Alternate Planets, Suns, Stars, and Solar Systems Thread

What about a scenario that gives an axial tilt to the barycenter at some point, thereby lessening the frequency of eclipses?
As long as the axial tilt is enough that the shadows of the planets don't cross over each other much, this should work. With the 50 000 km sma example, this would be around 8º of axial tilt minimum (arcsin(R_planets/SMA)) (note: Earth is around three times this). This means eclipses would (somewhat like reality) have two "seasons" per year, when the orbital nodes line up with the sun. The greater the axial tilt, the shorter the eclipse seasons are. During the eclipse seasons, there will be a total eclipse every day, with the exceptions of the first and last days of each season, which are a transitional period with partial eclipses. The centers of each eclipse season on the equator line up with the spring and fall equinoxes. The eclipse seasons themselves are the same length everywhere on the planet, but they don't happen at the same time everywhere. The eclipseless winters are short, and the eclipseless summers are long. At the poles, the entire summer half of the year has no eclipses. At the equator, the eclipseless seasons are the same length.

I'm not sure what the climactic effect of a noon eclipse every day in fall and spring would be, but it probably wouldn't be negligible. The eclipses would (again assuming 50 000 km sma of the planets' orbit) last roughly an hour (arcsin(R_planets/SMA) * (hours/day)/180º) at the equator on the equinoxes, and their length over the course of the year would follow a sine wave (with the points where it dips below the axis being summer and winter, when eclipses wouldn't happen) (I don't know the exact equation).

As for the societal impacts, It's easy to imagine the first eclipse marking the new year, especially because this would coincide with the beginning of spring. It would become trivial for early civilizations to know the exact length of their year by timing between the beginnings of eclipse seasons. They would probably notice a discrepancy in their calendars; cities with similar latitude to Athens and Alexandria would see their first eclipses several days apart (assuming a year length similar to that of earth; it could be on the same day if there are few enough days per year). Some calculations from there allow them to determine:
-Their planet is round
-The radius of their planet (likely more accurately than OTL early estimations)
-The radius of their twin planet
-probably some other things too
The inner hemispheres will have much more advanced astronomy. Finding longitude would never be a problem in the inner hemispheres, with or without axial tilt; simply look up.

It wouldn't get very dark at night, seeing as the other planet would reflect quite a bit of light. The darkest times would be midnight around the equinoxes, because the eclipses would block out most light on the other world, so there wouldn't be much to reflect. In winter and summer, there would be no true darkness.

Each planet would probably have much better maps of the other planet than their own, seeing as they could just look up to map the other planet.

Galileo's telescopes had 20x magnification. With around 90 000 km distance between the planetary surfaces at their nearest points, and assuming proper contrast, it should be just about possible to make out features smaller than a km on the other world, which would present some interesting opportunities for civilizations on both worlds.
 
Bifrost.png


Inner system of Bifrost

Bifrost-1: Falun is the inner world of Bifrost, tidal locked to Bifrost the dark side is covered by thick glaciers of water, co2 and nitrogen. Smaller than Earth but with 4% higher gravity.

Bifrost-2: Hekla a slightly bigger version of Venus

Bifrost-3: Kimbrien, semi-arid and cold planet slightly smaller than Earth, but with 99% earth gravity, thick atmosphere, 24-hour day, and 450-day long years

Bifrost-3A: Mani, airless moon of Kimbrien with 3% Earth gravity.

Bifrost-4: Storen, hot or lukewarm gas giant with a 1100-day long year

Bifrost-4A: Oppland, Mars sized arid moon with heavy volcanic activity, thin poisonous atmosphere

Bifrost-4B: Tausen, Mars sized ice covered ocean world, thin atmosphere

Bifrost-4C: Nidaros, Earth sized cold ocean world, thick atmosphere, 141-hour day

Bifrost-4D: Hann, the colder cousin of Tausen


The Asteroid Belt splits the inner system from the two gas giants and four ice giants in the outer system.

General information: Bifrost is richer in heavy metal than Sol thanks to the Bifrost being younger. A unique fact which was a major reason for the colonization of the system is the fact that it has nine Jump Points, making it an important hub in the local Nexus. Bifrost lies a 115 jump from Sol in the closest jump line.

