  
  
Gaussian gravitation constant 
k = 1.720 209 895 x 10^{−2} 
k 
Change: 
 IAU GA 2012, Resolution B2, defined the au as fixed
value and stated that k be deleted from the system of
constants and solar mass parameter (previousl called the heliocentric
gravitational constant), GMS, be determined observationally in SI units.
 The block is the previous definition, notes and references.

Status: 
 Auxiliary defining constant.
 IAU 2009 adopted constant.
 Adopted CBE 2009 August 10.

Notes: 
 The Gaussian gravitational constant, k, is listed as an auxiliary
defining constant as it continues to be used to define the relationship
between the astronomical unit and
GM_{S}. This value from the IAU
1976 System of Astronomical Constants is retained here and has been used to
derive the GM_{S} value. However,
other estimates of GM_{S} can be determined directly by
to fitting modern planetary ephemerides (e.g. INPOP08, DE423,
EPM2008) observations.
 The Gaussian gravitation constant remains a defining constant of the
IAU and was used to derive the value of au
that is given (Pitjeva and Standish, 2009).
For users who need a consistent value for the heliocentric gravitational
constant, k should also be used to derive GM_{S}
through the equation
au^{3} k^{2} / D^{2}
= GM_{S}
where D is the time interval of one day of 86400 s. Note that
estimates can now be determined directly by fitting modern planetary
ephemerides to observations.
 There is a difference in opinion regarding the use of k.
Some would use k in the traditional way along with a measured
astronomical unit, au, to calculate the heliocentric gravitation
constant, GM_{S}. Others believe that au should
become a defining constant, which would fundamentally change the status
of k. Although k has been retained to be consistent with
historical systems, it is expected that a recommendation will be discussed
at the 2012 IAU General Assembly that will resolve this issue.

References: 
 International Astronomical Union (IAU), 1976,
"Proceedings of the Sixteenth General Assembly,"
Transactions of the IAU,
XVIB, p. 31, pp. 5266.
 Gauss, C.F., 1857,
Theory of the Motion of the Heavenly Bodies Moving About the Sun in
Conic Sections,
Boston: Little, Brown and Company, p. 2.
 Pitjeva, E.V. and Standish, E.M., 2009,
"Proposals for the masses of the three largest asteroids,
the MoonEarth mass ratio and the astronomical unit,"
Celest. Mech. Dyn. Astr., 103, pp. 365372,
doi: 10.1007/s1056900992038.

  Top 
  
  
Astronomical unit 
au = 1.495 978 707 00 x 10^{11} m 
au 
Uncertainty: 
3 m 
Change: 
 IAU GA 2012, Resolution B2, defined the
astronomical unit to be a fixed number of kilometres.
 The block is the previous definition, notes and references.

Status: 
 Other constant.
 IAU 2009 adopted constant.
 Adopted CBE 2009 August 10.

Notes: 
 The value for the astronomical unit is TDBcompatible.
 An accepted definition for the TCBcompatible value of
the au is still under discussion.
 The current best estimate for the astronomical unit, au,
has been taken from Pitjeva and Standish (2009) and is an average of
recent estimates for the au defined by
k.

References: 
 Pitjeva, E.V. and Standish, E.M., 2009,
"Proposals for the masses of the three largest asteroids,
the MoonEarth mass ratio and the astronomical unit,"
Celest. Mech. Dyn. Astr., 103, pp. 365372,
doi: 10.1007/s1056900992038.

  Top 
  
Heliocentric gravitational constant 
GM_{S} = 1.327 124 420 99 x 10^{20} m^{3}s^{−2} [TCBcompatible]
GM_{S} = 1.327 124 400 41 x 10^{20} m^{3}s^{−2} [TDBcompatible] 
GM_{S} 
Uncertainty: 
1.0 x 10^{10} m^{3}s^{−2} [TCBcompatible]
1.0 x 10^{10} m^{3}s^{−2} [TDBcompatible]

Change: 
 IAU 2012 GA Resolution B2
recommends that this constant, the heliocentric gravitational constant,
be renamed the solar mass parameter and that it be determined
observationally in SI units.
 The block is the previous definition, notes and references.

