What makes the composition of an interstellar comet unique?

Interstellar comets are like space travelers who come from far away and bring special treasures with them.

Comet composition is what makes a comet special, it's like its "bag of stuff" that comes out when it gets close to the sun. Most comets we see in our solar system have been around for a long time, so they've already shared some of their stuff with us. But interstellar comets, like 2I/Borisov, are visitors from outside our solar system, they come from another neighborhood in space.

Imagine you're eating a piece of candy every day for years, and then one day, someone gives you a brand-new bag of candy that no one else has ever seen. That’s like an interstellar comet!

Comets are made mostly of ice, dust, and some gases, kind of like frozen mud with sparkles in it. But because interstellar comets have never been near the sun before, their stuff hasn’t changed much, so we get to see what they were originally like, without any “candy melting” from being near the heat of the sun.

It’s like getting a brand-new bag of candy instead of one that's already been eaten and shared. That’s why scientists love studying them, they give us a peek at space candy straight from the start!