Alien Planet 48 Light-Years Away Is A Water World, Suggest NASA’s Webb

Scientists using the James Webb Space Telescope have concluded that a nearby exoplanet could be the best candidate yet to find water—and even an Earth-like atmosphere.

Over 5,000 exoplanets—planets that orbit stars other than our sun—have so far been discovered, but relatively few are close enough to study in detail. Just 49 light-years distant in the constellation Cetus, LHS 1140 b is 1.7 times the size of Earth.

With the discovery, LHS 1140 b becomes one of the most promising exoplanets yet in the search for liquid water beyond the solar system.

Best Bet

Discovered in 2017 by the MEarth Project, LHS 1140 b has been suspected of being both a mini-Neptune gas giant planet and a rocky, terrestrial planet. However, a paper accepted for publication this week in The Astrophysical Journal Letters using data JWST collected in December 2023 reveals that it potentially harbors an atmosphere and even a liquid water ocean.

“Of all currently known temperate exoplanets, LHS 1140 b could well be our best bet to one day indirectly confirm liquid water on the surface of an alien world beyond our solar system,” said Charles Cadieux, lead author and a doctoral student at Université de Montréal. “This would be a major milestone in the search for potentially habitable exoplanets.”

Ice, Snow Or Water

Although the scientists estimate that 10 to 20% of its mass is water, LHS 1140 b could be a “snowball” or ice planet. Since the planet is tidally locked to its star and always shows the same side to it—much like the moon does to Earth—it’s possible that any liquid ocean exists on its permanently dark side.

If that’s true, they estimate that it could be 2,500 miles (4,000 kilometers) in diameter, about half the Atlantic Ocean’s surface area. It’s thought that the ocean’s surface temperature could be a comfortable 68 degrees Fahrenheit (20 degrees Celsius).

Habitable Zone

Called a “super-Earth” because it’s about seven times the mass of Earth, LHS 1140 b orbits a red dwarf star, one of the most common types of stars in the Milky Way. Red dwarf stars are much smaller and dimmer than our sun, so LHS 1140 b is a temperate world despite taking just 25 days to orbit a star a mere one-fifth the size of our sun.

For context, Mercury takes 88 days and temperatures on its surface reach a scorching 800 degrees Fahrenheit (430 degrees Celsius), according to NASA. So LHS 1140 b orbits within the so-called “habitable zone” around its star—the distance where water can exist as a liquid. That’s crucial because water is thought to be essential to life. Red dwarf stars tend to release many damaging flares, which douse any planets in orbit in radiation lethal to life—but not LHS 1140.

“This is our first tantalizing glimpse of an atmosphere on a super-Earth in the habitable zone,” said Ryan MacDonald, NASA Sagan Fellow in the U-M Department of Astronomy, who helped analyze 1140 b’s atmosphere. “Compared to other known habitable zone exoplanets, such as those in the TRAPPIST-1 system, the star LHS 1140 appears to be calmer and less active, making it significantly less challenging to disentangle LHS 1140 b’s atmosphere from stellar signals caused by starspots.”

Earth-Like Atmosphere?

The researchers hoped to find a nitrogen-rich atmosphere like Earth’s. “This is the first time we have ever seen a hint of an atmosphere on a habitable zone rocky or ice-rich exoplanet,” said MacDonald. “LHS 1140 b is one of the best small exoplanets in the habitable zone capable of supporting a thick atmosphere, and we might just have found evidence of air on this world.”

However, the scientists state that more JWST observations will be needed to confirm the signature of nitrogen gas. “While we need more JWST observations to confirm the nitrogen-rich atmosphere and to search for other gases, this is a very promising start,” said MacDonald.

Progress will be slow. JWST can only see LHS 1140 b pass in front of its star—and therefore have its atmosphere backlit by starlight—eight times each year. So, say the astronomers, several years of observations will be required to detect carbon dioxide and confirm the presence of liquid water on the planet’s surface.

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