Astronomers utilizing the Atacama Large Millimeter/submillimeter Array (ALMA) have potentially located a ‘sibling’ of a planet in orbit around a far-off star. They’ve discovered a debris cloud which they theorize could be the elements of a forming planet, or the remnants of an already formed one. If this find is confirmed, it would represent the most solid evidence to date that two exoplanets can inhabit a single orbit.
This theoretical idea of pairs of similarly sized planets sharing the same orbital path around a star was first suggested twenty years ago. These co-orbital or Trojan planets, as they are termed, have been a topic of speculation but not confirmation until now, states Olga Balsalobre-Ruza of the Centre for Astrobiology in Madrid, Spain, who spearheaded the paper published today in Astronomy & Astrophysics.
Our own Solar System hosts Trojans, rock-like bodies occupying the same orbit as a planet. Jupiter’s Trojan asteroids are a renowned example – more than 12,000 rock-like bodies orbiting the Sun along the same path as Jupiter. The existence of Trojan planets around stars apart from the Sun has been theorized by astronomers but hard evidence has been elusive.
The team of international researchers now claims to have found the most compelling observational proof of Trojan planets to date in the PDS 70 system. This young star system is known to host two Jupiter-like planets, PDS 70b and PDS 70c. Their analysis of archival ALMA observations revealed a debris cloud in PDS 70b’s orbit, right where Trojans would be expected.
Trojans are found in Lagrangian zones – two extended regions in a planet’s orbit where the combined gravitational pull of the star and the planet can entrap material. In one of these zones in PDS 70b’s orbit, astronomers detected a weak signal indicative of a debris cloud potentially as heavy as two times our Moon.
The team speculates this debris cloud may hint at a Trojan planet existing in this system or a planet being formed. This detection opens new queries about the formation and evolution of Trojans and their frequency in various planetary systems, adds Itziar De Gregorio-Monsalvo, ESO Head of the Office for Science in Chile, who participated in this research.
To fully verify their detection, they need to wait until after 2026 to employ ALMA to confirm whether both PDS 70b and the debris cloud have moved significantly along their shared orbit. This discovery would be a significant advancement in exoplanetary research, says Balsalobre-Ruza.
The forthcoming expansion of ALMA’s capabilities, planned for 2030, is eagerly anticipated as it will dramatically enhance the array’s capacity to characterize Trojans in many other stars, concludes De Gregorio-Monsalvo.
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