idkIn the near-future, when the discovery of alternate Earths become the talk of nations, an unlicensed scientist had discovered one such alternate universe, categorized as #9, in which nine rocky planets have the following exact features:
These Nine Earths orbit a complex series of stars--first, a binary of G-type main-sequence stars, or "yellow dwarves" (Bestla, 1.15 solar masses; and Borr, 0.84 solar masses), then a trinary of K-type main-sequence stars, otherwise known as "orange dwarves": Odin (0.8 solar masses), Vili (0.7 solar masses) and Ve (half a solar mass). The Nine Earths, in turn, orbit those two star systems in a habitable zone. But how wide of a habitable zone would such systems result in?
- Set in a habitable zone in which liquid water is possible
- At least one large satellite to stabilize the axial tilt
- A predominantly iron core, which means each of the Nine Earths has a solid, active magnetic field
- The inner core measuring a radius of 760 miles (This doesn't change with any of the planets' outer diameters, especially Mars-sized Jotunheim, the smallest of the Nine Earths. So if planets of different sizes have such cores of these parameters and dimensions, would they affect radiation and climate in any way?)
- A predominantly silicon crust
- A predominantly silicon-magnesium mantle
- Atmospheric pressure no greater than one bar
- Clear, tangible evidence of life. (However, the lifeforms on all of the Nine Earths are microbial, which would be perfect for our criminal's first phase of his overall terraforming plan--dump pioneering colonies of photosynthetic cyanobacteria on the primeval oceans--if the two last of the Nine Earths didn't throw a monkey wrench at that.)
The Nine Earths are listed as following, in order of orbit:
- Alternate Earth 9a, "Muspellheim", Venusian in size, orbiting the pantheon from the inner boundary of the habitable zone. The oceans and continents are alive with volcanic eruptions of all types--low gas/low viscosity (quiet lava eruption), high gas/low viscosity (lava fountain), low gas/high viscosity (dome-building eruption) and high gas/high viscosity (classic Ring of Fire eruption). The oceans, in turn, have an average pH between 7 and 8.3, comparable to Yellowstone's Grand Prismatic Spring back home. Would our cyanobacteria colonists survive in such conditions? After oxygenation, would complex, multicellular life follow suit?
- Alternate Earth 9b, "Alfheim", Terran in size. Atmosphere is predominantly carbon dioxide and methane, but the clouds are so concentrated in sulfur particles that atmospheric albedo is 100%. Should the atmosphere ever be oxygenated, would the albedo drop? And would complex, multicellular life thrive in an atmosphere in which there is a lot of sulfur in the clouds?
- Alternate Earth 9c, "Jotunheim", Martian in size. The smallest of the Nine Earths. Would the lower gravity still hold a solid, breathable atmosphere?
- Alternate Earth 9d, "Vanaheim", Terran in size. In a certain respect, a real-live Abyssia.
- Alternate Earth 9e, "Asgard", Venusian in size. Earthlike in every respect except for its Venusian diameter and mass and therefore, its gravity.
- Alternate Earth 9f, "Midgard", Terran in size. The most Earthlike of the Nine Earths. Granted, like most of the others, it is Archaen in size and environment, so it's currently not hospitable for us, but that is why we have cyanobacteria as Phase I.
- Alternate Earth 9g, "Svartalfheim", Terran in size. We have now come to the point so far into the habitable zone that the climate is getting cooler. Its thinner atmosphere--1/12 the thickness of Earth's--coupled with the surface's black rocks give this the lowest albedo of the Nine Earths, 1%.
- Alternate Earth 9h, "Helheim", Venusian in size. Waters at the poles are frozen solid, but those at other latitudes are liquid oceans thickly veiled in clouds of steam. Colonization by cyanobacteria would be declared redundant for this one.
- Alternate Earth 9i, "Niflheim", Terran in size. The last of the Nine Earths orbits the pantheon from the outer boundary of the habitable zone. As a result, the mean surface temperature is 0 degrees Celsius. 30% of the atmosphere is oxygen, but all hint of water is locked in ice, two miles at the thickest. Beneath the ice are rich sources of two factors of greenhouse gases--volcanoes and methane hydrates. Because of all this oxygen, colonization by cyanobacteria is deemed redundant. But our criminal would not settle for dark-loving germs, so he improvised by shooting one nuclear missile into the atmosphere which, upon contact, will detonate and release 100 megatons of methane into the atmosphere. Would this be enough to launch a global chain reaction?
a4: The very interiors of planets are... extremely odd. A smaller core for a more massive planet may mean the core's more dense, and that's likely to make the core at least a little hotter, but I don't think this would.
a9: Generally, habitable zones for close binaries are found by taking the luminosities of both stars- from there, simple worldbuilding tutorials like Artifexian's solar system videos should answer that question for you.
b1: You should be able to get a brand of cyanobacteria that thrives in such conditions- even if you had to guess how cyanobacteria lived on early Earth to do it.
b1b: Probably, eventually- barring catastrophic climactic change or a big solar flare?
b2: ...Possibly. I don't recall, but I think sulfur dioxide is pretty sucky for clouds.
b2b: If it was evolved for it.
b3: Again, possibly. If I recall correctly, its lack of a magnetic field is integral to the loss of Mars' own atmosphere- if it's younger, or if you find a way to get its core running longer (higher mass is an easy solution), it'll probably be fine.
b9: That probably involves complicated fluid dynamics calculations, but so long as the methane doesn't get messed up it should at least tip the temperature a little longer- though you certainly don't need to be above zero celsius to have liquid water, even if it's the same pressure as Earth's surface.