Where and how should we look for intelligent life outside of our Solar System?
This ultimate question was last week given another dimension with the discovery of TOI-561b, a 10 billion years-old exoplanet a little larger than the Earth that has existed since almost the dawn of our Milky Way galaxy.
It’s not thought that intelligent life is thought to be living on TOI-561b itself. It may be one of the oldest rocky planets yet discovered, but it orbits its star in just 10.5 hours and is not thought to be in the “habitable zone” of its star.
Instead, it offers a clue. If rocky planets like our own have been forming for far longer than originally thought, then surely the older and more stable a planet, the more likely it will host some kind of lifeforms.
Either way, how do we increase our chances of finding intelligent life outside of our Solar System?
Here are three things we need to do to ramp-up the search for extra-terrestrial intelligence (SETI):
1. Look close to home
Is there any point in looking for Earth-like rocky planets beyond our immediate cosmic neighborhood? “We don’t want to talk to aliens that are 1,000 light years away—we want to be looking for rocky planets and alien civilizations that are close to home so we can have a conversation,” said Lauren Weiss, team leader and postdoctoral fellow at the University of Hawaii. She recently led the team that discovered the 10 billion-year-old “Super-Earth.”
“We want to talk to the ones where maybe our grandkids, or their grandkids, might actually receive a message,” she added. We can send messages—and we already are—that travel at light-speed, so if an exoplanet is 10 light-years away we could search for a reply in 20 years. Just about do-able. If the exoplanet is 50 light-years away it would take 100 years. Is anyone going to remember to listen out for the reply?
We need to find close exoplanets. Cue NASA’s Transiting Exoplanet Survey Satellite (TESS), which is now six months into its 27 months-long TESS Extended Mission. TESS studies sections of the sky in search of stars that periodically dim slightly, a telltale sign that a planet is passing across it. “Our best prospect right now is the TESS extended mission,” said Weiss. “It’s been wonderful at finding nearby small planets, some of which are small enough that they’re actually rocky, but they are really hard to find in the present dataset.”
“The way we are going to find more of those rocky planets—especially ones around the nearest stars—is by being better at detecting these really tiny dips from the rocky planets,” said Weiss.
Space-based missions will be critical, too, such as the James Webb Space Telescope (JWST), which will launch on October 31, 2021.
2. Build extremely large telescopes
There are already scores of huge optical, land-based telescopes on the world’s mountains, but if we’re truly to explore exoplanets and their atmospheres then we need to to go bigger. Why?
Looking for stars that dim when a planet transits across it is a very limited way of looking for exoplanets. Astronomers employing this “transit method” are only ever going to see exoplanets in star systems that we have a side-on line of sight to—the planet must be aligned between the telescope and the star to be detected.
We need telescopes that can find exoplanets around all kinds of stars regardless of our accidental view of star system’s orientation. That requires bigger telescopes that can detect the “radial velocity” of stars—the very slight “wobble” in a star that orbiting planets cause. That requires more light-gathering power than we currently have.
“Only a small fraction of stars have planets that transit their stars,” said Weiss. “There are lots of rocky planets out there that are not transiting their stars, so we need to build 30 meter-class ground-based telescopes.” She argues that they are critical for discovering and characterising these nearest rocky worlds.
Such extremely large telescopes are already in the works:
3. Directly image exoplanets
As well as being able to find exoplanets using new methods, giant telescopes will also be able to image them directly. “Eventually we will directly image these rocky planets,” said Weiss. “That is the way we have to go.”
However, the new class of extremely large telescopes will be able to directly image rocky exoplanets in a star’s habitable zone—and even characterise their atmospheres.
Wishing you clear skies and wide eyes.