A exoplanets Identified in 2017 as one of the most promising places for life outside the Solar System to flourish, it just got even more promising — and a whole lot weirder.
of alien world LHS-1140b shows signs of being an ‘eyeball’ planet, with an icy global ocean and a single, iris-like region about 4,000 kilometers (about 2,500 miles) forever gazing at its host star.
“Of all the currently known exoplanets, LHS-1140b may be our best bet to one day indirectly confirm liquid water on the surface of an alien world beyond our Solar System,” says astrophysicist Charles Cadieux of the University of Montreal. “This would be a major milestone in the search for potentially habitable exoplanets.”
LHS-1140b, whose discovery was announced only a few years ago, has a radius about 1.73 times that of Earth and 5.6 times its mass; larger than our planet, but still small enough to be considered a terrestrial world. It is also orbiting much closer to its star than Earth, completing an entire orbit in just 25 days.
If that star were at all like the Sun, it would be too close for life. Instead, it’s a cool, faint, red dwarf—so the distance between the star and the exoplanet is noisy in what we call the habitable zone. It’s not cold enough to freeze all surface water, but not close enough to evaporate into oblivion.
However, the proximity means that the exoplanet is likely to be tidally trapped. This is when its rotational period coincides with its orbital period, so that the same side always faces the star. It’s the same phenomenon we see with the Earth and the Moon, and why we never see its far side from Earth.
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Being in a habitable zone does not automatically mean that it has the necessary conditions to support life. To learn more about LHS-1140b’s chemistry, we need to look into its atmosphere, if it has one. And that’s what Cadieux and his colleagues have done, using the power of JWST.
At just under 50 light-years away, the system is close enough to us that we can gather detailed information about how the light changes as the exoplanet passes between Earth and the star. Some starlight will pass through the atmosphere; as it does so, some wavelengths are absorbed or amplified by the atoms inside. Exactly which atoms are at work can be determined by looking at which wavelengths are being affected.
By doing so, the researchers were able to detect in advance the presence of nitrogen, the dominant component in the Earth’s atmosphere. If LHS-1140b were gassier, like a small Neptune, it would have a more hydrogen-rich atmosphere. The presence of nitrogen suggests a secondary atmosphere—one that formed after the birth of the exoplanet, rather than with it.
In a study published last year, the team also combined LHS-1140b’s density and radius to calculate its density. They got a figure of 5.9 grams per cubic centimeter. This is not dense enough for a world that is simply made of rock; given its size, the best fit is either a mini-Neptune or a water world covered by ocean. If we rule out mini-Neptune, what we’re left with is a global ocean exoplanet.
However, considering tidal blocking, this global ocean may not look like what you might think. The side that is permanently facing the star can be cold enough to freeze. Only the blob directly in front of the star would be warm enough to melt, resulting in a world that looks like a creepy eyeball floating in space.
However, that patch can reach 20 degrees Celsius (68 degrees Fahrenheit) at the surface – warm enough for a thriving marine ecosystem.
We don’t know for sure what’s going on, but it looks like the most promising candidate we have to meet for an exotic alien ecosystem outside our planetary neighborhood, so you can bet there will be a lot more. staring into that strange (possible) eye.
“Discovering an Earth-like atmosphere on a soft planet is pushing Webb’s capabilities to its limits—it’s doable; we just need a lot of observation time,” says physicist René Doyon of the University of Montreal.
“The current hint of a nitrogen-rich atmosphere requires confirmation with more data. We need at least one more year of observations to confirm that LHS 1140b has an atmosphere, and likely two or three more to detect carbon dioxide.”
The research has been accepted in The Astrophysical Journal Lettersand is available on arXiv.