The Inner Solar System
There are many living worlds in the Solar System, but in the Outer Solar System they tend to be dark and cold. Most life is trapped in the subterranean seas of iceshell moons, huddled around a few hydrothermal vents. There are a few ancient, inhuman thinking machines. But these are very different from organic life, and it's debated whether they are even conscious.
It is not so in the Inner Solar System! Here we find the Seven Earths, the blue gems of creation. For hundreds of millions of years, these worlds have hosted bewilderingly diverse biospheres: several of them are even home to humans!
§ 1 - Auster
Auster is the first and hottest planet, a tidally - locked super - Earth. His dayside is covered by seas of lava, but his nightside is relatively cooler, only home to sporadic molten patches.
Being large and geologically active, Auster has a thick atmosphere despite being so close to the Sun. This makes him extremely windy, making eolian processes a central factor in his geology.
There are a very few settlers on Auster, but most of his inhabitants are geologists. And most of them will soon return to cooler and wetter worlds!
§ 2 - The Hermeoids
The Hermeoids (or the Inner Asteroid Belt) is a torus - shaped region of space, stretching from 0.3 - 0.5 AU. It is home to multitudes of asteroids, most of them with high metallicity. There is a single dwarf planet here, Hermes.
Most of the Hermeoids are nominally ruled by the Cartin Dynasty, a Martian royal house that relocated there after The Years of Ash and Sorrow.
Scientists generally believe that the Hermeoids are the remains of a planet which was destroyed by a giant impact.
§ 2.1 - Hermes
Hermes is a tiny, very metallic dwarf planet, covered in craters. Hermes is the capital world of the Cartin Dynasty, and it has the largest cities this side of Hesperus.
Many geologists believe Hermes is a part of an ancient planet's core, though this is hotly debated.
§ 3 - Hesperus
Hesperus is the dawnstar and the evenstar, the brightest object in night skys of Tellus. He has a much different composition than most of the inner planets, being a mini - Neptune. He does have a large rocky core, but it is obscured by miles upon miles of gases and volatiles. His outer layers are deep blue, making him associated with sapphires in many cultures.
Battered by the solar wind, Hesperus' atmosphere is being gradually stripped away. It's estimated that he might have had an additional 1.5 - 2 earth masses when the solar system formed. In tens of millions of years, Hesperus' atmosphere will be totally carried away, leaving just a rocky, airless core.
Hesperus has three little airless moons, all rich in useful minerals. They've been settled over the last couple of centuries, and today they're home to more humans than anywhere other than the Seven Earths.
§ 3.1 - Eryx
Eryx is the nearest moon to Hesperus, and consequently is subjected to great tidal forces. This makes him quite geologically active, scarring his surface with earthquakes and volcanism. As a result, he appears less cratered than Hesperus' other moons.
§ 3.2 - Aeneas
Aeneas is Hesperus' largest moon, 8% as massive as Tellus. In ancient times, he appears to have been a verdant ocean world. But the sun grew brighter and hotter, and his seas turned to steam. Soon they were carried away by the solar winds, leaving miles upon miles salt flats.
There is still some liquid water on Aeneas, almost all of it in aquifers (though there are a few ponds in polar depressions). A few hardy microbes cling to life here, but most of the Aenean biosphere is long dead.
There was once an industrial civilization on Aeneas, revealed by a thin layer of micro - plastics and industrial byproducts. The ruins of their ancient machines and colonies can be found on Eryx and Himeros, where there has never been any erosion from wind or water. Many believe that ancient thinking machines are descended from Aenean civilization, though they have never confirmed nor denied this.
Either way, civilization has come to Aeneas once more! He has many valuable minerals, and his aquifers and higher gravity make him very attractive to settlers. First they were Martians, but many people have come from other planets more recently.
§ 3.3 - Himeros
Himeros is a little rocky world, heavily - cratered and criss - crossed by rupes. He's 0.055 times as massive as Tellus and quite dense, about 70% of his mass is accounted for by metals.
Thousands of people live and work on Himeros. His high metallicity makes him an ideal location for mining, and his low gravity and nonsexistent atmosphere makes it easy to export minerals. However, his low gravity makes few people want to live there for long periods of time. It's common for miners to work on Himeros while their families live in orbit or on Aeneas.
§ 4 - Venus
Venus is the first of the seven Earths, a warm and living waterworld. Usually, her surface is obscured by clouds. It always seems to be raining on Venus.
Venus is more oceanic than Tellus; while she has thick granitic plates, these are mostly shallow seas rather than continents. Her only landmasses would be great mountain ranges on the Earth, and these are few and far between. The rain and wind are very good at eroding would - be islands.
However, most Venusians don't live on dry land! Rather, they tend to live on mats of floating plant matter or in huge marine forests, growing out of the water like mangrove trees.
