Astronomers Discover Possible Sibling Planets in PDS 70 System

by Tatsuya Nakamura
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exoplanet siblings

Astronomers have made an intriguing discovery using the Atacama Large Millimeter/submillimeter Array (ALMA). They have detected a debris cloud in the PDS 70 system, which could suggest the presence of two planets sharing the same orbit. This finding represents the most significant evidence to date of such a phenomenon and raises new questions about the existence and characteristics of Trojans in different planetary systems. The credit for this discovery goes to ESO/L. Calçada.

The astronomers used ALMA to identify a debris cloud that may indicate the existence of a “sibling” planet sharing the orbit of a known planet around a distant star. This observation provides compelling evidence for the potential presence of two exoplanets sharing the same orbital path.

The image captured by ALMA showcases the PDS 70 system, situated nearly 400 light-years away from Earth. The system consists of a central star, around which the planet PDS 70b orbits. In addition to PDS 70b, astronomers have identified a cloud of debris on the same orbit, which could either be the building blocks of a new planet or remnants of a previously formed one. The dominant feature in the image is a ring-like structure representing a circumstellar disc where planet formation is taking place. Another planet, PDS 70c, is also visible in the system, located next to the inner rim of the disc at the 3 o’clock position.

Olga Balsalobre-Ruza, a student at the Centre for Astrobiology in Madrid, Spain, who led the study published in the journal Astronomy & Astrophysics on July 19, explains, “Two decades ago, it was theorized that planets of similar mass could share the same orbit around their star, known as Trojan or co-orbital planets. For the first time, we have found evidence supporting this idea.”

Trojans are rocky bodies that share an orbit with a planet, a phenomenon observed in our own Solar System, with Jupiter’s Trojan asteroids being the most notable example. Astronomers have hypothesized that Trojan planets could exist around stars other than our Sun, but until now, evidence has been scarce. Co-author Jorge Lillo-Box, a senior researcher at the Centre for Astrobiology, describes exotrojans (Trojan planets outside the Solar System) as elusive, saying, “They are allowed to exist by theory, but no one has ever detected them.”

The PDS 70 system, hosting two Jupiter-like planets named PDS 70b and PDS 70c, became the focus of this study. The international team of scientists, in collaboration with the European Southern Observatory (ESO), utilized ALMA’s capabilities to uncover the most compelling observational evidence yet for the existence of Trojan planets. By analyzing archival ALMA observations of the PDS 70 system, they identified a debris cloud in the orbit of PDS 70b, where Trojan planets are expected to reside.

Lagrangian zones, regions in a planet’s orbit where the combined gravitational forces of the star and the planet can trap material, are occupied by Trojans. The astronomers detected a faint signal from one of these zones in PDS 70b’s orbit, indicating the presence of a debris cloud with a mass roughly twice that of our Moon.

If confirmed, this debris cloud could signify the presence of a Trojan planet in the PDS 70 system or a planet in the early stages of formation. Balsalobre-Ruza expresses her astonishment, stating, “Who could imagine two worlds sharing the same year duration and habitability conditions? Our work is the first evidence that this kind of world could exist. We can imagine a planet sharing its orbit with thousands of asteroids, as in the case of Jupiter, but the idea of planets sharing the same orbit is mind-blowing.”

While awaiting full confirmation, the team plans to continue their observations using ALMA until 2026. They aim to track the motion of both PDS 70b and the potential sibling debris cloud along their shared orbit around the star. Successful confirmation would mark a groundbreaking achievement in the field of exoplanetary research.

The team’s future endeavors will benefit from the extended capabilities of ALMA, scheduled for 2030, which will greatly enhance the array’s ability to characterize Trojans in numerous other star systems. Itziar De Gregorio-Monsalvo, ESO Head of the Office for Science in Chile and a contributor to this study, concludes, “The future of this field is very exciting, and we eagerly anticipate the extended ALMA capabilities, which will significantly improve our understanding of Trojans in various planetary systems.”

This research sheds light on the potential existence of sibling planets in the universe and raises intriguing questions about the formation and prevalence of Trojans in different planetary systems. The findings, once confirmed, will contribute to our understanding of the complexity and diversity of exoplanetary systems.

Frequently Asked Questions (FAQs) about exoplanet siblings

What did astronomers discover in the PDS 70 system?

Astronomers discovered a debris cloud in the PDS 70 system using the ALMA. This debris cloud potentially indicates the presence of two sibling planets sharing the same orbit.

What is the significance of this discovery?

This discovery provides the most substantial evidence to date of the existence of Trojan or co-orbital planets. It raises new questions about the nature of Trojans in different planetary systems and expands our understanding of exoplanetary dynamics.

How were the observations made?

The observations were conducted using the Atacama Large Millimeter/submillimeter Array (ALMA), a powerful astronomical observatory. Archival ALMA data of the PDS 70 system were analyzed to identify a debris cloud in the orbit of one of the planets, PDS 70b.

What are Trojan planets?

Trojan planets are rocky bodies that share the same orbit as a planet. They are commonly observed in our Solar System, with Jupiter’s Trojan asteroids being the most well-known example. This discovery suggests that Trojan planets could exist around stars other than our Sun.

What are Lagrangian zones?

Lagrangian zones are regions in a planet’s orbit where the combined gravitational forces of the star and the planet can trap material. Trojans occupy these zones. The debris cloud detected in the PDS 70 system’s Lagrangian zone indicates the potential presence of a Trojan planet or a planet in the early stages of formation.

How will this discovery be confirmed?

To confirm the findings, astronomers plan to continue observing the system with ALMA until 2026. They aim to track the motion of both PDS 70b and the debris cloud along their shared orbit. Confirmation of their synchronized motion would provide further evidence of sibling planets in the system.

What are the future implications of this discovery?

This discovery opens up new avenues of research on co-orbital planets and Trojan systems. It raises questions about the formation and prevalence of Trojans in various planetary systems. The extended capabilities of ALMA, planned for 2030, will further enhance our understanding of Trojans in different stars systems.

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