Tidally Locked Worlds

Ever wake up in the dark from a bad dream and say, well, it’ll be light soon, it will be better.

We inhabitants of Earth are lucky in that way, we have night and day. What would it be like to live with either day or night only? Or perpetual dusk?

There are plenty of bodies in our universe like that. Our Moon is one example of a tidally locked body. Due to gravitational influences, it’s a body whose rate of rotation matches it’s orbit time around another body. The Moon’s rotation rate is 27 days, and its orbit time is 27 days. That means from Earth we see the same old side of Luna all the time. However, because the Moon orbits Earth vs the Sun, its entire surface gets bathed in sunlight and dark over its orbital journey. There is no perpetually dark side of the Moon but there is a perpetually far side, one we never see from Earth.

What if the Earth were tidally locked in orbit around the Sun? Then one side of Earth would experience perpetual day, one side perpetual night, and within the day/night interface – perpetual dusk. That would be different! It likely would have had significant impact on how life evolved over time. No one on Earth knows how but life on Earth would be different. On Earth we see an incredible variety of lifeforms, each evolving within their environmental niche. Those niches could be similar and very different on a tidally locked Earth.

Tidally locked is not a bad thing, it just produces a different set of challenges and maybe opportunities for life.

Ever since the first exoplanet was discovered in 1992, the search for exoplanets ramped up and now we know of over 5000 confirmed planets beyond the solar system. Some of these planets are tidally locked with their home star and astrobiologists speculate about the affect that has on the possibility of life on those planets. Well, now we have the James Webb Space Telescope, with its big, sensitive eye. Now we have tools to identify exoplanet atmospheric gases, and detect byproducts of living, we think.  Remember the Viking Mars landers? They ran tests for biosignatures and got fooled by Mars’ reactive soils.

Life on a tidally locked planet could be tough. Even in the habitable zone, the star facing side gets constantly roasted by ultraviolet and infrared, it’s hot. The ocean might be nearly boiling in places. The other side gets no light, no heat. It is likely frozen solid, maybe even some of the atmospheric gasses are frozen out. That would cause significant atmospheric pressure gradients and wild winds coming from the hot side.

The zones between torrid and frozen might be able to support life, but weather there could be too chaotic. Think of high and low pressure/temperature fronts constantly slamming into each other.

These places sure would be interesting to visit.

What’s in the Sky?

August 15th; before sunrise; southwest: A waning gibbous Moon and Jupiter share the sky.