As a result, the Venusians have little metallurgy. However, this doesn't mean they don't have technology. They have bred hundreds of plant species for their own purposes--woods as strong as steel, predatory plants to act as sentries, even floating plants to serve as airships. To be sure, their technological progress has been slower than that of Tellurians or Martians, but Venusians civilization is also much older, and they tend to have longer life - spans.
§ 5 - Tellus
Tellus (or the Earth) is a warm, living world. She is mostly covered in vast salty oceans. She has six continents, Australia, Eurasia, Antarctica, North America, South America, and Africa.
Tellus was in the early industrial age until the 1920s, when large numbers of Martians immigrated to escape natural catastrophes on that world. This was mostly peaceful, millions of Martians peacefully migrated to the plains of Argentina and the North American prairies. But some did forcibly invade, most notably the Martian Karoshin Dynasty, which conquered Northern China, Siberia, and Korea.
Nevertheless, Martians' technology caused an economic boom, and soon Tellurians were exploring and colonizing the solar system too.
§ 5.1 - Cynthia
Cynthia is Tellus' sole large moon (and, as a fraction of her orbital parent, the most massive moon in the solar system!). About 0.1 times as massive as Tellus, Cynthia is a living world with a thick atmosphere and rich biosphere. Her surface is split between shallow seas (called Maria) and dry land, often covered in purplish vegetation.
She is tidally locked to Tellus, making her day last as long as a Tellurian month. As a result, many animals hibernate or have very unusual sleep cycles. Cynthian humans have naturally split brains, one hemisphere sleeps for several hours while the other controls the body. Both typically share memories, personalities, and preferences, but occasionally something goes wrong and they function as two separate people.
§ 6 - Mars
Mars--or Laran--is the smallest of the three habitable planets, just under two thirds as massive as Tellus. Most of his surface is covered in cold deserts, dyed red by iron oxide.
But, there are four shallow seas, and more lakes, each sheltering steppes and woodlands around their coasts. As a result, plants and animals are more isolated on Mars than the other planets; there are two Martian species rather than one!
Martian civilization is very old, only second to the Venusians. There were ancient ruins on Mars before Tellurians discovered agriculture. This is one of the reasons they were the first people to explore the Solar System: they had a big head start.
In the Early twentieth century, Mars suffered a series of great volcanic eruptions, causing a terrible period in Martian history called the Years of Ash and Sorrow. This forced many Martians to flee to other worlds (mostly Tellus, Hesperus, and the Hermeoids). But, today Mars has recovered spectacularly, and most Martian countries have very high standards of living.
§ 7 - Jove
Jove is a huge gas giant, orbiting at the fringes of the habitable zone. Unlike the outer gas planets, whose topmost clouds are made of ammonia, Jove is warm enough for clouds of water vapor! This allows a number of exotic gasbag organisms to live there, though none of them are smart enough to have interesting conversations.
Jove has four large moons, as well as a faint ring system.
§ 7.1 - Vulcan
Vulcan is a desolate moon, about 3% as massive as Tellus. His atmosphere is very thin, and there is little liquid water. Jove's tidal forces cause frequent Earthquakes and intense volcanism, staining his surface an unpleasant yellow color and creating lakes of molten rock. His ejecta create a plasma torus, irradiating the surrounding area.
§ 7.2 - Okeanos
Okeanos is a little waterworld, it has a few native microbes, but no complex life. But this has made him the ideal canvas for humans! Many people have grown floating islands or built great ship - cities. Many health tourists come there, hoping the relatively sterile, low - gravity environment will help them. He is also a popular honeymoon location for Celish newlyweds!
§ 7.3 - Cels
Cels is a warm garden - world, with most of her landmass concentrated in the Northern hemisphere. Her interaction with Jove's magnetosphere creates beautiful aurorae, but they also produce intense radiation which can be dangerous for people and animals. As a result, many of Celish creatures live underground or have thick, radiation - resistant shells.
This has led Celish people to spend most of their time underground, living in caves, warrens, or vast subterranean fortresses. They've grown short and thin to fit through tight spaces, with big eyes to see better in the dark. They have a much stronger sense of place attachment than other humans, and they tend to be a bit inflexible and obsessive across many areas of life.
§ 7.4 - Boreas
Boreas is Jove's last major moon, a little slushball world. Most of his surface is covered in thick sea - ice, but the tropics are slushy--maybe even clear and liquid in the Summer! He has no native people, but is home to many interesting animals, like the antifreeze shrimp and the fur - bearing shark. But most notable are Borean Sea Dragons, who are more intelligent than humans by most metrics.
Boreas has little of value, at least little that can't be gotten for cheaper elsewhere. So, most of his inhabitants are scientists, though there are a few small fishing settlements.