In recent years, we have come to see what a typical planetary system really means. As far as we know, this generally excludes most of the planetary types seen in our own Solar System. No neatly sorted terrestrial and gaseous planets; little spacing between inner planets; and, occasionally, hot Jupiters. While it is certainly easier to detect planets with a much shorter orbital period, this does not excuse the problem that in fact a seemingly disproportionate number of stars seem to have tidally locked planets with orbital periods of a few days. Even the star Gliese 674, just 15 light years away, is orbited by a planet of this type. Clearly, we are the exception.
Protoplanetary disks tend to be fairly dense closer to their parent stars, according to the simple laws of gravity. It should logically follow that several protoplanets form with extremely rapid periods during the early years of the planetary system. Many systems tend to retain as many as five full-sized planets within 1 AU of their star, most within the orbit of Mercury. Our Solar System lacks a single asteroid within Mercury's orbit.
Perhaps this has not always been the case, though. This is the story of the lost worlds of our Solar System.
After the Sun sparked into light, after the Earth acquired its moon, after the moons around the other planets began to form; there were still two worlds inside the orbit of Mercury: Vagans and Fervens.
Fervens, from the Latin for fiery, was normally the innermost of the three worlds and about 0.1 times Earth's mass. It was a rocky world with its atmosphere stripped away by solar radiation, orbiting the Sun in only 11 days and tidally locked to the Sun. Outside Fervens' orbit, there was Vagans (wandering, stray), a geologically active world 1.1 times Earth's mass. It orbited the Sun in 14 days, another tidally locked world. Mercury itself lay essentially in its present day position, semi-tidally locked in an 88 day orbit.
Vagans and Fervens, located in the same orbital plane, had overlapping orbits. Fervens’ orbit was elliptical enough to be further from the Sun than Vagans for a day or two of each orbit. Thus far, they had managed not to collide due the vastness of space. But on astronomical timescales, such a collision was unavoidable.
Anticipating the collision for millions upon millions of years, it finally occurred. The impact occurred when Fervens was on its swift inwards trajectory towards the Sun. It was a grazing impact on Vagans, but enough to destroy Fervens. The velocity of Fervens severely disturbed Vagans, sending it very close to the Sun. Just a couple million kilometers away, Vagans got as near to the Sun as it would ever get, before entering a hyperbolic orbit and getting flung outwards as high velocity.
In fact, Vagans was forcefully flung out that it was sent out of the Solar System. Not long afterwards, a close encounter with Jupiter and Saturn made it pick up speed. It had no star. Vagans had become a rogue planet. This world, without light, could not possibly have plants. Without a star, any organisms that might arise on it would be unable to see. Looking out into the depths of space, it would be impossible to find. But rogue does not mean lifeless.
Hadean Eon (4.55–4.12 Ga)Edit
About 4.6 billion years ago, the sun formed by accretion of nebulous matter due to a supernova. The tortuous and slow accretion process finally allowed the sun to burst into light. Meanwhile, its protoplanetary disk began to accrete as well. In the innermost reaches of the Solar System, matter began to accumulate, forming Vagans, already close to its present size within 100 million years.
With an orbit crossing that of Fervens', a collision with Fervens 4.12 Ga brought Vagans into brief a hyperbolic trajectory around the Sun before flying away at high velocity. The Solar System in the earliest days of the Late Heavy Bombardment, Jupiter and Saturn took on a near 1:2 resonance, meaning that Vagans was able to near both of the planets and gain enough velocity to get completely ejected from the Solar System. This brought an end to Vagans' Hadean eon.
Cryozoan Eon (4.12–2.34 Ga)Edit
The longest and, during some periods, arguably the most boring eon in Vagans' history, during the Cryozoan eon Vagans was much colder than it is today, even deep under the surface. It was only towards the end of the eon that Vagans finally began to produce a stable carbon dioxide, methane, and nitrogen atmosphere, as chemosynthesis really began to pick up pace. Near the beginning of this period, Vagans accumulated water ice from collisions with objects in the early Oort Cloud, and about halfway through the eon, the first simple life evolved on the rogue planet.
Eocryozoan Era (4.12–3.90 Ga)Edit
The era beginning with the ejection of Vagans from the inner Solar System and ending at the point at which it has completed its cooling phase, Vagans still remained a relatively warm planet for much of this era, the shortest of its eon. The scorched planet of over a thousand degrees Celsius took some time to finally become a cold planet.
