Confirmed exoplanet · Database record + computed analysis
LHS 1140 b
A confirmed world orbiting LHS 1140, 48.9 light-years away.
A super-Earth
1.73 Earth radii. Worlds between Earth and Neptune in size are the most common in the galaxy, yet our Solar System has none, which is why each one matters. With 5.6 Earth masses packed into that size, its density points to rock and iron rather than gas.
The orbit
Its year, one full orbit, takes just 24.7 Earth days.
Temperature and starlight
Its equilibrium temperature (the airless-world estimate) is about -47 °C. In the range where, with the right atmosphere, liquid water is conceivable; a real atmosphere could shift the true surface figure a lot (Earth's equilibrium value is −18 °C, yet we average +15 °C). It receives 0.43 times Earth's starlight, the same order as our own world.
Its sun
Its star is a red dwarf (3,096 K surface), type M4.5 V: small, dim, flare-prone, and destined to outlive the Sun many times over. It shares the system with 1 other known planet.
How far is that, really?
At 49 light-years, tonight's light from this system left it around the year 1977. That is close by galactic standards, which makes it a prime target for follow-up telescopes. A Voyager-speed probe would need roughly 864,781 years to get there.
How we found it
It was found by the transit method: the planet crosses its star's face on schedule, dimming it by a tiny, repeating fraction. The dip's depth gives the planet's size. The discovery was announced in 2017 from MEarth Project.
Everything above is computed from the archive’s measured values for this planet. Where a quantity is missing, the statement is omitted rather than guessed.
The deep dive
Researched for the Atlas from Wikipedia — LHS 1140 b (8,337 characters read) · updated Sep 20, 2026
01 How LHS 1140 b Was Found in 2017
LHS 1140 b was discovered in 2017 by the MEarth Project, a survey specifically designed to search for planets around small, nearby red dwarf stars. What makes this discovery especially powerful is that the planet was detected using two independent techniques simultaneously. Transit photometry — watching the star dim slightly as the planet crosses its face — pinned down the planet's radius. Radial velocity measurements — tracking the tiny wobble the planet's gravity induces in the star's motion — yielded its mass. Having both numbers in hand is rare and scientifically precious: it lets astronomers calculate density directly and say something meaningful about what the planet is made of. Because of this dual detection, LHS 1140 b belongs to a very short list of potentially habitable exoplanets with both a measured mass and a measured radius, a list that otherwise consists entirely of the TRAPPIST-1 worlds.
02 A Star Quieter Than Almost Any Other
The host star LHS 1140 is a red dwarf of spectral type M4.5V, carrying only 18.4% the mass and 21.6% the radius of the Sun. Its surface temperature is just 3,096 K — compared to the Sun's 5,778 K — and its luminosity is a mere 0.0038 times solar, making it roughly 260 times dimmer than our own star. Red dwarfs are notorious for violent flares that can strip away planetary atmospheres over billions of years, but LHS 1140 is a striking exception. The discovery team found no major flare events, and the star rotates unusually slowly, completing one rotation every 130 days — far slower than most stars of its size. This sluggish rotation is directly linked to lower magnetic activity and fewer energetic outbursts. The star is also at least 5 billion years old, older than our solar system, meaning LHS 1140 b has had ample time to settle into whatever atmospheric state it currently occupies without being constantly bombarded by radiation.
03 From Rocky World to Ocean Planet: The Density Revision Deeper
The story of LHS 1140 b's composition has been dramatically rewritten over successive measurements. Early estimates pegged its density at an astonishing 12.5 g/cm³ — more than twice Earth's average density of about 5.5 g/cm³ — implying a colossal iron-nickel core occupying up to 75% of the planet's total mass. That picture began to shift in 2018 and 2020, when revised radius measurements pushed the density down to 7.82 g/cm³ and the core mass fraction to 49±7%, still high but no longer extreme. The 2020 study went further, suggesting roughly 4% of the planet's mass is water, hinting at an ocean world with an average ocean depth of 779±650 km — a range so wide it reflects how hard it is to model interiors from the outside. Then in 2023, more precise mass measurements settled on 5.60±0.19 Earth masses paired with a radius of 1.730±0.025 Earth radii, giving a density no longer consistent with a rocky planet at that size. The current best interpretation is that LHS 1140 b is an ocean world carrying 9–19% of its mass as water, or possibly a dense mini-Neptune.
