Alternate Planets, Suns, Stars, and Solar Systems Thread

crossposting from the map thread
Earth 5,757,738,947 (Africa Uber Alles)
A strangely convergent world, where changes in paleotectonics have lead to the African continent being the only continent to rise fully above the ocean. Industrial advances in the Asian archipelagos have thrust the world into the modern age at last, and as it plunges into war, men fear what these new weapons will do.



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The Central Solar System (once called the Inner Solar System, until people realized how crazy the space beyond Neptune really was) is defined as the region extending from the Sun to the Junoan orbit. Here are all the major planets and bodies that make up this place, in their natural state before human expansion (but I'll give a quick description of who colonized it and the culture of the places).

The most dominant body of the solar system is the sun, officially designated in the European continent as Sol, although everyone up until the expansion to the outer stars of the solar system called it the sun. Sol is a G2V type star, which is the largest in the system and bigger than 90% of other stars. It is a massive 1,392,700 kilometers across, much, much bigger than the rest of the solar system combined. The Sun was kinda/sorta colonized by weird sun worshiping cults, manufacturing companies in need of energy and daredevils from the rest of the solar system. They mainly live in orbital habitats.

Next to the sun, at around 0.05 AU is the Apollo Belt, a group of small, scorched planetoids orbiting very close to the star. The largest of them is the very small dwarf planet Apollo, which is about 761 km across, followed by Tonatiuh, Aetheon and Pyrois, each of which are less than two hundred kilometers across. The rest are very small, but are still home to resources rivaling the much bigger Kemtoid belt. These planetoids are believed to have come from an old planet breaking up near the sun or probably from Apollo itself. Like the sun, the belt was colonized mainly by companies from all over and gold diggers who heard about the materials there.

Vulcan is the first actual planet from the sun, and it is a pretty cool place. The planet is tidally locked to the sun, with a lava ocean known as Mare Pandoris facing the sun. It has a small atmosphere of choking hot carbon dioxide, along with some rock vapor. Yes, rock vapor, and this tends to rain as boiling hot rocks on the far side of the planet. The sun also squeezes Vulcan to immense degrees, causing volcanoes (no pun intended) to erupt regularly. Despite being a literal hell, Vulcan is home to immense resources beyond imagining, having massive amounts of diamonds, gold, platinum and many other goodies, making Vulcan worth the challenge to mine. Vulcan is a little bigger than Earth, at around 14,476 km, but is twice as massive. It zips around the sun having an orbit of only 25 days, and it lies 0.147 AU from the star that tortures it. Vulcan was colonized by Germanic Europeans, Mercurians and Selenites. Its culture really values toughness and respect, and the planet was subjugated by Mercurian corporations for a while. Oh yeah, Vulcanian humans are short and stocky due to the immense gravity of the planet, and think of themselves as dwarves.

Mercury is the next planet, and it is basically a calm version of Vulcan, although it is home to less resources and is much smaller. The planet is home to gargantuan cave systems, tunneling deep into the planet. Mercury has no atmosphere, which means that the planet is full of craters that cover it many layers deep. The planet is actually pretty small, at only 4,879 km, and orbits around 0.32 AU from the sun. Mercury has a bit of an eccentric orbit, generally wobbling around the sun more than the other planets. Mercury was colonies by the Chinese, Middle Easterners, Indians and Americans, and it is society is very <s>corporatist</s>, technophilic, superstitious and religious.

The next planet is Minerva (OTL Venus, ITTL Venus is up later), which is a roughly Earth sized planet covered in a thick layer of clouds made up of Carbon Dioxide. Minerva is home to intense pressures at its surface, and it is very hot, although not so much as Vulcan. The planet is geologically active, and has a very long rotation, and its day is longer than its year. Minerva orbits at 0.55 AU, and is 12,103 km in diameter, although it is half the mass of Earth. Minerva was initially colonized by a ragtag of groups from Mars, Luna and Mercury, and then was 'recolonized' by Africans who settled on the planet once the terraforming was complete (the terraforming was done entirely by African corporations, so there's that).

Mars is the next planet, and it is probably the most Earth Like of the main planets, with oceans and land. It is home to some very primordial life, such as bacteria and some more evolved creatures, which are basically like Jellyfish on Earth. Mars is well known for its red oceans, which are full of iron and other chemicals. The planet is similar to Earth in pressure, is a little hotter than Earth in temperature but is home to toxic chemicals in the atmosphere. Mars is 11,788 km in diameter and is 0.85 AU from the sun. The planet has two moons, Phobos and Deimos. They are 1,316 and 1,406 km in diameter respectively, and they are both generally made up of rock and ice, with no atmospheres unlike Luna. I made a post on colonial Mars which you can check out here:, but as of 2361, they have turned out very conservative in nearly every aspect.

Earth is the fifth planet from the sun, and the homeworld of humanity and the majority of other races. It is home to oceans, land, ice sheets and a vast diversity of life, more than any other planet. The planet is 12,742 km in diameter and orbits 1 AU from the sun (the AU is based off of this measurement). Humanity evolved on Earth, and formed many great empires, and first took to the stars here. Earth was cool until WW6 caused Kessler Syndrome and the Selenites got involved in ruining it.

Orbiting Earth is the moon Luna, a bizarre but surprisingly habitable world. Luna is covered in a dense layer of mist and clouds, giving it a whitish appearance from Earth. Under the mist, lies many mountains and small lakes, although underneath them is a massive biological network made up of fungal like organisms tunneling deep into the planet. Luna's atmosphere is fine for humans, although there is too much oxygen. The moon is tidally locked to Earth, with days and nights 15 days long, orbiting 413,399 km from Earth. The moon is 3,514 km in diameter, although the layered fungal canopies give it a lot of land area. Luna was mainly colonized by North Americans, Europeans and East Asians.

Venus is the next planet from the sun, covered in a massive ice sheet, as it had been for billions of years. The planet is intensely reflective, appearing as a bright star from Earth, even more so than Mars, which Earth is closer to. Venus is home to a decent atmosphere, although its pressure is a little weak, and its atmosphere does not have much oxygen. The planet is still cold, at around Antarctic temperatures. It has some very basic bacterial life, although this still is not enough for oxygenation. Venus has two moons, Adonis and Cupid. Adonis is the smaller one, orbiting closer to Venus, and it is basically a captured object from the kemtoid belt. Cupid is the bigger one, orbiting farther out. Venus is 10,753 km in diameter and orbits 1.86 AU from the sun. Venus was mainly colonized by the American-Chinese lead Pacific Sphere alliance, and they became one of the nicest places to live in the system.

Juno is the next planet in, and it is quite an interesting world. The planet is a gas dwarf, with an immense atmosphere making up half of its mass, greatly decreasing its density. The atmosphere is mainly made up of hydrogen, and looks green and yellow from space. Juno orbits at 2.21 AU, right next to the Kemtoid belt. It has several moons, most of which are captured Kemtoids, the biggest ones being Bellona, Hebe, Eris, Eileithyia and Enyo. These are no more than 400 km across. Juno was colonized by a lot of random groups which each took a moon for themselves, and decided to coexist.

Orbiting ahead and behind Juno, the Ceres and Vesta fields act as Lagrangian companions to the planet. These fields are made up of many captured planetoids centered around a large planeload, those being Ceres and Vesta themselves, each of them being 1,300 km across (bigger than any object in the Kemtoid belt). They are considered to be disjointed from the belt, although they regularly overlap. Ceres was colonized by former Soviet countries and Vesta was colonized by the Japanese and South Americans.
Oh, this is really neat! I appreciate that you kept Venus intact, and of course the updated tally of 6 and a half (up from 2 and a half) major female names in the inner system. I find the minor moon masses a little odd- I think some of them suggest a mainly icy composition for places where ice would sublimate away quickly. I also think Eris is massive enough to be spherical, but it's definitely marginal. Juno reminds me of a thing @deleonism and I did- we also had a green gas dwarf named Juno!

Thinking about the "Mars as big as Moon" hoax, I was wondering what the actual effects would be of a Mars-sized body orbiting roughly twice as far from Earth as the Moon. Would this have any significant effects on Earth and the Moon (such as increased volcanism and convection, higher tides, etc) or would the distance be enough to effectively cancel out any gravitational effect of alt-Mars on Earth? Additionally, what if rather than appearing to be the same size as the Moon, alt-Mars orbited out far enough to appear only half its size, or a quarter, or an eighth?
This tide calculator seems to think the tides would be comparable, even a little weaker!
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Ea, Our Second Chance

Background for a speculative biology/future history project I've been working on for a while. I've been posting it on the SpecEvo forum, though I'm considering parallel-posting it here on AltHistory as well.


