Question

To determine a planet's average density, we can use:

a) The transit method alone.
b) The astrometric and Doppler methods together.
c) The transit and Doppler methods together.
d) None of the above.

Answer 1

To determine a planet's average density, the transit and Doppler methods are used in conjunction. The transit method provides size, while the Doppler method estimates mass, enabling the calculation of density.

Step-by-step explanation:

To determine a planet's average density, the most effective method is to use the combination of the transit and Doppler methods together. The Doppler method allows us to estimate the mass of a planet. However, it primarily gives us the minimum mass since we often lack the orientation angle of the planet's orbit. Still, when paired with the transit method, which provides the size of the planet, we can calculate the planet's volume. Using the mass and volume, we derive the average density of the exoplanet. For example, the planet orbiting the star HD 209458 was the first to be detected using the transit method, and subsequent Doppler measurements revealed its mass, allowing scientists to deduce it was a gas and liquid world.