The Doppler Technique Only Provides a Measure of the Minimum

Multiple Choice

The Doppler technique only provides a measure of the minimum mass of a planet because

A) only a small part of the planet's motion is measured.
B) without a transit observation,the size and therefore density of the planet is unknown.
C) we do not know the exact composition of the planet.
D) only the motion of star toward the observer is measured,not the full motion.
E) we do not have the technology to make a direct image of a planet yet.