The idea of life in other star systems has long intrigued mankind. However, it is likely that before life can be identified we must discover the planets upon which this life would spawn. Within the star system TRAPPIST-1, seven Earth-sized planets have been discovered, three of which are within the star’s habitable zone. The star is 40 light years away, which is closer than many stars but still farther than humans currently have the capability of reaching by physical means. So how did we find all these planets?
The planets were all located by transit, which is a method used by astronomers that tracks the brightness of a star over time. Therefore, when a planet or planets cross in the path of the sun (in relation to Earth) then the visible brightness of the star decreases. The difference in visible light is unnoticeable to the human eye, but telescopes can detect differences of as little as one hundredth of a percent of the total light given off by a star. Across time a graph is formed that shows transits as dips in the star’s brightness. Once a planet can be identified by its transit three times, it is confirmed to exist.
The planets in the TRAPPIST-1 system were relatively small, so without their frequent orbits, it would have been incredibly difficult to learn of their existence. Transit identification methods favor planets that are large and that have quick orbital periods. Large planets block more light, thereby making their transits more noticeable. A faster, shorter orbit means that the planet transits more often, making it easier to identify the pattern and track it across multiple revolutions.
Now that we know the TRAPPIST-1 system holds good chances of life, it will be exciting to see what else we are able to discover about the planets.
NASA has a page dedicated to this system that I used to find out specific information about the TRAPPIST-1 discovery, along with a ton of other info: https://www.nasa.gov/press-release/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around