Tidally Locked Planets and Life
Tidally locked planets are still a subject of much speculation and not much is known about them.
Tidal locking is when an object rotates just as fast as it orbits. This causes the same part of the object to face inwards forever as it orbits. When a planet is tidally locked with a star one side becomes extremely hot while the other one stays far cooler. Even though there is a more constant temperature this could still pose a major challenge to life.
Snowball Bifurcation
Snowball bifurcation basically means a sudden global ice age. These have happened multiple times in Earth’s past. These ice ages are less likely to happen on tidally locked planets.
When a planet is tidally locked the star heats only one side of the planet. That means the properties of the part of the planet facing inward control the climate. One example is a planet covered in water. Frozen water is one of the most reflective naturally occurring compounds, while liquid water is the opposite. Once water starts to freeze, it can start a chain reaction. Since ice reflects light the surface cool down, forming more ice. Eventually the entire surface will be covered in ice.
On a tidally locked planet these major changes are much harder to reverse. There are often no seasonal changes to melt the ice. This means that either the amount of energy the star produces must change, or the material of the atmosphere/surface must change heavily. This could be caused by any major event, but also requires another major event to reverse, unless the planet has silicate-weathering feedback. Silicate-weathering feedback releases carbon from rocks and warms the atmosphere back up.
Evolutionary Pressure
Evolutionary pressure is an event or series of events that pushes organisms to evolve. In early Earth these were often “snowball Earth events”, which were prolonged cold periods. During this point in time the complexity of life on Earth increased drastically. This is because each species had to quickly evolve to survive the cold or die out. This forced evolution on a large portion species at the same time.
Other problems for life may arise. Since the planet is tidally locked there would be no day-night cycle. This could make it harder for life to survive on the dark side of the planet. There would also likely be a major temperature difference on each side of the planet. Life would evolve for a specific area. That decreases the amount of travel and intermixing between ecosystems, which would also slow down evolution due to lack of pressure.
Since the climate of a planet changes less often there would be less evolutionary pressure. That decreases the chance that any life we find will be intelligent. That also means any life will not be able to survive any major disasters, decreasing its overall maximum lifespan. That makes it just a bit harder for us to find life.
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Most of the information came from this paper posted on arXiv.
Tidally locked, like the moon.
Never really thought about tidally locked planets and a star. That would lead to some really odd planetary conditions...
You are really diving into some interesting papers :)
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Thick atmosphere could provide heat transfer between day and night sides. I saw somewhere an article about possible life in terminator zones of such worlds. I saw several models, but all they are pure theoretical, of course. Have to get more info. First time i read about it in Roger Zelezny's sci- fi novel Jack from the shadow .
Very interesting. Maybe one day I'll visit space. For now, I'm on Earth steeming on :)
Interesting!
The weather patterns at the day side/night side interface must be completely volatile, too, with the mixing of hot gas from the day side with the cool atmosphere of the other.