The solar system of Utu, Ea's star. Mass measures are given in the picture as Earth's-masses (Me), 1 Me being about 6.0 million billion billion kg; distances are given in astronomical units (AU), 1 AU being equivalent to Earth's average distance from the Sun, or about 150 million km. Body sizes are proportional to each other, as are distances between bodies, but sizes and distances are not proportional to each other (if they were, even the star would be just barely visible).

As a G4-class star, Utu is somewhat smaller and colder than our Sun, which is a G2-class star (Utu has a radius of 650,000 km and a surface temperature of 5530 K, whereas the Sun has a radius of 700,000 km and a surface temperature of 5778 K).
In broad strokes, Utu's system is similar to our own, if slightly smaller, with a number of rocky planets surrounded by gas giants on wider orbits. The outer gas giants protect the inner planet from major meteorite impact by absorbing or deflecting most objects on irregular orbits, or by capturing them as moons.

Asherah (0.38 Me, 0.64 AU) is the closest planet to Utu. In its formation it was closer still; as the high temperatures slowed the consolidation of its crust, its surface is now covered in crystals, mainly quartz, that make it highly reflective. After the moons Nanna and Ereshkigal, it's the brightest object in Ea's night sky.
Ea (0.64 Me, 1.03 AU) is the only planet in the system with liquid water oceans and an oxygen-rich atmosphere. As such, it was chosen for human colonization. Its native red flora is well visible from space.
Attis (0.18 Me, 1.9 AU) and Cybele (0.31 Me, 1.9 AU) are twin planets that orbit around each other as they revolve around Utu. The tidal forces due to each other's gravity deform and fissure the crust (compare Jupiter's moon Io). They are being considered for mining because of the deposits of heavy radioactive metals brought to surface by this process.
Dagon (0.79 Me, 2.6 AU) is the farthest rocky planet. Like Venus, it has a hot core but no significant tectonic activity; instead, pressure builds up for hundreds of millions of years until it is released in a planet-wide eruption that melts most of the crust. Today the surface is frozen and static, but the immense scars of the last eruption are still visible. Thanks to the periodic outgassing, it's the only rocky planet in the system other than Ea with a significant atmosphere.
Bel (256 Me, 6.1 AU) is the first gas giant, and the only planet of Utu's system with visible rings. It's mostly composed of hydrogen, helium, and ammonia, and its surface, like Jupiter's, is divided in parallel belts of alternately rising and falling gases (similarly to what occurs in Ea's own atmosphere).
Marduk (298 Me, 13.2 AU) is the largest planet in the system. Its atmosphere appears bluish due to a presence of methane, which glows where it's ionized by electric storms. A counterclockwise cyclone, known as the Eye of Marduk, persists in the northern hemisphere.
Ashur (156 Me, 21.8 AU) is the farthest planet of Utu's system. At the present is poorly studied.
The orbit of Ashur was reached just before the Planetary War by the Hanno 3 probe. The further regions of Utu's system, containing a large number of dwarf planets, comets, and other such objects, are to date relatively unknown.


Three hundred years have passed since we've last heard of Earth.

We don't know where to look or listen in the night sky, and all our radiotelescopes haven't caught so much as a whisper from any direction. As far as we can tell, every single human that lives, lives here on Ea, where the starship brought us so many generations ago. And when one considers the state of our former planet at the time of our departure, this statement is likely to be true in the most literal sense.

We don't even know how far it traveled, or in what direction. How many centuries did it spend cruising through the void with its irreplaceable cargo, before its thousand sensors told it of the presence of an Earth-like planet in this corner of the galaxy? The navigation centers, consumed by the rigors of space, were of little use; and once the pods descended on the parched surface, quickly sacrificed by the travellers to survive those first terrible years, the starship was a distant concern. For centuries it hovered silently over Ea, burning red at dawn and sunset, shining with reflected light in the night-time, watching over us as it had during our long sleep.

But this is no cause for sadness; as much as our ancestors loved their green world, we have found reason to love our own red one.

We know much about Earth, of course – we saved the records, the documents, the encyclopedias, the art catalogues. We know about the Sun, the Moon, and Mars. We know about the Sahara, the Amazon, and the Great Barrier Reef. We know about elephants, whale sharks, and hummingbirds. We know about Jesus, Buddha, and Muhammad. We know about Napoleon, Hitler, and Genghis Khan. But few of us know Earth, the world that was. Very few, those ten thousand who first stumbled out on the yellow sands of Ea, still dazed from cryopreservation – or the even fewer who remain, some living quietly in unknown corners of the planet, some guiding our societies with their peerless wisdom.

We had hoped that none of the tragedies of Earth would repeat. Yet before the pod shields had cooled we began to argue about the best way to live, and words quickly gave way to weapons. The most honorable solution we found was to part ways with each other: there was a whole planet to fill, beautiful and untouched, and we were few, then. People were allowed to pick what sort of society they would rather join, and eventually great nations formed. Some built themselves a paradise of earthly pleasures, others find fulfillment in industry and creation; some placed their trust in the Creator of all worlds, others sharpen their minds to carve truth out of confusion; some find comfort in the protection of a wise leader or in the provisions of bountiful nature, others take pride in tracing their own path in the world.

Most of us, sitting here, remember well the horrors of the Planetary War. But a greater number of us, I hope, remember the promise we've all made afterward. Seven powers shall share this world as equals, each managing its domain after its own conscience, each agreeing to let the others do the same.

We may not know Earth anymore, but we have begun knowing Ea. Much of it we have lost, replaced with what we remember of Earth. This was a cold and arid place, we were told; so we blasted apart the polar caps, drilled boreholes through the crust, and scattered to the wind all sorts of seeds, spores, and eggs, to make it more like the world that was. We were anxious to overcome the new challenges, from the ruthless global winter to the marine eruptions that troubled our fleets. We were adrift and alone, and we clung to whatever reminded us most of home. Only recently we've started truly to appreciate the world that is. The world of red forests and blue flesh, the world of floating jungles and living stones that once baffled us so much. This too was a mistake of our forefathers; this too is a pledge to do better.

Here we are on Ea, second planet from Utu, our second chance, perhaps not yet definitively wasted. We have all made a leap of faith through the unknown, searching for the deepest unity of our species, for a responsible place in the universe, for a deeper understanding of the cosmos we share, to pursue growth and excellence, to experience happiness without compromise, to exercise our capacity to live and create, to honor the memory of our ancestors; any of these things, and all together, depending on what is in our heart and our mind.

Let us toast these three centuries of life, then, and let the next ones be better still.

– First Speaker Irene Järvinen, address to the Planetary Assembly, Landing Point, opening toast for the Third Centenary (300 AL)


Agarthanon, the origin world

Agarthanon was terraformed roughly 2 million years ago by an unknown race of beings or entities in space. Agarthanon forms a binary pair with the planet known as Enok. The 2 planets revolved around each other every 27 days. They seeded it with human life, its origins are unclear. Over the eons, the people of Agarthanon developed through the stone age, bronze age, iron age, etc. They still kept a sleep schedule like that of our Earth, as their biological clocks were roughly aligned to 24 hours like ours but over time, they evolved. The people of this world also had access to a degree of magic, which only increased their power.

By the time of the modern era (roughly our technology) the planet was heavily polluted. The planet didn't develop the sort of anti-trust laws as our Earth did, so big business boomed rapidly at the expense of the life on this planet. Rivers ran polluted. Oceans were polluted with chemicals from industrial plants. Workers worked without pay, and all of the nations on the planet were roughly controlled by the same few businesses. They had set up colonies on the other planet of Enok, but only then it was rudimentary. People's lives were miserable.

There were several worker's uprisings, the workers themselves taking upon a new ideology than the planet's ruling class in order to take down the corrupt establishment. This was called Equalism. Equalism advocated for the equality of the working class and the business owner, much like that of our world's communism. Many of these revolutions failed, but one succeeded. The one that Starlight started herself. Starlight wasn't like the others. While the others were focused on idealism and utopianism, she realized that the only way to win this war was through sheer brutality and destruction. By her order, many of the ruling elites were assassinated and the Agarthanon civil war began.

The civil war would last several years and do massive damage to the planets landscape which was battered by bombs and magical weaponry. Eventually, the Equalists came out on top, and so the Equalist Union was born. Their rule at first, was stable. The people were hungry, starving, and begging for a change, and Starlight brought that to them. She managed to have the planet repaired somewhat but many areas were lost in the devastation. It was decided that they would flee the planet as attempts to restore the environment had completely failed. Massive starships were built with the last remaining resources.

