Which of the following cannot be determined with the Doppler technique? a. the mass of the planet b. the orbital period of the planet c. the size of the planet d. the size of the planet's orbit

a. the mass of the planet

Explanation:

Doppler's effect explains the shift in the frequency of light or sound wave coming from an object as it moves closer or farther from the observer. A real life example is passing of an ambulance. As it approaches we can hear high pitched siren (increased frequency) and as it moves away we can hear a low pitch siren (decreased frequency). The same technique is used in astronomy to find the movement of the celestial objects with respect to Earth.

Option b, c, and d can be found out using this method. As the planet will rotate, one end will move towards the Earth and opposite one away from Earth. This will show the frequency shift which can be used to calculate to give us the rotation period and size of the planet. Also, as the planet will move in their orbit, their positional change will result in frequency shift. Using that we can find out the orbital period and size of the orbit. But we can not find out the mass of a planet. We can find the mass using Newton's law of gravitation.