Interstellar history: Bifrost was discovered by the Copernicus the fourth Jump Exploration ship in 2102, the claim to the system was sold to Brahe a Danish interstellar colonization company in 2130. There was little interest in the system because of its peripheral geography and lack of easy to terraform worlds. Brahe which had less resources than bigger players, saw an opportunity in the many Jump Points and rich resources. As such it established a research outpost (Uranienborg) in the system in 2136, which grew into a full colony over the next decades. Sadly, for Brahe the peripherical nature of Bifrost meant that few other colonies were established in the region and most which was established were isolationistic. As such Brahe began to focus on other projects and mostly left Bifrost in benign neglect. So, outside the initial settlement of 40.000 Danes, 10.000 Estonians and 10.000 Belarusians the settlement received few settlers over the next several centuries, more or less developing its own culture or cultures. In the 26th century this change as the region began to rapidly change, many of the local early colonies had at that point developed into respectable economies with a renewed interest in contact with the greater galaxy, while the Inner World had begun expanding outward making Bifrost into the important regional hub the leadership of Brahe had imagined.

Of course, with the growing powers of the region and greater contact with the Inner World, Brahe also became a target of wannabe conquerors and pirate. But as Bifrost had kept a strong presence in space thanks to lack of easy settleable planets, it was able to keep these from conquer or raid the system.

Bifrost also lay claim to several system with little human settlement in the local region.


Human Settlements: Uranienborg was the first human habitat in the system, it was placed in the asteroid belt to avoid gravity wells and giving it access to raw material. In the first century most human settlement stayed in the belt, but it was decided early on that planetary colonization was necessary. Kimbrien and Nidaros was the two world which could be terraformed while keeping being settled. While Nidaros with its world ocean and small island continents would be easier to terraform than the dry world of Kimbrien with it limited water sources, Kimbrien had a lot more potential for resource extraction. It was decided to focus on Kimbrien but also start a minor biological seeding project of Nidaros.

By modern day, the terraforming is still an ongoing project. Kimbrien have reached a 7% oxygen atmosphere and the population lives in domed cities and underground. While a dry planet, the large lowland regions are dominated of massive peat swamps, while the highland have large alpine and tundra deserts. In the massive crater Tallinn taiga have begun to spread. Both the flora and fauna are extremely limited. The capital of Bifrost Nyhavn lies on Kimbrien.

Nidaros on the other hand have shown itself to be a much easier success the large oceans are a carbon sink and the over the centuries the oxygen level have increased to 22%. But at the same time the inland regions of most of the island continent are covered with kilometer thick ice sheets, leaving only coastal areas for human habitation, some coastal temperate forests do exist and a few arctic deserts. Life on Nidaros have a much greater complexity with ocean being incredibly rich in life. Nidaros rich aquaculture is a major export of the planet, though forestry is also major industry even with the limited area for it.

At last, there’s the world Falun. Falun is rich in both metals and volatiles thank to the tidal locking keeping the volatiles from being lost. As such there exist a heavy human presence in the twilight zone where they live in domed or underground habitats and make heavy use of the free energy of Bifrost. While not competitive in the production of spaceship with the Belt, Falun is still the beating industrial heart of the system and to lesser extent local space.

Population:
Bifrost (entire system): 800 million.
Kimbrien: 680 million.
Nidaros: 70 million.
Falun: 40 million
The Belt: 5 million
Other: 5 million

Political system: Bifrost is a semi-feudal hereditable monarchy ruled by a grand duke. The title grand duke is simply an attempt to translate the local title of the monarch and a truer translation would be “Grand Warlord”. While original a corporate free state ruled by the shareholders, the growing population of non-shareholder resulted in the old regime collapsing in the late 22nd century and after two and a half centuries of warring states, the warlord of Uranienborg used the increase external trade to fund his conquest of the system and the establishment of the monarchy. The Grand Duke power comes from his control over the jump points, which both give him control over the import and export of goods from Bifrost and control over the trade flowing through Bifrost. This control over the trade have resulted in the Grand Duke keeping power over the system, through the extinction of one ducal line resulted in a sideline taking over. Beside the Asteroid Belt around 15% of all the settlements of Bifrost is under direct control of the Grand Duke.

