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Introduction to Dwarf Planets


Eris

Pluto

Makemake

Haumea

Ceres

 

Initial Impressions of Pluto

Surface Ice on Pluto

More Geological Activity on Pluto

Pluto's Moon Charon

Pluto's Atmosphere Indicates Current Geological Activity

Introduction

While the Solar system has eight major planets, there are a number of smaller planetary bodies called  Dwarf Planets. The term Dwarf Planet was adopted by  International Astronomical Union in 2006 following the discovery of Eris, however the term was first used in 1990. Currently five are officially  recognized, but many more may exist.

What are Dwarf Planets

A dwarf planet is a planetary body that has enough mass to be round, orbits the sun directly (it is not a moon) and it is in a zone of similar objects that cross its path. This is actually a rather sloppy definition it would be better to make such a category based on orbiting the Sun and being below a certain mass, placing the cut off point between planet and dwarf planet just below the mass of Mercury and Earth's moon. The dwarf planets in the solar system are found in the asteroid and kipper belts. The category of dwarf planet was adopted by International Astronomical Union (IAU) in 2006 following the discovery of Eris. As a result Ceres was up graded from an asteroid to a dwarf planet and Pluto was downgraded from a planet to a dwarf planet.

Known Dwarf Planets

There are currently five officially recognized dwarf planets, though there are probably many many more. They are Ceres, Pluto, Eris, Makemake and Haumea. There are another six almost certain dwarf planet, 2007 OR, Quaoar, Sedna, Orcus, 2002 MS and Salacia, with at least a dozen other highly likely prospects.


Eris

Eris
NASA's Jet Propulsion Laboratory | California Institute of Technology

Eris is the second largest dwarf planet next to Pluto it does however have more mass than any other know dwarf planet. Its discoverey on January 5, 2005 by a team at Palomar Observatory prompted reconsideration of Pluto's designation as a planet since at the time  it was thought to be larger than Pluto but it is actually 23 km smaller than Pluto. Eris has one moon called Dysnomia.

Mass 1.67 X 1022 kg 0.0028 Earth
Radius 1,163 km 0.18 Earth
Surface gravity 0.793 m/s2 0.084 g
Escape velocity 1.384km 0.122 Earth
Length of Day 25.8 Hours 1.1 Earth days


NASA's Jet Propulsion Laboratory | California Institute of Technology

Aphelion 97.56 AU
Perihelion 37.77 AU
Eccentricity 0.44
Orbital period 557 Years
Inclination 44o

 


Pluto

Pluto
NASA's Jet Propulsion Laboratory

Pluto was discovered on 18 February 1930 by Clyde Tombaugh.  Pluto was considered our solar system's ninth planet for 76 years before being downgraded to a dwarf planet in 2006. It is one of two dwarf planets that have been visited by probes. This occurred with the flyby of NASA's New Horizons spacecraft in on July 14, 2015. Pluto has 5 moons Charon, Nix, Hydra, Kerberos, and Styx,of which Charon being the largest.

Mass 1.3 X 1022 kg 0.0022 Earth
Radius 1,186 km 0.18 Earth
Surface gravity 0.620 m/s2 0.063 g
Escape velocity 1.212 km 0.107 Earth
Length of Day 153.6 Hours 6.4 Earth days
Temperature 44K −230 C (−390 F)


Curacy of: NASA

Aphelion 49.32 AU
Perihelion 29.66 AU
Eccentricity 0.25
Orbital period 248 Years

 


Haumea

Haumea

Haumea was discovered on  December 28 2004 and has two moons Hiʻiaka and Namaka. It is one of the fastest rotating object in the solar system causing it have an oblong shape.

Mass 4 X 1021 kg 0.00066 Earth
Radius 996 km 0.25 Earth
Surface gravity 0.44 m/s2 0.045 g
Escape velocity 0.91 km 0.081 Earth
Length of Day 4 Hours 0.17 Earth days

Aphelion 51.48 AU
Perihelion 34.95 AU
Eccentricity 0.191
Orbital period 285 Years
Inclination 28.19o


Makemake

Makemake

Makemake was discovered by a team at the Palomar Observatory on March 31, 2005. Its discovery helped prompted the reconsideration of the definition of a planet resulting in and to creation of  the new dwarf planet classification. Makemake has no known satellites.

Mass 3X 1021 kg 0.0005 Earth
Radius 739 km 0.187 Earth
Surface gravity 0..5 m/s2 0.051 g
Escape velocity 0.75 km 0.067 Earth
Length of Day ?? ??

Aphelion 52.84 AU
Perihelion 35.59 AU
Eccentricity 0.156
Orbital period 309 Years
Inclination 29o


Ceres

Ceres

Ceres was discovered on January 1 1801 by  Giuseppe Piazzi. It was the first dwarf planet discovered and the closest to Earth though it was first classified as planet, then downgraded to an asteroid, and then upgraded to a dwarf planet. It was the first dwarf planet to be visited and orbited by a space craft.

Mass 9.43 X 1020 kg 0.00015 Earth
Radius 473 km 0.11 Earth
Surface gravity 0.29 m/s2 0.029 g
Escape velocity 0.51 km 0.045 Earth
Length of Day 9 Hours 0.375 Earth days

Aphelion 2.98 AU
Perihelion 2.56 AU
Eccentricity 0.0758
Orbital period 4.6 Years
Inclination 10.59o

 

Conclusion

While the category of dwarf planet is new and could use a better definition without it the planet count would be 13 and counting. This new category provides a long needed middle ground between asteroids and planets while not being overly complicated. While some agree with Pluto's demotion Ceres fans have something to happy about. The category of dwarf planet is largely a welcomed  addition to astronomy but its definition could uses some refinement.



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