Hypothetical Planets
Various unknown astronomical objects have been hypothesized throughout recorded history. For example, in the 5th century BCE, the philosopher Philolaus defined a hypothetical astronomical object which he called the "Central Fire", around which he proposed other celestial bodies (including the Sun) moved.Marco Ceccarelli, ''Distinguished Figures in Mechanism and Machine Science'' (2007), p. 124. Types of hypothetical astronomical objects Hypothetical astronomical objects have been speculated to exist both inside and outside of the Solar System, and speculation has included different kinds of stars, planets, and other astronomical objects. * For hypothetical astronomical objects in the Solar System, see: List of hypothetical Solar System objects * For hypothetical stars, see: Hypothetical star * For hypothetical brown dwarfs, see: List of brown dwarfs * For hypothetical black holes, see: Hypothetical black hole * For extrasolar moons, all of which are currently hypothetical, se ...
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Earth With Two Moons
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surface is made up of the ocean, dwarfing Earth's polar ice, lakes, and rivers. The remaining 29% of Earth's surface is land, consisting of continents and islands. Earth's surface layer is formed of several slowly moving tectonic plates, which interact to produce mountain ranges, volcanoes, and earthquakes. Earth's liquid outer core generates the magnetic field that shapes the magnetosphere of the Earth, deflecting destructive solar winds. The atmosphere of the Earth consists mostly of nitrogen and oxygen. Greenhouse gases in the atmosphere like carbon dioxide (CO2) trap a part of the energy from the Sun close to the surface. Water vapor is widely present in the atmosphere and forms clouds that cover most of the planet. More solar energy is ...
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