Effervescent Universe

April 5, 2011

Areiosan geology varies markedly over time; early crust of the planet is dominated by hydroxide minerals that formed when rocks come in contact with superheated water. In this process called serpentination, water comes in contact with certain rocks; it forms these hydroxide minerals and hydrogen gas, which can later form methane in a reaction with organic molecules. Over time, this hydroxide mineralogy would be replaced by sulfide minerals. Sulfur is a reactive element that tends to replace carbon in some molecules, just as any oxygen at the time would obliterate any methane in the atmosphere. Although methane is quickly broken down into carbon dioxide, the early planet was producing more methane abiotically than could be destroyed naturally. This helped to keep the early planet from freezing over under a lukewarm Hemera. When Areios’ crust was forming at the beginning of time, the planet glowed like an incandescent light bulb for millions of years until it cooled down enough for the crust to solidify and water to form on the surface. As water vapor condensed and rained down on the planet, the temperatures began to cool.

At the time, the atmosphere was heavily laced with sulfur compounds, and this mingled with the water vapor in the atmosphere to create acid rain. Because sulfuric acid has a higher boiling point than water, sulfuric acid was the first to rain down on the planet, eating away at the surface and acidifying the oceans. Once the atmosphere was purged of sulfur compounds, the atmosphere became less choked with smog. On Earth, sulfur compounds spewed from volcanoes block the Sun’s rays, causing an overall cooling effect. Once the sulfur was done raining down from the sky, solar radiation poked through the atmosphere and heated the planet up a little bit, but it wouldn’t be enough to keep water vapor in the atmosphere, generating a greenhouse effect. Next in the progression, water condensed and rained down on the planet, covering its surface with pools of toxic seas. With this atmosphere mostly made of nitrogen, hydrogen, helium, noble gases the water vapor and carbon dioxide churned out by volcanic activity wasn’t enough to keep the planet warm. The oceans froze from the poles outward as the planet lurched out its rotation, thanks to the gravity of Alkyneous as was plowed back into deep space by the gravity of Hemera. With this Milankovitch cycle allied with the drastic cut back in greenhouse gases, the planet was fast becoming an iceball. Carbon dioxide is more soluble in cold waters, so the falling temperatures sped up the process of scrubbing carbon dioxide out of the air. Soon it got so cold worldwide that carbon dioxide even began to condense into dry ice, marbling the ice water now dominating the surface. With the atmosphere all but scrubbed of water, sulfur, carbon, Hemera shone brightly on the planet for the first time since its creation. But with ice reflecting most of the light back out into space, Areios stayed cold for quite some time.

But eventually, the planet swung back into an orbit close enough to Hemera that allowed carbon dioxide frozen on the surface to thaw out. With all of the ice on Areios pressing down on the tectonic plates, continental drift slowed to a halt. And because the shifting of tectonic plates provides substrate for carbon dioxide to react with rocks to form carbonate minerals, carbon dioxide and especially methane began to build in the atmosphere. The thick layer of ice on Areios’ surface conceals an active interior; the mantle is still radiating heat underneath miles of ice, spewing out dark colored rocks and oxygen-rich minerals kept safe from the rest of the environment by a thick coating of ice. With Hemera shining brighter on the planet than ever before, with carbon dioxide levels ratcheting up with no tectonic cycle to stop its progress, and with oxygen accumulating as oxidized minerals in the mantle and kept under miles of ice, Areios was primed for a great thaw.

First the tropics thawed, exposing dark colored continental rocks and raising sea levels. Then as more ice melted into lakes and seas, the liquid water absorbed heat as it exposed more surface area underneath receding ice. The plate tectonic cycle started back up, shuffling the continents into a supercontinent, creating vast expanses of shallow seas and driving ocean currents to spread the heat around to the poles as retreating back to all but the tiniest corners of the poles. With most of the oxygen safely trapped in the crust, methane and carbon dioxide reach record high concentrations and Areios returns from the deep freeze with a planet straddling ocean and an atmosphere primed for the creation of life. Oceans became saturated with carbon dioxide and other organic molecules that washed into the sea from the continents once new area of continental shelf become exposed to wind and water currents. The oceans became a veritable laboratory of organic chemical reactions and now that temperatures were on the rise, a lot of interesting chemistry was going to occur.

