Venus is a beautiful sight in the western sky as twilight descends. One evening this coming week consider setting a chair outside where you can quietly contemplate our nearest neighbor planet and consider a bit of its history and fate. Unfortunately, sometimes a story doesn’t seem to have a happy ending. It’s sad, but reality is what it is.
Venus and Earth were both born, so the current science says, as debris left over from the formation of the Sun. Venus, formed about 1/3 closer to the Sun than the Earth did, so Venus got twice the intensity of solar radiation than the Earth. (This may seem odd but remember that light intensity increases as the square with distance.) With the young sun 1/3 dimmer than today, the infant Venus may have had liquid water and perhaps even oceans early on, but two things kept it from becoming a Goldilocks world like the Earth.
Earth and Venus both had lots more volcanic activity when younger. This put huge amounts of heat trapping greenhouse gases into their atmospheres. On Earth it was cool enough to retain oceans. The oceans absorbed most of the volcanic carbon dioxide where it was chemically stored away over time as enormous layers of limestone rock.
By comparison, on Venus the temperature was too warm, the oceans evaporated, and the greenhouse gasses built up in the atmosphere. We first found out about this “runaway greenhouse effect” in the 1960s when radio telescopes showed that Venus was not the cloudy and humid world science fiction writers had portrayed. Venus was HOT. The surface temperature 900 degrees, even at the north and south poles. The atmosphere was 96% carbon dioxide and so thick that it was more than 90 times denser than the Earth’s atmosphere. You could almost swim in it. The clouds that keep us from seeing the surface were, and are, raining sulfuric acid rain that boils away before it hits the ground!
Soviet landers sent back pictures of the surface 49 years ago. NASA’s Magellan orbiter radar mission in the 1990s is our best information for now. Future missions are planned.
What about the far future? Is there any hope for Venus. Some people have wondered if humans could “terraform” Mars by melting its frozen water and making the planet habitable. This wouldn’t work for Venus. Even if we could somehow move Venus out to Earth’s distance from the Sun, Venus’ water is gone. I wouldn’t plan on booking Venus for your next vacation.
As you enjoy the beautiful sight of our evening “star” at sunset. I hope you don’t remember this article as a bummer. Be thankful that you have the consciousness to appreciate the beauty and the reason to understand this amazing cosmos of which we find ourselves a part.
For questions or comments: James Hill, Mississippi NASA/JPL Solar System Ambassador. jhill6333@gmail.com
