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Calidian
Calidian
Image from Steve Bowers
The 'dark' side of a Calidian world is intrinsically luminous because of its high temperature. Such planets are less dense than cooler worlds with the same composition and mass, so they are greater in diameter
In NoLWoCS, Calidians (prefix: Cali-; eg. CaliNeptunian, CaliJovian) are the hottest of giant planets, with tropopause temperatures above 2100 K. Above this temperature, the highest temperature clouds, that of aluminium oxide and titanium dioxide, dissipate, and the planet becomes cloudless. At these temperatures, the dayside may be hot enough to perceptibly glow due to blackbody radiation, even under full sunlight.

Calidians are very rare; giant planets in very close orbit often do not last long before their orbits decay and they fall into the star, or they lose all their atmospheres and become terrestrial planets. Protoplanetary disc-driven inward migration also generally stops at orbital periods of a few days, too far for the planet to become a Calidian. Likewise, few forming planets ever become hot enough to reach this temperature range, and those that do quickly cool off after a few million years.
 
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Development Notes
Text by AstroChara
John M. Dollan
Initially published on 31 December 2007.

Overhauled 2025-10-14 by AstroChara
 
 
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