Snowball Earth

This is a depction of Areios covered from pole-to-pole with glaciers in an analgous Snowball period

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Encroaching Universe

April 2, 2011

Check out this animation of the Snowball Earth Hypothesis. This animation from Essentials of Geology by Stephen Marshak and Rita Leafgren shows the four proposed stages to the formation and destruction of Snowball Earth conditions:

1) During “normal” climate periods there are ice caps at the poles; sea level rises and falls.
2) During “metastable” climate times ice sheets expand and contract dramatically.
3) “Runaway snowball” conditions develop and ice nearly envelopes the Earth; atmospheric carbon dioxide is not absorbed by the frozen ocean.
4) The rising concentration of unabsorbed carbon dioxide gas leads to a “runaway greenhouse effect”; Earth warms and the ice shell rapidly vanishes.

Entwined Universe

March 28, 2011

Plate tectonics on Earth are heavily aided by the presence of water to weaken the integrity of the crust at subduction zones, and this lowered resistance helps oceanic plates sink below the lithosphere. Venus is approximately the same size as Earth, but it doesn’t have plate tectonics like Earth does. Some geophysicists like cite a myriad of variables that might determine whether or not an Earth-mass planet is active tectonically. Besides the presence of water, the thickness of the crust can determine the amount of resistance of a tectonic plate which will impact whether a plate will buckle or deform in the first place when it collides with another plate. A thicker crust is less likely to deform than a thinner crust. This is determined by how vigorous the internal convection of the mantle is, which is in turn determined by how hot the bulk of the planet is. A hotter interior causes convection of the molten material of the mantle to rise and sink faster, hitting the underlying material of the lithosphere harder and driving the movement of tectonic plates all the faster. Smaller objects like Mars or Mercury have a smaller mantle, which indicates a lack of a supply of fissionable elements in the core, and this means less radiogenic heat is produced from the breakdown of heavier elements. For these smaller planets, the mantle cools faster than an earth-sized planet and as the mantle hardens and cools, the crust gets thicker and tougher to subduct. So plate tectonics on a smaller planet shuts down earlier in that planet’s history, which leads to a whole host of problems for habitability. The tectonic cycle regulates (p.758) the amount of carbon dioxide and sulfur dioxide on the surface of the planet, so shutting down this system is disastrous. Carbon dioxide and sulfur dioxide build up, resulting in either an increase of these gases in the atmosphere or the crust.

Areios has a much hotter interior, which keeps the crust from forming too thick and pushes the tectonic plates so quickly that any crust generated from mid-ocean ridges would get recycled into the mantle quickly. This tectonic cycle is a fast-forward version of Earth’s tectonics, so carbon dioxide would get scrubbed from the atmosphere by hyperactive plate tectonics faster than volcanoes could spew it out. During a period of maximum glaciation, ice covers the continents, weighing down the plates and halting the process that scrubs carbon from the atmosphere. This builds up a greenhouse effect that eventually overcomes the frozen climate. It’s not until the end of a disastrous ‘Snowball’ period (p.759) that carbon dioxide levels rise to support planet-wide photosynthesis. More on that later…

The atmospheric composition of a planet is determined in part by the geology of the crust. As we’ve seen before, on Earth and Areios, carbon dioxide in the atmosphere gets pulled out of the air by minerals in the crust that get dragged back into the mantle by tectonic forces. But this isn’t the only way that the crust influences the composition of the atmosphere. When Areios was first forming, volcanoes would spew out water vapor and other volatiles that would eventually condense into the oceans. To be sure, just like on Earth, some of the water on the planet’s surface was delivered by ice-bearing comets (p. 752) and meteorites, but a significant amount of the planet’s early atmosphere was baked out of the crust. Like carbon dioxide, sulfur dioxide is released into the atmosphere by volcanoes, but because SO2 is so reactive, it doesn’t stay in the atmosphere like carbon dioxide does and is scrubbed out of the atmosphere quicker. This chemical exchange between the rocks and the air is only made more complex by adding the chemical reactions associated with life. Our instruments may one day be able to detect the presence of life based off their biosignatures it leaves in the atmosphere; the discovery of oxygen or methane in abundant quantities would all but confirm the existence of life there.

These interactions with the crust keep the composition of the atmosphere on Earth and Areios constant. However, in the history of both the Earth and Areios, a single prolonged episode in geologic history shot millions of tons of oxygen gas into the atmosphere. This may be the single most significant event in the history of life on these terrestrial planets because it means the rise of the complex organisms and eventually the humans and the Areia, but also it spelt the demise of any anaerobes that couldn’t seek refuge in an anoxic environment. The Great Oxidation Event may have been a mass extinction for anaerobic life, but it leads to the creation of the most recognizable organisms on our planet; the Eukyotes.

