Watching for a tiny dip
How Do We Find Planets Around Other Stars?
A planet crossing its star blocks a sliver of light, and that repeating dip gives it away.
-
Step 1 of 5
The planets themselves are impossible to see.
A planet shines only by reflected light and sits beside a star billions of times brighter, so it is completely lost in the glare.
-
Step 2 of 5
But a planet passing in front blocks a sliver.
When the orbit is lined up with us, the planet crosses the star's face and blocks a tiny fraction of the light heading our way.
-
Step 3 of 5
The dip is astonishingly small.
A planet the size of Jupiter blocks about one per cent of its star's light, and an Earth-sized world blocks around one hundredth of that.
-
Step 4 of 5
Repetition is what proves it is a planet.
One dip could be anything. The same dip returning at exactly the same interval means something is orbiting on a regular schedule.
-
Step 5 of 5
The timing and depth reveal a lot.
How often the dip repeats gives the orbit, how deep it goes gives the size, and both together suggest whether liquid water could exist.
The Kepler telescope watched 150,000 stars at once for this dip and found over 2,600 confirmed planets.
The short version
Most planets around other stars are found not by seeing them but by the tiny, precisely repeating dip they cause in their star's light.
Try it yourself
Hold a pinhead in front of a torch across a dark room. The light barely changes, which is the scale of dip telescopes must detect.
Topics