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Vesperian Type Worlds
Tidally locked terrestrial worlds | |
 Image from Steve Bowers | |
| Twilight, a tidally locked terrestrial world | |
Worlds that orbit a star closely (generally less than 0.5 AU) tend to become tidally locked to the star in a relatively short amount of time. Since the habitable zone for red dwarfs (and for many orange dwarfs) falls inside this limit, many worlds located around these stars which might otherwise become temperate Gaian worlds become tidally locked Vesperian worlds by the time Terragen explorers reach them.
In the Extended World Classification system tidally-locked worlds of any kind are known as Videntian worlds; a terrestrial Vesperian world with water present would be given the classification Videntian AquaGaian.
Worlds such as this can vary greatly, with remarkably different surface conditions resulting from having a permanent day and night side. However, a small but significant fraction of Vesperian worlds have developed biospheres that are stable for hundreds of millions, even billions of years. A particular set of circumstances must be met for a Vesperian world to become suitable for life, and the types of stars that they orbit are almost exclusively late K and early M-type stars. However, these worlds are so numerous that, in an overview of the Milky Way, these worlds might actually be at least as numerous as more standard Gaian Type worlds.
Many vesperian worlds, like Senrau, have atmospheres which rotate constantly, bringing cool air from the frozen darkside to the hotter lit side and vice versa. This rotation is in part driven by the slow actual rotation of such a world; of course, any tidally-locked planet rotates once every orbit. The amount of rotation is therefore dependent on the orbital period. Planets very close to their star will have short years, and therefore more rapid atmospheric rotation; tidally-locked planets with longer orbits show much less atmospheric rotation, sometimes none at all.
 Image from Steve Bowers and The Astronomer | |
| Senrau, showing the atmospheric currents which transfers heat from one hemisphere to the other. | |
On other worlds which have thinner atmospheres of a few bar or less, the most hospitable location is at (or near) the terminator between the permanent light side and the permanent dark side. Here warm winds melt the ices of the dark side while cool winds refresh the searing heat of the permanent day side. Examples of this kind of world include Dante, Raphael and Twilight.
 Image from Steve Bowers | |
| Bullseye, a vesperian world with a semi-permanent substellar cyclone, caused by the interaction between solar heating and the planet's rotation. | |
In some planets the circulation of the atmosphere is more dramatic and irregular, and can sometimes form double permanent rotating cyclone storms near the substellar point. An example of such a world is Bullseye. The direction of the rotating storm may reverse periodically, and may be affected by the axial tilt of the world (usually minimal in a vesperian planet) or by the effects of other planets in the system.
Polyphemian subtype worlds
Icy worlds with a subsurface ocean, where the heat from the local star has melted a large patch of open water. In EWoCS these worlds classified as Glacial Videntian AquaGaian types. Image from Steve Bowers | |
| Netenwe has a large, irregularly-shaped open stretch of water on the sunward side, which is shaped not only by the heat of the local star, but by the circulation of the atmosphere. | |
 Image from Steve Bowers |
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Development Notes
Text by John M. Dollan and Steve Bowers
Initially published on 18 November 2008.
Minor image updates by the astronomer, 2020
Initially published on 18 November 2008.
Minor image updates by the astronomer, 2020
