Which physical characteristic of an exoplanet cannot be revealed solely by utilizing the transit method?
Answer
The planet's mass
The transit method provides two primary pieces of information directly from the observation of light blockage: the planet's size (derived from the depth of the dip) and its orbital period (derived from the time between successive dips). While these are vital parameters, the transit method, by observing light alone, cannot measure the slight gravitational influence or wobble that an orbiting body exerts on its parent star. This gravitational tug, which is directly proportional to the planet's mass, requires a different observational technique, specifically the radial velocity method, to be accurately determined. Therefore, mass remains undetermined by transit data in isolation.
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