How do we know Kepler-78b is a planet?
How do we know for sure that this distant world is an exoplanet and not a comet or an asteroid?
Asked by Lauren Walsh
The Kepler space observatory discovers planets using a technique known as the transit method. It continually measures the brightness of distant stars, looking for a tell-tale dip in the light coming from the star as the planet moves in front of it, blocking out a portion of its light. These dips are measured over a period of time, allowing scientists to work out a world’s size and orbital distance from its star.
From these light curves, scientists can determine an object’s orbit. Comets generally have elliptical paths meaning their light curves will differ to that of a planet. In addition, comets, asteroids and other orbital space objects are much smaller than planets. Light curves show us that Kepler -78b and its fellow exoplanets are too big to be comets.
Answered by Sophie Allan at the National Space Centre
Image courtesy of NASA
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