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.

Question

Quizplus · Accepted Answer

The Doppler technique measures the motion of a star towards and away from us as a planet orbits it. This motion is influenced by the gravitational pull of the planet. However, since we only see the component of this motion along our line of sight, we cannot determine the full motion of the star in space. This limitation means we can only calculate the minimum mass of the planet, as the actual mass depends on the inclination of the planet's orbit relative to our line of sight, which is not known from Doppler measurements alone.

The Doppler Technique Only Provides a Measure of the Minimum