アメリカ自然史博物館のインスタグラム(amnh) - 7月1日 06時47分

Today is both #MeteorWatchDay and #AsteroidDay. Thousands of years ago, the world-famous Willamette meteorite, traveling some 64,000 kilometers per hour, crashed into Earth’s surface. Billions of years before that, an early planet orbiting the Sun was shattered, perhaps in a collision with another protoplanet. While planets including Earth gradually formed and matured, the fragment orbited the Sun. Eventually, it landed in Oregon just outside of what is today the city of Portland. Over many centuries, rainwater interacting with its iron sulfide deposits produced sulfuric acid, which slowly etched and carved large cavities. The Willamette is made of iron and weighs 15.5 tons. It is the largest ever found in the United States and the sixth-largest in the world. Only about 600 of the 25,000 meteorites found on Earth are made of iron. The material was created deep inside stars, which produce energy by fusing lighter elements into heavier ones - for example, hydrogen into helium. The force of nuclear fusion eventually shatters stars much more massive than our Sun, casting fused elements, such as iron, into interstellar space. Over eons, these elements collect inside clouds of gas and dust. Within such an iron-rich interstellar cloud, our Sun formed 4.5 billion years ago, giving rise to comets, asteroids, planets and all life on Earth. So when we study the Willamette meteorite, we are also studying the chemical record of our origins and our place in the universe. #astronomy #meteor #meteorite #naturalhistory #meteorcrater #meteorshower #amnh #portlandhistory #portland

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