Britannica
Sources used in this answer
How does the transit method reveal the size and orbital period of an extrasolar planet?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
Habitable zone
The habitable zones (green) for stars that are like the Sun (middle), hotter than the Sun (top), and cooler than the Sun (bottom). The red areas are those in which liquid surface water would be lost as a result of a runaway greenhouse effect, and the blue areas are those in which liquid surface water would be completely frozen.
The transit method is a powerful tool in astrobiology and astronomy used to detect extrasolar planets by monitoring the brightness of distant stars.12
How the Transit Method Works
When a planet’s orbit is aligned such that it passes directly between its host star and a telescope, it causes a periodic, measurable drop in the star's brightness.12
- Determining Size: The depth of the dip in starlight is proportional to the area of the planet’s disk relative to the star’s disk. By measuring how much the star dims during the transit, astronomers can calculate the size (radius) of the extrasolar planet.12
- Determining Orbital Period: Because these transits occur periodically as the planet completes its orbit, astronomers can determine the orbital period by measuring the time interval between successive dips in brightness.12
This method is particularly significant for identifying planets within a star's habitable zone, where conditions might allow for liquid water.23