The recent discovery of seven potentially habitable exoplanets orbiting the star TRAPPIST-1, just 40 light-years away, greatly raises the odds of finding alien life on other worlds with whom we might one day have a real chance of directly coming into contact.
But before we get ahead of ourselves, we’ll need to figure out for certain whether there are signs of life on those and other planets. A group of scientists at Caltech’s Exoplanet Technology Laboratory believe they have a solution for turning our most powerful telescopes into alien-hunting instruments.
The technique is called “high-dispersion coronagraphy,” and is intended to help scientists find biosignatures on exoplanets. Biosignatures are disturbances in an environmental equilibrium; they reveal the existence of an unknown force or process. Certain colors might indicate photosynthesis, for example, or a certain kind of excess gas might indicate an organic life source.
In order to study faraway planets, scientists need to block the light emanating from the stars they orbit. Stars are brighter than planets — anywhere from a thousand times to several billion times brighter — and that light can interfere with our ability to take a good look at anything around them. To fix this problem, scientists employ a coronagraph, which is a device in a telescope that helps block starlight.
Scientists have been using coronagraphs for some time, but this new high-dispersion coronagraphy technique innovatively combines it with a high-res spectrometer. Spectrometers expose the “fingerprints” of chemicals; researchers can use them to find elements that are associated with life, such as oxygen.
But here’s the real kicker: scientists realized that using a coronagraph with a high-res spectrometer specifically caused even more light to be filtered out than usual. Using these two instruments together allows researchers to “improve the sensitivity of our system by a factor of 100 to 1,000 over ground-based methods,” explained Dimitri Mawet, the head of the Caltech team who made the discovery.
The team used optical fibers to combine the coronagraph with the high-res spectrometer. The fibers, it turns out, also help to remove starlight. These discoveries were, in the words of team member Garreth Ruane, “serendipitous.”
When high-dispersion coronagraphy is put into practice, scientists will be able to learn much more about the molecules that exist in exoplanets’ atmospheres, as well as the planets’ appearances, rotation rates, and weather patterns. We’ll need that information if we want to discern whether life exists outside of our galaxy.
Right now, we only have one in-progress telescope that’ll be up to the job of locating biosignatures using high-dispersion coronagraphy. It’s called the Thirty Meter Telescope (TMT), and it will become the world’s biggest optical telescope when it’s finished in about a decade. Scientists will be able to use TMT to apply this new technique to planets around M-dwarf stars, the most common star in the galaxy, which are smaller than our sun. Stronger telescopes designed in the future could help researchers apply the technique to planets around bigger stars.
Since TMT won’t be finished until the late 2020’s, right now this is a waiting game, at least in terms of using the new technique to help solve the mystery of extraterrestrial life. High-dispersion coronagraphy has already been tested in laboratories, and scientists can use it for now on certain gas exoplanets. But we’ll have to wait for the blessed day it can be used on the Earth-like exoplanets around TRAPPIST-1.