At the beginning of this period, Vagans remained in the Oort Cloud, though not in any stable orbit, for over 700,000 years. Still a planet in the outer reaches of our Solar System and almost slowing to the point of once again orbiting the Sun, it finally became a true wanderer when after one orange dwarf star in the Sun’s stellar nursery finally passed through the right region of the Solar System as to fling Vagans violently out. Picking up pace as it neared the star, it passed through the outer Oort Cloud, colliding with a number of comets, bringing to the planet one essential ingredient for life: water.
Vagans continued to travel through interstellar space, gradually cooling to a frigid −170°C on average. It seemed uninhabitable for anything other than the simplest life, at least for the time being. And so, the Eocryozoan era was brought to an end.
Palaeocryozoan Era (3.90–3.32 Ga)Edit
Vagans' immense speed caused by its gravitational interaction with the orange dwarf star led it for a time not to orbit in the spiral arms of the galaxy, but rather to be flung out into a high velocity state near the edge of the galaxy, over 45,000 light years from the center.
As the planet’s strong gravitational influence in a space devoid of interference by a stellar wind became apparent, its primitive atmosphere began to evolve, full of hydrogen and helium picked up from interstellar space, with trace amounts of carbon dioxide from the planet's still evolving tectonic system. At last, by the end of the period, convection in Vagans' interior began to settle down. The volcanoes had been unleashed.
Mesocryozoan Era (3.32–2.99 Ga)Edit
The extremely high proportion of rocky material in Vagans' composition was never too influential in its early history. Soon though, it would play a vital role in its development of a unique biology. Other than its solid metallic inner core and liquid outer core, which produced a weak magnetic field, the rest of the planet was almost invariably composed of 98.4% silicon dioxide. The planet was a complete ball of rock. As for the other 2.6%, it was mostly other silicon compounds, such as silicone, and after interactions with Oort cloud objects, small amounts of water in the crust. It was the plainest planet in the Solar System.
Vagans never had a very differentiated mantle and crust from a chemical standpoint. The only difference between the two was a slightly higher concentration of metal oxides in the mantle. During the Mesocryozoan era, the lithosphere in fact began to act physically as if it were part of the asthenosphere. There was little to no difference in density between the two layers due to their similar silicon dioxide composition. Since magma was able to quickly rise through cracks in the relatively dense crust, thousands of volcanoes began to spring up out of the surface. More and more of the lithosphere began to convect with the asthenosphere, becoming part of it. Only the highest layers remained as lithosphere due to low temperatures, meaning the lithosphere was only about 10 to 20 kilometers thick.
Even though it did not achieve the temperature necessary to convect, the surface still warmed significantly. The planet's frozen ice began to thaw, starting at the sea floor. Hydrothermal vents created subsurface oceans. The lithosphere finally began to act like it was composed of tectonic plates, both oceanic and terrestrial. Again, they were both mainly composed of silicon dioxide, with a slightly higher concentration of metal oxides in the oceanic crust, but not quite as much as the mantle. At last, in the deep sea, life could arise. But other than in carbon dioxide, the planet had essentially no detectable traces of carbon whatsoever. It would have to go with what it had: lots and lots of silicon.
Neocryozoan Era (2.99–2.34 Ga)Edit
At last, at the very end of the Mesocryozoan era, 3 billion years ago, life arose on Vagans. But it was no Earthly life. It was a cell living deep in the ocean with a silicone membrane, a chemical metabolism, relying on water partially to keep structure, and a silicon-based genetic material. Except for the problem that it relied on many molecules and atoms extremely rare under Vagans' ocean, including CO2, H2, ammonia, and chlorine. The primitive state of this life meant it could still not flourish, especially as evolution took a long time to pick up pace.
As volcanism began to pick up pace, its byproducts began to enter the ocean. Except for chlorine, all of the molecules mentioned began to enter the ocean. Soon, the abundance of certain elements became clear. Since Vagantian life had cell membranes made of the fairly common silicone, there was little restriction to creating specialised organelles, and so life had already begun to evolve eukaryotic cells by 2.4 Ga. And finally, as competition between these microbes increased, natural selection began to come into play.
The chlorine in the genetic code was ditched. These cells did not have a limit for how much membrane they could have. A three-base genetic code, consisting of a single oxygen atom, an O2 group, and ammonia as bases was favoured, despite the exponentially larger code. And soon, these organisms consisting of rather bland molecules began to take over Vagans. Far more methane began to enter the atmosphere. And so began the warming of the planet.
