you just know that's gonna leave a mark…

We knew planetary collisions should happen relatively often in young solar systems. Now we have hard evidence of one such an event.

So astronomers are taking a look at a young star about 100 light years away with an infrared telescope and find a cloud of glass floating around the young sun. As you probably know, there needs to be a lot of heat to make glass and in space it only happens when something really big slams into another really big object with a whole lot of force. Like so…

Now note that this isn't just a conceptual representation of what could maybe happen somewhere in the vast expanses of the universe. This is an animation of what really happened around a 12 million year old star called HD172555 not too long ago. As Phil Plait notes in his detailed write-up, the rendering isn't exactly what a real planetary impact would be like since there should be an explosive plume of matter flying off into space as the shockwaves converge on the antipodal point of the collision.

And there's also the matter of how long the actual event would take. Objects the size of planets and large moons are staggeringly massive. Mercury tips the scales at 330 quintillion metric tons. The Moon is some 73 quintillion metric tons. When objects of the same mass smash into each other, it would take hours to melt and rearrange that much rock. In reality, a planetary collision is like two trucks smashing into each other in extreme slow motion and melting into a new shape while parts fly in the direction of the impact. But these are just technicalities. What's really important here is the indirect evidence of a full scale planetary collisions around a young star as per current theories of solar system formation.