Below the Grand Duke the high nobility of the realm are the burgraves, again this title is a loose translation of the local title, whose direct translation would simply be “city lord”. The burgraves rule their settlements like absolute princes. They’re represented in the Council of the Realm, where they have power over taxes being raised on their settlements. There’re other categories of nobility below the burgraves like the lords, but they swear direct fealty to the Grand Duke or burgraves and aren’t represented in the council. The nobility has their own armed forces

Outside the control of the emperor is the guilds, the guilds represent the neutral parties in the warring states who was necessary to keep the terraforming going and infrastructure running. The two major guilds are the Spacefarer and Terraforming Guilds, but several minor guilds also exist. The guilds are represented in the council as their own estate. The guilds are more secular monastic (through non-celibate) order than traditional medieval style guilds.

Nidaros is a disruption in this system, since the terraforming allowed people to live outside the fortified city domes, there have been a rise of small coastal settlements which neither the Grand Duke nor the nobility can keep control over. The lack of the need for complex infrastructure to survive have resulted in the population growing increasing independent minded. A major uprising 40 years ago resulted in the Nidaros being given wide autonomy and its own parliament which swear direct loyalty to the Grand Duke.


Culture and ethnicity: The vast majority of Bifrostian ancestry come from Europe and as such they’re recognizable as being European descendent. The three languages of the settlers still exist, though they have diverged significant and many dialects of these three languages would be seen as distinct languages if they existed elsewhere. The main language is of course Danish descendent, but both Estonian and Belarussian do well and is recognized as co-official languages and sole official languages in many dome cities. On Nidaros and Falun Danish is solely spoken. The Asteroid Belts are distinct in that it has a heavy presence of outsiders as it’s a major trading hub. Half of the three million people of Uranienborg are immigrants and expats. Beside that the capital of Nyborg is home to another million immigrants and expats.

Cultural the Bifrostian have as much in common with their 21st century ancestor as those had with their 11st century ancestors. While their culture borrows heavy from the symbols of their parent culture on Earth, they’re very distinct including from each other as several centuries of civil war radical changed them. There’s also significant difference between the different planets and social classes.

The nobility is militant and feuding culture, low level civil wars between the different noble families often break out, through the Grand Duke limits the collateral damage. But if two families declare a feud on each other open warfare is banned, but assassination are overlooked. Outside feuds the Grand Duke deal harshly with such behavior. But it still creates a paranoid and vicious culture.

The commoners are in general browbeaten into submissiveness, they’re careful, polite, softspoken and obedient. But they’re also deeply care about their word and deal with rulebreakers viciously. Many foolish outsiders have found that out.

The Nidarosians are different from other Bifrostians, they’re clannish, rude, and independent minded, but share the belief in the importance of one’s word and deal harshly with anyone trying to take advantage on them or break the social contract.

The Nyborgians and Uranienborgians are more cosmopolitan, tolerant and easy going through they share the general politeness of most Bifrostian. This is large externt caused by the Grand Duke protection of them against the nobility.
 
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…the 50 000 km sma example… …around 90 000 km distance between the planetary surfaces at their nearest points…
For Earth-size (or even Earth-like) worlds, isn’t this too close? Too far for planetary bulging, maybe, and too far for atmospheric sharing, but this is wildly tidal and volcanic, isn’t it?
 
For Earth-size (or even Earth-like) worlds, isn’t this too close? Too far for planetary bulging, maybe, and too far for atmospheric sharing, but this is wildly tidal and volcanic, isn’t it?
They will be quite a bit more geologically active than OTL Earth. The tides won't be too wild, though, because the planets are tidally locked. The distance from Pluto to Charon is less than 20 000 km, while the radius of Pluto is almost 1200 km, and Charon more than 600. However, there aren't wild tides on either of these OTL bodies, because tidal locking stops tides. There is still a tidal bulge - it's just frozen in place.

If it still does feel too close, which is perfectly reasonable, there's no problem in picking a more distant example (or making the planets smaller) - I only chose 50 000km because it gave them an orbital period of roughly one Earth day - I admit that it might be considered a bit close to the Roche limit at 20 000 km. The maximum distance (not SMA) for eclipses to happen would be given by (distance to sun) * (sun radius / planet radius). Also, one might want to place the worlds nearer the outer edge of the habitable zone to compensate for the extra heat from more geologic activity.
 

