ALMA Observes an Exoplanet and a Possible Sibling Sharing the Same Orbit

Jovian Explorer
4 min readAug 1, 2023


The system features a star at its center, around which the planet PDS 70 b (highlighted with a solid yellow circle) is orbiting. On the same orbit as PDS 70b, indicated by a solid yellow ellipse, astronomers have detected a cloud of debris (circled by a yellow dotted line) that could be the building blocks of a new planet or the remnants of one already formed. The ring-like structure that dominates the image is a circumstellar disc of material from which planets form. Credit: ALMA (ESO/NAOJ/NRAO) /Balsalobre-Ruza et al.


In recent years, our understanding of exoplanets and planetary systems beyond our solar system has expanded significantly, thanks to advancements in observational technologies and space missions. One such exciting discovery is the potential sighting of an exoplanet accompanied by a possible sibling sharing the same orbit. This observation was made using the Atacama Large Millimeter/submillimeter Array (ALMA), a powerful radio telescope capable of capturing detailed images of celestial objects at millimeter and submillimeter wavelengths. This article will delve into the latest research and findings on this remarkable discovery, analyzing its implications for our understanding of planetary formation and dynamics in other star systems.

ALMA and the Detection

A Starry Night at ALMA Credit: ALMA (ESO/NAOJ/NRAO)

The ALMA observatory, situated in the high desert of Chile, is a collaboration between international organizations including Europe, North America, and East Asia. It comprises 66 high-precision antennas, which act in unison to create an extremely sharp radio “vision” of the universe. This sophisticated technology allows astronomers to observe astronomical phenomena that were previously beyond reach.

The groundbreaking observation of an exoplanet and a possible sibling sharing the same orbit was made using ALMA’s advanced imaging capabilities. By detecting millimeter and submillimeter emissions from dust and gas in a nearby star system, astronomers were able to uncover intriguing features hinting at the presence of two bodies gravitationally interacting in close proximity.

Evidence for Co-orbital Exoplanets

This chart shows the southern constellation of Centaurus and marks most of the stars visible to the unaided eye on a clear dark night. The dwarf star PDS 70 is marked with a red circle. Credit: ESO, IAU and Sky & Telescope

The research team scrutinized the ALMA data and identified peculiar patterns in the dust and gas distributions around a young star. Through meticulous analysis and numerical simulations, they were able to propose two plausible scenarios to explain the observed phenomena: (1) the existence of a single exoplanet with an elongated and warped circumstellar disk, or (2) the presence of two exoplanets sharing the same orbit, locked in a co-orbital configuration.

In the first scenario, the elongation and warping of the circumstellar disk are attributed to gravitational interactions with a single exoplanet. However, the team also considered a more intriguing possibility: the presence of two exoplanets with similar masses and orbital periods that share the same orbit.

Co-orbital Configuration: An Unusual Planetary Dance

Co-orbital configurations have been observed in our solar system where two or more celestial bodies share the same orbit around a central star. Prominent examples include the Trojan asteroids associated with Jupiter and some of Neptune’s moons. However, this phenomenon in exoplanetary systems remains largely unexplored.

The proposed co-orbital exoplanet and its possible sibling might be locked in a stable configuration due to their gravitational interactions and the balance between the forces acting upon them. Such a stable dance in a star system could provide us with valuable insights into the formation and evolution of planetary systems under different conditions.

Implications and Future Prospects

If confirmed, the discovery of co-orbital exoplanets would challenge our current models of planetary system formation. It could indicate that dynamic processes, such as gravitational interactions and resonances, play a more significant role in shaping planetary orbits than previously thought. This finding could also provide clues about the migration of planets within their host star systems and the influence of planet-planet interactions during their early history.

However, it is crucial to exercise caution and await further observations and analyses to validate the co-orbital hypothesis. The detection of exoplanets and their orbital dynamics is a complex task, and other mechanisms, such as disk warping due to external perturbations, cannot be ruled out at this stage.


The discovery of a potential co-orbital exoplanet and its companion by the ALMA observatory represents an exciting leap forward in our understanding of planetary systems beyond our solar system. This unique configuration could revolutionize our current understanding of planetary formation and dynamics in other star systems if confirmed. However, more observations and analyses are necessary to establish the veracity of the co-orbital hypothesis and explore its broader implications fully.

As our observational capabilities continue to improve, we expect many more groundbreaking discoveries that will reshape our knowledge of exoplanets and the incredible diversity of planetary systems in the cosmos.

1. ALMA Observatory website: (

2. Tentative co-orbital submillimeter emission within the Lagrangian region L5 of the protoplanet PDS 70 b (