Venus may owe its extreme atmosphere to an ancient run-in with the gas giant Jupiter, which could have fundamentally altered the planet’s orbit, and led to the loss of massive amounts of its water reserves.
If you were to look through a telescope at the night sky, you could be forgiven for thinking that the planets that make up our solar system exist in perfect isolation against the inky blackness of space. In reality, the gravitational influence of each of the planets has molded the orbits of its neighbors. Over the course of billions of years, this give and take has resulted in the relatively stable cosmic waltz of planets that we observe today.
These gravitational shunts placed the Earth in an orbit that allowed for the emergence of life. Other planets such as Venus – which has been generously described as Earth’s twin – were not so lucky. Venus is similar in size and mass to Earth, and yet is cursed with a radically different and super dense atmosphere.
A new paper has examined how the gravitational influence of Jupiter, as it migrated through the solar system in the distant past, could have placed Venus on the evolutionary path to becoming the inhospitable world we see today.
To this end, the researchers built a computer model of the solar system that simulated the positions of the planets, their varying gravitational influences, and the effect that they would have had on each other’s orbital paths.
"One of the interesting things about the Venus of today is that its orbit is almost perfectly circular," said Stephen Kane, an astrobiologist from the University of California, Riverside, 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?".
The eccentricity, or roundness of an orbit, is measured on a scale that runs from 0 to 1. An orbital eccentricity of 0 would mean that the planet has a completely circular orbit. Conversely if a world had an orbital eccentricity value of 1 it would simply slingshot itself into space.
Venus has an eccentricity of 0.0006 – the roundest in the solar system – while Earth has a value of 0.0167.
The model revealed that roughly 1 billion years ago, Jupiter orbited much closer to the Sun, and that at this time Venus had a more eccentric orbit of 0.3, which according to the researchers would have rendered it a more habitable planet.
However, as the gas giant moved outward, its powerful gravity interfered with Venus, forcing it into a more circular orbit. During this orbital forcing encounter, tidal heating and other processes could have led to the planet periodically heating up and cooling down.
The team argue that the change in eccentricity may have accelerated the atmospheric evolution of Earth’s twin, and caused it to lose much of its water. This in turn would have led to the runaway greenhouse effect that has rendered the surface of the planet uninhabitable.
Whilst Venus has dramatically diverged from Earth’s evolutionary past, it may still be capable of playing host to life, albeit not as we know it.
Scientists recently detected the presence of a gas called phosphine in the atmosphere of Venus. On Earth, phosphine is produced by bacteria and microbes, and so the discovery has been taken as potential evidence that there could be organic life existing high in that alien atmosphere.
Kane mused that the lifeforms could be "the last surviving species on a planet that went through a dramatic change in its environment."
The paper has been published in the Planetary Science Journal.