 

Epeirogenic Universe

March 22, 2011

On Earth, geologists can understand the geologic events of the past by analyzing the different rock types and using clues to discern what forces creating them. The rock cycle explains how the three different rock types come to be via natural processes of volcanic eruptions, weathering and erosion, and heat and pressure (and time). Igneous rocks are created when lava on the surface cools and hardens into a solid mass. The density, composition, and texture of igneous rocks can tell a geologist where and how it formed; granitic rocks (rocks that contain a higher proportion of silicate materials) tend to be less dense than basaltic rocks (rocks with a higher percentage iron, calcium, or magnesium metals and less silicates). A geologist can usually tell what an igneous rock is made out of by coloring at the color of the rock; darker means more basaltic, and lighter hues suggest a granite-type. And lastly, the texture of a rock tells a geologist how fast the rock cooled; rocks with a glassy texture cooled too quickly to form grains, which means the rock formed on the surface, where the different between the molten interior of the earth and the room temperature outside meant that rocks solidified rapidly. Large grains mean the rock had time to form slowly, which suggests that it formed under the Earth, when higher temperatures allowed mineral grains to slowly coalesce.

Igneous rocks are classified by their composition and their rate of cooling

What kind of rocks are the Earth’s crust made out of? The Earth’s crust is made up of silicates, minerals like quartz or olivine, and Areios shares the same basic bulk composition as Earth, with some minor chemical differences that we won’t need to worry about. The crust is made up of plates that are pushed by the convection of the underlying mantle at a snail’s pace; only a few centimeters a year. There are two different kinds of plates that vary by their age and composition. The oceanic plates overlie the Earth’s ocean and are made up of denser basaltic rocks and the continental plates which are less dense make up our continents and some of the underlying mantle. When these jostling plates come into contact with one another, they create volcanic eruptions, earthquakes, tsunamis and other natural hazards. Because oceanic plates are denser, when they collide with continental plates, they sink into the mantle and are partially melted and become part of the mantle. When two oceanic plates collide, the denser one will sink below the mantle. But when two continental plates collide, typically they ram up against one another to form mountain ranges like the Himalayan Plateau (a collision between the Indian and Asian plates). Plates can also move apart from one another in an event called rifting. Rifting occurs beneath the Atlantic Ocean along mid-ocean ridges where the material from the mantle rises and punches a hole through the crust, allowing magma to well up to the surface, where it hardens to form new oceanic crust. As more magma rises up it pushes older rockers farther out from the ridges, creating new crust material. Oceanic crusts will eventually get pushed into subduction zones where old crust gets recycled into the mantle. This system of continental drift drives the movement of tectonic plates.

Areios has tectonic plates and despite the many differences in Terroan and Areiosan geology, the processes on both planets are analogous. Areios has roughly the same volume of land area covered by ocean as the Earth, but because Areios’ land area is larger, oceans make up a smaller percentage of the total land. This is important because water acts as a lubricant for subduction and this process that creates and destroys crust is responsible for the regulation of carbon dioxide. The biggest change in in the tectonic system from Earth to Areios is that the process on Areios happens much quicker, so it voraciously scrubs any carbon dioxide out of the atmosphere as quickly as it can be released from mid-ocean ridges. This makes it harder for photosynthesis to occur on Areios because CO2 is the fuel for photosynthesis. Along with the high levels of sulfur compounds that bleach chlorophyll and the lower levels of sunlight, photosynthesis doesn’t appear until later on in Areiosan history and the plant kingdom never arises on Areios at all. We’ll discuss how this omission impacts the biosphere later on, but for the time being it suffices to say that the animal kingdom on Areios would have to adapt to a world without green.

Elemental Universe

March 15, 2011

Areios is unique in this solar system in that it has liquid water on its surface, just like our Earth does. This liquid water helps to keep the climate moderate because of its high specific heat that allows water to absorb a tremendous amount of energy before it vaporizes. Water gets cycled throughout the environment through the perennial process of evaporation, condensation, and precipitation. Water also gets transformed chemically as it moves from the living to non-living environment. Water isn’t the only chemical to get recycled; nitrogen, phosphorus, sulfur, and carbon get converted into different forms through chemistry between the living and non-living parts of the environment. Areios undergoes more or less the same processes as the ones we find on Earth.

