Forget "habitable super earths" how about a nice "mini earth?
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Forget "habitable super earths" how about a nice "mini earth?
Core of iron, more dense than earth, so it's smaller but has the same gravity. Then a crust like earth and atmosphere. I guess the atmosphere would need to be deeper to have enough pressure?
I wonder how small you could go?
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Hm. If we keep the size and use a denser core, bad things happen.
- Iron: Density = 7.87 g/cm³
- Nickel: Density = 8.91 g/cm³
Earth's Core: The average density is estimated at around 12.6–13 g/cm³ due to the high pressures and temperatures compressing the iron-nickel alloy.
Gold: Density = 19.32 g/cm³ at standard conditions.
We can expect 24–26 g/cm³ density from a gold core earth.
g = GM/R2, we change M but keep the rest, so this scales linearly with the mass, and since the core is about 10-20% of the total earth mass, around 1.1 times current g, so around 11 m/s2 (10% higher as an upper estimate).
Escape velocity scales with this, we get 12-12.5 km/s instead of 11.2 km/s, and chemical multistage rockets gibvt you 13 km/s at best.
Space travel with chemical engines on gold core earth would be almost payload-less.
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Set core radius to 50% of earth radius, so core volume is 12.5% of earth volume.
Earths core is density 12 for materials with a surface density of 8, we assume (falsely, pressure is likely lower) the same for gold 19.2 *1.5 = 29-ish.
Mantle density is unchanged 4.5.
We get a mean planet density of RhoPlanet = 29*0.15 + 4.5 * 0.85 = 8.15-ish.
Surface gravity is g = GM/R2 becomes 4/3*math.pi*G*RohPlanet*R
We want the surface gravity to be the same, 9.81, so 4/3*math.pi*G*RohPlanet*RPlanet = 4/3*math.pi*G*RohPkanet*REarth
or RohPlanet * RPlanet = RohEarth * REarth
or RPlanet = RohEarth/RohPlanet * REarth = 5.514/8.15 * 6371 = 4310
Your gold core planet would have around 4310 km diameter, 2/3 the diameter of earth.
With more math we get around 80% of the escape velocity of earth, around 9 km/s.
That will also lead to a thinner atmosphere composed of heavier gases such as oxygen and nitrogen, but likely no helium or hydrogen over geological timescales (not too different from earth).
Assuming an atmospheric pressure of 70% earth (70 kPa), and assuming humans need a partical pressure of 16 kPa to function effectively, we need the oxygen percentage to be over 23%. It was about 35% at one point in time on earth, in the late Carboniferous. With that, we could go as low as 50 kPa total atmospheric pressure. At that pressure a human would begin to require a pressure suit, though, for other reasons.
La Paz airport in Bolivia is at 4000m, 63 kPa. Air pressure at cruise altitude is 20-30 kPa.
Surface area of a world 2/3 the size of earth is 4/9, so 44%. This deletes the Pacific Ocean, the Americas and sadly also New York. It could be the world of Chris Columbus, where you leave Spain westward bound and end up in India instead of the Caribbean. Maybe the golden City of the (deleted) incas are really in the core of the Earth on this world.
Could probably retain atmosphere, could use higher percentage of oxygen (not too bad) and would be living at sea level like currently in La Paz or something.
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@futurebird Total amount of gold available to humans is around 200_000t,
https://www.visualcapitalist.com/sp/chart-how-much-gold-is-in-the-world/
https://www.answers.com/earth-science/How_much_gold_has_been_mined_in_human_history
https://goldsurvivalguide.co.nz/how-much-all-gold-in-world-worth/That is a cube of 21.something m edge length at standard conditions. So no gold core earth any time soon.
Image: https://x.com/KatysCartoons/status/1504463231380865031
