Two Planets Sharing The Same Orbit Around A Star? Astronomers Find Strong Evidence

Astronomers have discovered strong evidence of two planets sharing the same orbit around a star. The astronomers used Chile's Atacama Large Millimeter/submillimeter Array (ALMA) and detected a cloud of debris that could be the building blocks of a new planet or remnants of one that has already formed.

The team spotted a cloud of debris that might be sharing the orbit of one of the two exoplanets known to orbit the young star PDS 70, which is a star 400 lightyears away known to host two Jupiter-like planets called PDS 70b and PDS 70c.

🦄 Did we find one of the unicorns of astronomy?

🤔 Theory says two planets could share the same orbit but evidence is scant.

📡 Using @almaobs, in which ESO is a partner, astronomers have now found one possible such sibling of an exoplanet ➡️ https://t.co/kBjY7bTTLT 1/ pic.twitter.com/GngTSBOebp

— ESO (@ESO) July 19, 2023

By analysing archival ALMA observations of this system, the team spotted a cloud of debris at the location in PDS 70b's orbit where Trojans are expected to exist.

Astronomers believe the debris could be the building blocks of a new planet or the remnants of one already formed. If confirmed, this would be the strongest evidence yet that two exoplanets can share one orbit.

A new study reveals the existence of so-called Trojan planets, or co-orbital planets, which is when pairs of planets of similar mass share the same orbit around their host star.

The findings have been published in the journal Astronomy & Astrophysics.

According to European Southern Observatory, a similar example can be found in our own Solar System in the Trojan asteroids of Jupiter- which are more than 12 000 rocky bodies that are in the same orbit around the Sun as the gas giant.

Astronomers have predicted that Trojans, in particular Trojan planets, could also exist around a star other than our Sun, but evidence for them is scant.

"Our research is a first step to look for co-orbital planets very early in their formation," says co-author Nuria Huelamo, a senior researcher at the Centre for Astrobiology. "It opens up new questions on the formation of Trojans, how they evolve and how frequent they are in different planetary systems," adds Itziar De Gregorio-Monsalvo, ESO Head of the Office for Science in Chile, who also contributed to this research.

To fully confirm their detection, the team will need to wait until after 2026, when they will aim to use ALMA to see if both PDS 70b and its sibling cloud of debris move significantly along their orbit together around the star. "This would be a breakthrough in the exoplanetary field," says Balsalobre-Ruza.

"The future of this topic is very exciting and we look forward to the extended ALMA capabilities, planned for 2030, which will dramatically improve the array's ability to characterise Trojans in many other stars," concludes De Gregorio-Monsalvo.