On Earth, the nitrogen cycle converts inert nitrogen gas into a form useable for life. Organisms called nitrogen fixers can break the triple bonds between the nitrogen atoms in N2 which few other organisms on Earth can do. These nitrifying bacteria appear mostly in the root of certain plants on earth and play a valuable role in supplying nitrogen to the environment, which is usually a limiting factor for plant growth. These bacteria can convert N2 to nitrate or nitrite, which plants can use. Other bacteria can convert nitrate or nitrite into ammonia. Before these organisms were around nitrate and nitrite were produced in lightning strikes, and production of usable nitrogen was limited. Still other bacteria called nitrifiers convert ammonia to nitrate while denitrifiers convert it back into nitrogen gas.

Phosphorus on Earth comes from rocks, which is released by weathering or through human intervention (think mining, extraction industries). When leached from rocks, phosphorus makes its way into the water and is quickly taken up by organisms because like nitrogen, phosphorus is a limiting factor for growth. When phosphorus gets into the water supply, it causes rapid algae growth to use up the available oxygen in the water, which causes the fish to suffocate in these dead zones at the mouths of major rivers. Right below phosphorus on the periodic table is arsenic; scientists recently discovered an organism that can substitute phosphorus in its DNA for arsenic. Because arsenic is so chemically similar to phosphorus, arsenic is deadly to humans because arsenic will replace any phosphorus in our bodies, but we can’t metabolize it. The arsenic cycle behaves analogously to the phosphorus cycle, which is what we would find on Areios instead of the phosphorus cycle. Instead of a life form that can tolerate higher levels of arsenic like GFAJ-1, life on Areios all but exclusively uses arsenic wherever phosphorus is used in biochemistry on Earth; in ATP, nucleic acids, and in the minerals that make up their bones and teeth. This alternative biochemistry makes the Areia fundamentally different from Terroa, or what I what classify as life from Earth, and this biochemical disparity effectively segregates these two trees of life because we Earthlings are toxic to the Areos as much as they are toxic to us. Contact with arsenic-life would be disastrous for both parties because of how poisonous we would be to one another. Perhaps even touching one another might be hazardous!

GFAJ-1 may be the first organism discovered that can replace the phosphorus in its DNA for a compound called arsenate.

The sulfur cycle is the most radically different from our world to Areios because sulfur plays a much bigger role in Areiosan metabolism. We’ll talk more about the role sulfur and sulfate-reducing bacteria in upcoming posts, but for now, understand that sulfur compounds are important in Areiosan ecosystems in a way that is significantly different from how it’s used on Earth. On Earth, sulfur is produced in hydrothermal vents in the form of hydrogen sulfide and in volcanoes as sulfur dioxide. Plants release minute traces of carbon vinyl sulfide in respiration and burning coal produces sulfur trioxide. These gases come in contact with water vapor and a series of reactions creates trace amounts of sulfuric acid droplets. This acid rain falls to the earth and reacts with the crust to form sulfide or sulfate minerals. These minerals eventually become part of the crust and get subducted into the mantle where sulfur gets spewed out by volcanoes and hydrothermal vents once more. Human presence alters this cycle through mining and burning coal, which has exacerbated acid rain damage, particularly in the Northeastern U.S. and Eastern Europe.

On Areios, the sulfur cycle is a bit more complex than on Earth. For one thing, some organisms build yellow mounds out of crystalline sulfur, like coral, or termite and ant hills on Earth. Some creatures incorporate a sulfur-eating bacterium on their skin that produces sulfuric acid to ward off predators. Areiosan cell metabolism relies more on sulfur compounds than our Terroan life. The earliest eukaryotes on Earth were thought to resemble an archean cell housing a rickettsia-esque bacteria (like the one that causes Rocky Mountain spotted fever). We’ll go more in depth on this endosymbiotic arrangement later, but it was thought that the rickettsia could detoxify peroxides in the cell, converting it to water while eliminating any oxygen that would be deadly to an anaerobe. On Areios, the first eukaryotic cells were meant to detoxify hydrogen sulfide and convert it to water and a solid sulfur precipitate.

