence for their source bodies and parent bodies (how they relate to other rocks), we have to factor in the element of time that is longer for space rocks than for Earth rocks, and sometimes we are dealing with formation environments completely unlikely what we have on Earth.

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-    More than 50,000 meteorites have been retrieved from all over the world, ranging from the deserts of Africa to the snowy plains of Antarctica. In terms of their origins, it is estimated that 99.8 percent of these meteorites have come from asteroids, with 0.1 percent coming from the Moon and 0.1 percent coming from Mars.

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-     The reason why we’ve found meteorites from the Moon and Mars is due to pieces of these planetary bodies being catapulted off their surfaces (or sub-surfaces) after experiencing large impacts of their own, and these pieces then travel through the Solar System for thousands, if not millions, of years before being caught in Earth’s gravity and the rest is history.

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-    The ingredients for making life formed in space and were delivered to Earth.  We know organic molecules formed in gas clouds, were incorporated in our solar system, and processed in asteroidal and cometary bodies under higher temperatures in the presence of water. These were then delivered to Earth which wouldn’t have been very hospitable in early times due to sterilizing impacts. We also know that there must have been a lot of planetary rock swapping early when impact rates were high. Life itself may have been transplanted to Earth from Mars.

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-    One of the most fascinating meteorites ever recovered did come from Mars, which was identified as “ALH84001”, as it was found in Allan Hills of Antarctica on December 27, 1984, during the 1984-85 field season where researchers from all over the world gather in Antarctica to search for meteorites using snowmobiles.

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-   Despite being collected in 1984, it wasn’t until 1996 that a team of scientists discovered what initially appeared to be evidence of microscopic bacteria fossils within the 4.25-pound meteorite.

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-    ALH84001, which is one of the most famous meteorites ever recovered, helped catapult the field of astrobiology to new heights when scientists uncovered what initially appeared to be microscopic bacteria fossils within this meteorite, though those findings remain inconclusive to this day.

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-    While ALH84001 is estimated to be 4.5 billion years old, which is when Mars is hypothesized to have possessed liquid water on its surface, radiometric dating techniques revealed that ALH84001 was catapulted off Mars approximately 17 million years ago and landed on Earth approximately 13,000 years ago.

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-    Like many scientific fields, this “meteoritic version of CSI” requires individuals from a myriad of backgrounds and disciplines, including geology, physics, geochemistry, cosmo-chemistry, mineralogy, and artificial intelligence, just to name a few, with radiometric dating frequently used to estimate the ages of meteorites by measuring the radioactive isotopes within the sample.

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-    It is through this constant collaboration and innovation that scientists continue to unlock the secrets of meteorites with the goal of understanding their origins and compositions, along with how our Solar System, and life on Earth (and possibly elsewhere), came to be.

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-    While meteorites are space rocks that crash land on Earth after traveling through the heavens for millions, and possibly billions, of years, these incredible geologic specimens are slowly helping scientists’ piece together the origins of the Solar System and beyond, and even how life might have come to be on our small, blue world, and possibly elsewhere.

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-    Rocks from space are the best kinds of rocks to study. Way more cool than most rocks on Earth because they are in some ways more puzzling.  How will meteorites help us better understand our place in the cosmos in the coming years and decades? Only time will tell, and this is why we science!

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-    “ALH84001” is one of the most famous meteorites ever recovered.  It help catapult the field of astrobiology to new heights when scientists uncovered what initially appeared to be microscopic bacteria fossils within this meteorite, though those findings remain inconclusive to this day.

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-    Meteorites can they teach us about finding life beyond Earth?   Studying impact craters, planetary surfaces, exoplanets, astrobiology, solar physics, comets, planetary atmospheres, planetary geophysics, and cosmochemistry, and how this myriad of intricately linked scientific disciplines can assist us in better understanding our place in the cosmos and searching for life beyond Earth.

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-    A Bronze Age Arrowhead was made out of a meteorite.   It’s sometimes hard to remember that meteorites have been hitting our planets for millions of years. And some of them are made of valuable materials such as titanium or iron.   Theoretically, at least, our bronze and iron age ancestors could utilize these ready-made metallic rocks without having to dig underground to access them, like they would with regular tin or iron veins.

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-    Now, a new study of an arrowhead made out of a meteorite points out just how valuable iron age society thought these meteorites were and hints at a trade network that reached farther than archeologists initially thought.