04 What 43% Sunlight Means for Temperature
Despite sitting just 0.0946 AU from its star — less than a tenth of the Earth–Sun distance — LHS 1140 b receives only 43% of the energy per square meter that Earth gets from the Sun. The star is simply too dim to compensate for the closeness. With no atmosphere at all and an assumed albedo of zero, the planet's equilibrium temperature works out to 230 K, which is −43 °C, as cold as winter at Earth's poles. Give the planet an Earth-like albedo and that drops further, to 201 K (−72 °C). However, equilibrium temperatures exclude greenhouse warming. Add a greenhouse effect comparable to Earth's and the surface climbs above 266 K (−7 °C). Because the planet is significantly more massive than Earth, it likely holds a thicker atmosphere capable of a stronger greenhouse effect; at twice Earth's greenhouse warming, the surface could reach a comfortable 296 K — about 23 °C, a pleasant spring day. These numbers place LHS 1140 b near the outer edge of the habitable zone, where warmth depends heavily on atmospheric thickness.
05 An Orbit So Circular It Puzzles Scientists Deeper
LHS 1140 b completes one orbit in just 24.737 days, but its path is very nearly a perfect circle. Orbital eccentricity is measured at less than 0.29 to 90% confidence, and researchers note that this circularity cannot be explained by tidal forces from the star gradually smoothing out an originally elliptical orbit — the star is too weak for that. Instead, the near-circular shape is described as likely natal, meaning the planet probably formed on a circular trajectory and has stayed that way. This distinction matters for habitability: a highly elliptical orbit would swing a planet in and out of the habitable zone, causing wild seasonal temperature swings. A stable circle keeps incident flux nearly constant year-round, at least in terms of orbital geometry. The orbital period of 24.737 days is also short enough that, like most close-in red-dwarf planets, LHS 1140 b is a strong candidate for tidal locking, with one hemisphere permanently facing its star, though the article does not explicitly confirm this.
06 The Eyeball World Hypothesis
Tentative hints of atmospheric nitrogen detected by the James Webb Space Telescope in July 2024 inspired a striking visual model for what LHS 1140 b's surface might look like. If those detections are confirmed, scientists suggest the planet may be mostly covered in ice, with a region of liquid water concentrated in a roughly circular patch facing the star — a configuration nicknamed an "eyeball" planet. This geometry would arise naturally if the planet is tidally locked, with perpetual daylight on one hemisphere melting surface ice and perpetual darkness freezing the other side solid. The nitrogen detection itself would be historic: it would represent the first evidence of a secondary atmosphere around a potentially habitable exoplanet anywhere. A secondary atmosphere is one that outgassed from the planet's interior after formation rather than being inherited directly from the primordial stellar nebula, suggesting active geological or volcanic processes have been at work throughout the planet's long history.
07 Helium Escaping Into Space — But Only Sometimes Deeper
In July 2026, a team using the Magellan Clay Telescope at Las Campanas Observatory reported detecting helium leaking from LHS 1140 b's upper atmosphere. The observation was a 6.5-hour transit spectroscopy session in September 2024 that simultaneously captured transits of both LHS 1140 b and the neighboring planet LHS 1140 c. During LHS 1140 b's transit, the team measured an excess absorption feature attributed to helium, interpreted as a hydrodynamic outflow driven by stellar X-ray and extreme-ultraviolet heating — essentially, high-energy light from the star boiling gas off the top of the atmosphere. Curiously, a follow-up observation in 2025 found no helium absorption at all. Modeling reconciled this by suggesting that lower stellar activity at the time of the second observation simply produced a weaker outflow, making the signal disappear. This time-variable behavior means the helium escape is episodic rather than constant. Critically, separate JWST observations conducted between 2023 and 2026 found no helium signal and no evidence of atmospheric mass loss, leaving the overall picture genuinely unresolved.
08 What JWST Has and Hasn't Found
The James Webb Space Telescope has become the primary tool for probing LHS 1140 b's atmosphere, and its findings have been both illuminating and sobering. On the positive side, JWST observations published in 2024 conclusively ruled out a hydrogen-rich atmosphere — the kind that would indicate the planet is essentially a small gas world — and instead support a high mean molecular weight atmosphere, possibly a mixture of nitrogen, water vapor, and carbon dioxide. This result actually strengthens the ocean world interpretation, because a lightweight hydrogen envelope would have been lost to space long ago if the planet is as geologically active as theorized. However, JWST observations made between 2023 and 2026 failed to detect helium and found no evidence for any atmospheric mass loss, sitting in tension with the ground-based Magellan detection. An earlier tentative detection of water vapor was made in late 2020 with the Hubble Space Telescope, though at a low signal-to-noise ratio. The full atmospheric picture remains an active area of research.