Not all could board these starships, and so the second Agarthanon civil war began. Many had realized that Starlight's ways of governing were not much better than the previous. And using their own resources, from what little had left, a few of them managed to escape to the nearby planet of Daeldrum. A lush, green, and ripe world for colonization. They crash landed on the surface and would lay the basis for humanity on Daeldrum, and would soon lose their history and revert to the stone and tribal ages. The Equalists knew this, and as an act of mercy, proceeded to leave the escaped people alone on the surface...but that'd contradict her next move.

While on Agarthanon, Starlight with remaining armies had fallen back towards the area of the starships that were ready to be launched. Defending them with their last breathe, the army cleared the way for the launches to begin. Starlight and her elites, as well as the remaining army had blasted off, and fled the planet. While in orbit, Starlight observed the devastation of the world from above.

Agarthanon was dead, and those who has thwarted her had layed below. On her command, the starships had bombarded the inhabited areas and launch platform from the surface to ensure that no human life would remain on the planet. She also wanted to make those who oppose her suffer, and with that, all human life went extinct on the planet. Those who survived the bombs didn't survive the starvation, death, and disease which came after ward. The bombs had caused an Earthquake on the fault lines of the planet which released toxic gases from within the planet's crust. Then, the gasses spread throughout the planet and rendered a lot of the planet extinct to life. Only the most hardy of life would survive.

The starships left the solar system and went to experiment with technology, eventually coming up with ways to enter into other dimensions, perfect their magic, and create new technology that suited their ways. During their time in space, Starlight became much more ruthless and power hungry, and all of her opponents were gone.
Some changes to the Solar System provides us with three habitable world's. :p

Solar System:

Mars / Moon / Moon
Mars is in a closer orbit coupled with a full-sized moon and a diminutive asteroid as well as the positive effects of an active magnetic core have made incredible changes to Mars. No longer a dying world the red planet is still red, but green and blue also invade the surface. With a gravity about half that of Earth's, and a atmosphere roughly comparable to our own Mars is a lush planet with large Iron-rich deserts, and the solar system's largest active super volcano.

Mars itself has an day/night cycle of 25.75 hours, nearly identical to that of the Earth.

Earth / Moon
- Same as modern day

Venus / rings / Moon
The twin of Earth, Venus is the fourth planet from the sun and is very temperate - a little warmer then Earth because of the more robust greenhouse gas effect, but still quite habitable.

Scientists believe that the ring system of Venus was formed after two Moon-sized object collided hundreds of millions of years ago. The asteroid debree couldn’t reform into a moon, and instead became trapped in a circularized orbit around the planet Venus. Venus is the only Terrestrial planet in our solar system to have developed rings like the outer gas giants, and even though the rings have consolidated their orbit at an equatorial 125 km circular orbit they are visible from almost everywhere on the surface of the planet.

Venus itself has a uninhabitable moon, approximately the same size as our own Moon. This moon has over the eons stabilized the rotation of Venus, and allowed an 28 hour "day." Venus is a wet jungle world, drier then Earth but wetter then Mars or Vega. Scientists have calculated that 65% of Venus is covered by water, and that ninety-three percent of the water on Venus is salt water. Air pressure and Gravity are both approximately 85% that of "normal sea-level" conditions on Earth.

Vega / captured asteroids
Vega is the Mars analogue planet, dead or dying - just on the border of the inner habitable zone, and close enough to the asteroid belt to guarantee the capture of a number of asteroids from the main belt Vega is about as inhospitable as they come. Vega has no active core, and it has a surface water percentage of 15% liquid water on its surface which is quickly evaporating along with the decaying atmosphere.

Asteroid Belt





Why invert the placement of Venus and Mars? Why not keep Venus as #2 planet but have the collision involve Venus itself with, say, a stray asteroid or another moon with a degrading orbit. That collision causes Venus to eject and lose alot of its atmosphere (thereby losing enough greenhouse gases and lowering atmospheric pressure that, in turn, lowers atmospheric temps or prevents the OTL runaway greenhouse effect)-- but the collision still creates a ring system. (Perhaps the ring system could even have enough of an albedo effect to prevent the greenhouse effect from resuming.) Afterall, Mars,with a magnetic field, would have retained is former atmosphere and, thus, also retained its surface water. This translates to significantly increased atmospheric pressure and higher temps.

As for Vega, I had a cousin who drove a Vega. It too was a worthless POS, just like your Vega.

At first glance, I think you'll have a warmer Antarctica and a colder Europe. The prevalence of large inland seas seems likely to act as a regulator on continental climates- expect Mediterranean-analogues, probably.

concur on the colder europe, that continent in the north atlantic prevents not only the gulfstream going east, but also a deep haline conveyor forming to the south of greenland. same with the islands to the south of south-africa, which might also block thermohaline circulation, although some stream might form more to the south.
the whole gulfstream thing might be restricted to the southern hemisphere, and maybe the pacific basin
i think antarctica is probably the same, there seems to be enough separation at cape horn (situation looks like otl) to allow the antarctic circum-polar current to form
Oh, the tight constriction of the South America/Antarctica gap leaped out at me, but I don't think it means Antarctica is significantly warmer. Note it can be warmer, and still not melt, and having it not melt is the main thing, otherwise if it were "green" because the ice melted we have to assume either less ocean water on this planet to start with, or more continental rock piled higher to get the same continent areas, roughly.
p.s. I think we can safely call that particular Island 'Atlantis' since the myth appears to have been firmly established even prior to the Imperial Roman Era - which seems to represent the point of divergence for this particular Extraterrestrial Roma - although it's interesting to wonder what names the local Imperium has hung on the other island real estate not known to Our World!:)
Oh yes!

Let me take a stab at the alternate history of this planet, in the context of the Trek setting it came from. For this one episode, we hear about some sociological law of parallel development not referred to generally in the rest of the franchise history, but this is apparently a case of unusually close parallelism. These Romans might even be a branch of Terran humanity settled on this planet say 10,000 years ago but we can just as well assume they are home-grown humanoids, it makes little difference (except maybe theologically, for those who remember exactly how the episode "Bread and Circuses" ends, with Uhura's insight!)

So, looking at the map, from a Eurocentric POV as is suggested by the implication that the Romans gradually conquered and Latinized the whole damn planet pole to pole, I notice that the outlet into the Mediterranean is wider, but that in itself does not suggest anything much to me on the time scale of human history. (I think we can assume this planet has ice ages and is in an interglacial pretty closely synched with Earth's own cycle). Analogs of Greece and Italy are there, and though not shown on the map, I think we can assume a river analogous to the Nile is there too. So we have Egypt, the Levant as the west end of a presumptive Fertile Crescent since Iraq appears to be there, presumably Iranian/Persian highlands. What doesn't exist is the Red and Black Seas! In place of the latter the Caspian appears to be larger, and connected via a wide channel to the Persian Gulf. So Anatolia, which the OTL Terran Greeks called "Asia," is integral with the European plains shading into steppes. And there is this honking inland sea north of Iran, and separating Iran from the shore lands of Mesopotamia.

Meanwhile we can presume Africa south of the Med dries out into a Sahara that stretches straight into Arabia, no Red Sea, no Mecca, no Yemen. (Actually, there is a little bay where the mouth of the Red Sea is on Earth, so maybe a Yemen. But separated by hard desert with no better route than going overland to the upper Nile for contact between this "Punt" region including later Ethiopia and the Med world).

I think the preconditions of a Hellenic/Hellenistic history laying the groundwork for ATL Rome exist well enough; we can see a Persian power rising (crossing the Persian Gulf channel instead of descending directly from the Persian highlands, I suppose via having politically secured an ally on the east shore) and a Hellenic confederation to resist its advance--I assume Anatolia exists as a highland zone shading into grassland to the north, so the Persians would tend to want to stick to Anatolia rather than expand north and east--at this point. Meanwhile they are also diverted to spread north along the Super-Caspian but not to go west directly from there I suppose. This shields all Europe from exposure to steppe nomads.

So we can have some version of Alexander, Hellenistic kingdoms, and the Romans first consolidating a portion of Italy, taking on Carthage in North Africa, eventually getting hegemony over Italy and all points west, and turning their attention to adventures in the eastern Med. Unlike OTL, the Eastern Med is not as rich because presumably there is less regional spice production and less trade in it, though what trade comes comes either via Mesopotamia and thence into Syria, or by Arab controlled desert overland routes. Roman society is drawn eastward but not as much, and not so much absorbed and anchored in eastern Med predecessor societies.

