Most values listed in the factsheets are from the following sources: IAU/IAG Working Group Report, 2006 Astronomical Almanac, 2000, 2001 Global Earth Physics, American Geophysical Union, 1995 Astrophysical Quantities, C.W. Allen, 1981, 2000 Recent journal articles and personal communications Note that the values listed on the factsheets are not "official" values, there is no single set of agreed upon values. They are based on ongoing research and as such are under study and subject to change at any time. Every effort has been made to present the most up-to-date information, but care should be exercised when using these values.
Mass (1024 kg) Mass of the body in 10^24 kilograms Volume (1010 km3) Volume of the body in 10^10 km^3 Equatorial radius (km) Radius of the body at the equator in kilometers Polar radius (km) Radius of the body at the poles in kilometers Volumetric mean radius (km) Radius of a sphere with the same volume as the body Core radius (km) Radius of the planet core in kilometers Ellipticity (Flattening) The ratio (equatorial - polar radius)/(equatorial radius), dimensionless Mean density (kg/m3) Average density of the body (mass/volume) in kilograms/(meter^3) Surface gravity (m/s2) Equatorial gravitational acceleration at the surface of the body or the 1 bar level, not including the effects of rotation, in meters/(second^2) Surface acceleration (m/s2) Effective equatorial gravitational acceleration at the surface of the body or the 1 bar level, including the effects of rotation, in meters/(second^2) Escape velocity (km/s) Initial velocity required to escape the body's gravitational pull in kilometers/second GM (x 106 km3/s2) Gravitational constant times the mass of the body in 10^6 kilometers^3/seconds^2 Visual geometric albedo The ratio of the body's brightness at a phase angle of zero to the brightness of a perfectly diffusing disk with the same position and apparent size, dimensionless. Bond albedo The fraction of incident solar radiation reflected back into space without absorption, dimensionless. Also called planetary albedo. Visual magnitude V(1,0) The visual magnitude of the body if it were one AU (1.496 x 10^8 kilometers) from the Earth at a phase angle of zero, dimensionless. Solar irradiance (W/m2) Solar energy on the body in Watts/(meter^2) Black-body temperature (K) Equivalent black body temperature is the surface temperature the body would have if it were in radiative equilibrium and had no atmosphere, but the same albedo, in Kelvin. Topographic range (km) Difference in elevation between the highest and lowest points on the planet's surface, in kilometers. Moment of inertia (I/MR2) The moment of inertia of the body expressed as the rotational inertia divided by the body's (mass x radius^2). A hollow spherical shell has a moment of inertia of 2/3, a homogeneous sphere 0.4 J2 (x 10-6) The ratio of the difference in the moments of inertia to the mass of the body times the radius^2, (C-A)/(M R^2), x 10^-6, dimensionless Number of natural satellites The number of moons orbiting the planet, as certified by the IAU Absolute magnitude (Comets) The magnitude of the comet at 1 AU for Y = 10, where Y is the photometric parameter giving the observed dependence of the magnitude on heliocentric distance, also designated H(10).
Instantaneous values referenced for Julian Date 2451800.5 (13 September 2000) [Astronomical Almanac 2000, p. E3] Semimajor axis (106 km) Mean distance from the Sun (or other central body in the case of satellites) from center to center in 10^6 kilometers Sidereal orbit period (days) The time it takes the body to make one revolution about the Sun relative to the fixed stars in days. For Pluto, it is the time from the last zero longitude crossing to the next (24 July 1820 - 2 July 2068). Tropical orbit period (days) The average time for the body to make one revolution about the Sun from one point in its seasonal orbit to the equivalent point (e.g. equinox to equinox) in days. For Earth, this equals exactly 1 year. Not known for Pluto. Synodic period (days) The time interval between similar configurations in the orbit (e.g. opposition) of the body and Earth, in days. Perihelion (106 km) The point in a body's orbit closest to the Sun, in 10^6 kilometers. Aphelion (106 km) The point in a body's orbit furthest from the Sun, in 10^6 kilometers. Mean orbital velocity (km/s) The average speed of the body in elliptical orbit, in kilometers/second. Max. orbital velocity (km/s) Maximum orbital velocity, at perihelion, in kilometers/second. Min. orbital velocity (km/s) Minimum orbital velocity, at aphelion, in kilometers/second. Orbit inclination (deg) The inclination of the orbit to the ecliptic, in degrees. For satellites, this is with respect to the planet's equator. Orbit eccentricity A measure of the circularity of the orbit, equal to (aphelion - perihelion distance)/(2 x semi-major axis). For the Galilean satellites, the forced eccentricity is given. For a circular orbit eccentricity = 0. Dimensionless. Sidereal rotation period (hrs) The time for one rotation of the body on its axis relative to the fixed stars, in hours. A minus sign indicates retrograde rotation. Length of day (hrs) The average time in hours for the Sun to move from the noon position in the sky at a point on the equator back to the same position, on Earth this defines a 24 hour day. Obliquity to orbit (deg) The tilt of the body's equator relative to the body's orbital plane, in degrees (J2000).
250-year least squares fit elements referenced to J2000 (Global Earth Physics, p. 14) Longitude The point in a body's orbit around the Sun, defined from 0 to 360 degrees. The 0 point of longitude is defined as the first point of Aries. This is the position of the Sun as seen from Earth at Earth's vernal equinox, so at the vernal equinox the Earth is at a longitude of 180 degrees. Longitude of ascending node (deg) The longitude in a body's orbit at which it crosses the ecliptic plane with increasing latitude (i.e. crosses the ecliptic from south to north). Longitude of perihelion (deg) The longitude in a body's orbit at which it reaches the point closest to the Sun. Mean longitude (deg) The longitude a body was at in its orbit at 12:00 Universal (Greenwich) Time on January 1, 2000, also known as J2000 or Julian Day 2451545.0
Surface Pressure: Atmospheric pressure at the surface, in bars, millibars (mb = 10^-3 bar), or picobars (10^-12 bar). Surface Density: Atmospheric density at the surface in kilograms/meters^3. Scale height: The height interval in which the atmospheric pressure changes by a factor of e = 2.7183 Average temperature: Mean temperature of the body over the entire surface in Kelvin. Diurnal temperature range: Temperature range over an average day in Kelvin. Wind speeds: Near surface wind speeds in meters/second Atmospheric composition: Relative composition by volume of gasses in the atmosphere. Mean molecular weight: Average molecular weight of the atmospheric constituents in grams/mole Atmospheric composition (by volume): Relative volume of constituents in the atmosphere, by percentage or ppm (parts per million).
Astronomical Unit (AU) - The mean distance from the Sun to the Earth = 149,597,900 km. Bar - A measure of pressure or stress. 1 bar = 10^5 Pascal (Pa) = 10^5 kg m^-1 s^-2 Ecliptic - An imaginary plane defined by the Earth's orbit. Equinox - The point in a body's orbit when the sub-solar point is exactly on the equator. Gravitational Constant - Relates gravitational force to mass, = 6.67384 x 10^-11 meters^3 kilograms^-1 seconds^-2 Opposition - An orbital configuration in which two bodies are on exact opposite sides of the Sun or are on the same side of the Sun forming a line with the Sun (neglecting inclination) Phase Angle - The angle between the Earth and Sun as seen from the body.