A new study has found that Venus’s dense and stormy atmosphere is the reason why a day on this scorching planet is longer than a year.
Venus is a strange and inhospitable world, the size of the Earth, and orbits the sun at about two-thirds of the distance between our planet and the star.
The planet is surrounded by a dense and toxic atmosphere of carbon dioxide and sulfuric acid, and is facing a runaway global warming phenomenon that pushes temperatures on its surface to 900 degrees Fahrenheit (475 degrees Celsius), preventing life.
There is another strange thing in this world: while Venus completes its orbit around the sun in 225 Earth days, it takes 243 days for the planet to rotate on its axis. This means that a day lasts more than a year on Venus.
And a new study by UCSD astrophysicist Stephen Kane now suggests that Venus’s thick, windy atmosphere may be to blame.
“We believe that the atmosphere is a thin, nearly discrete layer on top of a planet that has little interaction with the solid planet,” Kane said in a statement. “Venus’ strong atmosphere teaches us that it is a more integrated part of the planet and affects absolutely everything, even how fast the planet rotates.” .
Without an atmosphere, Keane suggests, Venus’ rotation would accelerate to a rate proportional to its orbit around the Sun, a phenomenon known as orbital closure or tidal confinement.
The constrained orbs are gradually subjected to the gravitational influence of a much larger body. The gravity of a larger object keeps the period of rotation of the smaller object synchronized with its orbit around the larger object.
This means that a smaller object completes one orbit at exactly the same time as it completes one orbit: one year equals one day. As a result, the gradually closed object is constantly facing its larger neighbor from the same side. Perhaps the best known example is the Earth’s moon.
Orbital closure occurs over long periods of time. It may take millions of years for the year to coincide with today.
To investigate why Venus’ rotation is so slow, Kane first calculated how long it would take for a planet like Venus to gradually constrain. The calculation took into account the size and mass of the two bodies, and the rates of gravity and rotation.
He discovered that, in fact, it should only have taken 6.5 million years for Venus to gradually be constrained. And this is only a small part of the 4.5 billion years that the Solar System has existed.
So there must be a reason why Venus’s rotation hasn’t matched its orbit yet, and Keane thinks the reason is the atmosphere.
“Extremely fast winds cause the atmosphere to be pulled along the surface of the planet as it rotates, slowing its rotation while loosening the grip of the Sun’s gravity,” Kane said in the statement.
Ironically, the sun itself acts as a force that enables the atmosphere to rein in the tides, Kane said.
“The gravity of the Sun wants to gradually tidal constrain Venus, however, the energy from the Sun provides a lot of transmission in Venus’ atmosphere, which prevents orbital closure, because it makes the atmosphere more dynamic,” Kane said.
Revealing interactions between the planet’s atmosphere and its effect on orbital closure could have implications far beyond Venus.
As exoplanet hunters like the James Webb Telescope stumble across exciting new and potentially habitable worlds, Keane argues that scientists should take into account that some of them experience orbital closure similar to Venus.
“First of all, when we look at exoplanets, we want to make sure that we can distinguish between a planet similar to Earth and a planet similar to Venus, and then we want to understand the effect of the atmosphere on the planet and its rate of rotation,” Kane said.
Kane also notes that current methods of searching for exoplanets are “indirect techniques” that researchers cannot see directly and “infer the existence of the planet from the effect on the star.”
These conclusions come from models based on information gained from studying the planets in our solar system. Understanding as much as possible about planets close to tides, such as Venus, could help us learn more about planets in other star systems that would likely host life.
The study was published April 20 in the journal Nature Astronomy.
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