Several years ago, astronomers pointed a telescope at another star and discovered something remarkable: seven planets, each one about the same size as Earth. These planets were very close to their star, and all seven orbits of Mercury would fit within its. This star, however, is much smaller and cooler than the one we live in. At least three of these rocky planets lie within the zone that can support liquid water. Although ET is not guaranteed due to its size and sunniness, it could be an indicator that ET exists. However, this area of the universe might offer a good place to begin if you are looking for evidence of extraterrestrial life.
The system, which orbits a star known as TRAPPIST-1, is unusual; scientists had never found one like it before, nor have they since. We can’t see the exoplanets, which are named b, c, d, e, f, g, and h; from 40 light-years away, they were just tiny blips in telescope data. Artists at NASA have illustrated them, their imaginations guided by details of the worlds in our system, including Earth’s clouds and oceans, but the exoplanets have fundamentally remained a mystery. So when the James Webb Space Telescope, the newest and most powerful telescope out there, was launched, experts and space enthusiasts alike were anxious to point it toward this cosmic alphabet and get a real glimpse of the worlds within.
Now the first results are out: The Webb telescope has observed b, the innermost planet, and found … nothing. No signs of carbon dioxide, a key component of our atmosphere, and which Webb is designed to detect even from many light-years away. There is no evidence that there was any atmosphere. Tom Greene (an astrophysicist from NASA) told me that they were surprised by the results. “I was a little disappointed.”
The good news is that we still have six other planets to check out, and the worlds that are farther away from their star might be more likely to have a substantial atmosphere. This means that we still have six chances to detect compounds and find atmospheres around rocks. More observations would also give us a richer understanding of whether stars like the one in the TRAPPIST-1 system, known as red dwarfs, are promising candidates in the search for habitable planets in the cosmos. It has huge implications. Red dwarfs are far more common than sunlike stars in our Milky Way. They also have the potential to harbor rocky planets. If even one TRAPPIST-1 planet has the conditions that we know are needed for life, it would suggest that the galaxy could be teeming with habitable worlds–and Earth might not be so special.
Other astronomers I spoke with shared Greene’s disappointment at TRAPPIST-1b’s lack of an atmosphere, but some aren’t surprised at all. Since the existence of the system was announced to the public in 2017, scientists have developed countless models for the planets, and the predictions were split. Jonathan Fortney from UC Santa Cruz, who was an astronomer and worked alongside Greene to find out more about b, said that some people believed that there would be no atmosphere on the planet. Others thought it might have a Venus-like atmosphere made mostly of carbon dioxide.
Before Webb came along, the Hubble Space Telescope observed most of the TRAPPIST planets, including b, and found no evidence of light and puffy atmospheres made of hydrogen. This was just fine with astronomers, because such a Neptunelike atmosphere wouldn’t be conducive to the kind of life that arose here on Earth. Scientists wanted to detect heavier gasses such as carbon dioxide, methane, and oxygen–a trio that, at least on Earth, indicates life respiring beneath the clouds–and for that, they needed the Webb telescope.
Greene and his team used Webb to assess b’s atmosphere in a new way: They measured heat in the form of infrared light radiating from the planet. A cooler result would suggest the presence of an atmosphere, circulating the star’s heat around the globe. Hotter results would indicate a hotter surface that absorbs the heat and then reflect it back as asphalt. The Webb data revealed the latter case to be true; with a day-side temperature of about 450 degrees Fahrenheit, TRAPPIST-1b is “just about perfect for baking pizza,” as NASA put it, but it’s also an airless ball of rock.
The planet might have had an atmosphere many eons ago, but its star likely took it away, Megan Mansfield, an astronomer at the University of Arizona who also uses Webb to study exoplanets, told me. Red-dwarf stars are cool stars, technically speaking–they are far less luminous than the sun–but they love to flare, blasting radiation out into space. Mansfield stated that these kinds of events can “pull the atmosphere from a planet,” especially if it orbits so close. TRAPPIST-1b might still have a very tenuous atmosphere, too ephemeral for Webb to detect, like the wisp of gas that envelops Mercury–but that’s not the kind of Earthlike environment researchers are hoping to discover in that system.
So astronomers will move down the line of planets to c, d, e, f, g, and h. Greene said he was more optimistic about detecting atmospheres around TRAPPIST-1’s other planets–at least before the disappointing discovery on b. It’s not too late to give up hope. Perhaps conditions are more comfortable farther out, where “there’s more space for that intense radiation and flaring from the star to spread out,” Mansfield said.
The Webb telescope already observed c and results are expected to be available soon, Greene informed me. If it also turns out to be an atmospheric dud, that might not be a reason for astronomers to worry. It orbits near the boundary of the habitable area, as does d. But e? Then they’ll be nervous. Planets e, f, and g stand the best chance of being Earthlike, with not only an atmosphere but also an ocean. “Every data point we get, just like the one we just got now, will help to refine those theories of what habitability means for planets in [red dwarf] systems,” Nikole Lewis, an astrophysicist at Cornell, told me. Researchers might be able to determine the water content of more promising planets by examining the surfaces of these planets with the Webb telescope. Lewis explained that because there is no atmosphere, the Webb telescope has the ability to study its surface and search for water molecules in the light that it reflects. Astronomers would hope to find the substance in other parts of the TRAPPIST system, if the signal is strong enough.
Not to us. A trek to the TRAPPIST system remains the stuff of science fiction. For the time being, humanity is tied to our calm, bright star, and to the planets and moons around it. Our fancy telescopes will be built and trained on the other planets of the galaxy. We wonder if they are able to see the ground from their silky clouds.
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