This essay is reprinted with permission fromThe Conversation, an online platform that reports on the latest research.
Have you ever witnessed a streak of light dart across the night sky and vanish? Ever ponder where that shooting star originated or how it ended up in your view?
As the director of the Peters Observatory at Hamilton College, I have observed many such streaks during my late-night sessions at the observatory. What you saw was not a star; it was the conclusion of a 4.6-billion-year journey of a comet or asteroid.
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Remnants from the early solar system
Around 4.6 billion years ago, the solar system was just forming. A vast sphere of gas and dust began to gather in the center, eventually forming our Sun. Simultaneously, dust condensing farther out began merging into the initial building blocks of planets, known as planetesimals.
Asteroids originated from planetesimals in the warmer, inner regions of the solar system, near the Sun. These planetesimals, composed primarily of rocks and metals able to endure intense heat, combined to form the terrestrial planets: Mercury, Venus, Earth, and Mars. The leftover planetesimals that did not form into planets are today’s asteroids, orbiting the inner solar system.
Comets emerged in the colder outer solar system, where water and similar hydrogen-based compounds froze into ice. The planetesimals in this region included both rock and ice.
Some planetesimals grew rapidly enough to capture large atmospheres of abundant early solar system gases like hydrogen and helium. These became the Jovian planets: Jupiter, Saturn, Uranus, and Neptune. Meanwhile, planetesimals that did not evolve into Jovian planets became comets, wandering through the solar system.
Origin of meteors
With asteroids still prevalent in the inner solar system, collisions with Earth are inevitable. When a rock fragment enters Earth’s atmosphere at great speed, it might produce a sonic boom. Traveling faster than sound, the rock generates a shock wave, causing the boom.
As the asteroid moves through the atmosphere, it collides with air molecules, producing extreme heat and pressure that usually vaporizes it. This vaporization leaves behind a trail of glowing particles, creating a bright streak of light in the sky known as a meteor or a shooting star.
Despite being mostly located in the outer solar system, comets can also produce meteors and meteor showers. Some comets follow long, elliptical orbits that take them through the inner solar system each year.
Often referred to as “dirty snowballs,” these comets are made of dust and ice. As they approach the Sun, they gradually melt, leaving a trail of gas and debris.
When Earth’s orbit intersects with a comet’s path, it collides with this debris. As the debris burns up in the atmosphere, it creates numerous light trails known as meteor showers. These showers occur annually because they happen at the same point in Earth’s orbit. Under a dark sky, you can observe dozens of meteors per hour during these events.
Finding meteorites
The meteors that survive their passage through the Earth’s atmosphere and land on the surface are called meteorites. These typically originate from asteroids that were once larger than a football field.
Identifying meteorites can be challenging as they resemble Earth rocks. They are often found in stable geological areas like deserts or ice fields, where they stand out against the landscape.
Meteorites are generally composed of stone, nickel, and iron, and are often magnetic. They may have irregular shapes or smooth crusts from burning in the atmosphere.
Due to their rarity, meteorites are valuable for studying the early solar system. If you think you have found one, compare its features with those of a meteorite and contact local geologists for verification.
The next time you observe a meteor, consider that you are witnessing the final moments of a journey that began billions of years ago, as it disintegrates in the Earth’s atmosphere.
This article was originally published on The Conversation. Read the original article.
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