EUROPAN WORLDS

Summary of properties:

Often only considered only as ice worlds beyond the terrestrial zones these worlds sometimes come into the light after the initial formative stages of the solar system and go on to generate the more commonly known Thalassean type planet. The Europan types worlds are also the stock character in Jovian satellite systems and here as well as close to the sun do these worlds offer a haven for life.

Detailed description:

            Europan worlds have two crucial differences from normal terrestrial worlds, the first is water, and lots of it, the second is temperature, which they are sadly deficit. Europan worlds are the frozen terrestrial planets of the solar system, though most spend their entire frozen lives around jovian planets, some do eventually stray into the warmer regions of the solar system, and eventually lead on to more exotic lifecycles.

            The most important structural difference is water, Europans do not have to originate in the frigid regions of the protoplanetary disc, they can even form in regions which we would only associate with the ‘traditional’ terrestrial worlds. Many solar systems are subject to a rough start, their protoplanetary discs attacked by the fierce glare of bright nearby stars, the strong UV radiation helps to photoevaporate a lot of the more volatile material off, in regions not only far from the sun, but also in the region of the forming terrestrial worlds. This desiccation, for lack of suitable words, is crucial to form the more familiar Earth like planets, but if the protoplanetary disc forms well away from these fierce short lived stars, they retain much more of their initial volatile materials. Europans therefore can have more than one origin, firstly form the cooler regions of more traditional protoplanetary discs, and secondly in the terrestrial regions of ‘wet’ protoplanetary discs.

            Though ice content is defining of Europans these planets still have a sizable amount of rock in them, as much as true terrestrial worlds, though over this rock there is a thick mantle of water ice. If the planet forms in a particularly cool region of the solar system, it will also be able to pick up a range of organically important volatiles which are not so readily available closer to the sun, such as methane, ammonia, and carbon dioxide. Though in the planet’s frozen state these materials are of little use to life, when these worlds as captured by Jovians and tidally heated, or move and thaw closer to the sun, this wealth of organic material makes these worlds rich.

            Unlike many other planetary types there is no clear distinction in size for Europans, most are small (less than 3000km) and become captured by, or form around Jovians, these worlds subsequently spend most of their lives frozen satellites around these planets, also being so small they can not retain sizable atmospheres. Larger icy bodies, or those further still from the sun may be able to retain atmospheres, usually of exotic composition, these icy worlds are really described as Titanian after the archetypal example, Titan.

            The most interesting Europans are those will eventually evolve into Thalassean worlds, these worlds are large, often in excess 15,000km, in traditional protoplanetary discs only their early sunward migration has prevented them growing into gas giants. These types of Europans are large enough to retain atmospheres, generally of a more life friendly nature than the initial proto-gaian worlds, often made up from nitrogen gathered early from the further parts of the solar system, and oxygen made from the photo-dissociation of ice. These worlds with sufficient heat will develop into the Thalassean worlds, and then perhaps move onto other planetary types. Europans therefore are planets of potential, like the Hadeans, which can under the right conditions become the abodes of life.