Planets that orbit large stars like our Sun usually do so at some distance from each other. But recently, scientists discovered something unusual when they noticed two exoplanets sharing the same orbit. If confirmed, this would mark the first time anything like this has been discovered.
Astronomers used the Atacama Large Millimeter/submillimeter Array (ALMA) to study the planetary system orbiting the star PDS 70, located 400 light-years away. Two known exoplanets orbit this star, named PDS 70b and PDS 70c. Observations of PDS 70 b also showed a debris cloud in its orbit that could create a sister planet that would share the same orbit. “Two decades ago it was predicted that pairs of planets of similar mass could share the same orbit around their star, the so-called Trojan or co-orbital planets. For the first time, we have found evidence for this idea.” lead author Olga Balsalobre-Ruza of the Madrid Astrobiology Center said in a statement.
There is evidence of small bodies sharing the same orbit as planets in our solar system. Some asteroids also share their orbit with Earth, but this is more common with Jupiter’s Trojan asteroids. “The exotrojans [pianeti trojan al di fuori del sistema solare] they have hitherto been like unicorns: no one has ever detected them”said coauthor Jorge Lillo-Box, also of the Center for Astrobiology. The debris cloud found in PDS 70 is twice the mass of our Moon, so it could become a planet in its own right. It’s even possible that a planet already exists within the dust. In 2026, researchers will again use ALMA to observe the system and how the planet and its cloud move in orbit. Their research has been published in the journal Astronomy & Astrophysics.