The spectroscopic radial velocity method preferentially detects a. large planets close to the central star b. small planets close to the central star. c. large planets far from the central star. d. small planets far from the central star. e. the method detects all of these equally well

Exoplanet detection is the science of identifying and studying planets outside our Solar System. There are various methods to detect exoplanets, but one proven method is through the radial velocity technique. When an exoplanet orbits a star, it exerts a gravitational pull on the star, causing it to ‘tug’ back and forth. This motion can be detected from Earth by observing changes in the star’s spectrum. These changes, or Doppler shifts, provide important clues about the presence of an exoplanet. To effectively detect these exoplanets, astronomers focus on large planets that are closer to their stars. These conditions create stronger signals, making detection easier.

Doppler shifts, an essential element in the radial velocity method, occur when the motion of a star changes the frequency of its light. If the star moves towards us, the light waves compress, causing a blue shift. Conversely, if the star moves away, the light waves stretch, causing a red shift. By observing these shifts in the spectrum of the star, scientists can infer the existence of an orbiting planet.

The magnitude of the Doppler shift is influenced by the gravitational pull of the planet. A larger mass or a closer orbit significantly affects the motion of the star, resulting in more notable Doppler shifts. This is why the radial velocity method is more efficient at detecting large planets near their host stars.

Gravitational pull is the force exerted by a planet on its host star, caused by the planet’s mass. The larger the planet, the greater the gravitational force it can exert. Their mutual gravitational attraction causes both the star and planet to orbit a common center of mass, creating a measurable 'wobble' in the star. For a star visible from Earth, this wobble can be detected as a shift in the star's spectrum due to the Doppler effect.

Planets that are closer to their stars have a greater influence due to the inverse-square law of gravity, which states that gravitational force increases significantly with decreased distance. Therefore, the radial velocity method is particularly sensitive to detecting large planets with close orbital paths around their stars, as they produce the most significant gravitational pulls and, subsequently, the most noticeable velocity shifts.