* Transit observations only give you the planet's size. A transit reveals the planet's silhouette blocking a tiny fraction of the star's light. This allows you to calculate the planet's radius, assuming you know the star's size.
* Mass requires additional information. To determine a planet's mass, you need to know its gravitational influence. This can be done by observing the radial velocity of the star as it wobbles due to the planet's gravitational pull.
In summary:
* Transit observations: Give you the planet's size (radius).
* Radial velocity observations: Give you the planet's mass.
Combining both methods is crucial for understanding a planet's characteristics. This is why astronomers often use both transit and radial velocity techniques to get a complete picture of exoplanets.
