About 48 light years from Earth, in the constellation Cetus, there is an icy planet that looks like it came straight out of space. Star Wars Central casting. One hemisphere always faces the primary star, forming a small molten mara on the star’s dayside, giving it the appearance of a giant eye.
What’s more, this ball of water, nearly twice the size of Earth, may offer our best chance of finding habitable conditions elsewhere in the universe.
The latest photos of LHS 1140 b (named for the red dwarf star it orbits, also known as LHS 1140) Discovered in 2017and even then it seemed an auspicious place for life.
Now, Recent PublicationsNow researchers at the University of Montreal have upped the ante: After analyzing data from the James Webb Space Telescope, they’ve concluded that the planet is more likely to be a rocky super-Earth than a gaseous mini-Neptune, and likely to have a nitrogen-rich atmosphere — two ingredients crucial to the emergence of biology as we know it.
Habitable planets
Astronomers are recording Over 5,700 exoplanets Since 1992, other moons have been suggested as possibly harboring life.
“However, we only know of three planets with atmospheres in the habitable zone: Earth and Mars, and LHS 1140 b could be the third,” said lead author Charles Cadieux, a doctoral student at the University of Montreal.
Jason Dittman, who led the team that discovered the planet and was not involved in Cadiu’s work, said the new discovery makes a strong case for allocating “critical” observing time with future telescopes.
“This is a planet where we should seriously consider investing significant amounts of our precious resources,” he says. “It definitely has a bright future.”
Potentially habitable super-Earths
Scientists have a complicated understanding of LHS 1140 b because they’ve never seen anything like it up close before. In our solar system, there’s a huge gap between Earth (the largest rocky planet) and the gas giants Neptune and Uranus, which are four times larger and have radically different compositions.
“For the in-between ones, we don’t know much about the composition of those planets,” Cadieux says.
LHS 1140 b, at 1.7 times the size of Earth, falls right in the middle, and what category it falls into will make all the difference: Without some kind of surface, which rocky planets have but gas giants don’t, there’s no place for life to take root.
To distinguish between the two possibilities, Cadiu and his colleagues observed LHS 1140 b’s “transits,” or periods when it passed between Earth and its star. By measuring how the spectrum of light from the star changes as it passes the planet, they were able to rule out the presence of a hydrogen-rich atmosphere, characteristic of gas giants. This method, known as transmission spectroscopy, confirmed that LHS 1140 b is likely a super-Earth rather than a mini-Neptune.
read more: What is the closest exoplanet to Earth?
Possible water and atmosphere in LHS 1140 b
Equally important, their measurements suggest for the first time the presence of a potentially habitable exoplanet atmosphere. Its spectral signature is best explained by the light-scattering effect of molecular nitrogen — the same phenomenon responsible for Earth’s blue skies. These results are preliminary; however, if LHS 1140 b’s atmosphere is indeed dominated by nitrogen, the planet would boast one of Earth’s life-supporting features.
And there’s another possibility the planet may have: water. Despite being a super-Earth, LHS 1140 b is much less dense than expected for a planet with Earth-like composition, suggesting that a whopping 10 to 20 percent of its mass could be water, most of it in the form of ice. The planet rotates in sync with its star, just as the Moon does with Earth, so there’s always a frozen side.
Unfortunately, we can’t directly see how much liquid water there is, but Cadiu’s climate simulations (which assume nitrogen and carbon dioxide levels are similar to those on Earth) have produced a perfectly circular ocean about 2,500 miles in diameter (about half the size of the Atlantic Ocean), with a calm ocean temperature of 68 degrees Fahrenheit.
read more: Space telescopes begin to reveal secrets of exoplanet atmospheres
Comparing exoplanets
While the JWST observations have brought renewed attention to LHS 1140 b, they have dampened hopes for another set of potentially habitable planets: the seven exoplanets that orbit it. Trappist 1Discovered in 2017, like LHS 1140 b, this object is entirely rocky and roughly the size of Earth, with some of it located within the “Goldilocks zone” where liquid water can exist on the surface.
“It’s a great system,” Dittman said, but JWST’s early results have been disappointing. Based on the TRAPPIST-1 analysis, b and cThe inner planets appear to have no atmospheres or water. “If this continues to be the case, we could be in trouble.”
Meanwhile, LHS 1140 b is looking increasingly intriguing: Its star is less active than TRAPPIST-1, meaning it emits less X-ray and ultraviolet radiation that could strip its atmosphere away than planets in its system.
But TRAPPIST-1 also has a big advantage: its star is so small that its planets are so much larger in comparison, facilitating the transmission of its spectroscopic signal. (Indeed, TRAPPIST-1’s intense stellar activity could also disrupt its signal, making the atmospheric data harder to interpret.) In other words, even if LHS 1140 b were a better candidate for an atmosphere, it would be more difficult to observe.
Dittman accepts this cosmic dilemma with a scientist’s calm: “We’re given the planet we’re given.”
read more: 6 exoplanets in space that could support life beyond Earth
Deciding where to search for extraterrestrial life
These considerations are forcing the astronomy community to make a difficult decision: where should we look in the search for habitable exoplanets, and for how long? As Dittman points out, Webb’s time is valuable, and thousands of scientists around the world compete for it each year. The telescope is expected to last perhaps another 20 years, but with its lenses spread across many projects, exoplanet researchers must choose their targets wisely.
When it comes to observing the atmospheres of distant planets, “you don’t have a lot of opportunities to see a lot at once,” Dittman says. In the case of 1140 b, telescopes can only observe four of its hour-long passes. “We basically need to see them all,” he says. “It’s like, if we don’t start now, we’ll never get anywhere.”
Jennifer Lotz, director of the Space Telescope Science Institute (which oversees the operation of JWST and the Hubble Space Telescope), said last month: 500 hours of web time To study the atmospheres of rocky exoplanets in the nearby solar system. It is not yet clear which planets the project will target, or how the research time will be divided between them.
Keep in mind that JWST has only explored a handful of planets so far. As it continues to comb the cosmos for signs of life, it may find more rocky, temperate planets with abundant atmospheres, adding to the list that began with LHS 1140 b. But for now, Cadieux is betting on eyes in the sky.
“I think it’s still going to be very unique in terms of livability,” he says.
read more: Why do astronomers look for signs of life on other planets?
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Cody Cottier is a contributing writer at Discover who loves exploring big questions about the universe and Earth, the nature of consciousness, the ethical implications of science, and more. He holds a BA in Journalism and Media Production from Washington State University.
