5:15 PM - 6:45 PM
[AOS11-P03] The study of the climate of a planet with oceans as considered from the early Martian climate
Keywords:early Mars, climate, ocean
Introduction
Understanding the water cycle on early Mars is important in understanding the planetary climate mechanisms. This is because the Martian terrain has many erosional valleys, fans, and other landforms with traces of water flow, suggesting that liquid water was present on Mars more than 2.5 billion years ago. It is considered highly likely that liquid water existed on Mars at that time and flowed over the surface. However, Mars is farther from the Sun than the Earth, and the temperature on Mars today is well below the melting point, so for water to exist in liquid form, the temperature would have to have been significantly higher than on Mars today. In addition, the sun was less luminous then than it is now, and the energy incident on Mars was lower, making it more difficult to maintain high temperatures. This would require an environment with abundant greenhouse gases. However, it is unclear whether a warm and humid environment was maintained over a long period of time or whether a short-term warm environment-producing event occurred, such as an eruption or celestial collision during a cold climate, causing ice to melt and water to flow temporarily. Mars' former water resources were likely abundant enough that if water did flow, it would have created oceans and lakes at lower elevations, but there are still many unknowns about the state of the oceans and these are still the subject of debate. If the oceans had existed for a long period of time, they could have functioned as a place where life had the possibility to born and grow, and they could have played a significant role in astrobiology. However, there is a lack of research on the interaction between oceans and atmospheres on planets other than Earth, and the factors that influence their stability are not known in detail. Therefore, in this study, we reproduced the early Mars climate using a simulation and investigated the water circulation and temperature in order to understand the conditions that would have allowed the oceans to remain liquid for a long period of time.
Methodology
The 3D-Global Climate Model (3D-GCM) was used as the simulation method. ROCKE-3D (Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments with Dynamics) was used for the calculations. SOCRATES (Suite Of Community RAdiative Transfer codes based on Edwards and Slingo) scheme was used to reproduce the unique radiative transfer scheme on Mars. For the oceans, we used the elevation of a line that was assumed to be the coastline, from the topographic data as a reference, and assumed that water filled the area below that elevation. We started with the ocean filled with liquid water and considered that equilibrium was reached when the heat budget stabilized, and observed the climate for the following 10 years. The coupled ocean-atmosphere model was used to reproduce the interaction more accurately between the ocean and the atmosphere.
Since there are many uncertainties in solar luminosity, rotation axis, atmospheric pressure, and atmospheric composition, we adopted several values within the range of possible environments about 3 billion years ago, and investigated the climate at each value while varying them as parameters.
Results and Discussion
Using the above simulations, we were able to infer the climate in various early Martian environments. This validation, which fully accounts for the coupling of the oceans and atmosphere, shows that Mars could have kept its oceans liquid under simpler conditions than previously thought. We were also able to find environments that are more consistent with the topographic features of Mars, and we were able to make inferences about the climate that more closely resembled the environment of that time.
Understanding the water cycle on early Mars is important in understanding the planetary climate mechanisms. This is because the Martian terrain has many erosional valleys, fans, and other landforms with traces of water flow, suggesting that liquid water was present on Mars more than 2.5 billion years ago. It is considered highly likely that liquid water existed on Mars at that time and flowed over the surface. However, Mars is farther from the Sun than the Earth, and the temperature on Mars today is well below the melting point, so for water to exist in liquid form, the temperature would have to have been significantly higher than on Mars today. In addition, the sun was less luminous then than it is now, and the energy incident on Mars was lower, making it more difficult to maintain high temperatures. This would require an environment with abundant greenhouse gases. However, it is unclear whether a warm and humid environment was maintained over a long period of time or whether a short-term warm environment-producing event occurred, such as an eruption or celestial collision during a cold climate, causing ice to melt and water to flow temporarily. Mars' former water resources were likely abundant enough that if water did flow, it would have created oceans and lakes at lower elevations, but there are still many unknowns about the state of the oceans and these are still the subject of debate. If the oceans had existed for a long period of time, they could have functioned as a place where life had the possibility to born and grow, and they could have played a significant role in astrobiology. However, there is a lack of research on the interaction between oceans and atmospheres on planets other than Earth, and the factors that influence their stability are not known in detail. Therefore, in this study, we reproduced the early Mars climate using a simulation and investigated the water circulation and temperature in order to understand the conditions that would have allowed the oceans to remain liquid for a long period of time.
Methodology
The 3D-Global Climate Model (3D-GCM) was used as the simulation method. ROCKE-3D (Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments with Dynamics) was used for the calculations. SOCRATES (Suite Of Community RAdiative Transfer codes based on Edwards and Slingo) scheme was used to reproduce the unique radiative transfer scheme on Mars. For the oceans, we used the elevation of a line that was assumed to be the coastline, from the topographic data as a reference, and assumed that water filled the area below that elevation. We started with the ocean filled with liquid water and considered that equilibrium was reached when the heat budget stabilized, and observed the climate for the following 10 years. The coupled ocean-atmosphere model was used to reproduce the interaction more accurately between the ocean and the atmosphere.
Since there are many uncertainties in solar luminosity, rotation axis, atmospheric pressure, and atmospheric composition, we adopted several values within the range of possible environments about 3 billion years ago, and investigated the climate at each value while varying them as parameters.
Results and Discussion
Using the above simulations, we were able to infer the climate in various early Martian environments. This validation, which fully accounts for the coupling of the oceans and atmosphere, shows that Mars could have kept its oceans liquid under simpler conditions than previously thought. We were also able to find environments that are more consistent with the topographic features of Mars, and we were able to make inferences about the climate that more closely resembled the environment of that time.