Aplanet's density can be measured by combining

a. doppler and transit observations.
b. direct imaging from the new generation of space telescopes.
c. spectral observations of the planet's atmosphere.
d. any method that measures the gravitational tug of the planet on the star.
e. doppler and astrometric observations.

a. Doppler and transit observations.

Explanation:

By means of the dopler effect, the radial velocity of an extrasolar planet can be measured, this is achieved by observing Doppler shifts in the spectrum of the star around which the planet orbits. This measure, combined with the transit observations, makes possible determine the density of the planet.

the answer is a 3.8cm

explanation:

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