A new computer model that simulates the evolution of planetary atmospheres has discovered that water could have survived on some planets in the fascinating planetary system.
For years, scientists have debated the likelihood that life exists on seven fascinating planets orbiting the star Trappist-1, the most famous planetary system outside our own. The reason? Although several of these planets orbit in their star’s habitable zone, the region around a stellar body where liquid water can exist because temperatures are just right, these worlds weren’t always so comfortable.
In the past, Trappist-1 exoplanets were subjected to much harsher conditions because their parent star tended to be much hotter. During those scorching hundreds of millions of years, any water that might have been trapped in the rocks of these planets would have evaporated and dissipated into space, scientists previously thought. That, of course, would ruin the possibility of the Trappist-1 planets developing life as we know it.
Trappist-1 exoplanets could be more habitable than previously thought But a new study, based on a novel technique for modeling the evolution of planetary atmospheres, suggests that all is not lost for life on Trappist-1 exoplanets.
The development of enormous water-rich atmospheres is a crucial step in the evolution of the ocean worlds. Therefore, better understanding these atmospheres could help scientists pinpoint where life might exist in the universe more precisely. According to current theories, when planets are formed, water is contained in their rocks. But due to the strong volcanism that occurs in the first years of life of these fledgling planets, the water evaporates into the atmosphere. When conditions are right, that water vapor has a chance to condense and form a liquid ocean in which life could arise. But when exactly those conditions occur remains a mystery.
Selsis said in a statement: “In the past, when we modeled these atmospheres, we made a very strong approximation, which was to say that these atmospheres are convective. That means stellar radiation is deposited very deeply near the planet’s surface, and the way the energy goes up and out is through convective motion. Hot air rises, cold air falls, and we assume that this is the main way that energy is transported out of the atmosphere and then radiated [into space]. This makes life a lot easier for us because when convection is the main driving force in an atmosphere, we know the temperature gradient, we know how temperature varies with pressure. It just has to do with the type of gas you add to the atmosphere.”
The opacity of the gas that surrounds a planet changes with altitude, affecting how much heat is trapped inside and how much heat escapes into outer space, Selsis explained. For a long time, scientists were unable to model any of these variables. Those opacity changes and their effects on other processes in the atmosphere remained a mystery. This led Selsis and his colleagues to suspect that previous simulation results, which did not include that information, might be wrong.
Selsis explains: “We were not entirely satisfied with the convective hypothesis. One reason is that with very deep atmospheres, little light will reach the surface. Probably not enough to drive convection.”
That’s where the Trappist-1 system comes into play. Previous models have shown that planets with water-rich atmospheres that receive only about 10% more sunlight than Earth quickly develop a vicious greenhouse effect, the process of trapping heat facilitated by certain gases, which is infamously driving change. climate on Earth. Because water vapor is a potent greenhouse gas, as water continues to evaporate from a planet’s rocks and the concentration of water vapor in the atmosphere increases, the temperature at the planet’s surface also increases. Eventually, the planet heats up so much that its crust and mantle melt into an ocean of magma, releasing water trapped in the rock into the atmosphere. Gradually, over billions of years, as powerful stellar winds whip around the planet, this atmospheric water dissipates into space. Earth’s hotter sibling Venus, which orbits 40 million kilometers closer to the Sun than Earth, is thought to have met the same fate. The same thing happened with the planets in the habitable zone of Trappist-1. Although the star Trappist-1 is smaller and cooler than the star at the center of our solar system, its seven planets orbit at distances much smaller than the distance between the Sun and Mercury, the innermost planet in the solar system.
“Small, red stars like Trappist-1 dim over time. When the Trappist-1 system formed, the planets that are now within the habitable zone, where water can exist, were for hundreds of millions of years much more irradiated than they are today, and that means that if they had water, it would fade away. would have evaporated.” However, the new model developed by Selsis shows that while conditions on all of these planets were undoubtedly hellish during their early years, they may not have been hot enough to melt the planets’ crust and mantle into magma. This means that a large amount of water could have survived within the rock in recent years, when the parent star cooled. Thus, oceans of liquid water could have formed on these planets, which today could support thriving life. Down the road, these findings could have huge implications for our chances of finding life outside our solar system, since small, cool stars like Trappist-1, called red dwarfs, are by far the most common type of star in our galaxy, the Milky Way