The carbon cycle is the final biogeochemical cycle we’ll discuss and is probably the one most people are familiar with; with climate change such a hot issue right now for the political establishment, people have begun to pay more attention to the processes that release or sequester carbon in the environment. Carbon dioxide is a stable gas in the atmosphere that traps heat and gives both Earth and Areios a comfortable greenhouse effect that would otherwise freeze the planet. Our current climate predicament has less to do with the amount of carbon dioxide in the atmosphere (because carbon dioxide levels have fluctuated wildly over the last four billion years), but it’s dire because of the rapidity that the changes have been taking place and because human activities influence carbon dioxide levels to an unprecedented extent. The greenhouse gas methane is 40 times more powerful than CO2 and on Areios as well as Earth; this gas plays a much more powerful role in the climate. We’ll see why this is important in an upcoming post…

Encompassing Universe

March 8, 2011

The Earth’s crust is made mostly out of oxygen and silicon, but that need not be the case for terrestrial planets. Terrestrial planets can be iron-rich, carbon-rich, water-rich, or silicate-rich. As terrestrial Earth-type planets go, any planet with a significant amount of mass will accumulate an atmosphere, but if the planet gets too massive, it will take on too much atmosphere and become a gas giant more akin to Neptune or Uranus. If a planet is too small, it won’t accumulate much of an atmosphere at all and that will prevent liquid water from accumulating on the surface making the surface of the planet dry and frozen like Mars. A smaller planet will have its liquid outer core and mantle solidify faster, so volcanism and the planet’s magnetic field will shut down much quicker than on Earth. With no volcanism to replenish the atmosphere, no magnetic field to keep solar wind at bay, and a generally smaller gravitational field that can’t hold on to as much atmosphere, smaller planets are less habitable than Earth-mass planets and greater and aren’t habitable for as long, either.

A terrestrial planet more massive than Earth but less than about 10 times the mass of the Earth is considered a super earth. Anything more than 13 times the mass of the Earth would cause the planet’s gravity to hold on to too much gas and the thick envelope of a gas giant’s atmosphere would form. One astronomer suggested that a gas giant could be stripped of its atmosphere and may became a chthonian planet if a nearby massive star goes nova and tears the atmosphere off the planet, which you would expect to find in a galactic area with high-metallicity and many nearby aging stars. Super earths can be classified by their composition and internal structure and they come in two major varieties; water-rich and rocky super earths.

Iron-rich planets would form closer to the protoplanetary disk of the star they orbit, where metal content is highest. Planets rich in iron would cool quicker than silicate-based planets and that means volcanism, plate tectonics and a magnetic field would halt much sooner on a planet that cools that quickly. Mercury in our solar system is most similar to this; Mercury’s lighter silicate crust could have been boiled away, leaving behind the iron core, which makes up a greater proportion of the planet’s mass.

Our Sun has a carbon: oxygen ratio of about 0.5, so CO2 is common in the atmosphere of planets with silicate crusts. Bur for super earths that would accumulate much more carbon than a planet like Earth, there would be less CO2 in the atmosphere and the crust would be made predominantly of silicon carbide and graphite, and a layer of diamonds would be present deeper within the crust as graphite gets squeezed by heat and pressure to form diamonds. During volcanic eruptions, molten diamonds would gush from the volcano along with silicon carbide.

Planets covered by ocean are called water worlds, and because of the pressure of the atmosphere, this water would form a layer of ice VII over the entire surface of the planet. Ice VII is a truly alien form of water that would be crushed into a solid form at near-boiling temperatures. Water worlds resemble planets like Uranus or Neptune that would have migrated closer to their star and melted. These planets would be composed of a volatile content identical to the ice-bearing comets where their water would have come from. Rocky-type super earths might have the amount of water comparable to what one might find on Earth, but because the planet has a much bigger radius, oceans would straddle less of the planet’s surface, like it does on Areios. In fact, the amount of volatile content like water that gets captured by a planet might vary on an order of magnitude of about 1,000. This means that a planet could wind up with next to no water on its surface, or it might be flooded with water all over its surface. While a water world may be habitable to life, space faring intelligent life can’t arise on a water world because if a species can’t even build fire, these creatures certainly couldn’t discover rocketry, radio telescopes or even metallurgy. This means that unless we build a rocket and fly to one of these water worlds, we may never come in contact with an intelligence that dwells there.

