Far beyond the planets, in the icy Oort Cloud, billions of comets are stored. Sometimes the tidal forces of our Galaxy — its vast but invisible dark matter, discovered by Vera Rubin and Fritz Zwicky — fling them away. Imagine a balloon you accidentally let go of: the wind carries it far, far away, and years later, deflated, it quietly drifts back through the window. That's exactly how some 'quasi-interstellar' comets behave: they return to the Sun after tens of millions of years, sneaking back almost unnoticed.

Such a leisurely wanderer, caught by the James Webb telescope, will allow scientists to spread its light into colors — that's called spectroscopy — and find out how much water and carbon it contains. These substances hint at how other planetary systems formed around distant stars. By comparing them with our Sun and its surroundings, we can understand what raged here in the past — for example, whether another star flew nearby and scattered the Oort Cloud. And most importantly, such comets are very rare: if we're lucky, we'll see them no more than once every few decades.