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-   It might come as a bit of a surprise that dozens of documented objects made out of meteorites are found at archeological digs. However, most objects were found in the Middle East and Asia. Europe, the home of what we now consider a “Western” society, only had two sites in Poland that turned up objects made by meteorites.

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-   Now, there is a third. An arrowhead found in a dwelling near Lake Mörigen in Switzerland in the late 19th century was confirmed to be made from a meteorite. It was dated back to the Bronze Age, somewhere between 900-800 BCE. -

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-    First is how the researchers, led mainly by a Swiss team of academics, determined that this arrowhead was made of meteorite. They turned to modern-day analysis techniques that engineers call Non-Destructive Testing (NDT). Typically, if an archeologist wants to determine whether a particular piece was made out of a meteorite, they would take a piece of it and subject it to destructive testing.

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-    The Swiss team took a gentler approach, subjecting numerous samples of collected archeological objects to different NDT techniques ranging from muon-induced X-ray emission spectroscopy to high-sensitivity gamma-ray spectroscopy.

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-   Of all the samples they looked at, though, only one appeared to be from a meteorite. Strangely, it didn’t seem to be local. In fact, they were initially looking for objects of possible meteoritic origin in that part of Switzerland because there had been a known meteorite strike known as the Twannberg iron meteorite that fell nearby.

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-   When the Twannberg meteorite fell, it broke into pieces. So far, 2000 individual pieces have been found with a total weight of over 150 kg. That’s a lot of easily recoverable metal sitting only a few kilometers from the site at Lake Mörigen, where the arrowhead was found. But strangely, the study found that the arrowhead was conclusively not made of the meteor that fell new Twannberg.

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-   Instead, they believe it was created using pieces from a different meteorite that fell in Estonia in 1500 BCE. Known as the Kaalijarv meteorite, it is the best fitting of the three other meteorites with the same chemical signature as the arrowhead. However, its landing site was over 1,600 kilometers away. That is quite the distance for an arrowhead to travel in the Bronze Age.

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-    Unfortunately, this will most likely remain a mystery as to why this particular arrowhead has the composition it does. But the high-tech techniques used by the researchers pave the use of such techniques for future meteoritic searches of archeological artifacts.

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-    Some metal meteorites have a tiny magnetic field. But How?   Iron meteorites are often magnetic. The magnetism isn’t strong, but it holds information about their origin. This is why astronomers discourage meteorite hunters from using magnets to distinguish meteorites from the surrounding rock, since hand magnets can erase the magnetic history of a meteorite, which is an important scientific record.

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-    Magnetic meteorites occur because they form in the presence of a magnetic field. The iron grains within the meteorite are aligned along the external magnetic field, which gives the meteorite its own magnetism. For example, the Martian meteorite known as Black Beauty gained its magnetism from the strong magnetic field of young Mars.

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-    Some meteorites are magnetic but shouldn’t have formed in a strong magnetic field. Iron meteorites are typically categorized by chemical composition, such as their ratio of nickel to iron. One type, known as IVA, is known to be fragments of smaller asteroids. Small asteroids don’t have strong magnetic fields, so IVA meteorites shouldn’t be magnetic, but many of them are.

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-    How IVA meteorites could become magnetic.   Small asteroids form through what is known as the rubble pile method. Small chunks of iron-rich rock aggregate over time, building up to become an asteroid. For a body to generate a strong magnetic field, there needs to be liquid iron to create a dynamo effect, and since small asteroids don’t experience this, they can’t have magnetic fields. Or can they?

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-   Asteroids are also subject to collisions over time. It’s these collisions which break off fragments that become the meteorites we find on Earth.   Impacts can create a magnetic dynamo within an asteroid. If a colliding body is not big enough to shatter the asteroid, but large enough to melt a layer of material near the surface, then a chain of events can occur.

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-    When a cold rubble core is surrounded by a molten layer, the core is heated up. Lighter elements evaporate out of the core and migrate toward the surface, which churns the layers to generate convection. The convection of iron generates a magnetic field, which imprints itself on parts of the asteroid. Later collision then creates magnetic fragments, some of which reach Earth.

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-    The magnetism of IVA meteorites comes not from the original formation of their parent asteroid, but rather from later collisions that stirred up their core. Knowing this, researchers can gain a better understanding of the history of our solar system, and how things such as planetary drift might have triggered more frequent asteroid collisions.

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-   Yet another reason not to look for meteorites with hand magnets. The very act of finding a meteorite could also erase the history of its collisions.

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May 9, 2024         METEORITES  -  messages from space?                 4461

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