What are the atmospheric, meteorological, oceanic and even magnetic consequences of an Earth-like planet having a longer rotation than our Earth? (36 hrs., 48 hrs., etc.)

 

What are the atmospheric, meteorological, oceanic and even magnetic consequences of an Earth-like planet having a longer rotation than our Earth? (36 hrs., 48 hrs., etc.)

Instead of three circulation cells per hemisphere like on earth (Hadley, Ferrel, Polar), you will just have one, due to the weaker coriolis effect. The same will be true of ocean currents; there will be only one gyre per hemisphere. There will be no subtropical ridges, or polar front. The prevailing winds blow you poleward and a little east (or west on a retrograde world) at every latitude. East-facing coasts will be hot and wet, westward-facing coasts colder and drier (or, again, reverse this on a retrograde world).

A current like the Gulf Stream would never cross the Atlantic, instead continuing up the North American continental shelf all the way into the Arctic Ocean, from which a cold current would flow down the coast of western Europe and Africa all the way to the equator like a mega-Canary current. A similar pattern would happen with the Kuroshio and California currents, or any other currents on opposite coasts of a major ocean where both coasts stretch from the equatorial to the polar regions.

I'm not certain of the consequences for the magnetic field.
 
Is it possible for an Earth-like world to have the same conditions as Earth if it orbits a dwarf star? Is it possible for Earth-sized object to even orbit them?
 
Is it possible for an Earth-like world to have the same conditions as Earth if it orbits a dwarf star? Is it possible for Earth-sized object to even orbit them?
The Sun counts as a “yellow dwarf” so I’m not sure what else you’d mean. Red? White? Just move the orbit inward for the former, and the latter is probably not going to give you earthlike conditions at any distance.
 
Instead of three circulation cells per hemisphere like on earth (Hadley, Ferrel, Polar), you will just have one, due to the weaker coriolis effect
at what speed of rotation would be transit from three-cells system to one-cell system?

Is it possible for Earth-sized object to even orbit them?
Yes

Is it possible for an Earth-like world to have the same conditions as Earth if it orbits a dwarf star?
For Red dwarfs orbit with Earth effective temperature will be closer very much than real Earth orbit. Tidal effect quickly will make planet on this orbit synchronized to star like Moon to Earth.
 
at what speed of rotation would be transit from three-cells system to one-cell system?
It's difficult to pinpoint exactly, but I believe somewhere around 34 hours, give or take a few in either direction.
Is it possible for an Earth-like world to have the same conditions as Earth if it orbits a dwarf star? Is it possible for Earth-sized object to even orbit them?
With red dwarfs it's important to note that solar weather can begin to pose a major problem, as well as tidal locking, so planets around red dwarfs are quite unlikely to be habitable. A K7 V type orange dwarf, mass around 0.6 solar masses, is a reasonable minimum size for a star. Orange dwarfs and yellow dwarfs are actually the most promising candidates for extraterrestrial life. The sun is a yellow dwarf.
 
For Red dwarfs orbit with Earth effective temperature will be closer very much than real Earth orbit. Tidal effect quickly will make planet on this orbit synchronized to star like Moon to Earth.
I believe a larger, brighter red dwarf (with about 40-55% of the Sun's mass) would be able to have an Earth-like planet in the habitable zone and not have it tidally locked.
 
If so, what distance would it have to have been?
I believe it would have to be at the outer edge of the habitable zone, meaning the planet will need a decent amount of volcanic activity and the greenhouse effect to avoid being frozen. It would probably be around 0.2 - 0.25 AU (about half of Mercury's maximum distance from the sun), but it depends on a variety of factors. It's likely that over billions of years, the planet would slow down and become tidally locked. There's also the possibility of a Mercury-like 3:2 orbital resonance or similar things.
 
You could also have an Earth-like moon of a gas giant or brown dwarf, or a binary planet; the planet(s) would still be tidally locked, but not to their central star. Additionally, tidal locking is probably not so bad as once believed for habitability, since oceans and atmospheric flows could redistribute heat across the planet.
 
View attachment 686216

Inner system of Bifrost

Bifrost-1: Falun is the inner world of Bifrost, tidal locked to Bifrost the dark side is covered by thick glaciers of water, co2 and nitrogen. Smaller than Earth but with 4% higher gravity.

