To give some properties, our 1750 km radius satellite has a small iron core of around 20% its diameter (as opposed to the Earth’s 50% diameter core), a high angular momentum and evidence of a near entirely molten mantle in its past given by lunar samples returned by the Apollo missions. As it turns out there is strong evidence staring us in the face every night – the Moon. Being much larger than Mars with a radius roughly two times greater, the Earth must have undergone several such collisions if we are to believe the widely accepted theory described above. Although the system is close to gravitational stability, there is still room for a few more collisions, and it is these events that shape the final characteristics of a planet most dramatically. It is at this stage that we encounter the holy grail of smashing things into each other – the epoch of giant impacts. Through many collisions between these objects, known as planetesimals, the bodies merge to form several tens of (proto-) planets similar in size to Mars (approximately 3500 km in radius). This contains a large population of kilometer-sized rocky objects that formed from an accumulation of dust on the scale of microns. Early in a planetary system’s formation, there is a so called protoplanetary disc orbiting around the recently formed star at the centre. How about we increase the size of the projectile by a factor of a hundred or more in diameter, what happens then? This may sound like the works of science fiction to our modern Solar System dwelling ears, but take us back about 4-4.5 billion years ago and such events were very real indeed. So now let’s ramp up the intensity a little. Unsurprisingly, this led to a tremendous loss of life on the planet and the eventual extinction of at least 75% of all species (but it did allow mammals to take precedence and thus permit the evolution of man – swings and roundabouts I suppose!). Meanwhile, the immense shockwaves created would trigger global earthquakes and volcanic eruptions, as evidenced by the Deccan Traps flood basalts. Aside from heating up its local surroundings to hellish temperatures, this would have excavated a large amount of material from the Earth and propelled fragments of the asteroid out of the Earth’s atmosphere, which would then re-enter, heating up further and creating wildfires all over the planet. ![]() This produced a crater 20 km deep and 150 km in diameter, and would have exerted the energy of over a billion times that of an atomic bomb. ![]() As you likely already know, there is strong evidence to suggest that 66 million years ago our distant ancestors experienced quite how devastating these events can be when a 10-15 km diameter asteroid hurtled into Earth at approximately 20 km/s, or around 20 times the speed of a rifle bullet. It’s not just humans that have tried their hands at the art of collisions however, the natural world is rather experienced to say the least. ![]() ![]() 50 caliber bullet penetrating through a thick piece of glass after letting YouTube dictate your entertainment for a little too long? In any case, we have all been fascinated by the simple act of crashing objects into each other at high speeds at some instance of our lives, and why not, it’s an awe-inspiring display of energy conversion after all. Ever day-dreamed about the immense destruction of the cannons on castles or warships of days gone by? Or maybe you’ve found yourself captivated by a slow motion video of a.
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