The Greatest Story of Meteorites

Where do meteorites come from and how come are they older than the Earth?


Meteorite sample - Ordinary Chondrite


METEORITES ARE WITNESSES OF THE FORMATION OF OUR SOLAR SYSTEM


The occurrence of falling meteorites has been present since the birth of Earth. We can easily say that they are among the most fascinating objects that we know. They are the oldest material on Earth but what makes them really valuable is the fact that since their formation that took place 4,6 billion years ago the material they carry with them has changed only slightly, making them the oldest matter in our whole Solar System. In some cases, we can even find inclusions and tiny particles formed in stars before the formation of our Solar System.


Meteorites are the only witnesses of our past, carrying information about the age, composition, and formation of the Solar System.


WHERE DO METEORITES COME FROM?


Meteorites come from objects in outer space. Let's have a look at how our Solar System was formed.


It all started when a cloud composed of gas and dust started to collapse due to its instability. As the cloud contracted, it started rotating faster, becoming disk-shaped. Most of the collapsing mass accumulated in the center, forming the core of our Solar System - the Sun. From the left-over mass, a protoplanetary disk around the Sun formed. Particles in that disk of gas and dust started attracting more matter and consequently each other, developing themselves into bigger celestial bodies such as planets.

At the end of the area of planetary formation, there were hundreds of medium-sized planetary embryos orbiting inside the inner Solar System. In the next hundred million years, these bodies collided further and merged into planets that we know today. Some celestial bodies remained smaller in mass and size not being big enough to get the same status as more massive planets. They are called asteroids.


Thousands of asteroids are known to occupy the main asteroid belt in a zone between the orbits of Mars and Jupiter. In fact, there should be a planet between Mars and Jupiter. For decades mathematicians were unsuccessfully trying to find an equation explaining the planetary distance. Including Kepler, who first noticed the curious gap and suggested that there was a planet between the two. Today we know that there are plenty of asteroids instead, that haven’t been able to merge into one planet due to gravity reasons.

Asteroids in the asteroid belt are parent bodies of the majority of meteorites that fall on the Earth’s ground. Lunar meteorites are a rare exception. These fragments of outer space originate from the Moon.


HOW DO METEORITES COME FROM THE ASTEROID BELT TO THE EARTH?


Although there are thousands of asteroids between Mars and Jupiter, there is still too much space for asteroids to bump into each other easily. One collision on a time scale of millions of years might be possible.


Yet those collisions do happen because some of the asteroids have unstable orbits due to gravitational disruption. Such collisions then send fragments across the asteroid belt towards Earth and other terrestrial planets. If they survive passage through the main belt they may establish elliptical orbits among the inner planets. Near-Earth Objects or NEOs are those asteroids that have escaped the border of the main belt. They float freely among the planets of the inner Solar System in which Earth is the largest target.

After surviving the passage through the asteroid belt, fragments of asteroids also need to survive their passage through the Earth's atmosphere, the last challenge on their way.


HOW CAN SPACE ROCKS BE OLDER THAN THE EARTH?


You might be asking yourself, since the Earth was formed at the same time during the same processes within the formation of our Solar System as asteroids, how come is the meteoritic material older?

Well, in the environment of outer space, rocks resist most weathering. Weathering is changing of rock's structure and minerals through contact with water, oxygen or biological organisms. So before rocks reach the Earth, they are far removed from the damaging effects of water and oxygen. Earth contains plenty of both, causing changes to rock material.


Whereas meteorites and material they carry with them have stayed unchanged since their formation. Hidden within these rocks there are very important traces about the origin of our Solar System. Meteorites tell us more about the early Solar System than all the telescopic studies of the planets.


©2020 by Stellar Milieux