You’ve certainly heard of meteorites before and how the idea of them striking Earth’s surface is a hugely unwelcome event. Still, humans have survived a total of roughly 24,000 meteorite strikes! While thinking of the next meteorite strike and dreading its consequences, have you ever wondered where these meteorites come from? Why do they have to strike Earth and terrify the inhabitants of the planet?
Well, before we get to that, you need to understand a few things…
What is a meteorite?
A meteorite is a rock or fragment(s) of rock, mostly composed of stone or iron, that breach the atmosphere and fall to Earth after breaking away from a larger celestial body, such as a meteor or an asteroid.
Consider this: when a meteor disintegrates close to Earth, many of its small fragments hurtle towards the planet, but thanks to the protective covering of our atmosphere, many of them do not survive the heat, so they burn up before reaching the Earth’s surface. The ones that survive the ‘fiery’ journey through the atmosphere and eventually strike Earth’s surface are called meteorites (You can read about them in detail by clicking here).
Where do meteorites come from?
The first thing that you should know about meteorites’ origin is that all of them come from within our solar system. Even within that huge amount of space, we can narrow down a few sites that chuck most of the meteorites towards our home planet’s surface.
You might be surprised to learn that nearly all meteorites (roughly 95%) are parts of asteroids that lie in a cluster called the asteroid belt between the orbits of Mars and Jupiter. The types of meteorite that are most commonly found on Earth are called chondrites. Chondrites are stony, non-metallic bits of rocks that are very similar to the rocks present in the asteroid belt, which have been observed with the GEMINI telescope.
Planets (especially Mars)
Some of the meteorites that strike Earth come from planets, especially Mars. These are small fragments that get blasted off when their parent planet is hit by a comet or a large asteroid. Zagami, the largest meteorite from Mars, fell in Nigeria in 1962. Its high deuterium-to-hydrogen ratio and gas isotopic composition matches with the atmosphere of Mars, while its comparatively young age confirms its Martian origin.
Our nearest celestial neighbor also sends its regards in the form of lunar meteorites every once in a while. So far, as many as 39 meteorites have been confirmed to have come from our favorite Moon.
Just like planetary meteorites, lunar meteorites also originate from high-impact collisions (that occurred long ago), which blasted off rock fragments from the lunar surface, and their orbit eventually brought them under the influence of Earth’s gravitational tug, causing them to hurtle towards Earth.
Establishing the origin point of a lunar meteorite is relatively easy, as we have extensive information regarding the surface of Moon, thanks to the many rock samples that astronauts have collected during various lunar missions. Dar al Gani, the largest known lunar meteorite, fell in the Libyan desert in 1998. After studying its composition, it was found that it contained huge quantities of a calcium-aluminum silicate, which is readily found in the lunar highlands.
A very small fraction of meteorites that reach Earth may also come from distant comets, which are typically found in the outer reaches of the solar system. Such meteorites are typically made of rock, ice and dust that may have split and fragmented from the rocky cores of comets.
Establishing the origins of meteorites can provide invaluable insights into the history of our solar system; they basically hold the record of important geological events that occurred in the ancient past when the solar system was just beginning to take form.