Eyeball ocean world? Webb reveals an intriguing super-Earth

• The exoplanet LHS 1140 b – in its star’s liveable zone – may need an environment and an ocean
of liquid water. It is usually comparatively close by, solely 48 light-years from Earth.
• It is perhaps what’s known as an eyeball planet, with a single liquid ocean surrounded by ice. Or it is perhaps fully ice-covered, with an ocean under the ice, just like Jupiter’s moon Europa or Saturn’s moon Enceladus.
• Both approach, additional observations are wanted. But when confirmed, it could be the primary doubtlessly liveable ocean world discovered exterior our solar system.

Meet the intriguing exoplanet LHS 1140 b

A brand new research from researchers on the College of Montreal means that exoplanet LHS 1140 b is probably a super-Earth. That will make it extra huge than Earth, but lighter than our solar system’s ice giants, Neptune and Uranus. This distant world lies in its star’s habitable zone, the zone through which liquid water may exist on a planet’s floor. And the researchers said on July 8, 2024, that the planet is probably going a water world. There are, they stated, two potentialities, given their present understanding. LHS 1140 b could have a world ice-covered ocean, just like Jupiter’s moon Europa or Saturn’s moon Enceladus. Or it may need an enormous “eyeball” liquid ocean on its floor, surrounded by ice. Creepy because it sounds, scientists name such hypothesized worlds eyeball planets.

This new evaluation, constructed from knowledge gathered by the James Webb Space Telescope and different space-based telescopes, tentatively hints that LHS 1140 b has a nitrogen-rich ambiance like Earth’s. In that case, then pc fashions favor the eyeball ocean state of affairs.

These outcomes make LHS 1140 b one of the promising exoplanets discovered to this point within the liveable zone of its star. And it’s comparatively shut, too, at solely 48 light-years away.

The analysis crew published the intriguing peer-reviewed findings in The Astrophysical Journal Letters on July 10, 2024.

Mini-Neptune or super-Earth?

LHS 1140 b has been the topic of debate amongst planetary scientists. They thought it is perhaps a super-Earth. However it additionally is perhaps a mini-Neptune, resembling our solar system’s planet Neptune in that it has a thick hydrogen-helium ambiance, most likely with deep layers of ice, rock or liquid oceans.

Earlier observations of LHS 1140 b had been inconclusive. Was it a mini-Neptune with a deep hydrogen ambiance? Or a super-Earth, a rocky world bigger than Earth with a attainable thinner, extra Earth-like ambiance and water? Or perhaps a Hycean planet, with a deep international ocean and hydrogen ambiance?

The latest outcomes favored the super-Earth interpretation.

What astronomers did know was that LHS 1140 b orbits throughout the liveable zone of its red dwarf star. That’s the area round a star the place temperatures might enable liquid water to exist on a planet. As well as, additionally they measured its radius and mass. The planet is 1.7 occasions the dimensions of Earth and 5.6 occasions its mass.

Now, the researchers say that the mini-Neptune state of affairs has been strongly excluded. That leaves LHS 1140 b as being some sort of water world. However what sort, precisely?

Nitrogen ambiance on an ocean world?

The astronomers mixed the brand new knowledge from Webb with earlier knowledge from Spitzer, Hubble and TESS. It confirmed that the planet is much less dense than it must be if it had been only a stable rocky world like Earth. The truth is, 10-20% of its mass could also be composed of water. That will imply a deep international ocean, both below a hydrogen ambiance (a Hycean water world) or a extra Earth-like ambiance of nitrogen.

Webb revealed that LHS 1140 b doesn’t have a thick hydrogen ambiance. That’s why the mini-Neptune speculation was dominated out. Nonetheless, it additionally implies that the planet is unlikely to be a Hycean water world, both. As an alternative, LHS 1140 b’s ocean could also be lined by ice, a minimum of principally.

Intriguingly, Webb’s evaluation does trace at a nitrogen ambiance on LHS 1140 b. The paper stated:

Our retrieval evaluation identifies tentative proof for a cloud-free N2-dominated ambiance on LHS 1140 b. Our tantalizing proof for a N2-dominated ambiance on a habitable-zone super-Earth raises a powerful name for added observations of LHS 1140 b to substantiate this outcome.

It is a nice thread concerning the discovery on X, by Ryan MacDonald on the College of Michigan:

An eyeball planet?

So, whether it is certainly a water world, as Webb suggests, then the information point out two potentialities. One is a world ocean lined by a layer of ice, just like the moons Europa or Enceladus in our solar system. The opposite is that LHS 1140 b continues to be principally ice-covered, however with a big eyeball ocean on the facet going through its star. That’s as a result of the planet is considered tidally locked to its star, so the identical facet of the planet all the time faces the star. Certainly, scientists have hypothesized about such planets – additionally known as eyeball planets – present earlier than, however LHS 1140 b could possibly be the primary one really found.

To make certain, that discovering nonetheless wants additional affirmation. But when it holds up, then the researchers say that the planet most likely does have an eyeball ocean. Extra particularly, the researchers calculated that the ocean could be about 2,500 miles (4,000 km) throughout, or about half the floor space of the Atlantic Ocean. This might be open ocean, like on Earth, surrounded by the ice masking the remainder of the planet. The simulation fashions of this ocean even point out that the temperature within the middle of the ocean could possibly be a balmy 70 levels Fahrenheit (20 C).

A significant milestone

However certainly, any type of ocean on LHS 1140 b could be an thrilling discovery. Lead writer Charles Cadieux, a Ph.D. pupil at College of Montreal’s Trottier Institute for Analysis on Exoplanets (iREx), said:

Of all presently recognized temperate exoplanets, LHS 1140 b might nicely be our greatest guess to at least one day not directly verify liquid water on the floor of an alien world past our solar system. This might be a significant milestone within the seek for doubtlessly liveable exoplanets.

Extra observations wanted to substantiate ocean world

Proper now, the outcomes from Webb strongly assist LHS 1140 b being an ocean world with a tentative nitrogen ambiance. Nonetheless, additional observations are wanted to completely verify this. Astronomers have to take extra eclipse and transit measurements of the planet, which might take a number of years. Additionally they need to search for carbon dioxide within the ambiance, as this may additional assist the findings. René Doyon, additionally at iREx, stated:

Detecting an Earth-like ambiance on a temperate planet is pushing Webb’s capabilities to its limits; it’s possible; we simply want a number of observing time. The present trace of a nitrogen-rich ambiance begs for affirmation with extra knowledge. We’d like a minimum of another yr of observations to substantiate that LHS 1140 b has an environment, and certain two or three extra to detect carbon dioxide.

Discovering exoplanets with liquid water is a crucial step towards figuring out which of them may very well be liveable, by earthly requirements. Will LHS 1140 b be the primary one? Solely time and extra observations will inform, however it is a tentatively thrilling and promising discovery.

Backside line: NASA’s Webb space telescope has revealed that exoplanet LHS 1140 b is a super-Earth ocean world. It could have an ocean on one facet or a world ice-covered ocean.

Source: Transmission Spectroscopy of the Habitable Zone Exoplanet LHS 1140 b with JWST/NIRISS

Via University of Montreal

Read more: Ocean worlds around red dwarfs … common?

Read more: Hycean planets might be habitable ocean worlds