OTOH, for a time, prospects to the west and north are more limited. As noted, the Gulf stream is trapped between North America--I will henceforth substitute the term "Hesperia" for the Americas-- and Atlantis, and the bodies of water to the east are colder. Scandinavia is probably uninhabitable save on the most marginal terms, essentially Greater Sami-land; the British Isles, which appear to be farther north and with Ireland reduced in size, are very marginal; European coasts north of Iberia are distinctly colder, I'd say the coasts and lands south of Amorica (modern Britanny) are probably almost as warm as OTL, though somewhat colder and poorer, but around that mid-Gaulish latitude, the climate steeply worsens; the southern Baltic shore is scarcely better than say Labrador. There are "barbarians" north and east of the Rhine, but in fewer numbers and less developed.

As OTL then the Romans secure Gaul, and set up a watch on the Rhine, but stop there, and are rarely bothered much on this front. There is no attempt to Romanize Britain! Not in early centuries anyway.

The legions are accustomed to be offered land to colonize after their stint of service. In this Empire, such land in Iberia and North Africa and Gaul is quickly used up, but northeast of Greece there is Dacia and the lands beyond. (I believe the rivers that flow into the Black Sea on Earth here flow into a large river flowing out the Hellespont). The trouble with this land east of the Carpathians and north of Anatolia is twofold--one it is dryer with a somewhat less stable climate than these lands have in the west OTL, and two, it is exposed to a vast plain where hostile Central Asian peoples would contest it, but now it is instead exposed to Persian hostility as they or various successors control the arm of the Indian Ocean reaching up into the western boundary of Asia (I guess this sea will eventually be the definition of the boundary between Europe and Asia). Note that the vast steppe of OTL is broken up by the Super-Caspian and another inland sea connecting to the Pacific north of China.

Meanwhile, the northwest of the Empire is a rustic backwater, but some coastal trade exists, north of the Limnes to the impoverished tribes of the North Sea coast and Baltic. I presume despite obvious difficulties the southern reaches of Great Britain have tin in the southwest and trade has reached that far north; at a late date the Empire decides to consolidate all this, not putting too much effort into it, mainly focused on British tin.

At some point someone stumbles on the east coast of Atlantis. Eastern Atlantis is not very attractive, but desultory exploration reveals it gets better the farther south one goes, and rounding the southern cape, it is a lot warmer and wetter on the west coast, due to the Gulf Stream flowing into the narrow seas there. This is fortunate because the settlement of the zone north of Anatolia has been stagnating. Actually the land gets better there the farther east one goes due to the SuperCaspian sea, but the Persians are there and are hostile. So the Legions are somewhat preoccupied and there are manpower drafts on the western Empire, but the government in Rome can see possibilities in developing Atlantis and slow down their drive eastward in central Eurasia, and divert population northwest into Atlantis.

Atlantis, I would think, has already been settled in a sense, but only recently and somewhat, by Arctic Native Hesperians of an Inuit type filtering south from Greenland. Let us suppose that the peoples who settled the Hesperias happen to have lucked into stronger genetic bases for resistance to epidemic diseases, but still, the New World peoples will be pretty vulnerable to Old World diseases. Still around this time (equivalent to 500 CE or so I guess) the Roman world is less exposed and has had fewer plagues, and the process of colonizing Atlantis is fairly slow, so the native Atlanteans, who are small in number due to being mostly gatherer-hunters with only a few agricultural peoples and those just developing villages and so forth, undergo a demographic collapse, but less drastic than we'd expect OTL, and the survivors largely incorporate into Roman society.

The settling of Atlantis, concentrating as it does on the western Atlantean coast, soon leads to contact with North Hesperia, and so the Romans have launched a systematic expansionist drive westward. Perhaps with a slower progress, an analogy to the US Federal government encourages and sustains this process--early settlers are likely to become the gentry families of new provinces with autonomy, and Rome will appoint reliable locals to govern in the name of the Emperor, demanding tribute in the forms of money, and some Legionary manpower. Thus the stage is set for the very slow, gradual absorption of North Hesperia into the Roman sphere. The main settle-and-develop thrust is along the coast and into the eastern part of the Mississippi valley and Great Lakes, but it doesn't take long (well not more than a few centuries) for MesoHesperia to be "discovered." (It will help if the process of Roman expansion over the Appalachians is gradual enough that Mississippi valley civilizations do not collapse as rapidly and completely, and contact with these people communicate rumors of the rich cites far across the Gulf of Mexico).

Colonial policy there will be more along Portuguese lines--send some expeditions to grab some strongholds and seek regional allies for both trade and political advance.

The Atlantean enterprise raises questions of what else might lurk out in the seas, and expeditions southward along the African coast, motivated in part by the reasoning that circumnavigating Africa could connect to rich trade with the fabled Indian Ocean area, push on past the Saharan coast to "discover" West Africa, a region not entirely unknown.

But note that while by this time OTL, dromedary camels, domesticated in Somalia, had spread in use to Arabs, here there is no Red Sea and contact with that corner of east Africa is very sparse; we might suppose the use of dromedaries is spreading along the south Arabian coast but the great numbers of Arabs, and the social conditions leading to the foundation of Islam, do not exist anywhere near the Roman sphere; both Rome and the successive Persian and steppe peoples to the north know of Arabs only by a few trade kingdoms running small masses of very rare spices overland across a desert worse than OTL; most of this trade goes to the Persian Gulf and is monopolized by the Persians. So caravans across the Sahara are impeded. Contacting West Africa by sea is a big deal.

In Hesperia and in western Africa, the pattern is again the Portuguese one in these low latitudes, the Romans send ships south and west to set up client relations and gradually Romanize their contacts. Setting up bases southward on the African coast, the Romans don't find it nearly as dangerous a "fever coast" as they might a thousand years later--most decimating diseases that spread in the region they brought themselves. But they aren't much inclined to colonize inland, leaving this to their regional clients.

Getting down to South Africa though, they find "Mediterranean" climate much more appealing, and around OTL Cape Town and other ports they set up spreading settler colonies, gradually inducting native southern African peoples into their system.

Obviously if the Romans are expanding on the northeast of the Hesperias, and sending expeditionary trade/war missions south to the Antilles and into MesoAmerica, they are going to gradually feel their way to South Hesperia that way. Meanwhile, attempting to reach West Africa they will surely find themselves forced out west into the Atlantic to look for favorable winds and currents (the African coastal winds and currents flow northward). So they are liable to stumble on eastern Brazil sooner or later. This will lead them to discover the inland sea of Amazonia eventually. If Romans from the swathe of settlements from the northeast of America, Atlantis, the Med or the trans-Anatolian zone are uninterested in settling or manning outposts in such tropical country, by this point quite a few fairly Romanized West Africans (noting there is another isolated inland sea where Angola is OTL) might be interested. Will there be tropical cultivator peoples in the various rivers feeding into the Amazonian bays? I think it quite likely, and there might be a fair amount of civilization there too. Transplanting Amazonian crops into Africa could permit a surge in Romanized African population, and a certain number of these Africans will invade and settle the South American tropics, probably synergizing with disease-decimated but viable native societies. This gives a straightforward link to the Andean region; on the west side of the Andean ridge we have every reason to expect the trade-based societies that developed on Earth OTL to be forming there too.

Rome then is acquiring all sorts of deep pockets of manpower and wealth in the processes of absorbing western Africa, Atlantis, and the rest of the New World, essentially unchecked.

Realistically we'd assume at some point long before this, the limited communications and other liabilities of pre-gunpowder era empires would long ago have led to the Roman entity splitting up. But the TOS episode presents us with a unified world Empire, apparently. We can argue is otherwise and the canon episode involved the crew members dealing with just a fraction of world power, or we can suggest Roman imperialism is a recent reconstruction and a recent conquest by a Mediterranean based neo-Rome. But the straightforward way to watch the episode I always thought was that Rome Never Fell, so we have to assume that somehow or other the Romans gradually evolved their rather miserable political system into something stable that kept commanding allegiance for many thousands of years. I've offered some vague suggestions along those lines, that it has to do with maintaining the Legions by keeping up the practice of guaranteeing them decent new lands to colonize. It is still a staggering accomplishment, to keep loyalty and effective coordination running through the city of Rome all this time! Note that by pointing out the Black and Red seas do not exist, I think I can better justify the Imperials never abandoning ancient Rome itself as their political and cultural center; the riches of the East did not beckon; the defense of the purported northeastern colonial zone is a job largely for the settled Legionary population itself, with enough aid coming from the west to justify their ongoing loyalty, and soon gets counterbalanced by the Atlantis-Hesperia venture.

