The planet, almost the same size and composition as Earth, had oceans and an Earth-like atmosphere for almost two billion years of its history. It's long days, which would have had the day side exposed to the sun for more than two months at a time, would actually have kept the planet cooler by increasing evaporation and rainfall, which would have shielded the land from the strong sunlight.
|Venus more than a billion years ago, before climate change rendered the planet uninhabitable|
There would have been ideal conditions for life to not only evolve, but thrive. And such conditions could well have lead to the evolution of an intelligent lifeform, and the development of an advanced technological civilisation.
And there appears to be some evidence for that. Studies of the detailed radar maps of the surface beneath the planet's dense shroud of cloud show what look like immense surface structures. They could well be the remains of cities, or the launch facilities that were abandoned after the last inhabitants evacuated their dying world.
There could be many reasons why Venus became uninhabitable. It could have been the result of the activity of the civilisation: war, excessive use of fossil fuels etc. (which if proven could be a very valuable lesson for our civilisation). But it is more likely to have been natural in nature. The sun has become significantly hotter over the last few billion years. This would eventually have evaporated away Venus's oceans, thickening its atmosphere and trapping more and more heat in what would have been a runaway greenhouse effect. It would have been an event that was unstoppable, even for an advanced civilisation. Fortunately such a civilisation would have been well aware of the looming crisis, and would have had thousands of years to prepare for its evacuation. This makes it highly likely that a significant number of inhabitants would have been able to leave and set up colonies elsewhere in the Solar-System, and even beyond.
If the warming of the sun was not enough, there is strong evidence that Venus has suffered high levels of volcanic activity, and on a global scale. In the past the planet has suffered periodic and massive resurfacing events by lava flows. The most recent could have been 500 million years ago. Such an event would destroy most of the evidence of a civilisation, and multiple such events would explain the transformation and thickening of the atmosphere. Combined with the warming of the sun, life on Venus was doomed.
|One billion years ago: Venus is finally rendered uninhabitable by volcanic activity and the warming of the sun|
Ultimately we may be better off looking for evidence of an ancient technological civilisation on Venus elsewhere in the Solar-System, and most likely in the asteroid belt (see my previous article: 'Pre-Human Technology in the Asteroid Belt'). An advanced civilisation with knowledge of its home planet's impending demise would certainly have tried to escape, and the asteroids would provide a relatively easy and abundant source of materials for habitat and spacecraft construction.
Having said that, we need to explore Venus in much more detail, especially on the surface, and below it. So far only the Russian Venera landers in the 1970s and 80s have successfully returned images and data from the surface of the planet, and they only survived the hellish conditions for a few hours.
|Left: an image of the surface of Venus, taken by the Russian lander Venera 13. Right: the lander before launch|
A rover is required, one that could survive for months or more. NASA's proposed landsailing rover is the most promising. With recent success in developing electronics that can function under the extreme pressure and heat on Venus's surface, such a mission is looking more and more likely to succeed. And that means it is much more likely to get the funding to go ahead. If it does, it could be launched in about ten years.
Amazingly, there may still be life on Venus. The last remnants of the planet's once complex biosphere may be surviving in the clouds as dark streaks of microbial life. Russia and the U.S. are working on a mission that could prove such a theory, which will probably include a solar-powered aircraft that would target the dark streaks and analyse them.
We may discover that any life in the clouds of Venus is related to life on Earth, which would indicate a common ancestor. Perhaps the Venus evacuees migrated to Earth...
Venus is fascinating and brutally hostile place. There is so much to learn, and the confirmation of the existence of a civilisation that once lived there would be astounding. We need to get a sustainable mission down to the planet's surface as soon as possible. What we find could be invaluable and essential to the future of our species.