Status: 
 Body constant.
 IAU 2009 adopted constant.
 Adopted CBE 2009 August 10.

Notes: 
 To adhere with historical definitions, the value for GM_{S}
should be consistent with the au
using the equation
GM_{S} = au^{3}
k^{2} /
D^{2}.
 The value for GM_{S} given is taken from the
Folkner et al. (2008) fit to the DE421 ephemerides. It was not
derived using the value of au, but the
TDBcompatible value of GM_{S} given is consistent with
the value of au given (Pitjeva and Standish,
2009) to within the errors of the estimate.
 Since it is now possible to estimate directly a value for
GM_{S}, it is expected that a recommendation will be
discussed at the 2012 IAU General Assembly to change the historical
relationship between GM_{S},
k, and
au.

References: 
 Folkner, W.M., Williams, J.G., and Boggs, D.H., 2008,
"The Planetary and Lunar Ephemeris DE 421,"
Memorandum IOM 343R08003, 31 pp.
 Pitjeva, E.V. and Standish, E.M., 2009,
"Proposals for the masses of the three largest asteroids,
the MoonEarth mass ratio and the astronomical unit,"
Celest. Mech. Dyn. Astr., 103, pp. 365372,
doi: 10.1007/s1056900992038.

  Top 
  
Ratio of the mass of the Sun to Mercury 
M_{S}/M_{Me} = 6.0236 x 10^{6} 
M_{S}/M_{Me} 
Uncertainty: 
3 x 10^{2} 
Change: 
 2015 July NSFA WG recommends that this value be replaced by a more modern value.

Status: 
 Body constant.
 IAU 2009 adopted constant.
 Adopted CBE 2009 August 10.

References: 
 Anderson, J.D., Colombo, G., Esposito, P.B., Lau, E.L.,
and Trager, G.B., 1987,
"The Mass Gravity Field and Ephemeris of Mercury,"
Icarus, 71, pp. 337349.

  Top 
  
Ratio of the mass of the Sun to Uranus 
M_{S}/M_{U} = 2.290 298 x 10^{4} 
M_{S}/M_{U} 
Uncertainty: 
3 x 10^{−2} 
Change: 
 2015 July NSFA WG recommends that this value be replaced by a more modern value.

Status: 
 Body constant.
 IAU 2009 adopted constant.
 Adopted CBE 2009 August 10.

Notes: 
 Includes the sum of the masses of the body and its satellites.

References: 
 Jacobson, R.A., Campbell, J.K., and Taylor, A.H., 1992,
"The Masses of Uranus and its Major Satellites from Voyager Tracking
Data and Earthbased Uranian Satellite Data,"
Astron. J., 103(6), pp. 20682078.

  Top 
  
Ratio of the mass of the Sun to (134340) Pluto 
M_{S}/M_{P} = 1.365 66 x 10^{8} 
M_{S}/M_{P} 
Uncertainty: 
2.8 x 10^{4} 
Change: 
 2015 July NSFA WG recommends that this value be replaced by a more modern value.

Status: 
 Body constant.
 IAU 2009 adopted constant.
 Adopted CBE 2009 August 10.

Notes: 
 Includes the sum of the masses of the body and its satellites.
 Equivalently M_{P}/M_{S}
= 7.322 47 x 10^{−9}
± 0.001 50 x 10^{−9}.

References: 
 Tholen, D.J., Buie, M.W., and Grundy, W., 2008,
"Masses of Nix and Hydra,"
Astron. J., 135(3), pp. 777784.

  Top 
  
Ratio of the mass of (4) Vesta to the Sun 
M_{Vesta}/M_{S} = 1.35 x 10^{−10} 
M_{Vesta}/M_{S} 
Uncertainty: 
3 x 10^{−12} 
Change: 
 2015 July NSFA WG recommends that this value be replaced by a more modern value.

Status: 
 Body constant.
 IAU 2009 adopted constant.
 Adopted CBE 2009 August 10.

References: 
 Pitjeva, E.V. and Standish, E.M., 2009,
"Proposals for the masses of the three largest asteroids,
the MoonEarth mass ratio and the astronomical unit,"
Celest. Mech. Dyn. Astr., 103, pp. 365372,
doi: 10.1007/s1056900992038.

  Top 
  