So I think around 1000 CE, we'd have the Latinization of North Hesperia east of the Mississippi, a long establishment of ties and enhancement of pro-Roman clients in MesoHesperia and along the West African coast, and a pretty secure foothold on South Africa and ventures beyond the Madagascar Peninsula (see the map!) and into the Indian Ocean.

At this point, the Empire could also have resumed the pressure on reaching and securing the SuperCaspian--I suggest by having gradually reached north toward the Baltic and Romanizing native peoples living in what we'd call Great Russia, who advance eastward on the taiga boundaries to reach the northwest reaches of the Super-Caspian and secure its northern shorelands back to the northern forests, and then with rising intensity of Roman aid, fight their way down the western shore toward the southern coastal centers of local power, with the Empire also raising the pressure from the southwest. If the Persians have not been controlling the south shore all along, I daresay a regional rival succumbs and judges the Persians the lesser evil, and invites in Persian power to hold against Rome. While locked in this struggle the Romans are meanwhile coming into the Indian Ocean around Africa.

How long would it take the Romans to reach the Pacific? I think their fastest route is via a Central Hesperian client state that Latinizes pretty readily, probably in the narrower parts like Panama or the Nicaraguan route. It would take a while to filter through in Mexica proper, and while individual Romans might find their way from Amazonian western reaches, up over Andean passes to coastal cities on the Pacific, I don't think there is much promise of rapid movement of either goods or Roman forces that way. A Romanized Nicaragua is my bet. Sending modern ships up and down the Pacific coast is the best way to link up to Andean trade. But the Roman ships of around 1000 CE would not be much for deep Pacific sailing. Their knowledge of cosmology tells them their planet is round and they have some idea of where China is and where they are on a globe, but that tells them to take a great circle route dead against the prevailing currents that run along the northwest Hesperian coast. Contact with Polynesians might lead them on a different route, through the South Pacific and toward the Philippines in the wake of Magellan.

But the surer thing is to instead push around Africa, and seek out the markets of the Persian Gulf and India.

Again looking at the map, I observe the Super Caspian is actually an arm of the Persian Gulf, and that Mesopotamia was exposed to the middle reaches of this channel. Presumably the ATL-Persians are seafarers too, at least in these protected waters. (It might therefore have been reasonable for the Persians to prevail over Rome, but again the TOS canon episode has Rome come out on top, so I have been narrating it that way, so presumably the Persians never fostered a major surge of power south to east Africa by sea).

The Romans know they have no welcome in Persian Gulf ports so they steer east to India, where they again take the Portuguese style route of securing some strongholds and cultivating relations with chosen regional allies. From there they leapfrog on to Southeast Asia and Nusantara generally, which seem overall likely to be much like OTL Earth.

How likely are they to stray south and discover this world's version of Australia? It may take them remarkably long to do so, but if they do, they will find the far southwest coast extending into much more temperate climates, like that of Tasmania, and this would be their initial focus of settlement--once based there, working their way along the coasts they will find two Tasmanias, and a somewhat New Zealandish set of islands not terribly far east of these, and then up the east coast presumably find the Barrier Reef and the east Australian coast much as OTL. OTL Nusantaran peoples did not bother with trade or settlement in Australia, so it lies open for Roman incorporation I would think. A slower process and possible higher Aboriginal populations particularly in the southwest might make this a less overwhelming cultural steamroller than OTL Anglicizing the place was. But Romanize it will I think.

And so we have the Romans forcing a sea route through to China via Nusantara; Hesperian routes will develop later I think, and might start with ships that originated in South Africa and traveled east to China then setting out northward to skim along to northwest Hesperian islands and thence south along the Pacific coast down to the purported Nicaraguan port. Finding a reciprocal westward route would come later.

All this account I have left China out of it. Looking at the alternate world map, China has this big sea north of it, and islands equivalent to Japan and Korea seem to clutter up this sea's outlet to the Pacific. Han China would find on its northwest instead of open steppes, this shore covering a lot of it. Coastal Chinese people might be counted, under Imperial direction, to largely defend their own shores; China would incorporate most of the hospitable shoreline and muster sea power there to bring Korea and Japan into the broader tributary system. Basically then China would develop much as OTL; we don't have the canon TV show warrant to suppose their political solutions are far better than OTL, but certainly no reason to think they'd be worse. The Empire's successive dynasties would first consolidate their grip on the northern coast, and secure the northwest steppe boundary, then expand southward to incorporate south China, trying and sometimes succeeding in dominating Vietnam. In their most energetic phases we can suppose hegemony over Tibet and the far west securing the western end of the Silk Route will also happen, this basically brings the Chinese imperial system into contact with northern India and with the Persian system I have been presupposing.

The Chinese will have the same sort of self-satisfied disinterest in extensive relations with outsiders they had on OTL Earth; the Romans showing up belatedly at their southeastern ports will not have tremendous leverage versus longer established trade partners--but the Romans are slowly gobbling these up. The vast Roman system can scrape up a lot of silver and other precious metals the Chinese will not sneer at, as well as take over the production and trade of Nusantarian spices.

Recalling I am talking about events that might be a thousand years before the Enterprise encounters this planet in TOS, there is a long time for an end game in which the Romans gradually advance technology (much of this is actually Chinese, Indian, and Persian inventions at first, but I suppose we have to have the Romans slipping into a capitalist mentality sooner or later, and they'll internalize the accelerating ball of invention over this thousand year interim) and get a successive grip on Persian, Indian, east African, the remnants of Hesperia, the various Pacific islands, and finally, in a process I suppose would take hundreds of years, incorporate China.

It is entirely possible as noted that the planet Kirk et al got shanghaied into being gladiators on planet wide color TV was not entirely Roman ruled, that some Chinese or other superpower rival defied Rome still, but as noted my impression was otherwise.

I certainly would expect that Latin is a language very few Chinese speak proficiently, that China is a sort of satrapy of separated provinces giving nominal homage to distant Rome and with their capitals occupied by strategic numbers of western Legionaries and "advisors," but mostly with Chinese governors (who themselves do speak Latin fluently) overseeing largely traditional Confucian-imperial style bureaucracy and pulling the occasional fast one on their Roman overseers.

Something intermediate to this would be true of the former Persian zones--some, which never much liked Persian rule, would be quite heavily Latinized, others would cling to a distinctly non-Roman cultural format and give the Roman imperial authorities some headaches with occasional outbreaks of armed resistance.

So in the world at large; it is, outside the Mediterranean/European heartlands, a patchwork of more and less Romanized regions. Some former client states vigorously maintain a distinct cultural identity despite their consistent support of the Roman system; some places are deeply Latinized but also deeply resentful of this system, some less confusingly have Romanized deeply and think of themselves as basically Roman despite some of these zones being places with radically different climates and ecologies than the Mediterranean core land--there are African and South and Central Hesperian peoples who show scarcely any trace of European ancestry and live in warm humid rain forests or swamps cultivating crops and creatures no Roman would know what to do with, but growing up with Latin as their mother tongue and learning a Roman-centric history. And not far away from these centers--regions that only sullenly and partially acknowledge Imperial authority exists and pretend to be as independent of it as they can. Naturally these places are not major economic or demographic powers, or the Romans would have secured them more tightly some time back.

The whole planet at this point then is under Roman control, to the satisfaction of the Romans anyway, and "Romans" by identity span the entire ethnic spectrum of the planet. The most developed and prosperous zones are deeply Romanized, some in a mixed way, others 100 percent Latinized, in the modern mode of course.

Rome itself I imagine is some megacity the like of which we have not yet seen on our Earth, sprawling all around the ancient city core which is the domain of the central government. I'm picturing London as of 1900, Paris of 1939, Mexico City and Shanghai all jammed together with loads of major Imperial artwork monuments and a massively layered infrastructure of sewers, plumbing, light rail above and below ground, pneumatic tube networks, and relatively recent electrification and telephony all concentrated to a degree no one quite ever aspired to here on our Earth. It is sort of a 20th Century Terran analog of Trantor. All the other great cities of Earth are a bit stunted, or practically nonexistent, in its shadow; Rome relates to the planet the way Paris relates to France. (And Paris is just a town in a poorer part of Gaul, or rather in a region that has in recent centuries been developed for its industrial resources, but is not the first city of the region nor does any part of northern Gaul stand out as a focus of culture or possess much in the way of alluring charm. Paris is better off than London though; Britain is a peripheral backwater mainly known for mines, anciently for tin and more recently, via Yukon/Siberian type efforts, coal and iron. If a river analogous to the Thames even exists, the port on it has a certain importance, but not greater than closer ports to the coal and iron fields).

