Rogue planet

==Description==
A rogue planet (also termed a free-floating planet (FFP), isolated planetary-mass object (iPMO), interstellar, nomad, orphan, starless, unbound or wandering planet) is an interstellar object of planetary mass which is not gravitationally bound to any star or brown dwarf. Rogue planets originate from planetary systems in which they are formed and later ejected. They can also form on their own, outside a planetary system. The Milky Way alone may have billions to trillions of rogue planets.
==Formation==
There are in general two scenarios that can lead to the formation of an isolated planetary-mass object (iPMO). It can form like a planet around a star and is then ejected, or it forms like a low-mass star or brown dwarf in isolation. This can influence its composition and motion.
==Warmth==
Interstellar planets generate little heat and are not heated by a star. However, in 1998, David J. Stevenson theorized that some planet-sized objects adrift in interstellar space might sustain a thick atmosphere that would not freeze out. He proposed that these atmospheres would be preserved by the pressure-induced far-infrared radiation opacity of a thick hydrogen-containing atmosphere.
During planetary-system formation, several small protoplanetary bodies may be ejected from the system. An ejected body would receive less of the stellar-generated ultraviolet light that can strip away the lighter elements of its atmosphere. Even an Earth-sized body would have enough gravity to prevent the escape of the hydrogen and helium in its atmosphere. In an Earth-sized object the geothermal energy from residual core radioisotope decay could maintain a surface temperature above the melting point of water, allowing liquid-water oceans to exist. These planets are likely to remain geologically active for long periods. If they have geodynamo-created protective magnetospheres and sea floor volcanism, hydrothermal vents could provide energy for life. These bodies would be difficult to detect because of their weak thermal microwave radiation emissions, although reflected solar radiation and far-infrared thermal emissions may be detectable from an object that is less than 1,000 astronomical units from Earth. Around five percent of Earth-sized ejected planets with Moon-sized natural satellites would retain their satellites after ejection. A large satellite would be a source of significant geological tidal heating
== In Space Engine ==
There are rogue planets in Space Engine, and there may even be life on them. Probably due to the dense atmosphere, the greenhouse effect, etc, some rogue planets maintain stable temperatures. You can find a temperate marine terra with multicellular marine and terrestrial life - Example.
#https://en.wikipedia.org/wiki/Rogue_planet
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