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A dwarf planet is a celestial body that orbits the sun and has sufficient mass to be almost spherical in form.
A dwarf planet is a celestial body which meets only two of the three official criteria for being regarded as a planet. These standards were established by the International Astronomical Union (iau) in August 2006. First of all, for a heavenly body to be classified as a dwarf planet, it has to revolve around our sun, which obviously means that it has to exist in our solar system. Secondly, it must have sufficient mass to form a more or less spherical form under its own gravity (contrary, for example, to asteroids, whose forms are irregular). However, in the opposite direction of a planet, a dwarf planet has insufficient gravitational pull to clear its vicinity of any other celestial object of significant mass (with the exception of one of its satellites, moonlike).
Pluto was reclassified from a planet to a dwarf planet in 2006 because it is not gravitationally dominant in its neighborhood. However, it is the first known dwarf planet. At present there are five known celestial bodies in our solar system which qualify as dwarf planets: Pluto, Eris, Ceres, Makemake and Haumea.
A dwarf planet is a celestial body that orbits the Sun with sufficient mass to be more or less round in shape. Credit: NASA & ESA
Hubble has supported the study of various dwarf planets and their moons. For example, the telescope has helped to enhance our understanding of the Pluto system; Hubble observations in 2006 uncovered two small moons orbiting Pluto, Nix and Hydra, followed by the discoveries of two more moons in 2011 (Kerberos) and 2012 (Styx). In 2015, scientists gathered all available Hubble data on the four outer moons of Pluto to analyze the system in more depth than ever before. You can learn more about Hubble’s study of the Pluto system in this Hubblecast video.
Dwarf Planet. Credit: NASA, ESA and M. Buie (Southwest Research Institute)
In 2016, Hubble captured an image of the dwarf planet Eris and its satellite Dysnomia. Eris is the world's largest dwarf planet and the second largest in the solar system. Also in 2016, Hubble revealed the first moon ever discovered around the dwarf planet Makemake.
