What if the Earth were a Satellite to another Planet?

In the solar system, the Earth has an established position as a planet.  This planet Earth has a moon; it is the third planet from the sun at exactly the right distance, with enough water and an atmosphere with enough oxygen to support complex life forms such as humans.  This planet is absolutely right for life.  But a small change, such as a rise or fall in oxygen levels, or a change in position in the solar system could render life more difficult, more dangerous, even impossible; or easier.

The Earth is a planet, the satellite of a star.  It has captured its own moon, which is under the power of the Earth’s gravitational field.  But if the Earth were to become a satellite of the star’s satellites, it would be a moon, orbiting another planet.  The planet which the Earth orbited could be anything, from a planet exactly Earth’s mass, which orbits around the Earth while the Earth orbits around it, to a massive gas giant.  This essay looks at the effects of two possible fictitious planets as ‘hosts’, though there are an infinite number of possibilities.  In this essay there is firstly the twin planet Adelphos, and then the great gas giant Basileus.

There would be many physical effects but also effects on the way people behaved.  Pagan religions that worshipped the Moon would almost certainly have worshipped the planet, ruling over the sky.  But more important perhaps are the physical effects, some of which can be predicted….

The Twin Planet, Adelphos

This planet, called Adelphos, orbits around the Earth while the Earth orbits around it.  Adelphos is a twin planet, one of exactly equal mass to us.  Its diameter is four times the size of the Moon, just as the Earth’s is, so it dominates the night sky.   And at eighty-one times the mass of the Moon, it has great effects on Earth.

Orbiting the Planet
The closest situation to this in our solar system is Pluto and its moon, Charon, which is as much as half Pluto’s own size.  As a result, their gravitational forces are very similar.  Charon does not merely orbit around Pluto, but pulls Pluto into a slight orbit with it as well.  The same would be even truer of two equally massive bodies.  They both orbit around a central point of gravity (see Fig. 1).  It is like two disco dancers holding hands and spinning.

Our Moon
Our Moon still exists, a moon of two planets in this case.  Similarly, some solar systems in the galaxy are twin star solar systems.  The Moon may either orbit around the Earth (or Adelphos,) or both planets, depending on its distance from us and Adelphos (see Fig. 2.)  If it was at a certain distance from the Earth, it would simply be swung to a collision with Adelphos.

Tides
The main practical effect on Earth would be the tides.  The tides are mainly a result of the gravitational pull of the Moon on the seas.  As it is in reality, there is a certain angle of tide which varies slightly, (such as during the spring or neap tides.)  But if the Earth were the Moon of a planet exactly as massive as us, the angle of tide would be eighty-one times as exaggerated (see Fig. 3) meaning that the tides would be approximately eighty-one times as high.
However the tides may well move much slower, due to the orbital speed of the Earth and Adelphos.  Because Adelphos is much more massive than the Moon, the two bodies would move around each other much more slowly.  This is because of the angular momentum.  A larger object needs much less velocity to stay in orbit with another object than a smaller one would.  Too slow and it would be pulled in and collide; too fast and it would be flung out of orbit.  For this reason, the relative movement of Adelphos would be much slower than that of the Moon in reality if it were the same distance from Earth as the Moon.

Sea travel
Boats – even if they could be built –could only be launched at certain times.  If they were not landed sometime near to the time of high tide it would be a very long way out to sea for loading the people onboard or a long wait for a low tide.  Large boats might be built using a temporary enclosure at the top of the tide.
To make sure that they were not flooded, harbours and ports would have had to have been built near the highest tides, so they could only have been in service for a very small period of time compared to a long wait for the tide to come back in, which is very uneconomic.  There would not be many benefits in building a port.  This would have slowed down the history of trade by a considerable amount.  In fact there would be very little sea travel at all.  Technologies and resources would have spread slower, and nations, particularly islands, would have to be much more self-sufficient.  Ports may have been built on rivers, where the tide would not have such a great effect.  But no large vessel could be built or sail on a river next to which there was little enough risk of severe flooding because these rivers would be too narrow for large vessels.  The first fully operational ports on the sea would have been built when we had the technology to raise and lower them (like oil rigs) or float and anchor them.

There would also be great risk of flooding on most parts of the rivers.  As the tide comes in, the water flows up the river.  This would make most fertile land liable to severe flooding from time to time and more often than in reality.  Also the sea water may travel up a lot of the river, leaving very salty ground.

