Why Does Venus Rotate In Spite Of Sun's Gravity? The Answer Lies In Its Atmosphere, Says New Study

If Venus did not have a soupy atmosphere, it would have always faced the Sun the way the same side of the Moon always faces Earth. The Venusian atmosphere prevents tidal locking.

A sequence of images composited together to show path of Venus across the Sun. | Source: NASA

New Delhi: Venus would likely not rotate, had it not been for its thick, fast-moving atmosphere. 

If Venus did not have a soupy atmosphere, it would have always faced the Sun the way the same side of the Moon always faces Earth. 

Tidal locking is a phenomenon in which the gravity of a large object in space can keep a smaller object from spinning. 

According to a researcher at University of California Riverside, the atmosphere of Venus needs to be a more prominent factor in studies of Earth's sister planet because it is the atmosphere which prevents tidal locking. The same is true for other planets as well.

The study, led by researchers at University of California, and which describes Venus as a partially tidally locked planet, was published in the journal Nature Astronomy on April 20. 

In a statement issued by University of California Riverside, Stephen Kane, the lead author of the paper, said that the atmosphere is thought of as a thin, almost separate layer on top of a planet that has minimal interaction with the solid planet. He explained that Venus' powerful atmosphere teaches scientists that it is a much more integrated part of the planet that affects absolutely everything, even how fast the planet rotates.

What Slows Venus’ Rotation?

The rotation period of Venus is 243 Earth days, while its revolution period is 224.7 Earth days. Venus' atmosphere circulates the planet every four days. As the atmosphere circulates, extremely fast wind causes it to drag along the surface. This slows the rotation of Venus, and loosens the grip of the Sun's gravity, according to the study.

How Does Slow Rotation Impact Venusian Climate?

Slow rotation dramatically affects the sweltering Venusian climate, and the average temperatures reach up to 900 degrees Fahrenheit. These temperatures are hot enough to melt lead.

Kane said it is an incredibly alien, and a wildly different experience than being on Earth. He explained that standing on the surface of Venus would be like standing at the bottom of a very hot ocean, and that one could not breathe in it.

What Makes Venus Extremely Hot?

All of the Sun's energy absorbed by the planet is soaked up Venus' atmosphere, causing Venus to be extremely hot. According to the study, a rover with solar panels, like the one NASA sent to Mars, would not work on Venus.

The atmosphere of Venus also blocks the Sun's energy from leaving the planet. This prevents cooling or liquid water on its surface, which is a condition known as runaway greenhouse effect. 

What Is The Runaway Greenhouse Effect?

The runaway greenhouse effect occurs when a planet's atmosphere contains greenhouse gas in an amount sufficient to block thermal radiation from leaving the planet. According to NASA, the phenomenon occurs when a planet absorbs more energy from the Sun than it can radiate back to space. Under these circumstances, the hotter the surface temperature gets, the faster the planet warms up.

According to the study, it is not clear whether being partially tidally locked contributes to this runaway greenhouse state. This is a condition which ultimately renders a planet uninhabitable by life.

Significance Of The Study

It is important to know whether being partially locked contributes to the runaway effect because this will help scientists understand Venus. Also, the knowledge is crucial for studying the exoplanets likely to be targeted for future NASA missions.

The James Webb Space Telescope will observe several planets, most of which are very close to their star. These planets are even closer than Venus is to the Sun. Therefore, these planets are likely to be tidally locked, according to the study.

It is necessary to make sure computer models account for the effects of tidal locking because humans may never be able to visit exoplanets in person. Kane said that Venus is the opportunity for scientists to get the models correct, so that they can properly understand the surface environment of planets around other stars.

He said that researchers mostly use Earth-type models to interpret the properties of exoplanets.

According to the study, acquiring more knowledge about the factors which contributed to a runaway greenhouse state on Venus, Earth's closest planetary neighbour, can help scientists improve models of what could happen to Earth's climate one day. 

Kane said that ultimately, his motivation in studying Venus is to better understand Earth.