A silicate-rich planet would resemble the terrestrial planets in our solar system; the crust would be made of silicon dioxide mostly, and plate tectonics would control the amount of carbon dioxide in the atmosphere by virtue of subduction. Areios is a silicate-rich planet like our Earth, but because of its more massive size, volcanism wipes the atmosphere clean of carbon dioxide just as fast as volcanoes can spurt it out. The same volcanic processes on Earth appear on Areios, but at a much faster pace. The crust on Areios is the same thickness as on earth, yet with a larger mantle and more gravity pushing down on the crust; plate tectonics operate in the same mechanism as they would on Earth, with the denser basalt plates getting driven beneath the lighter continental crust.

Enterprising Universe

March 5, 2011

Richard Hoover of NASA’s Marshall Space Flight Center reported in the March Issue of the Journey of Cosmology that he had discovered evidence of microfossils in carbonaceous chrondites that fell to the Earth. Hoover’s research suggests that these fossils are not Earthly contamination, but evidence of life that lived on another body in the solar system. Fragments of their original environment traveled through space until these most primitive meteorites arrived to the Earth via meteorite impact. Here is a link to Hoover’s recently published article “Fossils of Cyanobacteria in CI1 Carbaceous Meteorites: Implications to Life On Comets, Europa, and Enceladus”. As reported by the Journal of Cosmology, “Members of the scientific community were invited to analyze the results and to write critical commentaries or to speculate about the implications. These comments will be posted on March 7 through March 10 2011.”

Expect more posts next week on any major developments surrounding Dr. Hoover’s recent discovery.

Electric Universe

March 1, 2011

In the very center of Areios is the core, a dense ball of iron and nickel that sloshes around inside the planet, generating a magnetic field like the one on Earth. The core is divided into an inner and outer layer, based on density and these two layers spin at different rates, causing a magnetic field to form from an induced dipole moment. The magnetic field on Earth is generated by the molten iron and nickel that gets swirled around by the tug of the Earth’s orbit. The magnetic field was actually induced by the magnetic field generated from the Sun, and kept going by the motion of the liquid iron outer core which can conduct electricity as it was churned by the Coriolis Effect.Magnetic Pole reversal

Because Areios will take longer to cool, its core won’t differentiate into inner and outer layers until much later in time relative to how it happened on Earth. Because the core won’t differentiate at first, there won’t be a magnetic field on Areios until the planet’s insides settle down. This is important because that magnetic field keeps solar wind from stripping the atmosphere away and it keeps out deadly radiation that would attack the organic machinery of cells. In the book The Life and Death of Planet Earth, Peter Ward describes what some astrobiologists believe happened to Venus and Mars when the magnetic field of a planet stops; solar wind tears water into hydrogen and oxygen, boiling away the atmosphere until the atmospheric pressure prevents water from collecting on the surface at any temperature. The result: a dry and frozen world like Mars, or a dry and broiling world like Venus. Because Areios won’t develop a magnetic field until later on, life probably couldn’t start until the radiation bombarding the planet could be deflected. Thankfully, Areios regenerates its atmosphere through volcanic venting and it has enough gravity to hold on to some of the gases that would otherwise leak out of an Earth’s sized planet’s atmosphere, so the atmospheric stripping one would expect from Hemera’s solar wind can be kept at bay, or at least mitigated for a while.

This magnetic field reverses from time to time, and we have evidence of this on earth in iron-bearing minerals that have spewed out onto the crust from the mantle. In the Atlantic Ocean, there are areas where new crust is being created; magma from the mantle forces its way onto the surface as lava that cools and forms the ocean floor. As it solidifies, new material pushes the old material out of the way as more lava wells up from the mantle in a process called seafloor spreading. Magnetized iron in mineral crystals from the mantle record which way the magnetic field is spinning at the time when it hardens into rock. These rocks record a trend of increasing or diminishing magnetization of iron in the mantle and they show evidence that over geologic time, the poles will reverse with the North Pole flipping down to the South Pole and vice versa. During the process where the magnetization flips, there are periods of weak magnetization that can be disastrous for life because this causes more ionizing radiation to leak through the atmosphere.

On Areios, the thicker mantle keeps the insides of the planet too hot to differentiate the mantle and core into two distinct layers until later on in Areios’ history. That means that for the earliest period in Hemera’s stellar life cycle, Areios is unprotected by the cosmic rays that Hemera would bring onto Areios’ surface. Only after Hemera stops blasting the surface of Areios with radiation does Areios develop a magnetic field. Four billion years after the formation of Areios, we see a number of habitability factors line up for the first time; Hemera stops having such violent solar flares, the bulk structure of the planet settles down to trigger its magnetic field, the planet’s volcanism shoot out less gas, which causes a geologic ice age period. All of these converging factors lead to the first Areiosan lifeforms, the Areia.

magnetic field

Click here for an animation of the Earth’s magnetic pole reversal by the Pittsburgh Supercomputing Center

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.

