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How Jupiter May Have Messed up Venus

From bottom up, this image shows our moon, Venus, and Jupiter as taken by astronaut Scott Kelly aboard the International Space Station in 2015. The curve at the top is Earth. NASA/Scott Kelly

Even though Venus and Jupiter are now about 416,399,477 miles apart from each other in our solar system, that wasn’t always the case. The gas giant was once much closer to the sun, and its migration farther out might have stripped Venus of a climate hospitable to life.

Getting Eccentric

University of California Riverside astrobiologist Stephen Kane believes that Jupiter’s wandering to and from our sun about a billion years ago fundamentally changed the orbit of Venus.

“One of the interesting things about the Venus of today is that its orbit is almost perfectly circular,” said Kane, who led the study. “With this project, I wanted to explore whether the orbit has always been circular, and if not, what are the implications of that?”

Based on the models of the solar system many of us made in grade school, it would seem that all planets orbit our sun in a circular fashion. But the truth is, they all have an elliptical course measured by what is termed the orbit’s eccentricity. An eccentricity of 0 is circular, while a rating of 1 is so decidedly not circular that a planet couldn’t even really maintain orbit; it would just drift out of the solar system.

Venus’ orbit currently has an eccentricity of .006, the most circular of all planets in our Solar System. However, using a model he created to evaluate planetary positions throughout the development of the Solar System, Kane believes that when Jupiter was closer to the sun about one billion years ago, Venus would have had an eccentricity of .3. This more elliptical orbit, Kane says, would have created a higher probability that Venus had life-sustaining characteristics, including water.

“As Jupiter migrated, Venus would have gone through dramatic changes in climate, heating up then cooling off and increasingly losing its water into the atmosphere,” Kane said.

Tidal Shifts

The researchers arrived at their conclusion by looking at the shift in the planet’s eccentricity based on tidal energy and other global conditions present all those years ago. Because of how the orbit changed, the researchers believe the planet was once water-rich. They also say that Jupiter’s influence would have accelerated water loss on the planet along with “the inevitable collapse of the atmosphere into a runaway greenhouse state,” they write in a paper published in The Planetary Science Journal.

Kane’s work is especially interesting in light of the recent discovery of phosphine gas in the cloud decks of Venus—something, some speculate, that could be emitted by microbes, which would represent the only kind of life that was able to remain on the planet after its climate changed so dramatically.

Looking Forward

While the research focussed on events that happened a billion years ago, Kane believes his work could have implications for modern humans.

“I focus on the differences between Venus and Earth, and what went wrong for Venus, so we can gain insight into how the Earth is habitable, and what we can do to shepherd this planet as best we can,” he said.