ARVAL: Solar System Data

Notes:
Given that the orbits are elliptical (but of low Eccentricity),
the Radius figures show the semi-mayor axis, which is also the average distance from the planet to the Sun.
An orbit's Inclination, is measured with respect to the Earth's orbital plane (the "Ecliptic Plane").
Sidereal Period is the time taken by a planet to complete an orbit around the Sun, measured relative to the stars.
Synodic Period is the time taken by a planet to complete an orbit around the Sun, measured relative to the Earth. It is the time taken by a planet to complete a cyle of its phases, the interval of time between two succesive equal phases.

Given that the planets present some Polar flattening, Diameters are equatorial.
The Earth's Mass is 5.9740 * 10²⁴ Kgr.
The Earth's Gravity is 9.8 m/seg².

A comma has been used as a thousands separator, and a dot as a decimal separator.

Data from the "Field Guide to the Night Sky", The Audubon Society 1991.

All of the above 9 Solar System objects were commonly considered to be "Planets", but there was no formal, scientific, definition. Pluto, discovered by Clyde Tombaugh (1906 - 1997) in 1930, was the smallest and farthest planet. See Hubble Views the Pluto System (also in ARVAL).

This changed, as in August 24 '06 the International Astronomical Union (IAU) approved this definition:

RESOLUTION 5A: Definition of "planet"

The IAU therefore resolves that planets and other bodies in our Solar System be defined into three distinct categories in the following way:

(1) A planet¹ is a celestial body that (a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and
(c) has cleared the neighbourhood around its orbit.

(2) A dwarf planet is a celestial body that (a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape²,
(c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects³ orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

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¹ The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
² An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
³ These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

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RESOLUTION 6A: Definition of Pluto-class objects

The IAU further resolves:

Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.

On 13 September '06 the IAU Minor Planet Center assigned to Pluto the asteroid number 134340, and to 2003 UB₃₁₃ the name "Eris" and the asteroid number 136199. The one known moon of Eris is now named Dysnomia.

Ceres and Eris are now "Dwarf Planets", Charon continues to be a satellite of the now Dwarf Planet Pluto, the second largest known member of the Kuiper Belt. Eris is the largest known, some 5% bigger than Pluto.
This membership is the reason why Pluto was demoted (2-c above).

The name 2003 UB₃₁₃ was provisional, as a "real" name had not yet been assigned to this object. A decision and announcement of a new name were not made during the IAU General Assembly in Prague, but at a later time.
Pluto and Eris are "Trans-Neptunian Objects", but not Ceres.

The orbit of Eris is even more eccentric than that of Pluto. Pluto moves from 30 to 50 times the Sun-Earth distance over its nearly 250 year orbit, the new planet moves from 38 to 97 times the Sun-Earth distance over its 560 year orbit, and its orbit inclination is 44°.

See IAU 2006 General Assembly: Result of the IAU Resolution votes (IAU Press Releases, 24 August 2006, Prague), IAU Minor Planet Center Circular 8747 (Sep 13 '06 .pdf), The discovery of 2003 UB313 Eris (Mike Brown, Caltech), Hubble Finds 'Tenth Planet' is Slightly Larger than Pluto (April 11 '06), and Largest Asteroid May Be 'Mini Planet' with Water Ice (Ceres, in ARVAL).

See also Classic Satellites of the Solar System, and The Search for The Kuiper Belt in ARVAL.

This page was updated in: September 16 '06, June 24 '14

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