Ensuing Universe

January 25, 2011

Areios orbits Hemera somewhere between where Mercury and Venus would be in our Solar System; at first, Areios lies just within its habitability zone where liquid water could exist on the surface, and because Hemera initially output less light when Areios was forming, it seems unlikely that life could arise on this frigid planet right from the start. On Earth, life may have formed just as soon as the crust solidified and the oceans condensed from the atmosphere, yet our planet would have been cooler than it is now were it not for the greenhouse effect. This early arrival for life suggests that life could be common in the universe if it can be spawned on a habitable planet so early in its formation. Because Areios is on the edge of the habitable zone, it may take some time to warm before it can be habitable for life. The habitability zone for life will change over time as Hemera evolves; Areios is positioned in the very outer habitable zone near the beginning of Hemera’s life and by the end of its main sequence stage, Areios is only just tucked inside the inner edge of that habitable zone. For the 38 billion years or so that Hemera is in the main sequence stage, Areios is within the habitable zone for 30 billion of those years. For the first and last four billion years of Hemera’s evolution, Areios will be sterilized of all life, first because of freezing temperatures early on and then because of the boiling temperatures near the end of Hemera’s life. As Areios’ surface temperature gets pushed hotter, Areios will have to shed more and more of its thick atmosphere like a jacket to cool off until its atmosphere is too thin to support liquid water on its surface and the oceans boil away. But more on the evolution of a habitable planet later…

Areios formed from the collision of planetesimals billions of years ago; these violent interactions also created two out of three of its moons and a third moon was captured later during a period of asteroid and comet bombardment. When the cataclysms of the planet formation ended, Areios was a still-molten ball of rock with a swirling ring of debris that would later become its moons. Areios is more massive than Earth and contains a bigger mantle and a thinner crust. The importance of this will be revealed later on, but this distinction is not trivial when it comes to the potential for life on Areios. Because of Areios’ girth, the planet would take longer to cool and the internal portions of the planet would stay hotter for longer because the core is wrapped in a much thicker insulating blanket of mantle. This early planet would soon cool on the outside, though, and a process called differentiation would occur; Areios was at first a well-mixed sphere or magma, but it began to cool and settle. The crust formed like a skin like a bowl of soup left to cool; this outermost layer is only a few kilometers thick, but covers the entire planet and serves as the palette for the thin veneer of life that is to come. The crust covers the mantle of the planet, which makes up the bulk of Areios’ mass. The mantle is a made of melted rock kept solid by the intense pressure coming down on it; unlike Jules Verne’s Journey to the Center of the Earth, there are no caverns or caves in the mantle because this solid rock can flow like a liquid and would quickly fill any void beneath the planet, despite the fact that pressures make the molten material behave like solid rock.

This is a depiction of what a planet like Areios would look like early in its formation.

As Areios formed, there were three processes that kept generating the internal heat of the mantle; the kinetic energy of impacts, differentiation, and radiogenic heating. During the formation of Earth, there was a period called the Late Heavy Bombardment where more comet and asteroid impacts struck the planet, boiling the oceans and melting the crust for a couple hundred million years before the rain of fire subsided. When these objects struck the Earth, their gravitational potential energy as they fell to the earth was converted to kinetic energy in the form of heat. Areios experienced a similar event to the late heavy bombardment for a couple of hundred million years after the planet formed and for a while the kinetic energy from those impacts kept heating the planet, but once those impacts subsided, the planet cooled enough to form crust and the oceans. Areios started out as a homogeneous ball of magma, but slowly the heavier metals started to settle in the core of the planet. As these denser materials sank into the mantle, their potential energy was converted into kinetic energy until the planet differentiated into the three distinct layers of the crust, mantle and core. Once these three layers were fully formed, the planet no longer generated heat by differentiation. The final and only ongoing way the interior of the planet generates heat is through radiogenic heating. When the planet formed, it incorporated some heavier unstable elements like thorium and uranium. Over time, these elements would decay into lighter elements like potassium or lead; this radioactive decay would release energy in the form of heat that keeps the internal parts of Areios hot. This Late Heavy Bombardment era for Areios would deliver water to the planet and later determined how much of Areios will be covered in lakes and oceans.