How? Long before scientists hunted for a world similar to Earth around other suns, one planet in the solar system was already referred to as Earth’s twin. Venus has nearly the same radius, mass, and composition as our planet, and lies just outside the solar system’s habitable zone. In the past, it may have had an ocean.
Today, there’s no sign of liquid water. Venus is an overheated world, with temperatures climbing to 864 degrees Fahrenheit (462 degrees Celsius). Lead melts on the surface of the planet, making it a challenge to explore. But understanding what makes a world into a cool, refreshing Earth or a hot, hellish Venus means understanding just why Earth’s ancient twin is so different today.
“Everything we know about planets comes from in situ data from within our own solar system,” says Stephen Kane. An exoplanet hunter at the University of California, Riverside, Kane has long been concerned that many of the planets beyond the solar system that have been dubbed Earth-like by scientists may in fact be more Venus-like — exoVenuses. The best way to fix that, he argues, is to return to visiting Earth’s twin.
“We have two examples of Earth-size planets [in our solar system], and one of them, we know very little about,” Kane says. And that needs to change.