Earth's Twin
Once people gained access to telescopes, they began to observe the planetary neighbors in greater detail. Astronomers observed that Venus was roughly the same size as Earth, had only slightly smaller gravity, and was covered in clouds. This left people with the impression that Venus could have Earth-life conditions underneath its clouds.
Under The Clouds
The Venera and Mariner space programs finally revealed what lay under the clouds: not a tropical paradise or even an ocean, but a pressure cooker of a planet with no ability to sustain complex life.To give an example of how harsh the conditions on Venus are, the Venera 5 and 6 probes were crushed by the massive air pressure at 60,000 ft above the surface. Even the most successful probes to Venus only lasted roughly an hour before they succumbed to the massive temperature and air pressure.
Why Did Venus Become Lifeless?
There is a lot to indicate that Venus may not only have possessed oceans in the ancient past, but they lasted long enough for some life to form up until about 700 million years ago. The crust might remodel itself every few hundred million years, finding evidence of ancient life is unlikely.
But despite having liquid water, Venus couldn't sustain any oceans or life. There are several ideas as to why:
- No magnetic field: Venus's magnetosphere is too weak to resist solar radiation, meaning any water on the planet was broken apart and evaporated by solar winds.
- No plate tectonics: plate tectonics on Earth helps absorb carbon dioxide from the atmosphere, but Venus's rotation was too slow for the crust to have plate tectonics. Some scientists speculate a volcanic event roughly 700 million years ago
pumped massive amounts of carbon dioxide into the atmosphere. With nothing to absorb all that excess, the planet became too hot to have an ocean due to a greenhouse effect. - Venus might have been further from the Sun, but Jupiter's movement during the formation of the Solar System may have pushed Venus closer to the Sun and out of a Goldilocks Zone.
It's All Up In the Air
Ironically, while the surface of Venus is lifeless, the upper atmosphere (31 miles above the surface) has the closest thing to Earth-like conditions in the Solar System.
Since the 1960s, scientists have speculated on whether extremophile organisms are in the clouds. In 2020, scientists detected phosphine, a sign of life, but ultimately this detection was found to be a false positive, and the results remain inconclusive.
Due to oxygen being lighter than carbon dioxide, some scientists believe floating cities could be built in this atmospheric zone, provided the spacecraft can be designed to survive the acidic clouds. Any potential terraforming of the planet would have to begin in these speculative cloud cities.