Thermozoan Eon (2.34–1.12 Ga)Edit
Vagans was destined to become a frozen world. For the majority of its history, it was so cold that many of the gasses in our atmosphere would begin to liquify. Reaching down to −200°C in the coldest places, it appeared as about the coldest thing in its cosmic neighborhood. A star? Much hotter. A brown dwarf? Still much hotter. A planet? Way, way, hotter. A rogue gas giant? Practically burning. And then, all of a sudden, 2.3 billion years ago, something miraculous happened. Life turned the planet habitable.
Palaeothermozoan Era (2.34–1.69 Ga)Edit
The time that the Earth turned itself habitable was a dark one. Its toxic carbon dioxide atmosphere kept the planet nice and toasty. Then, all of a sudden, oxygen began building up in the atmosphere, replacing the carbon dioxide, and freezing the planet. Life had brought upon itself the Great Oxygenation Catastrophe.
On Vagans, the time period from 2.34 to 2.15 Ga is defined as the Methanogenic period, when life brought the exact opposite of Earth's Oxygenation Catastrophe upon itself: a warming of the planet effective over a short time period, but close to useless in the long run. It made the planet no less uninhabitable at the surface, and ultimately, the warming stopped shortly after the Methanogenic period. Liquid water was still nowhere close to forming on the surface, except in the presence of hot springs. The planet had brought itself up to an average surface temperature of −60°C. At least it was something that deep undersea creatures could tolerate.
As life began to finally diversify, the first major split between Vagans' life groups, Vagabiota, occurred. The last common ancestor of all extant life on Vagans lived 2.14 billion years ago, when the Cryophilia and Thermophilia split. The Cryophilia were not necessarily psychrophiles, but they were much more suited to becoming them. They harvested energy which was abundant not only around geothermal locations. They changed their metabolism yet more to suit the conditions of Vagans, and just like that, they harvested energy from reacting any potentially metallic silicon they could find with water, producing SiO and H2. In some Cryophilia, they furthermore used the H2 waste product to react with carbon dioxide, the original reaction used by life on Vagans. That way, that did not need to collect natural H2 from hydrothermal vents.
Finally, near the end of the era, 1.8 Ga, another major leap in Vagans' evolution occurred. The Thermophilia, now experiencing a decline because of a slowing of geothermal activity, began to use an alternative food source: themselves. The first predators rapidly evolved, still unicellular organisms, but considerably larger than their prey, able to engulf and digest it. There was previously no food chain, but immediately, it began to topple.
Mesothermozoan Era (1.69–1.44 Ga)Edit
By the beginning of the Mesothermozoan Era on Earth (what is in our geological timescale the Statherian period), photosynthesis had long since evolved, organisms which used it supported by the constant stream of sunlight hitting the Earth for half of every day. There was still some time before any pressure to evolve predation came into existence.
Meanwhile, Vagans, with life supported by geological activity creating the substances they needed to survive, had quite immediate pressure for life to evolve predation as that geological activity began to calm down. Predation seemed to have two main advantages. Firstly, not all of the organisms had to share the precious compounds essential to chemosynthesis. Only those at the base of the food chain did. Secondly, it apparently meant that you yourself had a steady supply of food. The second was wrong.
By the end of the Palaeothermozoan era, a crisis was brought upon all life on Vagans. Life had experienced its first mass extinction due to an extreme excess of predation. The Cryophilia, mostly oblivious to this crisis because of there large numbers, were unaffected. But their sister group, the Thermophilia, faced near extinction on multiple occasions. Most of what remained of the Thermophilia were some of the original secondary consumers, now feeding on the Cryophilia which were left untouched.
The Thermophilia, however, would never invent anything in the way of chemosynthesis as efficient as the Cryophilia. What they would end up doing, through the entirety of the Mesothermozoan era and beyond, is stacking up the food chain once again, smaller at every level, but still effective, up to eight or so layers. Vagans’ organisms knew not to waste any resources or energy in the near absence of many essential compounds. This meant that over half of the energy from each level was passed onto the next level. In some ecosystems, the predators were only slightly outnumbered by the prey. Yet somehow, it managed to remain stable. And so, Vagans' extremely and overly complicated food web was born.