Bifrost-2: Hekla a slightly bigger version of Venus

Bifrost-3: Kimbrien, semi-arid and cold planet slightly smaller than Earth, but with 99% earth gravity, thick atmosphere, 24-hour day, and 450-day long years

Bifrost-3A: Mani, airless moon of Kimbrien with 3% Earth gravity.

Bifrost-4: Storen, hot or lukewarm gas giant with a 1100-day long year

Bifrost-4A: Oppland, Mars sized arid moon with heavy volcanic activity, thin poisonous atmosphere

Bifrost-4B: Tausen, Mars sized ice covered ocean world, thin atmosphere

Bifrost-4C: Nidaros, Earth sized cold ocean world, thick atmosphere, 141-hour day

Bifrost-4D: Hann, the colder cousin of Tausen


The Asteroid Belt splits the inner system from the two gas giants and four ice giants in the outer system.

General information: Bifrost is richer in heavy metal than Sol thanks to the Bifrost being younger. A unique fact which was a major reason for the colonization of the system is the fact that it has nine Jump Points, making it an important hub in the local Nexus. Bifrost lies a 115 jump from Sol in the closest jump line.

Interstellar history: Bifrost was discovered by the Copernicus the fourth Jump Exploration ship in 2102, the claim to the system was sold to Brahe a Danish interstellar colonization company in 2130. There was little interest in the system because of its peripheral geography and lack of easy to terraform worlds. Brahe which had less resources than bigger players, saw an opportunity in the many Jump Points and rich resources. As such it established a research outpost (Uranienborg) in the system in 2136, which grew into a full colony over the next decades. Sadly, for Brahe the peripherical nature of Bifrost meant that few other colonies were established in the region and most which was established were isolationistic. As such Brahe began to focus on other projects and mostly left Bifrost in benign neglect. So, outside the initial settlement of 40.000 Danes, 10.000 Estonians and 10.000 Belarusians the settlement received few settlers over the next several centuries, more or less developing its own culture or cultures. In the 26th century this change as the region began to rapidly change, many of the local early colonies had at that point developed into respectable economies with a renewed interest in contact with the greater galaxy, while the Inner World had begun expanding outward making Bifrost into the important regional hub the leadership of Brahe had imagined.

Of course, with the growing powers of the region and greater contact with the Inner World, Brahe also became a target of wannabe conquerors and pirate. But as Bifrost had kept a strong presence in space thanks to lack of easy settleable planets, it was able to keep these from conquer or raid the system.

Bifrost also lay claim to several system with little human settlement in the local region.


Human Settlements: Uranienborg was the first human habitat in the system, it was placed in the asteroid belt to avoid gravity wells and giving it access to raw material. In the first century most human settlement stayed in the belt, but it was decided early on that planetary colonization was necessary. Kimbrien and Nidaros was the two world which could be terraformed while keeping being settled. While Nidaros with its world ocean and small island continents would be easier to terraform than the dry world of Kimbrien with it limited water sources, Kimbrien had a lot more potential for resource extraction. It was decided to focus on Kimbrien but also start a minor biological seeding project of Nidaros.

By modern day, the terraforming is still an ongoing project. Kimbrien have reached a 7% oxygen atmosphere and the population lives in domed cities and underground. While a dry planet, the large lowland regions are dominated of massive peat swamps, while the highland have large alpine and tundra deserts. In the massive crater Tallinn taiga have begun to spread. Both the flora and fauna are extremely limited. The capital of Bifrost Nyhavn lies on Kimbrien.

Nidaros on the other hand have shown itself to be a much easier success the large oceans are a carbon sink and the over the centuries the oxygen level have increased to 22%. But at the same time the inland regions of most of the island continent are covered with kilometer thick ice sheets, leaving only coastal areas for human habitation, some coastal temperate forests do exist and a few arctic deserts. Life on Nidaros have a much greater complexity with ocean being incredibly rich in life. Nidaros rich aquaculture is a major export of the planet, though forestry is also major industry even with the limited area for it.

At last, there’s the world Falun. Falun is rich in both metals and volatiles thank to the tidal locking keeping the volatiles from being lost. As such there exist a heavy human presence in the twilight zone where they live in domed or underground habitats and make heavy use of the free energy of Bifrost. While not competitive in the production of spaceship with the Belt, Falun is still the beating industrial heart of the system and to lesser extent local space.

