Astronomers reveal planetary system with reversed order of planets in nearby star

Astronomers have identified an unusual planetary system around the star LHS 1903, located approximately 116 light-years from Terra. Essa configuration presents a sequence of planets considered inverted in relation to the patterns observed in most known systems, with a rocky planet positioned after gaseous bodies. The discovery used combined data from ground-based and space-based telescopes, including Agência Espacial Europeia’s CHEOPS satellite. The finding was detailed in a study published in the magazine Science on February 12, 2026.

The system has four detected planets, whose characteristics defy expectations based on our Sistema Solar. The three innermost planets follow a partly familiar progression, starting with a rocky world and followed by two bodies of predominantly gaseous composition. However, the fourth planet, the most distant from the star, turns out to be small and dense, with signs of being rocky, similar to Vênus in terms of composition.

This arrangement goes against the traditional model of planetary formation, where planets close to stars tend to be rocky due to high radiation that prevents the retention of extensive gaseous atmospheres. In more external regions, lower temperatures favor the accumulation of gases, resulting in giants such as Júpiter and Saturno.

Characteristics of the star LHS 1903

The star LHS 1903 is classified as a red dwarf, a smaller and less luminous stellar type than Sol. Essas stars represent the majority in the universe and are frequent targets in searches for exoplanets due to their abundance.

They emit less energy, which makes it easier to detect planetary transits, a method that identifies variations in starlight when a planet passes in front of it. The distance of 116 light years allows detailed observations with current instruments.

Detection and confirmation of planets

Researchers combined observations from multiple instruments to map the system. Inicialmente, the data suggested a conventional configuration, with rocky inner planets and gaseous outer planets.

In-depth analysis, especially with the CHEOPS satellite, has revealed the properties of the fourth planet. Esse external body has a high density, indicating a rocky rather than gaseous composition.

Other ground-based telescopes contributed radial velocity measurements, which detect the slight movement of the star caused by the planets’ gravity. Essa technique complemented the transits to determine precise masses and orbits.

Unusual sequence of four planets

The innermost planet is rocky and compact, followed by two larger gaseous worlds. The fourth planet breaks the pattern by being rocky and dense again.

• First planet: rocky, close to the star, with high density.
• Second and third: composed mainly of gases, similar to mini-Neptunes.
• Fourth planet: rocky, positioned in the outer region, with Venusian characteristics.

This order reverses the expectation of gas giants in the most distant orbits. The configuration raises questions about the processes of material accretion during formation.

Traditional models of planetary formation

In standard models, protoplanetary disks have temperature gradients that influence the composition of worlds. Perto from the star, the heat evaporates light gases, leaving only rocky materials to form terrestrial planets.

Further away, cooling allows hydrogen and helium to accumulate, creating extensive gaseous envelopes. No Sistema Solar, Mercúrio, Vênus, Terra and Marte are rocky, while Júpiter,

These patterns derive from computer simulations based on observations of young disks around forming stars. Most exoplanetary systems detected so far follow variations of this scenario.

Inside-out formation hypothesis

One proposed explanation involves sequential formation starting from the inner regions of the disk. The early planets consumed much of the available gas as they grew.

When the fourth planet began to form in the outer area, little volatile material remained. Isso resulted in a rocky world instead of a gas giant.

Other possibilities, such as planetary migrations or collisions that removed atmospheres, have been evaluated and ruled out by current data. The gas depletion hypothesis gains support from the observed configuration.

This idea suggests that the timing of accretion determines the final composition. Sistemas with rapid formation can produce varied arrangements.

Comparison with other known systems

Few systems exhibit similar deviations, but examples include configurations with inner mini-Neptunes and rocky outer Neptunes in some red dwarfs. A maioria dos exoplanetas detectados por missões como Kepler e TESS segue o padrão de rochosos próximos e gasosos distantes.

Red dwarfs host many compact worlds due to their smaller stellar radius, which amplifies transit signals. Estudos of systems like TRAPPIST-1 show rocky multiples, but without clear inversion as in LHS 1903.

Implications for planetary diversity

The discovery reinforces the variety of planetary architectures in the universe. Red Anãs, being the most common stars, may harbor configurations not predicted by initial models.

Future research aims to observe protoplanetary disks at different stages. Instrumentos like Telescópio Espacial James Webb contribute to spectroscopy of exoplanetary atmospheres.

The presence of an outer rocky planet raises interest about potential habitability. Regiões cooler temperatures could allow liquid water on surfaces, depending on the trapped atmosphere.

Technical details of the observation

The CHEOPS satellite specializes in precise measurements of planetary radii via transits. Seus data was crucial to confirming the density of the fourth planet.

Combinations with missions like NASA’s TESS have provided early detections. Velocidade radial from ground-based telescopes helped estimate masses.

The publication in Science includes analysis of light curves and dynamic models. Orbital periods range from days to weeks, typical of compact red dwarf systems.

Variations in protoplanetary disks

Disks around young stars exhibit structures like gaps and rings, influencing where planets form. Turbulências and viscosity affect the distribution of dust and gas.

In red dwarfs, disks dissipate more quickly due to their lower mass. Isso may limit the time for formation of external gas giants.

Observations of Atacama Large Millimeter Array reveal details of forming disks. Esses data helps refine simulations that now incorporate scenarios like LHS 1903.

Additional research perspectives

Teams plan continuous monitoring to refine orbital parameters. Espectroscopia transmission can reveal atmospheric compositions of gaseous planets.

Searches for additional planets in the system continue, although current boundaries indicate four main ones. Comparações with other red dwarf systems expand the catalog of diverse architectures.

The discovery highlights the need for flexible models that accommodate sequential formations. Avanços in computing allow more complex simulations of disk evolution.