If you were standing on the surface of Venus today, you’d be dead thanks to the toxic atmosphere and extremely high temperatures. But a few billion years ago, you might have been just fine, according to a new climate analysis from NASA’s Goddard Institute for Space Studies (GISS). You may even have been a little chilly. Present-day Venus has a crushing carbon dioxide atmosphere 90 times thicker than Earth’s with clouds of sulfuric acid and a surface temperature of 864 degrees Fahrenheit (462 degrees Celsius). In short, it’s pretty bad for life as we know it. Even our most robust landers have only survived a short time on Venus. Scientists have long suspected that Venus started with very similar components as Earth, but its development simply took a different path. Using the same climate models created to track global warming on Earth, scientists have extrapolated what Venus might have been like a few billion years ago.Based on topographical data, Venus probably had a shallow sea covering much of its surface in the past. It still had more dry land than Earth, though. That would have limited the amount of water evaporation from Sun exposure, and thus the greenhouse effect from water vapor. The Sun was also about 30% less bright two billion years ago. The GISS analysis takes into account Venus’ slow rotation, too. A single day on Venus is equal to 117 Earth days. Each spot is exposed to sunlight for two months at a time, which would have led to a thick layer of clouds and rain on ancient Venus. This also served to reduce solar heating on the surface. The result was an average temperature several degrees cooler than Earth today. However, Venus was not stable in this state. When the sun increased in brightness, this tenuous balance was lost as harsh ultraviolet radiation broke water molecules in the atmosphere apart. Hydrogen was lost to space and carbon dioxide built up. A runaway greenhouse effect took hold and Venus became in uninhabitable hellscape we know today. These findings could help inform future NASA missions like the James Webb Space Telescope, which will search for exoplanets that may have things in common with ancient Venus.