Scientists find planet with potential for life

An exoplanet in its star’s habitable Goldilocks zone is now suspected of having a liquid water ocean and an atmosphere.

The planet, called LHS 1140 b, is about 1.7 times the size of Earth and is located about 48 light-years away.

This distant world, first discovered in 2017, now turns out to be a rocky world like ours, but with 10 to 20 percent of its mass made up of water, according to a new paper to be published soon in the journal Science. The letters of the astrophysical journal this week (currently available on the arXiv preprint server).

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

ice world
LHS 1140 b may be completely covered in ice (left), similar to Jupiter’s moon Europa, or it may be an icy world with a liquid substellar ocean and a cloudy atmosphere (center). This planet is about 1.7…

B. Gougeon/University of Montreal

LHS 1140 b orbits a red dwarf star about 20 percent the size of our own Sun and is located at a specific distance from its sun, putting it in the “Goldilocks” or habitable zone. This refers to the range of distances from a star where conditions are just right for liquid water to exist on a planet’s surface. If a planet is too close to its star, it will be too hot, causing water to evaporate, while if it is too far from its star, it will be too cold, causing water to freeze.

The size and type of star have a large effect on the location of the habitable zone. For example, the habitable zone is closer to a smaller, cooler star (such as a red dwarf) and farther from a larger, hotter star.

Until now, astronomers weren’t sure whether LHS 1140 b was a rocky planet like Earth or a gas giant more like Neptune. Eventually, they determined that the exoplanet was a so-called super-Earth.

Using data collected by the James Webb Space Telescope (JWST), they found that LHS 1140 b is less dense than expected for a completely rocky world, with 10 to 20 percent of its mass made up of water. This means the planet could be an icy world with a liquid ocean beneath the ice, like Jupiter’s moon Europa.

They also discovered that the planet has an atmosphere, which may contain a similar amount of nitrogen as our own planet. The presence of this atmosphere would allow the planet to maintain liquid water on its surface.

“This is the first time we’ve seen a hint of a habitable-zone atmosphere on a rocky or ice-rich exoplanet. Detecting atmospheres on small, rocky worlds is a key goal for JWST, but these signals are much harder to see than for the atmospheres of giant planets,” co-author Ryan MacDonald, also a researcher at the Université de Montréal, said in the statement.

“LHS 1140 b is one of the best small exoplanets in the habitable zone that can support a thick atmosphere. We may have found evidence of air on this world.”

Using models, the astronomers predicted that if LHS 1140 b has an atmosphere like Earth’s, it would consist of a layer of ice surrounding the planet, with a single circle of surface ocean about 2,500 miles across, about half the size of the Atlantic Ocean. According to the paper, this ocean could have a surface temperature as high as 68 degrees Fahrenheit.

This discovery makes LHS 1140 ba a good candidate for life beyond our world, as the planet’s atmosphere and liquid water could support life similar to that on Earth.

“This is our first tantalizing glimpse of an atmosphere on a super-Earth in the habitable zone. Compared to other known exoplanets in the habitable zone, such as those in the TRAPPIST-1 system, the star LHS 1140 appears to be quieter and less active, making it significantly less challenging to disentangle the atmosphere of LHS 1140 b from stellar signals caused by starspots,” MacDonald said.

“Our initial exploration of LHS 1140 b with JWST has revealed that this may be the best habitable zone exoplanet currently known for atmospheric characterization. While we need more JWST observations to confirm the nitrogen-rich atmosphere and to search for other gases, this is a promising start.”

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