What Would the Temperature Be on the Dark Side of a Tidally Locked Earth?
If one side of the Earth were to always face away from the Sun, it would create a permanent night on that side. Over time, the temperature on this perpetually dark half of the planet would dramatically drop. This scenario is particularly relevant in the study of planetology, as many of the early exoplanet discoveries are likely to be in a similar tidally locked state due to the biases in early exoplanet probes.
Factors Influencing Temperature on the Dark Side
Various factors influence the temperature on the dark side of a tidally locked Earth:
Initial Conditions
The initial temperature would depend on the time of day before the change. If it was daytime, the temperature could be relatively warm, starting at approximately the same temperature as the sunlit side of the Earth.
Heat Retention
The Earth retains heat due to its atmosphere and the heat stored in the ground and oceans. However, without sunlight, this heat would gradually dissipate. The atmosphere and oceans would play significant roles in moderating this temperature drop, but the lack of solar heating would eventually lead to a steady decline.
Radiative Cooling
The dark side would primarily lose heat through radiative cooling. This process involves emitting infrared radiation into space, which leads to a further drop in temperature.
Atmospheric Effects
The presence of an atmosphere would help moderate the temperature to some extent. However, over time, the lack of solar heating would result in a steady decline towards extremely cold temperatures.
Other factors such as the thickness and composition of the atmosphere would also play a crucial role. In areas where the atmosphere is thin or absent, such as in the polar regions, temperatures could drop to as low as -100°C or -148°F.
Short-Term and Long-Term Temperature Predictions
Short-Term: Initially, temperatures might remain relatively mild due to residual heat from the Sunlit side. As the day progresses, the temperature could drop but to a lesser extent than in the long-term scenario.
Long-Term: Over a longer period, the temperature would gradually decrease. The perpetually dark side would eventually cool significantly, potentially reaching temperatures similar to those found in the coldest regions of our planet today.
For example, in the polar regions of Earth, where the atmosphere is thin and temperatures are already extremely low, the temperature could drop even further.
The Role of Planetology and Exoplanet Discovery
Planetology is a very active field that models the climate and weather of tidally locked planets. This is because many of the exoplanet discoveries are likely to be tidally locked, just like the hypothetical dark side of the Earth. Planetologists use Earth weather and climate software to simulate the climates of these distant worlds, which includes handling rock, ice, and water surfaces, three-dimensional spatial and temporal variability, and various gaseous compositions of the atmosphere, including multi-phase boundaries like liquid-gas of water and clouds.
Exoplanet exploration programs have run simulations for all the interesting bodies in our solar system and predict observations. These models are incredibly advanced and provide insights into the potential habitability of these planets. They help us understand how temperature, atmospheric composition, and other factors might affect the environment on these worlds.
Habitable Regions and Water Ice
While the dark side of a tidally locked Earth would likely become extremely cold, there are still potential habitable regions near the day-night boundary, especially in areas where the rotational dynamics allow for slightly more balanced conditions. These regions might be particularly suitable for life forms that can tolerate extreme cold.
This scenario is evidenced by the survival of water ice near the poles of the Moon and Mercury. These were previously believed to be impossible, but the presence of water ice in these regions demonstrates the surprising resilience of certain environments to extreme cold. Under certain planetary scenarios, regions near the day-night boundary could be habitable.
Ultimately, the study of tidally locked planets is crucial for understanding the potential for life in the universe. By studying these planets, we not only learn about the conditions on other worlds but also gain a deeper understanding of the variables that influence climate and habitability.