Some climate models suggest Venus could once have had liquid water and habitable temperatures, until a dramatic transformation hundreds of millions of years ago. One leading idea is that widespread volcanic resurfacing helped push the planet into the runaway greenhouse state that left it hotter than Mercury today.

Some climate models suggest Venus could once have had liquid water and habitable temperatures, until a dramatic transformation hundreds of millions of years ago. One leading idea is that widespread volcanic resurfacing helped push the planet into the runaway greenhouse state that left it hotter than Mercury today.

Venus today is the most hostile planet in the solar system. Its surface sits at about 465 degrees Celsius, hotter than Mercury despite being almost twice as far from the Sun, under an atmosphere of carbon dioxide pressing down at roughly 90 times Earth’s. Yet some climate models suggest it may not always have been this way, and that the planet next door could once have held liquid water and mild temperatures before a transformation tipped it int…