Population:
Bifrost (entire system): 800 million.
Kimbrien: 680 million.
Nidaros: 70 million.
Falun: 40 million
The Belt: 5 million
Other: 5 million

Political system: Bifrost is a semi-feudal hereditable monarchy ruled by a grand duke. The title grand duke is simply an attempt to translate the local title of the monarch and a truer translation would be “Grand Warlord”. While original a corporate free state ruled by the shareholders, the growing population of non-shareholder resulted in the old regime collapsing in the late 22nd century and after two and a half centuries of warring states, the warlord of Uranienborg used the increase external trade to fund his conquest of the system and the establishment of the monarchy. The Grand Duke power comes from his control over the jump points, which both give him control over the import and export of goods from Bifrost and control over the trade flowing through Bifrost. This control over the trade have resulted in the Grand Duke keeping power over the system, through the extinction of one ducal line resulted in a sideline taking over. Beside the Asteroid Belt around 15% of all the settlements of Bifrost is under direct control of the Grand Duke.

Below the Grand Duke the high nobility of the realm are the burgraves, again this title is a loose translation of the local title, whose direct translation would simply be “city lord”. The burgraves rule their settlements like absolute princes. They’re represented in the Council of the Realm, where they have power over taxes being raised on their settlements. There’re other categories of nobility below the burgraves like the lords, but they swear direct fealty to the Grand Duke or burgraves and aren’t represented in the council. The nobility has their own armed forces

Outside the control of the emperor is the guilds, the guilds represent the neutral parties in the warring states who was necessary to keep the terraforming going and infrastructure running. The two major guilds are the Spacefarer and Terraforming Guilds, but several minor guilds also exist. The guilds are represented in the council as their own estate. The guilds are more secular monastic (through non-celibate) order than traditional medieval style guilds.

Nidaros is a disruption in this system, since the terraforming allowed people to live outside the fortified city domes, there have been a rise of small coastal settlements which neither the Grand Duke nor the nobility can keep control over. The lack of the need for complex infrastructure to survive have resulted in the population growing increasing independent minded. A major uprising 40 years ago resulted in the Nidaros being given wide autonomy and its own parliament which swear direct loyalty to the Grand Duke.


Culture and ethnicity: The vast majority of Bifrostian ancestry come from Europe and as such they’re recognizable as being European descendent. The three languages of the settlers still exist, though they have diverged significant and many dialects of these three languages would be seen as distinct languages if they existed elsewhere. The main language is of course Danish descendent, but both Estonian and Belarussian do well and is recognized as co-official languages and sole official languages in many dome cities. On Nidaros and Falun Danish is solely spoken. The Asteroid Belts are distinct in that it has a heavy presence of outsiders as it’s a major trading hub. Half of the three million people of Uranienborg are immigrants and expats. Beside that the capital of Nyborg is home to another million immigrants and expats.

Cultural the Bifrostian have as much in common with their 21st century ancestor as those had with their 11st century ancestors. While their culture borrows heavy from the symbols of their parent culture on Earth, they’re very distinct including from each other as several centuries of civil war radical changed them. There’s also significant difference between the different planets and social classes.

The nobility is militant and feuding culture, low level civil wars between the different noble families often break out, through the Grand Duke limits the collateral damage. But if two families declare a feud on each other open warfare is banned, but assassination are overlooked. Outside feuds the Grand Duke deal harshly with such behavior. But it still creates a paranoid and vicious culture.

The commoners are in general browbeaten into submissiveness, they’re careful, polite, softspoken and obedient. But they’re also deeply care about their word and deal with rulebreakers viciously. Many foolish outsiders have found that out.

The Nidarosians are different from other Bifrostians, they’re clannish, rude, and independent minded, but share the belief in the importance of one’s word and deal harshly with anyone trying to take advantage on them or break the social contract.

The Nyborgians and Uranienborgians are more cosmopolitan, tolerant and easy going through they share the general politeness of most Bifrostian. This is large externt caused by the Grand Duke protection of them against the nobility.
How did you manage to "make" this solar system?
Whether it is in the representation of the planets or their assembly.
 
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