Editing Planet

[[Category: Astronomy]]
== Explanation ==
A planet is a massive astronomical body that is in an [[orbit]] around a [[star]]. The criteria for an object being a planet falls within the limits of its mass. The mass of the object for it to be called as a planet should be larger than that of an [[asteroid]] but not large enough to have its own [[thermonuclear fusion]] in the core.

Planets are categorized as [[Terrestrial planet|terrestrial]] and [[Giant planet|giants]]. For example, in our [[solar system]], the planets [[Mercury]], [[Venus]], [[Earth]], and [[Mars]] are the terrestrial planets as they are mostly made up of silicate rocks and other metals. The other four planets, [[Jupiter]], [[Saturn]], [[Uranus]], and [[Neptune]] are the gas-giants as they mostly contain gas.

== Frequently Asked Questions ==
=== What are the formal requirements for an object to be a planet? ===
As per the International Astronomical Union, for an astronomical body to be classified as a planet, it has to pass the following three criteria.<ref>International Astronomical Union | IAU. (2017). Iau.org. Retrieved 9 August 2017, from https://www.iau.org/news/pressreleases/detail/iau0603/</ref>
* The said astronomical object should be orbiting a star.
* The mass of the object should be massive enough to have its own [[gravity]] shape itself into a [[spheroid]], assuming a [[hydrostatic equilibrium]].
* The object has cleared its neighbours around the orbit, with its gravity.

=== Why do planets rotate about an axis? ===
When a planetary system forms from a [[nebula]], the [[angular momentum]] is conserved in the [[accretion disk]]. This accretion disk is where the primordial [[planetesimal]]s are believed to evolve. As the [[protostar]] begins to evolve, the planetesimals evolve into [[protoplanet]]s along with a rotation to conserve the angular momentum of the system. And due to [[inertia]], they continue to rotate on its axis unless any external forces like an asteroid impact or a [[satellite]] affect it.

=== Why planets orbit in the same plane? ===
When the nebula collapses, the dense gases at the centre spins fast to conserve angular momentum of the total system. This creates an accretion disk around it in a plane. The planets orbit in the same plane as that of its primordial accretion disc where it evolved.

== References ==
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