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the surface of the exoplanet lhs-1140b may be completely covered with ice, or it may have an ocean, making the entire planet look like a creepy giant eyeball (the earth is on the far right at the same scale). (image credit: benoit gougeon/university of montreal)

in 2017, this exoplanet was identified as one of the most promising worlds outside the solar system to support life, and now the possibility has become even higher.but something's not right。

at first glance, the exoplanet lhs-1140b looks like a"eyeball": the surface of this planet is covered with oceans, but most of it is hidden under the ice. there is only a liquid ocean with a diameter of about 4,000 kilometers, which stares at its parent star for a long time like the iris of an eye.

"of all the temperate exoplanets known so far, lhs-1140b is probably the best candidate for indirect evidence of the presence of liquid water on the surface of an extrasolar body," said charles cadieux, an astrophysicist at the university of montreal in canada. "this would be an important milestone in the search for potentially habitable exoplanets."

we discovered lhs-1140b a few years ago. it has a radius about 1.73 times that of earth and a mass about 5.6 times that of earth. although lhs-1140b is larger than earth, we still consider it a terrestrial planet. it is also closer to its star, lhs-1140, than earth is, orbiting it in just 25 days.

if lhs-1140 were like our sun, this orbit would be too close for life. fortunately, unlike our sun, it is acool, dim red dwarfs, so the distance between the star and the exoplanet is exactly at the so-calledhabitable zonethis means that the water on the surface of lhs-1140b will neither freeze completely nor evaporate completely.

even so, being so close to its parent star means the exoplanet is likely to betidal lockingthat is, its rotation period is synchronized with its revolution period, so it always faces the star with the same side. the moon is also tidally locked to the earth, so we can never see the back of the moon from earth.

being in the habitable zone doesn't mean a planet has what it takes to support life. to learn more about the chemistry of lhs-1140b, we need to study its atmosphere, if it exists. that's what cadieu and his colleagues did with the james webb space telescope (jwst).

the star system is less than 50 light-years away, so we can collect detailed information about changes in the starlight when an exoplanet crosses the line between earth and the star. at this time, some of the starlight will penetrate the planet's atmosphere, and the atoms in it will beabsorb or amplify specific wavelengths of lighttherefore, as long as we can observe which wavelengths of light are affected, we can determine what kind of atoms exist in the atmosphere.

this way, researchers canpreliminary determination of nitrogenthe presence of nitrogen also suggests that this is a secondary atmosphere—one that formed later than the planet was, rather than simultaneously.

in a study published last year, the team also calculated the density of lhs-1140b based on its mass and radius, and the result was 5.9 grams per cubic centimeter. this density is a bit low for a purely rocky planet, and based on the observed size data, a more appropriate guess is that this isa mini neptuneorocean planetif you rule out the mini-neptune, there's only one possibility left: an exoplanet with an entire surface covered in ocean.

but given tidal locking, this global ocean might not be as global as you might think. the side facing away from the star might be cold enough to freeze.only a small area facing the star can be warm enough to melt, making it look like a creepy and strange "eyeball" hanging in space.

however, surface temperatures in the area could reach 20 degrees celsius - too high for a thriving marine ecosystem.warm enough.

we don’t know for sure what this planet actually is, but it looks like the most promising candidate yet for finding an alien ecosystem outside our solar system, so you can bet that more scientists will be looking into the eyes of that (possible) strange “eyeball” in the future.

“detecting temperate planets with earth-like atmospheres is pushing the jwst to its limits, but it’s doable, we just need enough observing time,” said rené doyon, a physicist at the university of montreal.

"we now need more data to confirm the presence of a nitrogen-rich atmosphere. we need at least one year of observations to confirm whether lhs 1140b has an atmosphere, and probably another two or three years to detect the presence of carbon dioxide."

the relevant paper has been accepted by the astrophysical journal letters, and the preprint version has been published on the preprint library arxiv (not peer-reviewed).