Atmospheric dynamics of an Earth-sized planet near a tidal zone

(ORDO NEWS) — When two bodies in space are close enough to each other, their gravity acts like a brake, slowing them down until the rotation of one of them “locks” in line with its orbit.

This tidal lock means that one side of the smaller body is constantly facing the larger one – which is why we only see one side of the Moon from Earth.

Earth’s evil twin, Venus, is close to the threshold of tidal lock. So close that it could almost be tidally closed to the Sun… but it isn’t.

Venus takes 225 days to complete one orbit around the Sun, and 243 days to complete one revolution. Moreover, unlike other planets, it rotates in the opposite direction of its orbit around the Sun.

This is a small but significant difference. The only thing preventing Venus from fully locking in is the planet’s thick, turbulent atmosphere, which wraps around Venus in just four days: 60 times faster than the planet itself.

This, according to astrophysicist Stephen Caine of the University of California, Riverside, means we need to pay much more attention to planetary atmospheres when studying not only Venus, but also other planets orbiting distant stars.

“We think of the atmosphere as a thin, almost separate layer on top of a planet that has minimal interaction with the solid planet,” Kane explains.

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

Venus’s atmosphere is quite wild, and it’s thought to be one of the key characteristics that caused Earth and Venus – so similar in so many other ways – to become such different worlds.

This is a puzzle that planetary scientists would like to solve, as it means the difference between a lush, habitable world (Earth) and a toxic, acidic hell (Venus).

On Venus, the insanely fast-moving atmosphere – due to the phenomenon of superrotation – results in winds of over 400 kilometers per hour (about 250 miles per hour).

This super-rotation causes the atmosphere to pull on the planet’s surface, which appears to slow the planet’s rotation as well as counteract the Sun’s pull and prevent tidal lock.

The slow retrograde rotation means that one day on Venus, from sunrise to sunset, lasts about 117 days. The dense, toxic atmosphere traps most of the sun’s heat: only 3 percent of the incoming sunlight reaches the surface, the rest is absorbed by the atmosphere.

As a result, the surface of Venus is the hottest of any body in the Solar System other than the Sun, averaging around 482 degrees Celsius (900 Fahrenheit).

“It’s incredibly alien, it feels wildly different from 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.”

Because the atmosphere traps solar energy, Venus simply keeps warm: the greenhouse effect. We don’t know what role tidal lock may play in this greenhouse effect, but studying Venus may provide some clues.

Most of the exoplanets we find are very close to their host stars; the tools we use to find them are much better at finding nearby worlds. Therefore, many of these worlds may be tidal.

Since the greenhouse effect planet is inhospitable to life as we know it, figuring out how tidal locking affects habitability could help us find habitable worlds in the orbits of other stars.

When looking for habitable exoplanets, astronomers look for objects roughly the size of Earth. But the mere size of the Earth is unlikely to be sufficient.

Venus is more or less similar to Earth, but any terrestrial organisms trying to live there would not be able to survive. Simply using the Earth as a model for exoplanets, even those trapped in the intertidal zone, may not give accurate results.

“Venus is our opportunity to get these models right so we can properly understand the surface environment of planets around other stars,” Kane says.

“Right now, we’re not very good at that. We’re mostly using Earth-like models to interpret the properties of exoplanets. Venus is waving both hands, saying, ‘Look here!'”

Venus, he says, is an instrument right here in our solar system that we can use to try to understand the climate of alien worlds.”

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