# Eikonal Blog

## Dwarf planets

Definitions (from “Pluto’s Dwarf Planet Family Could Get Bigger” by Ian O’Neill (Discovery News; 2010.04.09) – http://news.discovery.com/space/plutos-dwarf-planet-family-is-about-to-get-bigger.html)

• The 2006 IAU definition of a dwarf planet states that such a body should be massive enough to achieve hydrostatic equilibrium, it must orbit the sun, but it cannot “clear its own orbit.”
• The ‘potato-limit’: “the rule that they must be of certain brightness, dwarf planets have a minimum radius of 420 km (260 miles).”

All except Ceres are trans-Neptunians residing in the Kuipert belt.

Name Location Discovery details Orbit radius Orbital period Size (radius) Mass Length of the day Misc
Eris (= 2003 UB_313; initially called “Xena”) Kuipert belt
Pluto Kuipert belt 1930.02.18 by Clyde Tombaugh it has very excentric orbit, with $aphelion =$ $7.375 x10^9 km =$ $49.305 AU$ and $perihelion =$ $4.436 x10^9 km =$ $29.658 AU$ $90,613.305 days_{Earth} =$ $248.09 years_{Earth} =$ $14,164.4 days_{Pluto}$ $1,153 \pm 10 km =$ $0.18 R_{Earth}$ $(1.305 \pm 0.007)\times 1022 kg =$ $0.002 M_{Earth} =$ $0.178 M_{Moon}$ $6.387 230 day_{Earth} =$ $6 \ d \ 9 \ h \ 17 \ m \ 36 \ s$ Has four satellites:

• Hydra: discovered by Hubble telescope in 2005. 30 to 115km diameter.
• Charon: discovered in 1978 by the US Naval Observatory. 1,200km diameter.
• Nix: discovered by Hubble telescope in 2005. 30 to 115km diameter.
• P4 (yet unnamed): diameter 13 to 34 km [of 8 to 21 miles]
Makemake Kuipert belt
Haumea Kuipert belt
Quaoar (= 2002 LM60; = 50000 Quaoar) Kuipert belt announced 2002.02.07 by Michael Brown and Chadwick Trujillo of Caltech $~ 6.5 x10^9 km = 4 x10^9 miles$ $~ 288 years_{Earth}$ $~ 650 km = 400 miles$ likely composition: made mostly of low-density ices mixed with rock
Sedna (= 90377 Sedna) Kuipert belt discovered in 2003
Ceres asteroid belt

Sources:

## Oort Cloud

a sphere one light year in radius stretching a quarter of the distance to Alpha Centauri

## Potential planet: Tyche

Related here: Astronomy & Astrophysics – https://eikonal.wordpress.com/2011/05/09/astronomy-astrophysics/ | Astronomic tables and calculators – https://eikonal.wordpress.com/2010/01/28/astronomic-tables-and-calculators/ | Inside black holes – https://eikonal.wordpress.com/2011/04/12/inside-black-holes/ | Physics Sites – https://eikonal.wordpress.com/2010/02/12/physics-sites/