Emissive Universe

February 22, 2011

Areios’ bulkier shape contains a more massive mantle hidden by a fragile lithosphere. Because Areios has such a thick mantle and a comparatively thin crust, there is more volcanism on the planet because magma from beneath the surface has a thinner crust to penetrate before it reaches the surface as lava. The tectonic cycle that builds and destroys land on Areios would operate in fast-forward; with portions of the crust being created and destroyed just as quickly, weathering would deplete carbon dioxide in the atmosphere and prevent a greenhouse blanket from keeping the planet warm enough to have liquid water on the surface. Also, increased volcanism would hurl sulfur dioxide out into the air, forming clouds that would reflect light back out into space. This would cool the planet down even more were it not for the water vapor spewed from eruptions and the dark colored basaltic rocks covering the planet to absorb incoming solar radiation. And as time goes by, Hemera would get brighter as it spends more of its fuel. Once life takes a foothold on Areios, methane-producing bacteria warm the planet up drastically in a climatic event akin to the Great Oxygenation Event of the Cambrian Era. But until then, the planet is frigid except in select spots where hydrothermal vents and hotspots keep it warm.

The atmosphere on Areios is regulated by this tectonic cycle that creates and destroys crust. Carbon dioxide produced by volcanoes would get scrubbed out of the atmosphere by the subduction of crust into the mantle. Because this process happens so much quicker on Areios, carbon dioxide would get scrubbed out of the atmosphere quicker than the processes operating on Earth. Areios’s mass keeps lighter gases like hydrogen from escaping so easily and this thicker envelope of gas around the planet means that carbon dioxide and other gases are available in higher concentrations than on Earth. So while carbon dioxide would get removed from the atmosphere by a hyperactive tectonic system and unceasing weathering, it would get replenished about as quickly by volcanoes and other natural processes. Clouds formed in the atmosphere can reflect heat if they form high in the atmosphere or they can absorb heat if they are lower in the atmosphere. Venus has clouds of water vapor and sulfuric acid, which would reflect light from the surface of the planet, but because it receives more incoming solar radiation than Earth and because its atmosphere is rich in the greenhouse gas carbon dioxide, what infrared radiation that does get in sticks around for much longer and heats up the surface of the planet enough to boil the carbon dioxide trapped in the carbonate-bearing rocks in the crust, heating up the planet more so. We’ll see how the chemistry in the crust can impact the composition of the atmosphere with an in-depth discussion of the plate tectonic system on Earth. When life arises on the planet, it too will manipulate the composition of the planet’s atmosphere; bacteria would convert carbon dioxide and hydrogen gas into methane, warming up the planet. As Hemera’s luminosity increases, photosynthesis can be achieved on Areios by a creature that develops a chloroplast to harness the light shining through Areios’ hazy atmosphere, one day creating oxygen for animal life.

Greenhouse Effect

Earth's atmosphere can reflect or absorb solar radiation.

With volcanoes spewing out hydrogen sulfide, water vapor and sulfur dioxide, radiation coming in from Hemera would disassociate the atoms of those molecules and form sulfuric acid in the atmosphere. Sulfuric acid would block some of the radiation from coming in, but on a planet as cold as Areios, the sulfuric acid in the sky would precipitate out and rain down on the surface, causing weathering to speed up as acid wears down the crust. Because of the thicker atmosphere on Areios caused by a greater gravitational pull from Areios’ larger mass, the partial pressure of carbon dioxide in the atmosphere would mean carbon dioxide gets incorporated into the crust more readily. This would cause carbonate rocks to neutralize the acid, creating bicarbonate in the crust. While Areios has less aluminum in the crust compared to Earth, acid rain would cause toxic metal leaching in the oceans. Water vapor and other gases with a higher freezing point would freeze into a solid on the surface and raise the albedo of the planet. Albedo is a measure of reflectivity, so raising the albedo would mean more light is being reflected back into space rather than being absorbed by the planet. This is especially disastrous for life when the planet gets cold enough to freeze carbon dioxide. Carbon dioxide is a greenhouse gas, but if it gets cold enough, it will bypass the liquid phase and sublime into a solid ice. As an ice, it would no longer trap heat and instead it would reflect it back out into space, making the planet even colder in a negative temperature feedback loop.

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