In 2008, the IAU cosmochemistry group (group of scientists) published a committee opinion solicited not by any specific proposal, but by a request from the International Astronomical Union (IAU), on the status of the discovery of HD 98800 b, the first exoplanets (planets beyond the Solar System) directly imaged by direct imaging by the Hubble Space Telescope (HST) and confirmed by radial velocity measurements in early 2015. The committee believed that the situation concerning exoplanets could be more accurately described with the term "exomoon". A sub-committee of the IAU's expert group on small bodies made a similar recommendation in 2017 for a "sub-Neptunian planet". The Committee on Small Body Nomenclature of the International Astronomical Union decided that an exomoon (and exoplanet) should be defined as follows:
An exomoon of an extrasolar planet is an object of sufficient mass and diameter that exists in orbital resonance with the planet. Exomoons have diameters less than one-half the diameter of the planet, which is 5,700 kilometers (3,600 mi) for a terrestrial planet. Any system composed of an Earth-like terrestrial planet and a circumplanetary object (such as a moon) that has a temporary maximum distance from the central planet of less than 5,700 kilometers (3,600 mi) is an exomoon system. Situations in which it is not possible for the circumplanetary object to have a temporary maximum distance from the surface of the planet below 5,700 kilometers are excluded from the definition of an exomoon, and the object is not included as a planet. Furthermore, the orbit of a circumplanetary object cannot cross the orbit of the planet (except on the planetary equator). The orbital plane of the circumplanetary object and the orbit of the planet must be coplanar.
The geological formation of the satellite lyons from the early moon Theda, the earliest form of a life-bearing world.Because the surface of Theda began to be oxidized, we could say that life appeared here, but it is not certain whether the life occurred on the surface, or on a subsurface ocean. d2c66b5586