From the episode, indigenous technology as of the time of this limited contact was plainly equivalent to Earth's around the 1960s. At any rate, broadcast color TV was a thing, using the same sorts of studio cameras Desilu was using for the series! We can speculate on divergences--perhaps there is no knowledge of say nuclear power, the Roman Empire having prevailed in its endgame with China long before that would become a thing and with technology stagnating since. Or it could be the planet is networked with nuke plants, we don't know. Is their medicine as good as 1960s developed nations? As far as Dr McCoy is concerned there is no difference between US medicine in 1986 and the practices of the High Middle Ages, it's all horrifyingly backward witch doctor stuff to him. Do they have intercontinental jet liners, or do important Romans of the imperial governing classes and big shot merchants putter about in airships? We certainly didn't see any airships in shot, but neither did we see anything like a Boeing 707. So maybe electronics are a bit precocious, and maybe they have been for some time and the current era is one of stagnation--but I suspect the nature of the mass culture we get glimpses of, the OTL USAian style TV broadcast format, suggests overall a society not unlike the mid-20th century developed world nations, at least for the more favored of the Roman system client states (all of which I think would be formally incorporated as imperial provinces by now, probably with the more favored ones enjoying special autonomous rights, suspiciously watched over by skeptical imperial agents lest anyone stray into secession).

The analog Roman Earth then is pretty much like Earth of the 1960s in overall development, and is in an age of modernization, perhaps at a more deliberate pace than OTL 1960s-90s. Similar issues of high polarization, of favored Roman provinces that have a combination of high utility and reliable loyalty and service to the Empire having a very comfortable standard of living for large citizen middle classes and regional poverty being in closer reach to this comfortable standard, versus less favored provinces that either are simply backwaters or have a history of disloyalty and are under more punitive regimes being more "traditional" and thus much poorer; in this time a combination of opportunistic entrepreneurialism and Imperial policy is trying to modernize everywhere, but keeping a close watch on social developments and reckoning carefully how much police force they need to keep on standby should this or that zone spin out of immediate control.

The Romans have, sometime in the past, secured the whole world, more or less; the Legions, which have been somehow maintained if modernized, ceased to need to fight peer combat wars some time back, but are now instead the top layer of world police forces. As such the Empire is prudently maintaining recruitment and training at a fairly high level. Presumably OTL notions of democracy and universal justice have not developed, at least not in those exact terms--I presume no principles of civil rights check what the Imperial police can do, but they might be checked and overseen through other channels.

Again, people who have seen the episode get some canon insight into social forces that might oppose Imperial absolutism.
Do you know any internet site where you can pick a point on the map and choose it as one of the poles and then see the world with latitudes and longitudes?
Is G.Projector working out for you? I was really pleased when the "Oblique Equirectangular" option was introduced, as my Mac computer cannot run the proffered alternative program. If G.Projector isn't giving you what you wanted, try PM'ing me and I'll either coach you through it or join you in wishing for better capabilities!
Thinking about the "Mars as big as Moon" hoax, I was wondering what the actual effects would be of a Mars-sized body orbiting roughly twice as far from Earth as the Moon. Would this have any significant effects on Earth and the Moon (such as increased volcanism and convection, higher tides, etc) or would the distance be enough to effectively cancel out any gravitational effect of alt-Mars on Earth? Additionally, what if rather than appearing to be the same size as the Moon, alt-Mars orbited out far enough to appear only half its size, or a quarter, or an eighth?

An excellent rule of thumb re tidal effects: if the body looks about the same size as Earth's Moon does to us in the sky, it will be exerting about the same tidal effect as Luna does on Earth.

We can see this must be the case if all bodies were of the same density. If the body is at half the distance from Earth as Luna is, each kg of its mass has 8 times the tidal effect (because tidal effect goes as the inverse cube of distance). But if it covers the same angular span in the sky as Luna does, that must mean it has half the diameter or radius, and thus 1/8 the volume--so if it has the same density as Luna, it must have 1/8 the mass and thus the tidal effect is exactly the same.

Now look at the tidal effect the Sun has. It is roughly in the ball park of half that of Luna, and yet famously the Sun and Luna look to be the same size as seen from Earth, which is why Earth might be unique in the Galaxy for having total Solar eclipses that exactly cover the photosphere but don't cover the corona. (This is also temporary; the Moon has been receding from Earth since it formed and will recede further; fairly recently on a cosmological scale, Luna was closer, months shorter, and its disk larger than Sol as we see it, and fairly soon in the future, a matter of a million years or maybe less, it will have receded so that even a perfect total eclipse will leave some photosphere exposed and wash out any view of the corona).

OK, how dense is Luna? Looking it up, it is given as about 3.346 the density of water. What about the Sun? Again a quick look up with Google says 1.41 the density of water. So if we divide the latter by the former we get less than half, which agrees pretty neatly with the ratio of tidal forces that governs whether a tide is a spring tide or a neap tide.

So there you go; if the body looks bigger than the Moon, it is pulling harder, bearing in mind the densities of different kinds of objects can vary quite a bit. Saturn is less dense than water, I believe Earth at nearly 6 times water density is about as dense an object as we find in the Solar System. A factor of 6 fudge factor there, but recall the tidal force is inverse cube, so the cube root of 6 which is 1.817 gives the range we can fool with, which is not tremendous.

The density of Mars is given at 3.933 times that of water, so it would have to look a wee bit smaller than Luna to have the same tidal effect. To be exact, its angular size would then be 94.75 percent the apparent size of the Moon at its current distance. Mars's actual diameter is 6792 km, while Luna's is 3475 km, so it would have to be kept at 2.0627 the distance Luna is, or 780,000 km off.

We could arrive at the same ratio by simply dividing Mars's mass by Luna's and taking the cube root of that ratio of course. But I wanted to emphasize the "if it looks like Luna it has a tide like Luna's, if it has the same density as Luna" rule of thumb, since most bodies we'd want to fool around with would be rocky things with densities in the close ballpark of Luna's. We can have a bigger disk with the same tide if our extra body is a big drop of water. But not spectacularly larger. (Other bodies than Luna would tend to be brighter, the Moon has a low albedo, but then so do small dry rocky bodies generally; give it an atmosphere, give it ice, or even Mars is brighter, so lots of bodies we might monkey with are going to shine more light when full, and few would be a lot dimmer).

So I don't think the answer you were previously given
The potential for another Permian extinction, yeah.

Was very helpful or accurate. You never mentioned bringing Mars in any closer than making it look like Luna. That far out, its effect matches the Moon.

Now clearly doubling the tide--which will happen when Luna and Mars are lined up, but when they are at right angles they actually cancel each other partially--some of the time is going to be somewhat problematic. But nothing triggering an immediate Permian extinction! Earthquakes and volcanic eruptions that might have waited a bit longer will be triggered a bit earlier, but that would be a passing effect; "annealed" as it were by this increased tide periodically, stresses will build up to a lesser level before being released, but the energy source for tectonic events remains mainly Earth's internal heat generation and flow, which remains the same. The magnitude of the events would not be greater than we'd expect, just a bit alarming to have a bunch of them happen at once. If in fact it were possible for Mars to have been orbiting Earth out there all along these past 7 or so billion years, we would mainly have the periodic double tidal pull itself to reckon with; high tides would go higher. The longer term effect is that these tides correspond to a rate of drag on Earth that drives stuff like Luna's recession from Earth; Mars would also be driven outward. Earth would be slowed down more rapidly, so if we snuck Mars in at the formation of the Earth-Moon system, Earth would now be turning more slowly. But we could propose to offset that by having Earth turning more rapidly initially I suppose.

The real killer here does not apply to your speculation in particular, but all across the board of this entire thread:

It turns out that Solar System stability is in a sense an accident. In another sense it isn't, but the point here is that we can't monkey around even a little bit with masses and positions and motions of Solar system bodies and expect the rest of the system to stay stable. Adjust things just a little bit, and we can expect that over periods of just a few million years, the planets all start getting badly out of whack and pretty soon we have stuff like Mercury crossing the current orbit of Mars and maybe getting ejected from the system completely. So moving Mars from where it is to near Earth is going to ruin the whole inner solar system.

But this is true of all the speculative alternate solar systems in this entire thread.

