Question

Imagine a star very similar to our own Sun in both size and mass. This star moves very slightly back and forth in the sky once every 4 months, and you attribute this motion to the effect of an orbiting planet. What can you conclude about the orbiting planet?
(a)-The planet must be farther from the star than Neptune is from the Sun.
(b)-You do not have enough information to say anything at all about the planet.
(c)-The planet must have a mass about the same as the mass of Jupiter.
(d)-The planet must be closer to the star than Earth is to the Sun.

Answer 1

Answer:

(c) The planet must have a mass about the same as the mass of Jupiter,

(d) The planet must be closer to the star than Earth is to the Sun.

Explanation:

Astrometry is the ideal method to detect high-mass planets that are close to their star. That is because the gravitational effect that it will have the planet over its host star will be greater. This effect can be seen as a wobble in the star as a consequence of how they orbit a common center of mass¹. The center of mass will be closer to the most massive object, So, in the case of an extrasolar planet with masses like Jupiter (Jovian), this point will be a little bit farther from the star, making the wobble more notable than in a system with a low-mass planet.          

Key terms:

Astrometry: study of the position of the stars over time in the sky.

¹Center of mass: a geometrical point in which the mass from a whole system is summed.