Why Venus is still spinning despite the Sun’s powerful grip

(ORDO NEWS) — If not for the thick, fast-moving atmosphere of Venus, Earth’s sister planet most likely wouldn’t be spinning.

Instead, Venus would be fixed in place, always facing the Sun in the same way that the same side of the Moon always faces the Earth.

The gravity of a large object in space can keep a smaller object from spinning, a phenomenon called tidal lock.

Since the atmosphere prevents this phenomenon, the UC Riverside scientist argues that the atmosphere should be a more significant factor in the study of Venus and other planets.

Those arguments, along with a description of Venus as a partially intertidal planet, were published today in a Nature Astronomy paper.

“We think of the atmosphere as a thin, almost separate layer on top of a planet that has minimal interaction with the solid planet,” said Stephen Cain, UCR astrophysicist and lead author of the paper.

“The powerful atmosphere of Venus teaches us that it is a much more integrated part of the planet that influences absolutely everything, even the speed of the planet’s rotation.”

It takes Venus 243 Earth days to make one revolution, but its atmosphere revolves around the planet every four days. Extremely fast winds cause the atmosphere to drag across the planet’s surface, slowing its rotation and weakening the Sun’s gravity in the process.

The slow rotation, in turn, has dramatic consequences for the sultry Venusian climate, which averages temperatures as high as 900 degrees Fahrenheit – hot enough to melt lead.

“It’s incredible, it’s a completely different feeling than on Earth,” says Kane. “Standing on the surface of Venus is like standing on the bottom of a very hot ocean. You wouldn’t be able to breathe there.”

One reason for the heat is that almost all of the solar energy absorbed by the planet is absorbed by Venus’s atmosphere and does not reach the surface. This means that a solar-powered rover like the one NASA sent to Mars won’t be able to operate there.

Venus’s atmosphere also blocks solar energy, preventing it from leaving the planet, which prevents cooling or liquid water from appearing on its surface, a condition known as the greenhouse effect.

Whether partial tidal lockdown contributes to the greenhouse effect that ultimately renders the planet uninhabitable as we know it is unclear.

Clarifying this issue is important not only for understanding Venus, but also for the study of exoplanets, which may be the target of future NASA missions.

Most of the planets likely to be observed by the recently launched James Webb Space Telescope are very close to their stars, even closer than Venus is to the Sun. Therefore, most likely, they are also in the intertidal zone.

Because humans may never be able to visit exoplanets in person, it’s important to make sure computer models account for tidal locking. “Venus is our opportunity to get these models right so we can properly understand the surface environment of planets around other stars,” Kane said.

“Right now, we are not very good at this task. We mainly use Earth-type models to interpret the properties of exoplanets. Venus is waving both hands, saying, “Look here!”

Gaining clarity on the factors that contributed to the greenhouse effect on Venus, Earth’s nearest neighbor, could also help improve models of what might one day happen to Earth’s climate.

“Ultimately, my motivation in studying Venus is to better understand the Earth,” Kane said.

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