Webb found strong evidence of a Saturn-mass planet in the habitable zone of Alpha Centauri A — our closest solar twin, just 4 light-years away — and then the planet seemed to disappear, sending astronomers into millions of simulated orbits to see how it could slip out of sight.

One night in August 2024, the James Webb Space Telescope recorded a faint dot of mid-infrared light next to Alpha Centauri A. The source was more than 10,000 times fainter than the star and appeared about 1.5 arcseconds away, equivalent to an expected separation distance near twice the distance between Earth and the Sun.

There were good reasons to take the matter seriously. The tests made the passage of an asteroid, a distant background object, or familiar image processing elements unlikely. However, Webb searched again in February and April 2025 and found no similar source. The potential planet, designated S1 in the analysis, appears to have disappeared.

Two papers linked in Astrophysical Journal Letters They argue that the planet remains a plausible explanation. Their case combines one detection, two non-detections, and millions of simulated orbits. This is one pair of studies, not a firm confirmation of a planet.

One of the closest goals is also one of the hardest

Alpha Centauri is the closest star system to the Sun, just over four light-years away. The central pair contains Alpha Centauri A, a G-type star very similar to the Sun, and Alpha Centauri B, which is somewhat smaller. The third member, Proxima Centauri, is located farther away from the pair. that ESA/Hubble image of A and B It makes them appear distinctly separate, but a careful search for the planet would have to contend with the detailed light pattern from both stars.

The mid-infrared web instrument, MIRI, used a coronal mask to suppress Alpha Centauri A. And this is just the beginning. Alpha Centauri B contributed its off-axis glow, the stars moved quickly against the background, and small differences in signal changed the remaining patterns that survived the subtraction.

The first two papers of 2025, led by Aniket Sanghi, describe the situation Observations and image analysis. Depending on the processing method, S1 was detected with a signal-to-noise ratio between four and six, which corresponds to a quoted significance of approximately 3.3 to 4.3 sigma. This is interesting, but it’s not the kind of overwhelming, one-era signal that makes following optional.

So the team injected artificial point sources into the raw and processed images and wondered whether the pipeline could recover them. He also tested whether S1 behaves like a fixed detector defect, a residual version of the star point spread function, or an unrelated moving object. These checks support an astrophysical source, but no processing test can provide the second view needed to prove the orbit.

The planet did not need to cease to exist for it to disappear

The coronagraph does not leave a completely transparent field around a dim star. Sensitivity lies close to the central mask, while diffraction features, detector behavior and imperfect subtraction make searching in some directions easier than others. The planet it is orbiting can move from a visible patch to an area where it is no longer restored by the same instrument and exposure.

This possibility became pivotal after Webb’s visits in February and April 2025. Both observations were undiscovered. The accurate statement is not that the planet was seen and then ceased to exist. Namely, S1 was seen once and would have been below the recovery threshold in subsequent positions for many plausible orbits.

NASA Calculate August 2025 for work This is called a “disappearing planet,” but it also has a crucial limitation: additional observations are needed. The phrase describes an observational problem, not a confirmed behavior of the scientist.

Millions of orbits turned absence into a restriction

The second paper, led by Charles Pechman, combined the limits of photography with… Orbital and physical modeling. The team generated millions of possible paths, kept the paths consistent with August S1’s position and brightness, and removed orbits that might be thermodynamically unstable due to Alpha Centauri B.

The models also took into account a point-like feature called C1 that was found in 2019 by the NEAR experiment on the European Southern Observatory’s Very Large Telescope. That earlier Study nature communications C1 is treated as a potential planet or concentration of warm exogenous dust and clearly requires independent confirmation. It is not known that S1 and C1 are the same object. Exercise 2025 asks what follows if this is the case.

Under this common-body assumption, plausible simulations gave a 52 percent probability that orbital motion would place the candidate in low-sensitivity regions during the two Webb follow-ups. In other words, missing it twice is not a particularly unlikely outcome. This account explains how observations can fit into a planet; It is not proven that the planet caused the original signal.

Surviving families usually live for periods of two to three years. They prefer an eccentricity of about 0.4 and an orbit tilted by about 50 degrees, or the corresponding retrograde geometry, compared to the orbital plane of Alpha Centauri AB. The distance between the star and the planet will vary approximately between one or two astronomical units.

Saturn’s mass is an estimate, not a measurement on a scale

S1 was measured in a single MIRI filter centered near 15.5 μm. Converting this brightness to a planet requires assumptions about age, thermal evolution, radius, reflectivity, and internal temperature. Models indicate a temperature of about 225 K, a radius roughly 1 to 1.1 times that of Jupiter, and a mass of about 90 to 150 Earth masses.

Saturn has about 95 Earth masses, which explains the useful abbreviation “Saturnian mass.” However, the range extends well above Saturn, and no dynamical mass has been measured. A single infrared flux point also cannot provide the composition of the atmosphere.

The filter will be unusual for live photography. Most of the directly imaged planets are young, hot giants far from their stars, where they are easily distinguished by separation and residual heat of formation. If S1 is real, it will be a mature, cooler giant that is much closer to its host star than the familiar, directly imaged cluster.

Space Daily Webb’s initial evidence was reported in 2025. The standing point is the same: this is the strongest photographic evidence yet for a planet orbiting Alpha Centauri A, not a confirmed entry in a planetary catalogue.

The habitable zone giant is not a twin of Earth

The phrase “habitable zone” refers to the range of orbital distances at which a suitably built rocky planet could hold liquid water on its surface. NASA Habitable zone overview He emphasizes that distance alone does not prove habitability. Atmosphere, pressure, composition, geology, and stellar activity are also important.

For S1, the distinction is still greater. The candidate appears to be a gas giant that does not have a solid surface like Earth’s. Its location would make it moderate by giant planetary standards, but it would not support surface life as we know it. Undiscovered moons can be discussed as possibilities, just as moons of the giant planets in our solar system are discussed, but Webb has not discovered a moon, liquid water, or any biosignature.

The phrase “our closest solar twin” also refers to the star, not the candidate planet. Alpha Centauri A more closely resembles the Sun in spectral type and age than the red dwarf Proxima Centauri. The possible world next to it doesn’t look like Earth in the available evidence.

Confirmation now has a moving target to find

Orbital simulations are useful because they convert three observation histories into forecasts. Instead of searching blindly, future Webb visits could target times when a significant portion of viable paths place the source outside the least sensitive region of the corona. Recovery in the correct change position will show proper joint movement and begin to narrow the orbit.

Measurements in additional filters can test whether the source has the spectral energy distribution of a cooling giant planet or of warm dust. Repeated astronomical measurements could link S1 and C1 or show that the apparent connection was pure coincidence. Radial velocity programs and astronomical measurements can add independent limits, although binary stars also make these measurements difficult.

A clean non-detection at a time and place when almost all habitable planetary orbits predict a sighting would also be beneficial. That would push the interpretation back toward a transient artifact or some form of dust structure that is not picked up by current tests.

For now, the disappearance is neither fatal to the planet’s cause nor evidence of it in itself. Millions of simulations show how a Saturn-sized world could slip past Webb’s blind spots. The next crucial step is easier to say and harder to get: the point of light must return.