HADEAN WORLDS

Summary of properties:

Hadean worlds are relatively rare in planetary systems, they are generally of terrestrial planet composition and because of the extreme amount of energy in their systems they are in constant volcanic upheaval. Often there surface is racked with lava, though plates may exist on the surface they are relatively thin and short lived, and always undergoing change from volcanoes punctuating there surfaces or from meteoric collisions. Hadean worlds are in short the first chapter of every terrestrial planets creation.

Detailed description:

These types of worlds are present generally only in the early stages of solar system development, growing from planetesimal impacts these worlds are constantly bombarded from collisions with small and occasionally large celestial bodies. Though the violence from these events may be able to eject some of the material from these early planet’s gravity well, most of the material is recaptured and the planet slowly grows.

The term micro-Hadean is used to describe a celestial object that is well on the way to form a full sized terrestrial planet (roughly between 500km, and 5000km), with further growth these small planets may grow on to more interesting stages of development, if however the source of their growth material disappears their path will change, lacking enough mass to retain an atmosphere there once molten, out-gassing surface cools and hardens, these airless bodies pass into a second category in planetary description, Mercurian, named after the archetypal example Mercury. Though Micro-Hadeans are the origins for most of these types of bodies, most micro-Hadeans follow other evolutionary pathways.

In the disorganized chaos in protoplanetary discs many of these young bodies will be gobbled up by the sun or flung out of the solar system, some however go on to gain more mass from the environment and become fully fledged Hadeans. The important transition is when the planet has enough mass to retain an atmosphere, the initial atmosphere may be very unpleasant from a biological point of view being a brew of gases from the molten rock of the planet’s composition, but this insulating layer is enough for the planet to develop more interesting lifecycles.

If the planet is close enough to the sun the combination of initial atmosphere and huge amount of heat input form the sun maybe enough to keep the planet molten well after the initial surface bombardment has finished, these types of Hadeans are described as ‘perpetual’ Hadeans, though this name could not be further from the truth. Though these planets may exist in this molten state for a long time, the ferocity of the sun’s local presence may be enough to strip the atmosphere from the planet over time, and expose the surface to cool, and eventually turn such a planet into a Mercurian, or if the planet is closer still to the sun, its extensive atmosphere may slow the planet in its path and lead to orbital decay where it falls into the sun. Some perpetual Hadeans around appropriate stars may also have a third option, this is particularly true for low mass stars whose birth may be spectacular and bright, but whose main existence will be dim and cool. When the heating from the sun declines the long wracked Hadean will slowly cool putting it back onto the pathway from which other planetary types can evolve.

Though Hadean planet may be still surfaced with seething lava, the planet’s composition and location have in part decided its fate. A large Hadean, large enough to maintain its atmosphere that is, basically has two initial pathways, firstly to cool down and become proto-Gaian, or secondly to generate thick greenhouse like atmosphere, and become Venusian.

As the energy from the planet’s initial formation is radiated away or dissipated the planet will slowly move out it’s brief (in terms of total lifecycle) Hadean phase into one of the paths available to it, however though the Hadean phase is the start of every world, many worlds end in the same manner as their sun expands and roasts them back to the stage they started their lives, these final lava wracked planets are called ‘end-stage’ Hadeans, and are usually brief as either the sun consumes the inner terrestrial planets, or the sun dims and dies, freezing the world now stripped of its atmosphere.