Oil
Oil would be much less abundant, for two reasons.  Oil is a fossil fuel, made up of literally trillions of dead micro organisms compressed over millions of years under the sea bed.  With much higher tides, a large proportion of these micro-organisms would have been washed up onto dry land.  Also a lot less of the sea bed would be permanently under the sea, meaning that less oil could have been formed.  And even if there was enough oil, oil rigs would be very difficult and expensive to build (they would have to be a lot taller and getting the building materials out to the site would be a hard job.)  Oil may not have even have become a major energy supply, which could have been a good outcome.  We would not have relied on it so much and so have found a different source of energy to use.  Nuclear power may be increasingly important, or a renewable source of energy.  It is very probable that tidal power however, would be our major power source.

The Earth could be tidally locked to Adelphos though, which would make things a great deal simpler.  This would happen if we had one side constantly facing Adelphos like the Moon does to us in reality.  Only one hemisphere would ever see Adelphos, and the tides would stay absolutely unmoving, (except for much smaller effects from the Moon and even less from the sun).  This would mean more land and easier travel.
But if the Earth spun on its axis in the opposite direction to the relative motion of Adelphos round us, the tides would be much faster, like repeated tsunamis.  Water travel would be almost impossible.  We might only just be developing technologies to launch a boat safely onto the sea.  And landing the boat would be similar to the bottom of a slope in a fairground log ride – steep gradient (the angle of tide), then to a wet landing onto the shore.  We may well have developed air travel before sea travel.  Only landmasses that are completely self-sufficient could have survived.

The Impact of Asteroids
65 000 000 years ago, an asteroid about ten to fifteen kilometres in diameter struck the Earth.  It made many species extinct, including all the dinosaurs.  But with Adelphos, and different gravitational effects, it is impossible to tell what would have happened to the asteroid (but also other asteroids may have been captured.)  It may have hit Adelphos or even the Moon, or may have just missed altogether.  Any of these results would probably mean that some dinosaurs would still be alive, although they may have evolved into less recognisable animals.  But the asteroid could have been even more catastrophic if it had landed in the sea.  The asteroid would penetrate straight through the sea and the crust, resulting in the sea running into the mantle.  This releases huge quantities of water vapour into the sky, destroying a large part of the ozone layer

What would Adelphos do for us?
Adelphos is a figment of imagination, so there’s no way of telling what might exist on it.  It may hold a very useful resource which we could transport back once we got into space.  It may have an atmosphere and even water, somewhere where we could settle in the near future.  It could be an extremely hot planet of crushing pressure and temperature, exactly like Venus.  Or it could just be a boring rocky planet made of similar rock to the Moon.

The Gas Giant, Basileus
In the previous part, there was a planet of equal size to the Earth.  Now the Earth is orbiting around a massive planet of gas.  It dominates the sky, day and night and dwarfs the sun.  Often it even blots the sun out of the sky.
The Earth is now in a fast orbit around a gas giant: Basileus.  Basileus is stunning, a great ball of weather, with many storms constantly raging on its surface.

Our Moon
Our moon would almost certainly become another of Basileus’ collection of satellites, for the same reason that Mercury and Venus have no moons.  Their gravitational pull cannot contend with that of the sun.  In the same way, Basileus would simply take any of the Earth’s satellites into its own orbit.

Tides
If the Earth was at the same distance from Basileus as it is to the moon now, life would be impossible.  The tides would be higher than the mountains and move at incredible speeds (because the angular momentum needed to keep the Earth in orbit would be phenomenal.)  The seas would have no boundaries; they would just go in the direction of Basileus.  In fact, the gravitational pull of Basileus would probably even start to suck at and take away some of our atmosphere, which is the main reason that life would be impossible.
So the Earth would have to be further from Basileus to support life.  Let us assume that the Earth is in a position where the gravitational effects are equal to that of the Moon in reality.

