New study finds exoplanet closest to Earth could be having wild weather

planets like Proxima Centauri b experiences tides hundreds of times stronger than those that move Earth’s oceans twice a day. The force of these tides also pulls on the planet’s atmosphere, but a recent simulation revealed that the tidal pull of Proxima Centauri b’s host star doesn’t have much of an impact on weather or climate. long-term.

Instead, weather patterns on Proxima Centauri b, and other planets in the habitable zones of red dwarf stars, seem to be governed by the fact that half the planet is in perpetual daylight while the other half is in an endless night.

What’s new – Red dwarf stars like Proxima Centauri and TRAPPIST-1 are smaller, dimmer and cooler than our Sun. Worlds like Proxima Centauri b and TRAPPIST-1e feel the gravitational pull of their stars much more strongly than we feel the tidal effect of our Sun, because they are much closer. Here on Earth, the Moon exerts more tidal force than the Sun, partly because it is so much closer. And the tides don’t just tug at the ocean; they can also move air.

But although the Moon’s tidal pull noticeably moves our oceans twice a day, it doesn’t have much of an impact on our atmosphere. What little air movement the Moon might have is almost completely overwhelmed by the effect of heat, or lack thereof. Hot air expands and rises, creating areas of lower atmospheric pressure; cold air compresses and sinks, creating areas of higher atmospheric pressure. Air tends to move from areas of high pressure to areas of low pressure – we call this wind.

On worlds orbiting red dwarf stars close enough to be potentially habitable, the tidal pull on the atmosphere can be up to 500 times stronger than what Earth’s atmosphere experiences. Proxima Centauri b may actually be close to the maximum tidal force a planet can sustain while maintaining a solid surface. But even Proxima Centauri b’s extreme tides don’t have much of an effect on its weather or climate, according to a recent simulation study by McGill University planetary scientist Thomas Navarro and colleagues.

“Gravitational tides [planets orbiting red dwarf stars] only have a moderate impact on their surface weather, with little or no impact on their climate,” they wrote in their recent post.

Navarro and his colleagues built a digital model of an Earth-like planet orbiting a low-mass star like Proxima Centauri, then tested it with different atmospheric compositions and other conditions. It turned out that the weather on Proxima Centauri b is primarily shaped by the fact that the planet is tidally locked to its star. In other words, the planet rotates once each time it orbits the star, so the same side of the planet always faces the star directly, in constant daylight.

How discs of matter can appear around Proxima Centauri. MARK GARLICK/SCIENTIFIC PHOTO LIBRARY/Science Photo Library/Getty Images

Dig into the details — Navarro and his colleagues built on the work of previous studies, which had modeled the atmospheres of tidally locked planets around stars like Proxima Centauri. But no one had focused on the effect of tides on the atmosphere before, so the team incorporated tides into their new model to see what might look different. The answer turned out to be: not much, but exoplanets orbiting red dwarfs still have a wild time.

It’s extremely windy, for one thing. The permanent dayside is constantly heated by the star, which creates an area of ​​low pressure as the warm air expands and rises. The wind blows from the dark and cool night at 35 to 70 kilometers per hour, depending on the model. This means that the entire surface of the planet usually experiences something between a strong breeze and a strong gale, always blowing towards the same place on the day side.

“You have all these winds coming from the same direction all the time,” Navarro said. Reverse. “Winds are created by low pressure which is a direct result of permanent heating.”

And this daytime spot, directly under the faint red star in the sky, is probably perpetually stormy. This is what you would expect from an area of ​​low pressure here on Earth, or even on a very different world like Jupiter. Navarro and his colleagues’ model also suggests that an area of ​​low pressure would cause heavy cloud cover over a wide swath of the dayside, keeping things more shaded than you’d expect in what’s called a “dayside.” permanent day.

Why is it important – Previous studies have modeled how tidal locking would shape a planet’s weather, but this one confirms that this is the primary effect involved in forming large-scale weather patterns on exoplanets around red dwarf stars. And that’s extremely important for astrobiologists, because most of the potentially habitable exoplanets we’re likely to find will be orbiting red dwarf stars.

For one thing, about three quarters of the stars in our galaxy are red dwarfs. Low-mass stars seem to form more often than more massive ones, and they also survive much longer; which gives red dwarfs a definite demographic advantage.

Illustration of what the surface of Proxima Centauri b. Mark Stevenson/Stocktrek Images/Stocktrek Images/Getty Images

And potentially habitable exoplanets around these smaller stars are easier for planet hunters to find than those orbiting larger, brighter stars. A red dwarf’s habitable zone — the region around a star where temperatures are good for liquid water to exist — snuggles much closer to the star than our solar system’s habitable zone, which begins to approximately the orbit of Venus and ends just outside the orbit of Mars. And if you’re looking for a small planet, it’s easier to see it the closer it is to its star.

And after – Understanding the conditions on these worlds is important if we are to understand how and where life might form – and thrive.

Of course, this assumes that Proxima Centauri b, or any other Earth-like world around a red dwarf, does in fact have an atmosphere. Many red dwarf stars are notoriously volatile, prone to emitting massive bursts of radiation and charged particles into space. This kind of stellar weather could strip the atmosphere of a nearby planet and spell very bad news for extraterrestrial life.

Several groups of astronomers plan to use the James Webb Space Telescope to study these exoplanets over the next few months. They will try to measure the atmosphere of Proxima Centauri B, investigate the atmospheres of several TRAPPIST-1 worlds, and find out if a handful of other red dwarf exoplanets even have atmospheres.

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