The “Eye Planet” could be the ideal place to look for life
An exoplanet identified in 2017 as one of the most promising places for life to flourish outside the Solar System just got even more promising — and a lot stranger.
The alien world LHS-1140b shows signs of being an 'eyeball' planet, with an ice-covered global ocean and a single iris-like region about 4,000 kilometers (about 2,500 miles) across that permanently faces its star guest. Data on this particular world has been published on arXiv .
“Of all the currently known temperate exoplanets, LHS-1140b may be our best bet to one day indirectly confirm the presence of liquid water on the surface of an alien world beyond our Solar System,” says astrophysicist Charles Cadieux of University of Montreal. “This would be an important milestone in the search for potentially habitable exoplanets.”
LHS-1140b, whose discovery was announced only a few years ago, has a radius of approximately 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 also orbits much closer to its star than Earth, completing an entire orbit in just under 25 days.
If this star were similar to the Sun, it would be too close for life. Instead, it is a red dwarf, cold and dim – so the distance between the star and the exoplanet is right in what we call the habitable zone. It's not so cold that all the surface water freezes, but not so cold that it evaporates into oblivion.
However, the proximity means that the exoplanet is probably side-locked, meaning it always shows the same face to its star. This happens when its rotation period synchronizes 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 the Earth.
The exoplanet on the opposite side of the star, facing the star and compared to the Earth
Being in a habitable zone does not automatically mean that the conditions necessary to support life are there. To learn more about LHS-1140b's chemistry, we need to peer into its atmosphere, if it has one. And that's what Cadieux and his colleagues did, 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 of the starlight will pass through the atmosphere; as it does so, some wavelengths are absorbed or amplified by the atoms within it. One can precisely determine which atoms are at work by observing which wavelengths are affected.
In this way, the researchers were able to provisionally ascertain the presence of nitrogen, the dominant ingredient of the Earth's atmosphere. If LHS-1140b were more gaseous, like a small Neptune, it would have a richer hydrogen atmosphere. The presence of nitrogen suggests a secondary atmosphere – one that formed after the exoplanet was born, rather than with it.
In a study published last year, the team also combined the density and radius of LHS-1140b to calculate its density. They got a figure of 5.9 grams per cubic centimeter. It's not dense enough for a purely rocky world; given its size, the best guess is that of a mini-Neptune or an ocean-covered water world. If we exclude mini-Neptune, what we are left with is an exoplanet with a global ocean.
Taking tidal locking into account, though, this global ocean may not look like you might think. The side constantly facing the star may be cold enough to freeze. Only the area facing the star directly would be hot enough to thaw, resulting in a world that resembles an eerie eyeball hovering in space.
This area, however, could reach a very mild temperature of 20 degrees Celsius at the surface – warm enough for a thriving marine ecosystem. Now, however, we need to go deeper into detecting the exoplanet's atmosphere.
“Detecting an Earth-like atmosphere on a temperate 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 further data. We need at least another year of observations to confirm that LHS 1140b has an atmosphere, and probably another two or three to detect carbon dioxide."
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The article The “Eye Planet” could be the ideal place to look for life comes from Economic Scenarios .
This is a machine translation of a post published on Scenari Economici at the URL https://scenarieconomici.it/il-pianeta-occhio-potrebbe-essere-il-posto-ideale-dove-cercare-la-vita/ on Tue, 09 Jul 2024 11:29:04 +0000.