Minimum mass

In astronomy, minimum mass is the lower-bound calculated mass of observed objects such as planets, stars and binary systems, nebulae, and black holes.

Minimum mass is a widely cited statistic for extrasolar planets detected by the radial velocity method. This method reveals planets by measuring changes in the movement of stars in the line-of-sight, so the real orbital inclinations and true masses of the planets are generally unknown.

If inclination can be determined, the true mass can be obtained from the calculated minimum mass using the following relationship:

M_\text{true} = \frac{M_\min}{\sin i} \,

For orbiting bodies in extrasolar stellar and planetary systems, an inclination of 0° or 180° corresponds to a face-on orbit (which cannot be observed by radial velocity), while an inclination of 90° corresponds to an edge-on orbit (for which the true mass equals the minimum mass).

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