Can life travel between planets?

There are several ways in which living organisms can travel millions of kilometres through space and spread between planets. The most common way in which this happens is through meteorites. Meteorites are rocks from space which crash on a planet’s surface. Most of the meteorites which crash on Earth are small asteroids. However, several of these meteorites are believed to be rocks which were once on the surface of Mars, our neighbouring planet. How is this possible?

When a big asteroid collided with Mars (like the one which killed the dinosaurs) sometime in the past, a large number of rocks from the surface of Mars would have been thrown into space. Many of these rocks fall back down to Mars due to the planet’s gravity. However, some of these rocks will be travelling fast enough to escape Mars and start orbiting the Sun. The orbits of some of these rocks would be elliptical and cross the Earth’s orbit. When the rocks get close enough to Earth, they are pulled by Earth’s gravity and crash onto our surface. Through this mechanism, rocks can be transported between planets and moons in the solar system.

How do we know that these rocks came from Mars? Rocks are porous and have small holes within them, similar to a sponge. These holes would have trapped air at the time the rock was formed. Extracting a sample of these gases from the rocks shows that their composition is similar to that of the Martian atmosphere. Thus, we can conclude that the rock was on Mars when it was formed.

So how can meteorites transport life across the harsh vacuum of space for thousands or millions of years before it reaches another planet? There are certain lifeforms on Earth which have been able to survive extreme conditions. For example, some types of bacteria can survive extreme temperatures and pressures for a long time and may be able to survive their journey in space. Organisms such as these may be able to reach another planet and lead to the spreading and evolution of life.

This also raises the question of whether life started on Earth or if microorganisms were brought here from a different world and later evolved into the millions of species that exist today. The truth is, we cannot be certain where and how life originated. And since it’s possible that life on Earth might have come from elsewhere, we might very well be aliens!

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