This strange world has no star to orbit, yet James Webb has revealed its changing weather from 20 light-years away

An exoplanetary system that is situated at a distance of 20 light-years from our planet has allowed astronomers to analyse the weather of an astronomical object which is neither a planet nor a star.

Based on the research conducted by the astronomers of Trinity College Dublin using data collected by the James Webb Space Telescope of NASA, the variations in the appearance of brown dwarf SIMP 0136 are caused primarily by two processes in its atmosphere: the changes in temperature and vertical structure of clouds.

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That means that we can conclude that the structure of the atmosphere of this brown dwarf is simpler than one can imagine. With the rotation of SIMP 0136, its atmosphere moves, resulting in small changes in its brightness, and Webb detects these variations.

Afterwards, the astronomers used the method of principal component analysis (PCA) to filter out major periods from the rest of the variation and measurement noise.

The outcome was that the majority of variability in the atmosphere of SIMP 0136 can be explained by just two principal components.

A world that sits between planets and stars

SIMP 0136 is one of a group of bodies called brown dwarfs.

These are more massive than usual gas-giant planets yet do not possess sufficient mass to have nuclear fusion that would make them become true stars.

For that reason, brown dwarfs are excellent natural laboratories where one can study atmospheres in an environment hard to duplicate anywhere else. Brown dwarfs' weather may be quite dramatic, featuring huge cloud masses that change during the rotation of the body.

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One more remarkable feature of SIMP 0136 is its relative proximity to Earth: it is located at a distance of about 20 light-years from our planet. Moreover, SIMP 0136 has already been studied in a number of works, including the research devoted to the emissions similar to auroras from this body.

The problem is that the atmospheric behaviour of SIMP 0136 cannot be described just using conventional seasons or weather caused by sunlight since this body does not rotate around any star like the Earth or Jupiter.

It means that one has to analyse the radiation coming from the brown dwarf and find differences depending on which part of its atmosphere rotates towards us.

Webb turns tiny brightness changes into weather clues

The Trinity team approached the data differently from methods that attempt to model every detail of a brown dwarf's atmosphere in advance.

Principal component analysis allowed the researchers to look for patterns that repeatedly appeared together in the observations. Rather than beginning with a detailed atmospheric model and asking whether the measurements fit it, the technique identifies the strongest structures already present in the data.

In practical terms, the method helps distinguish meaningful atmospheric behaviour from the background noise that inevitably accompanies astronomical observations.

The analysis showed that two major patterns account for most of the changes detected in SIMP 0136's light.

One is associated with temperature. The other appears to reflect differences in the vertical structure of the clouds.

That distinction matters because clouds are not simply a flat layer sitting above the atmosphere. Their distribution at different heights can affect how much radiation escapes from the object and, consequently, how it appears to distant observers.

By separating these effects statistically, researchers can begin to connect changes in brightness with physical processes taking place within an atmosphere that is otherwise impossible to examine directly.

Three weather states rotate across the view

The observations suggest that SIMP 0136 does not change in an entirely random fashion.

Instead, its visible atmosphere can be described in terms of three recurring weather states. As the brown dwarf spins, these regions move into and out of view, creating the brightness variations recorded by Webb.

The picture that emerges is a patchwork of atmospheric conditions.

Some regions appear to be hotter and associated with thinner clouds, while others are cooler and contain clouds extending farther vertically. These different regions coexist and rotate through the observer's line of sight.

Importantly, the researchers found that the underlying drivers remain identifiable even as the detailed appearance of the atmosphere changes over more than a dozen rotations.

Merle Schrader, a Ph.D. candidate in Trinity College Dublin's School of Physics and the study's first author, said the persistence of these drivers provides a way to understand how the weather patterns interact over time.

The study, published in Astronomy & Astrophysics, therefore points towards an atmosphere with recurring structure rather than one undergoing completely unpredictable rearrangement.

A new way to study worlds we cannot visit

Importance of the method

In addition to SIMP 0136, the method may find wider applications.

Brown dwarfs are dim and remote and, in many cases, astronomers know little about their atmosphere. For some objects, all that could be observed is small changes in light and not anything close to direct observation of their surface.

In the case of SIMP 0136, the researchers could use the already gathered large amount of data about this dwarf. That allowed them to compare their findings using PCA to the data gathered using conventional methods.

According to the researchers, the statistical approach could also be used to study other brown dwarfs about which not much is known about their atmospheres yet.

It would allow scientists to know whether the atmosphere of SIMP 0136 is typical for brown dwarfs and whether they all display different types of atmospheres.

In this case, there is one remarkable fact connected with the distance. The light studied in the research was collected by Webb in 2023, so it has been travelling for about twenty years before it reached the telescope.

At a distance of 20 light-years, SIMP 0136 is approximately 189 trillion kilometres away from the Earth.

FAQ

1. What is SIMP 0136?

SIMP 0136 is a brown dwarf about 20 light-years away from the Earth. Brown dwarfs are celestial objects which are too massive to be considered gas-giant planets, but at the same time, their masses are not enough to support fusion reactions.

2. How did James Webb study its weather?

By measuring tiny fluctuations in the brown dwarf's brightness during rotation of the object, Webb managed to detect periodic patterns. These patterns were identified by means of principal component analysis.

3. What controls the weather on SIMP 0136?

Most of the detected variability of the atmospheric conditions seems to be controlled by two main factors: the change in temperature and the vertical cloud structure.

4. Can this approach be applied to other worlds?

The authors propose that the statistical approach used in this study could be improved and used in order to investigate atmospheres of other brown dwarfs, especially the less studied ones.