solar mass parameter
Standard gravitational parameterexact by definition
The solar mass parameter is the product GM for the Sun, adopted by the IAU in 2015 as the nominal value of exactly 1.3271244e20 m³/s². Stellar and planetary masses in the literature are usually expressed as multiples of it, because the product is what an orbit actually measures.
Watch out: GM is known far better than either factor alone. The solar mass parameter is determined to about ten significant figures from planetary ranging, while the gravitational constant G is the worst-measured constant in physics at roughly two parts in 100000, so the Sun's mass in kilograms inherits that uncertainty. Quoting a stellar mass in solar masses is therefore more precise than quoting it in kilograms, and the nominal value here is fixed by convention so that published results do not shift when the measurement improves.
| 1 GMsun | 132,712,440,000 km³/s² |