What would happen if the world split in two? – Ronan, age 5, Melbourne, Australia
Fantastic question, Ronan. The short version of the answer to this question is: the world would end if that really happened. It will be the end of the world as we know it. All life on Earth is coming to an end, so this is going to be a bad day!
Fortunately, events that can divide a planet in two are extremely rare. However, believe it or not, when our Solar System was just forming, events like this happened more often than you might think.
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Take on the role of a detective
When looking at the Solar System, astronomers are essentially investigators. We see all the objects out there: planets, moons, asteroids and comets. By studying them, we are gathering clues as to what the Solar System looked like when it was new.
Wikimedia / Antonio Ciccolella, CC DI
Everywhere we look in the Solar System, we find evidence of a “giant collision”, as scientists call it. What does it mean? Well, it turns out that the final stages of the planet-forming process are REALLY brutal. There were many planet-sized objects floating around until they kept crashing into each other.
When two planet-sized objects collide with each other, the collision is truly catastrophic, more than enough to destroy the world. This is what we think has ever happened to the planet Mercury.
When Mercury formed, all clues tell us the planet was probably about twice what it is now. Long ago, however, moments after the formation of Mercury, an object of the same size crashed into the planet in a collision that almost completely destroyed it.
NASA / JPL-Caltech
The collision destroyed most of Mercury. All that was left was a metal core with a thin layer of debris on top. This event shows that a planet destroyed by a collision can leave a mark that is still visible to us for up to four billion (or 4,000,000,000) years later!
The Earth also collided
The most famous example of a destroyed planet is actually our own Earth. Astronomers think that when the Earth was formed, everything happened by itself. However, when we look at it today, the Earth has a companion: the Moon. So where does the moon come from?
All the clues we have collected tell a very dramatic story. Not long after the Earth formed, by itself, it moved to another planet called “Theia” by astronomers. The planet is the size of Mars and hit Earth relatively slowly (compared to when a collision between planets occurred).
Although slow, the collisions between the planets are still very powerful. The collision would have turned the entire Earth into a liquid state, wiping out any life form that might have evolved at that time. He destroyed the Earth and Theia.
The matter ejected from Theia and the Earth can merge in the space around our planet. Due to the very strong gravity of the Earth, most of the trapped debris gradually merged and formed the Moon.
SO WHEN YOU SEE THE MOON IN THE SKY, YOU CAN TELL EVERYONE IT IS A REMINDER OF THE GIANT COLLISION WHEN THE EARTH WAS YOUNG BECAUSE, AT ONE TIME, THE EARTH LITERALLY DIVIDED AS A COLLISION WITH ANOTHER PLANET!
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Zalfa Imani Trijatna of the University of Indonesia translated this article from English.
