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Home / Science / Snowball exoplanets could be better for life than we thought

Snowball exoplanets could be better for life than we thought



When astronomers discover a new exoplanet, one of the first considerations is whether the planet is in or out of the habitable zone. This label largely depends on whether the temperature of the planet allows liquid water or not. Of course it's not that easy. A new study suggests that frozen, icy worlds with fully frozen oceans could actually have habitable land areas.

The new study was published in the Journal of Geophysical Research: Planets of the AGU. It focuses on how CO2 flows through a planet and how it affects the temperature of the planet. The title is "Habitable Snowballs: Moderate Land Conditions, Liquid Waters and Effects on CO 2 Weathering."

A snowball planet is a planet similar to Earth but whose oceans are frozen over. The Equator , It is independent of an ice age in which glaciers grow and ice layers stretch, sometimes several kilometers thick. In an ice age, the equatorial oceans remain ice-free.

However, a snowball planet is frozen more thoroughly. On a snowball planet, all oceans are covered in ice, including all equatorial oceans. Scientists have considered these planets habitable because there is no liquid water on the surface.

The Earth has experienced at least one and maybe even three snowball phases in its history. Life endured these phases because the only living things were marine microorganisms. So the question is, if we look at a snowball exoplanet in the habitable zone of its star, is it possible that life survives there?

  The Cryogenic Period contained Earth's two most extreme ice ages. There is some scientific controversy because there is an ongoing debate over whether the earth was a snowball during one of these extreme ice ages, or whether a land remained ice-free. In any case, life in the oceans appeared and survived the Cryogenian. Picture credits: Wikipedia.
The Cryogenic Period contained Earth's two most extreme ice ages. There is some scientific controversy as it is currently debated whether the earth was a snowball during one of these extreme ice ages, or whether some of the land remained ice-free. In any case, life in the oceans appeared and survived the Cryogenian. Picture credits: Wikipedia.

This new research says yes, or at least maybe.

The lead author of this new study is Adiv Paradise, an astronomer and physicist at the University of Toronto, Canada. Paradise summed up the situation briefly: "They have these planets that they traditionally consider uninhabitable, and this suggests that they may be uninhabitable."

"We know that the Earth is through their own snowball Episodes was habitable because life was created before our snowball episodes and life remained long afterwards, "Paradise said in a press release. "But our whole life was in our oceans at that time. The country does not mean anything. "

Paradise and the rest of the team wanted to explore the idea that some land areas could remain life-sustaining even on a snowball planet. They used computer models to simulate various climate variables on theoretical snowball worlds. They adapted the configuration of the continents, the amount of sunlight and other features of their theoretical snowball worlds. They also focused on CO2.

CO2 is of course a greenhouse gas. This allows the atmosphere of a planet to capture heat, and it can help keep a planet moderate. Not enough, and a planet can freeze. Too much and temperatures can rise beyond a range where life can survive.

  carbon cycle diagram. Picture credits: NASA Earth Observatory.
carbon cycle diagram. Source: NASA Earth Observatory.

CO2 follows a known cycle in the life of a planet. The amount that remains in the atmosphere depends on precipitation and erosion. The rainwater absorbs CO2 and converts it to carbon dioxide. Once it is on the surface of a planet, the carbonic acid reacts with rocks. These reactions decompose the carbonic acid and bind it with minerals. Finally, this carbon gets to the ocean and is stored on the seabed.

But once the surface of a snowball planet has solidified, none of it can happen. The removal of CO2 from the atmosphere stops. There is no precipitation and no exposed land.

But in their simulations, some of their modeled snowball planets lost atmospheric CO2 even after they were frozen. This implies two things: there must be ice-free land and some rainfall.

   This graph shows the relationship between carbon dioxide produced by volcanic activity and carbon dioxide removed from rainfall and erosion for temperate and snowball climates. Planets remain stuck in the snowball state when volcanic activity and weathering rate equalize. Credit: AGU
This graph shows the relationship between carbon dioxide produced by volcanic activity and carbon dioxide removed from rainfall and erosion for temperate and snowball climates. Planets remain stuck in the snowball state when volcanic activity and weathering rate equalize. Credit: AGU

In some simulations, some snowball planets were warmer than others. Some of them had land areas warm enough to continue the carbon cycle: there was both rainfall and exposed rocks. These non-frozen areas were at the center of the continents, far from the frozen oceans. Some temperatures in these areas reached up to 10 degrees Celsius. With scientists believing that life can still reproduce at temperatures as low as -20 degrees Celsius, these results will pave the way for life on snowball planets, as in the earth-blown snowball phases.

But the study also found something else. Under the right conditions (or not under the right conditions, if you want to see more life outside), a planet can be caught in a snowball phase and never move out of it. It also depends on the carbon cycle.

Scientists thought that with volcanically active planets, CO2 gradually released into rocks is released and the atmosphere is warmed over time, as this is possible. & # 39; not be removed by precipitation. However, if the study is correct, a small amount of exposed soil and the resulting rain can balance the released CO2 and keep the planet in a steady, snowball-like state. Only a small amount of land would ever be ice-free. In this scenario, life is unlikely to happen.

  A series of illustrations showing how Earth may have become a snowball planet. Photo credits: NASA
A series of illustrations showing how Earth may have become a snowball planet. Source: NASA

Overall, the results of this study show how complex planets are. Each of them is in a unique situation, and the provisional designation as habitable or not habitable is only a starting point. There are a tremendous number of variables that shape every discovered exoplanet.

It is safe to say that we can rule out a large number of planets in terms of habitability. For example, hot Jupiter singe hot gas planets and can never support any form of life we ​​can imagine.

But for planets in the habitable zone or at the borders, we are unable to rule them out, even though they are unlikely to support life.

More science needed.

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