In fact, planetary systems around stars will probably be found in stable configurations they have been in for billions of years. But the reason for this is not that you can dump them any which way, whether we heed or scorn Bode's Law, or any other such rules of thumb, and expect them to be stable. The reason we find them in stable configurations is that over tens and hundreds of millions of years of pinballing all over the place, sooner or later the system will approach a pattern that just happens to be stable, and then it will repeat itself--this is the practical definition of stability.

So it seems that in our current state of art, we cannot well predict a stable configuration. We can have some confidence that many exist for a given set of bodies, but we don't know the rules telling us just how to line our ducks up in the right rows to achieve it.

That's why making Mars appear at 800,000 km in orbit around Earth would cause something worse than a Permian Extinction, might in fact result in Earth, Mars and Luna together getting ejected right out of the Solar system. Or drop us into an elliptical orbit that boils off our atmosphere and oceans while most of the time we freeze. Or all kinds of wacky gyrations, for tens or hundreds of millions of years to come. But not right away; it would probably be some millions of years before the nearer planets are so far out of whack they noticeably move us. Doomed we would be!

Since the whole premise of this thread ignores this deterministic chaotic consideration, I see no reason why you should be reproached in specific. Ignoring the general instability of solar systems as this thread does, the parameters you offered were quite reasonable. Mars that looks like the Moon has tides like the Moon, which aren't disastrous even if doubled. Mars backed off by another factor of two, out to say 1.6 million miles, would have only 1/8 the tidal effect of the Moon. It would throw off various processes currently governed by Lunar and Solar tide, but so what?

But if we backed Mars off that far, it would I believe fall outside Earth's Hill sphere--that is, the zone where the gravitational pull from Earth is greater than the tidal effect of the Sun. Objects outside our Hill sphere (or anywhere near this boundary in real life, I think) cannot stably orbit Earth; the Sun is more important and will dominate their motion. To be sure we know about various objects that are in resonance with Earth, which can be said in some distant sense to be kind of moons of Earth therefore, but these generally are far more distant and we would neither feel their tides on any serious level--nor see them as major objects in our skies.

I actually think 800,000 km out is getting dangerously near the outer part of our Hill sphere and that Mars could easily be perturbed right out.

So I don't actually recommend bringing large bodies near Earth! If we must do this, let us bring them in to a 24 hour orbit and tidally lock them. And do it in the past or with ASB engineering to smooth the shifting of Earth's shape into its new egg-shaped tidally imposed equipotential. If we can't have this exact solution, it is better to keep large bodies pretty darn far away.


Here is a list of some of the bodies in my own solar system. This is just the inner solar system.


The main star in this system, it is a sun-like star with 1.1x the mass of our own sun and is slightly brighter. It is a G3.6V class star.


A hot jupiter planet with the mass of 445x that of Jupiter and with an extremely low density, making the planet much larger than it really should be. It has a large gas trail behind it as it whips around the main star every 22 hours or so. 0.019 AU away from the main star. It regularly eclipses the face of the main star as viewed from other planets and can be seen through a telescope (with a solar filter of course) near to the Sun at all times.


A 1.5x Earth mass planet that is a trojan planet of Cari, orbiting at the L4 Lagrange point. It might actually technically be a moon, since its orbit is so dominated by Cari, however it doesn't orbit around Cari. Valcera and Cari are doomed to crash into the sun within a few million years. It has supersonic winds of molten rock vapor and deep lava oceans.
Both these planets get roughly 10,000x the sunlight than our Earth gets, making Cari's atmosphere lose air constantly and have a massive gas halo around it due to the atmospheric run-off effect.


At 4.16 Earth masses and 0.31 AU away from the star, Revargation is a hot house world similar to our Venus but to a much worse extent. It's surface pressure is roughly 2,000 to 3,000x greater than on Earth and it is what you might call a 'Gas Dwarf planet'. It has a solid surface that has never been seen before due to its extremely thick and hot atmosphere. It is broiling and churning with Carbon Dioxide and other elements. Its clouds are extremely reflective, much like Venus.


A roughly Neptune mass planet orbiting at 0.69 AU, it is a warmer version of Neptune in our solar system and has a prominent ring system. It is commonly seen in the evening and morning skies of Daeldrum, being brighter than Venus would be from Earth.

Moons: 15, 1 Major moon

- Maratha is a Mars mass moon going around Vesos every 10 days, it can be seen separately from Vesos in the sky of Daeldrum. It is a warmer and wetter version of Mars, having enough air pressure to maintain some standing water on its surface. It is home to microbial and some minor plant life on it, with small multicellular creatures on its surface.


An Earth mass world with roughly 10% more mass, 6% more gravity and similar air pressure, Daeldrum has a small ring over its equator and is at 1.1 AU away from the sun. It is home to human and other such intelligent life. It is tilted at roughly 25 degrees. Its 2 moons create massive tides on the planet's surface.

Moons: 2 major Moons

- Erina is a Lunar mass moon that orbits every 9.85 days around Daeldrum. Its surface goes through a similar process like that of Venus, a regular resurfacing event every few million years. In the current time, it is going through one and its surface is broiling with lava and eruptions much like jupiter's moon of Io. It is roughly 4 times larger in the sky than our moon.

- Malmoa is a Lunar mas moon that orbits every 26 days


A small planet that has roughly 3 times the mass of our Moon, and orbits at 1.6 AU, it is an airless selenic world that is pockmarked with lots of craters much like that of our moon. Roughly of a white / grey color. Its 2 inner moons orbit extremely close to the equator much like Mars's moons with the 2 outer ones taking several days to orbit around the planet.

Moons: 4 Minor moons

Agarthanon and Enok:

At 90% the mass of our Earth it was once like our Earth before a series of wars and geological disasters rendered most life here extinct millions of years ago. At 1.9 AU, it is now a wind wept and cold barren planet with its oceans remaining due to various corrosive chemicals that have made them unable to freeze under the current temperatures. It's landmasses are swept by large glaciers and sheets of ice. Remains of cities and civilizations remain here under the ice and snow and evidence of large scale wars on this planets surface still remain. Some life survives deep underground. Its atmosphere has a large amount of Ammonia, Sulfer. Its manmade carbon dioxide has been mostly washed out from the atmosphere over the eons.

Agarthanon forms a double planet system with Enok, a mars mass world that is roughly similar to our own Mars. The 2 worlds always show the same face to each other. Enok has a thin Mars like atmosphere, and on its surface are the ruins of colonies and cities from a failed terraforming project millions of years ago. The remaining humans from this world fled to Daeldrum and deverted back to the stone age.


Trithios is another Gas Dwarf type planet at 4.11 Earth masses and 3 AU away from the sun. Due to its greenhouse gasses it is roughly just above boiling temperature here. Its atmosphere is a froth consisting of water vapor, carbon dioxide and various other compounds. Its atmosphere at certain depths has a relatively same viscosity as the oceans of Earth and is host to various 'floating' lifeforms that resemble algae, and whales, fish.

Moons: 19 minor moons, 5 major moons

The 5 major moons of Trithios are barely able to be considered major moons. All but 2 of them are potato shaped lumps of rock, and the 2 that are round are barely even Ceres mass. They are pinpricks compared to Trithios.
Crossposted with the main Map Thread

For the past few days I have been doing the map of a inhabitable/terraformed moon on paint and now I have finally completed it (I spent a day and a half just changing the map from the original colors to basemap blue and green. Since I did this in steps, I ended up with some versions of the same map, and so I'll post them all together:
1 - Topography/Bathymetry (mostly) - The map most close to the original NASA ones, it is basically them shrunk to a fourth (I think) of the original size with the "shorelines" marked by me

2 - Far Side with the seas filled and most of the topography still shown

3 - Terraformed but lacking rivers

4 - Far Side terraformed with rivers but still showing the topography

5 - Terraformed with rivers

Just so everyone knows, I will admit that I played with the shores frequently while doing this map and not always used the same height for every shoreline. Also, as it is probably easy to notice by the sheer amount of rivers, the satellite lacks in any kind of desert overall, and In my head it is covered by a variety of forests (from tropical-esque to small amounts of boreal), grasslands and wetlands, and has a climate that is humid. How realistic that is? I don't know, but it is how it is


Middle Solar system of my solar system.


A small 2.5x Ceres mass world that is airless. It is heavily cratered and a light yellow and white color. It has 4 small asteroidal moons and orbits between Trithios and Baoman. It exists in the inner asteroid belt between Trithios and Baoman.


