Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have made an intriguing discovery: they might have found a “sibling” of a planet orbiting a distant star. The team spotted a cloud of debris in the same orbit as the planet, suggesting the possibility of two exoplanets sharing one orbit, a phenomenon known as Trojan or co-orbital planets.
The idea of Trojan planets has been around for some time, with predictions that planets of similar mass could share the same orbit around their star, much like the Trojan asteroids accompanying Jupiter in our solar system. However, evidence for such exotrojans beyond our solar system has been elusive.
Now, an international team of scientists has used ALMA to investigate the PDS 70 system, which is known to have two giant Jupiter-like planets, PDS 70b and PDS 70c. Analyzing ALMA observations, they identified a cloud of debris at the location where Trojans are expected to exist in PDS 70b’s orbit.
Trojans typically reside in the Lagrangian zones, specific regions in a planet’s orbit where the combined gravitational forces of the star and the planet can trap material. By studying these regions in PDS 70b’s orbit, astronomers detected a faint signal from one of them, indicating the presence of a cloud of debris with a mass up to approximately twice that of our moon.
The team believes this debris cloud could be a sign of an existing Trojan world in the system or a planet in the early stages of formation. Confirming this finding will require further observation until after 2026, during which ALMA will be used to track the movements of both PDS 70b and the sibling cloud of debris along their orbit around the star.
This discovery opens up new questions about the formation and prevalence of Trojan planets in various planetary systems. It could provide valuable insights into the early stages of planet formation and the dynamics of exoplanetary systems.
Looking ahead, the team is excited about the future prospects of studying Trojans in other stars using extended ALMA capabilities, planned for 2030. Such advancements would significantly enhance the array’s ability to investigate and characterize these intriguing co-orbital planets, shedding more light on their prevalence and nature in the universe.