Letting the Earth support Life
It was thought that solar systems could not be formed with gas giants close to their parent stars.  But so far most of the planets discovered outside our solar system (which are all gas giants) are quite close to their parent stars.
The planet 51 Pegasus B (see Fig. 4), the first planet to be discovered outside the solar system, is closer to its parent star than was previously believed possible.  It is now thought that the planet was formed much further away from the star and its orbit gradually closed in.
The gas giant is so hot that it leaves a gaseous tail behind it similar to that of a comet.  If Basileus were a “hot Jupiter”, it would probably radiate a certain amount of heat to us, depending on its temperature and distance from us.  But it could be considerably damaging when the Earth passed through this tail.  A lot of unwanted hot gas would rain down onto Earth.  It would depend what Basileus was made of, though it would probably be hydrogen and helium that detached itself from the planet because they are the lightest gases.  Hydrogen itself would not be very harmful, but at such temperatures it would be likely to combust when it reached the oxygen of our atmosphere.  This may create spectacular displays in the sky, but it would end up putting a lot of water vapour into our atmosphere, contributing to the destruction of part of the ozone layer.  But not all gas giants which are close to their parent star are “hot Jupiters”.  The planet Upsilon Andromedae c is 0.83 AU from its parent star Upsilon Andromedae and has a temperature of 380 Kelvin.
If, however, Basileus was in a stable orbit and stayed where it was formed, conditions on Earth would be very cold because of the distance from the star.   However humans might possibly still exist if there were more greenhouse gases, which would trap the heat.
Scientists at the BBC have recently been inventing life forms that they think could exist on planets similar to Earth.  One of their imaginary planets is Blue Moon.  Blue Moon orbits around a gas giant, and has thirty times more carbon dioxide – a greenhouse gas – in its atmosphere.  This means that the planet is warm enough for life, but also the atmosphere is very thick.  Earth in this scenario could well be similar to the Blue Moon.  If our atmosphere was as it is now, humans would probably have a very thick natural fur coat.  Most of the Earth would be a harsh icy world, and as soon as we learned about carbon emissions – unless we had grown used to our frozen Earth – the greenhouse effect would be warmly welcomed.

Eclipses
A solar eclipse would occur when Basileus blotted out the sun from the sky.  In fact, about a quarter of the Earth’s orbit (seven days because Basileus has the same gravitational effect on us as the Moon has in reality) could be in the shadow of Basileus at times (see Fig. 5).  On Earth, some plants would have recently germinated.  This sudden darkness could be fatal for these plants.  Most plants that were already fully grown would be able to survive though.

Flying Rocks
Gas giants have a lot of gravitational pull, and so attract a lot of rocks into their orbit.  Basileus would almost definitely have quite a few other moons, and it is also quite likely that it would have at least one ring – as all four gas giants in our solar system and the sun (which has the asteroid belt) do in reality – and we had better hope that the Earth’s orbit never went through that.  Just as we worry about asteroids from the asteroid belt colliding with the Earth in reality, so we would need to worry about rocks from one of Basileus’ rings.  Also, Basileus would attract a lot of other rocks from space which would hurtle towards it.  Many of them might be dangerous to us.  It is very likely that we would have been hit quite a few times in the past.

What could Basileus do for us?
It is very improbable that the gas giant itself could do anything useful for us, except that it might radiate some heat.  But there is no way we could land on it because there is no solid ground.  However one of its moons may well have a very useful or valuable resource such as oil or a useful metal.  The moons could provide a lot for us once we had the technology of space travel.

Conclusion

There would be billions of differences taking effect.  Some of them would be devastating or brilliant, or hardly significant.  Seasons would be daily, because the Earth’s axis would be tilted in relation to the planet, not the sun.
People would behave differently, especially with theological matters.  The Muslim festival of Ramadan would have to be based on the Earth’s orbit around the planet, rather than the Moon’s orbit around us, or something totally different.  Pagan religions would have had different rituals, without doubt.
The whole of history would have been different.  Could Julius Caesar have sailed his triremes across the English Channel with the unpredictable tides created by Adelphos, or would his men merely have had to walk across the low tide?  There might have been many events similar to when Moses crossed the Red Sea.  Asteroids and comets may have collided with the Earth many more times, and at catastrophic times and places.
It is the theory of the butterfly effect, on a much larger scale.  Can the flap of a butterfly’s wing in California stir up a tornado in Texas?  If a seemingly insignificant event or change in prehistory can lead to the whole of the modern world being different, how different would the world be now if a huge difference was made in the making of the solar system?
It is highly likely that in the vast expanse of the universe there would be some life supporting moons that orbit another planet.

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