Baoman is a Jupiter mass planet that is the jupiter analogue of this solar system. It is 320 times the mass of our Earth and has a large purple, Saturn like ring unlike our jupiter. Also unlike jupiter it has a bit more methane making it appear more blue, with white bands across its diameter.

Moons 121, (8 Major).

Just beyond Baoman's ring is a disk of asteroids that was once a moon that broke up and got too close, the rest of them created the ring, and there are roughly 9 asteroids ranging in size from 12 miles to 100 miles wide just beyond and in the ring system of Baoman.

Targara - Roughly mars mass and orbiting every 19 hours, Targara is an extreme version of Io. Its surface is heavily warped due to tidal interactions and it has a thin atmosphere due to its frequent outgassing and eruptions. It's surface is pock marked with volcanoes.

Bastion - A selenic world orbiting every 31 hours which is slightly more massive than our moon, it is host to some volcanism and is less extreme than Targara. Has a white reflective surface. Airless.

Vulfal - A little more massive than Bastion, this moon orbits every 2.151 days. It isn't really an ice world due to the tidal heating still and has some geologic activity on its surface but is airless.

Lacker - Orbiting every 3.507 days, Lacker is roughly the same diameter as Vulful but twice the mass. It is a denser moon and has 17% the gravity of Earth, however it is also airless.

Dack - About the same mass as Lacker but slightly larger, this moon is less dense than Lacker. It orbits every 5.7 days and is airless.

Iopia - A moon twice the mass of Mars, it has a magnetic field that shields it from Baoman's magnetic field. It has an atmosphere that is 1% the pressure of ours and roughly has 43% the gravity as on Earth. It is a fairly blue color.

Topiatania - Slightly less massive than Iopia, it also has a magnetic field and orbits every 15 days. It is very similar to Iopia. Both these moons would be great for colonization.

Fulgars - A brown ice world, it is host to subglacial life much like Europa. It is roughly 4 times the mass of our moon and orbits Baoman every 25 days.

Bentefairs - Around the same mass as Fulgars, this moon orbits roughly every 68 days and is in a slightly inclined orbit. It is fairly yellow in coloration.


A purple and white planet that has roughly the mass of Saturn, if a little greater. It has a wide purple ring system that is as large as the entire diameter of the planet and hosts an impressive collection of moons. It orbits at 10.6 AU.

Moons: 169, (8 major)

Mente - Another Io like world, this one has a powerful magnetic field and is 3 times the mass of our moon. It sits just beyond the edge of the ring and its outgassing and eruptions contribute to the mass of the rings. It is a very yellow moon with a very sulfuric atmosphere and clouds. It orbits once every 26 hours.

Dist - A Pluto mass world with cryovolcanism much like enceladus, it is fairly grey in color with a large black spot on its surface. It orbits every 2 days.

Rockfarga - Slightly larger than Pluto, this moon also hosts cryovolcanism and is roughly half and half of color much like Iapetus in our own solar system. It orbits every 3.9 days, both Rockfarga and Dist are host to multicellular subglacial life in their internal oceans.

Denelition - A fairly maroon and brown colored moon, it orbits every 7 days and is roughly 3 times the mass of Pluto.

Flack - A pluto mass moon that is extremely reflective on one side (white), and very dark on the other side and almost black. The black and white moon. It goes around once every 13 days.

Mistios - A dark brown colored moon, roughly 4 times the mass of Pluto, this moon is fairly cratered. Its white craters contrast with the dark brown surface. It orbits once every 26 days.

Popperia - A moon slightly less massive than Mars, it has a thin halo of an atmosphere surrounding its light brown and tan surface. It is host to Europa like marks on its surface and is host to subglacial life. It has a very thin ring system orbiting over the equator.

Thalnassa - One could argue this one isn't even a moon at all, but a planet in its own right. It is 4.5x the mass of our own Earth, and has a double ring system. It orbits in an inclined and eccentric orbit around Boettch every 9.5 years and is 0.30 AU away from Boettch. From Daeldrum, it can be seen seperately from Boettch.

It is a fairly purple world with seas of liquid hydrocarbons and various compounds much like that of titan. It has a thick atmosphere and is host to exotic biological crystalline life that dots the landscape. Small 'plants' made out of crystals grow here that resemble snowflakes and fractals. It is host to exotic fish and animal life as well, and has roughly 1.58x the gravity of our own Earth. It is a captured planet that orbits around Boettch.


A ringed planet that is 3 times the mass of Mars that orbits beyond Boettch at 17.5 AU, it is a fairly yellow color and is host to a magnetosphere, and a brilliant ring system. It has a thin atmosphere made of Nitrogen, it's icey surface is quite reflective and yellow-white.

Moons 23, (2 Major)

Lokayla's major moons are roughly the mass of Pluto and aren't really all that impressive although the inner one is host to cryovolcanism to a slight degree.

The next 4 planets are ice giants and are all tilted on their sides in similar manner to Uranus.


A very white Neptune mass world with a green ring system, it is situated at 34 AU away from the sun. It is a pale white-light purple color.

Moons (72, 9 major).

Ersharia's moons range from Miranda to Pluto mass, however, one moon stands out from the rest. Dorel is the 5th moon from Ersharia and is roughly Mercury mass and has a thin atmosphere and is very similar to Triton and how it looks.

Domachow and Ske:

Domachow is slightly less massive than Ersharia and its light green rings look like there are 3 seperate rings. It forms a binary pair with an large Ice world named Ske which is mostly brown in coloration and heavily cratered. Ske has an extremely thin atmosphere and orbits Domachow every 25.155 days. It is 1.58 times the mass of Earth. Beyond Ske are a pair of Pluto mass moons, and 10 other asteroids roughly in line with the Equatorial planes and Domachow and Ske. These worlds dance around each other at 71 AU from the sun.


A very blue planet with a similar mass to Domachow, it has a similar ring system to Domachow but it is of a grey and purple color. It orbits at 139 AU from the sun.

Moons (79, 7 major)

All of the moons of Amania are Ceres - Pluto mass but the very last major moon which is roughly half the mass of Mars. It isn't tidal locked and orbits every 96 days around Amania, however it lacks an atmosphere.

There is an asteroid belt between Amania and Manning it is called the middle asteroid belt and is host to 2 Pluto mass planets named Lousia and Brown. It is made up of icey objects. Louisa and Brown have multiple moons.


25 times the mass of Earth, and orbiting at 304 AU away from the sun, this is a very deep blue and purple planet. It is extremely dark and extremely cold here.

Moons (102, 8 major)

The major moons of manning are all extremely small and Ceres mass except for Vastias which is the first moon. Vastias has a thin atmosphere much like that of Pluto and is host to cryovolcanism and multicellular life under its surface.

Then there is an extremely expansive outer belt of icey and frigid objects between Manning and Accord, the next planet. It is host to a pleothera of small planets ranging in size from Ceres to Mercury mass. Notable ones are named Lederest, Hayit, Hann, and Fields. With Lisa being the largest of them all, being roughly Mercury mass. All of these objects have assorted moons.

Beyond the outer belt lays the planet Accord.


Accord is a ringed ice planet, it is 8.58 times the mass of our moon and is 695 AU away from the sun. It takes upon a pink to brown color and has a magnetic field with very little traces of an atmosphere since it is so cold out here. Due to its extreme distance from the sun it has captured its own 'Oort cloud' of small icey objects that are also its moons. Some of these can dip really low to the planet's surface much like comets to that of the sun. These objects take many thousands of years to orbit around Accord. I call these objects Moon comets due to some of their irregular orbits.

Moons: (1042, 15 major moons)

It's major moons are all Vesta to Pluto mass.


The final planet of this solar system, Tharkmo is 60% the mass of our Earth and is ringed like Accord and takes on a dark brown color. Its major moons are even more insignificant than that of Accord's. It also has rings.

Moons: (569, 8 major moons).

Tharkmo's major moons are Vesta to Ceres mass.
Just so everyone knows, I will admit that I played with the shores frequently while doing this map and not always used the same height for every shoreline. Also, as it is probably easy to notice by the sheer amount of rivers, the satellite lacks in any kind of desert overall, and In my head it is covered by a variety of forests (from tropical-esque to small amounts of boreal), grasslands and wetlands, and has a climate that is humid. How realistic that is? I don't know, but it is how it is
Well technically, a terraformed planet or moon wouldn't look anything like it used to unless you reshaped it to so all the craters of the moon would be eroded under the colossal amounts of heat and energy in terraforming and then eroded further by the new atmosphere and sea.

You could probably set the climate of the moon to whatever you wanted it to be after terraforming and it would be plenty plausible.