What essential characteristic of a planetary system cannot be determined using only radial velocity measurements?

Answer

The orbital inclination ($i$) relative to our line of sight.

The method is fundamentally limited because it cannot distinguish between true orbital speed and motion that is purely across the line of sight, which depends on the orbital inclination.

What essential characteristic of a planetary system cannot be determined using only radial velocity measurements?

#Videos

Detecting Exoplanets: Radial Velocity Method - YouTube

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