Searching for Life on the Newly Discovered Earthlike Planets

It’s impossible to know if the creatures living on the planet Trappist-1e suspect they’re being watched. Actually, it’s impossible to know if there are any creatures at all, but let’s assume they’re there–because it’s a fair enough assumption. Trappist-1e has a solid surface like Earth’s, after all. What’s more, it gets plenty of warmth from the star it orbits. That star, Trappist-1, is small and dim and much cooler than our sun, but Trappist-1e snuggles up close to the solar fires, so close that its year–the time it takes to complete a single orbit–is just 6.06 days. If the planet has an atmosphere (there’s no reason it couldn’t) and if it has water (water is ubiquitous in the universe), that water could pool across the surface in warm, amniotic oceans. And from oceans can come life.

That was the news announced in an explosive study published in the Feb. 23 issue of the journal Nature, and Trappist-1e was only part of the bombshell. The planet is just one in a solar system consisting of seven Earthlike worlds. At least three and perhaps all of the planets orbit in that close-but-not-too-close range known as the habitable zone–where the temperature is above freezing but below boiling so that liquid water can exist.

“Now we are looking at the planets’ chemistry,” said astronomer Ignas Snellen of the University of Leiden in the Netherlands, during a press conference announcing the discovery, “to see if there is life over there.”

The Trappist-1 system is indeed just right “over there”–39 light-years away in a galaxy that measures more than 100,000 light-years across. That makes telescope observations possible, especially with the aid of new instruments in development. Answers will thus come soon to the question of Trappist-system life. “We’ll know within a few years, maybe within a decade,” said astronomer Amaury Triaud of the Institute of Astronomy in Cambridge, England, a co-author of the Nature paper, at the same press event.

Such a tantalizing possibility that, after millennia of wondering, we may learn soon that we have cosmic company broke at a very good time. When things have gone sour on Earth, we have often looked to space. It was in 1961, with the U.S. and Soviet Union at dagger points, that President Kennedy announced America’s commitment to land men on the moon before 1970. It was in the summer of 1968, torn by war and assassinations, that NASA decided to send Apollo 8 on the first lunar orbit mission, during Christmas week.

There was a similar feeling of uplift with the announcement of the Trappist-1 worlds, coming at a time when America and the entire Western alliance are more fractured than they’ve been in decades. “NASA Discovers a Possible Way Out,” wrote the wags at the New York Post. “The Trappist-1 system has got us particularly excited about the prospect of new worlds,” wrote the International Business Times, “because we’re so sick of this one.”

But it wasn’t all snark and cynicism. Even in an increasingly insular, nationalistic time, the accelerating search for life on other planets is a deeply collaborative and international enterprise. The Trappist-1 team was led by astronomer Michaël Gillon of the University of Liège in Belgium, and the work was conducted with telescopes in Chile, Hawaii, South Africa, Morocco, Spain and England. In his Inaugural Address, President Donald Trump declared, “We stand at the birth of a new millennium, ready to unlock the mysteries of space.” The political will seems to be forming in the U.S. to press the hunt for planets and life further. And the likelihood of finding something has never seemed greater.

If the dream of life in space has all at once gotten real, it is the astronomers who search for exoplanets–worlds orbiting other stars–who have made that possible. Until 1995, we knew of just the nine that orbit our own sun, and that count actually fell to eight when Pluto was busted down to a dwarf planet. But things started to change when ground-based telescopes confirmed the first known exoplanet, a Jupiter-size world named 51 Pegasi b, orbiting a sunlike star 50 light-years from Earth. The census grew slowly, an occasional planet at a time, until NASA’s Kepler space telescope was launched in 2009, and the exoplanet population exploded to nearly 5,000.

Unlike early exoplanet telescopes, which look for the “wobble” in a star’s gravity as a planet moves through its orbit, the Kepler stares unblinkingly at a small patch of space, a keyhole that takes in 150,000 stars. Kepler looks for the all but undetectable dimming that occurs when an orbiting planet transits–or passes in front of–its star. It’s the equivalent of detecting a gnat crawling across a headlight, but so far, Kepler has spotted 4,706 confirmed or candidate planets this way, with more certain to come. Most astronomers believe that every one of the 300 billion stars in the Milky Way has at least one exoplanet.

From among all of them, astronomers look hardest for solid planets no bigger than 1.6 times Earth’s diameter, existing a habitable distance from their sun. These turn out to be more common than scientists ever suspected (largely because they’d discounted red dwarfs, which vastly outnumber yellow suns).

How many might hold life? Observations using the transiting technique can yield little more than a silhouette of the backlit planet. But if the planet has an atmosphere, light from the star would stream through it, getting scattered and absorbed in different ways depending on chemical composition. That produces a precise fingerprint of the atmospheric chemistry, with the biggest prize being biosignature gases like methane or oxygen or carbon dioxide. “A living world,” says astrophysicist Natalie Batalha, who heads the Kepler mission, “looks just screamingly different from a Mars or Venus.”

Investigators around the world are scrambling to take advantage of that fact. Telescopes in Chile and elsewhere have conducted preliminary chemical studies of some planetary atmospheres. The Hubble Space Telescope has analyzed two of the Trappist-1 planets and found that at least they do not have the heavy envelopes of hydrogen gas that would make them mini-Neptunes. Hubble is not equipped to determine more than that, but its follow-on, the $8.7 billion James Webb Space Telescope, is scheduled for launch in October 2018. Though not originally designed with exoplanets in mind, Webb will carry the spectroscopes necessary to do atmospheric studies.

Astronomers–and humanity as a whole–are expecting big things.