Just next door, cosmologically speaking, is a planet almost exactly like Earth. It’s about the same size, is made of about the same stuff and formed around the same star.

To an alien astronomer light years away, observing the solar system through a telescope, it would be virtually indistinguishable from our own planet. But to know the surface conditions of Venus – the temperature of a self-cleaning oven, and an atmosphere saturated with carbon dioxide with sulfuric acid clouds – is to know that it’s anything but Earth-like.

So how is it that two planets so similar in position, formation and composition can end up so different? That’s a question that preoccupies an ever-growing number of planetary scientists, and motivates numerous proposed Venus exploration efforts. If scientists can understand why Venus turned out the way it did, we’ll have a better understanding of whether an Earth-like planet is the rule – or the exception.