09 Ice Geysers as a Last Resort for Life
If LHS 1140 b turns out to have no atmosphere at all, astronomers have sketched out an alternative path to liquid water on its surface. Without an atmosphere, the planet would be blanketed in a thin ice envelope — a frozen world at first glance. However, the planet's large mass means it likely experiences significant radiogenic heating, the warmth generated by the slow decay of radioactive elements in its rocky interior. Tidal heating from the gravitational interaction with its star could add more energy still. Together, these internal heat sources could be sufficient to melt water beneath the ice shell, and that water might reach the surface through cryovolcanic venting — essentially geysers that crack through the ice and spray liquid water or water-rich slush into the environment. This is not so different from what happens on Jupiter's moon Europa, where a subsurface ocean is thought to be maintained beneath kilometers of ice. It is a reminder that habitability can take forms quite unlike anything familiar on Earth.
10 The Cosmic Shoreline and Its Neighbor Planet Deeper
The nearby planet LHS 1140 c provided an instructive comparison during the helium escape study. When the Magellan Clay Telescope observed the helium transit feature in LHS 1140 b, it simultaneously checked LHS 1140 c and found no helium absorption there at all. The researchers interpreted this as consistent with LHS 1140 c's position on the opposite side of the so-called "cosmic shoreline" — a conceptual boundary, defined by a planet's escape velocity versus the energy it receives from its star, that separates worlds capable of retaining atmospheres from those that inevitably lose them. LHS 1140 c sits in a position where atmospheric retention is predicted to be difficult, and the absence of a helium signal matched that expectation. LHS 1140 b, by contrast, falls on the retaining side of the shoreline, which is why finding an atmosphere there would be so consequential. The neighboring-planet comparison within a single observing session is a powerful method for isolating systematic errors and confirming that any signal is genuinely planetary in origin.
11 Size, Distance, and Why 49 Light-Years Matters
At 49 light-years away, LHS 1140 b is close enough on a cosmic scale to be studied in genuine detail, yet so far that the fastest spacecraft ever launched would take hundreds of thousands of years to reach it. What makes the distance meaningful for science is that the planet transits its star — it periodically crosses in front of LHS 1140 as seen from Earth. This geometry, which is purely a matter of luck in orbital alignment, is what allows telescopes to analyze starlight filtering through the planet's atmosphere during each transit. The planet's radius is well-constrained at 1.730±0.025 Earth radii, roughly equivalent to about 11,000 km — for comparison, Earth's radius is about 6,371 km. Its radius is described as similar to that of Kepler-62e, another super-Earth that has been discussed in habitability contexts. The combination of a transiting geometry, a nearby distance, a quiet host star, and a likely substantial atmosphere makes LHS 1140 b one of the most scientifically accessible potentially habitable worlds currently known.
12 Open Questions That Keep Scientists Watching Deeper
LHS 1140 b sits at the center of several unresolved debates that represent some of the most important open questions in exoplanet science. Most immediately, the helium detection from the Magellan Clay Telescope in July 2026 contradicts multiple sets of JWST observations that found no atmospheric helium or evidence of mass loss between 2023 and 2026. Resolving whether the signal is real, time-variable, or an artifact will require more observations from multiple independent instruments. More broadly, it is still not settled whether the planet is a true ocean world with a water mass fraction of 9–19%, a dense mini-Neptune with a thin volatile envelope, or something else entirely. The tentative nitrogen detection from JWST in July 2024 has not yet been confirmed, and confirmation would rewrite the planet's story. Whether the planet is tidally locked, whether its ocean — if it exists — is on the surface or buried beneath ice, and whether any of this adds up to a genuinely habitable environment remain questions that the next decade of telescope time will attempt to answer.
About this record
The measured values come from the NASA Exoplanet Archive, and any missing value has not been determined yet; the Atlas never fills gaps with guesses. More standout worlds: Proxima b, TRAPPIST-1e, K2-18 b, 55 Cancri e, and the detection methods that found them all.