This finding could become the most compelling evidence of co-orbiting exoplanets known to date.
Do these exoplanets share the same orbit?
A breakthrough observation of a distant celestial body’s orbit made using the Atacama Large Millimeter/submillimeter Array (ALMA) might reveal a planet’s cosmic twin. This intriguing revelation comes from a detected debris cloud that might indicate the birth or the vestiges of a second planet sharing the orbit of the first. If substantiated, this finding could become the most compelling evidence of two exoplanets sharing the same orbit.
Setting Theory Into Motion
A couple of decades back, the idea was floated that two planets of similar size might co-exist in the same orbit around their star. These co-orbiting planets were referred to as Trojan or co-orbital planets. “Now, we’ve come across the first real signs that endorse this concept,” comments Olga Balsalobre-Ruza, a Centre for Astrobiology student in Madrid, Spain, who helmed the paper’s publication in Astronomy & Astrophysics.
Unraveling the Mystery of Trojans
Our very own solar system houses Trojans, celestial bodies sharing a planet’s orbit. Over 12,000 rocky bodies orbiting the sun along with Jupiter are classic examples of this phenomenon. Scientists have speculated that Trojans, especially Trojan planets, might be found around stars other than our sun. However, such evidence has remained hard to find.
Until now, Exotrojans, or Trojan planets situated outside our solar system, have remained in the realm of theoretical possibilities. “Though they are theoretically plausible, their actual detection has eluded us,” says Jorge Lillo-Box, a senior researcher at the Centre for Astrobiology, and a co-author of the study.
A Spotlight on PDS 70 System
Using ALMA, where ESO is a partner, a group of international scientists has turned their gaze towards the PDS 70 system. This young star, which is already known to harbor two giant planets similar to Jupiter, PDS 70b and PDS 70c, has presented the strongest clues yet for the existence of potential Trojan planets. A debris cloud located within PDS 70b’s orbit, the expected location for Trojans, was identified during the analysis of older ALMA observations.
Two expansive areas within a planet’s orbit, known as Lagrangian zones, can capture material under the star’s and the planet’s combined gravitational influences. Within these zones in PDS 70b’s orbit, a faint signal from one of them suggested a cloud of debris, potentially as massive as twice our moon, could be lurking there. So, do these exoplanets share the same orbit? Further observations will tell, but so far, the evidence looks good.
Revolutionizing our Understanding of Planet Formation
This debris cloud might be indicative of a Trojan world already present in this system or a world taking shape. “Our work reveals for the first time that these co-existing worlds could be more than a figment of our imagination,” notes Balsalobre-Ruza. According to Nuria Huélamo, a senior researcher at the Centre for Astrobiology, this discovery triggers a cascade of questions related to Trojan formation, evolution, and prevalence in varying planetary systems.
To definitively validate their findings, the team is awaiting further observations with ALMA post-2026. This would allow them to ascertain whether PDS 70b and its potential twin, the debris cloud, move significantly within their mutual orbit. “Such a validation would create a ripple effect in the exoplanetary field,” Balsalobre-Ruza says.
Exciting Times Ahead in Trojan Research
“With ALMA’s planned upgrade in 2030 enhancing its ability to detect and study Trojans in multiple other stars, the future of Trojan research is looking up,” says Itziar De Gregorio-Monsalvo, ESO Head of the Office for Science in Chile, in closing. Hopefully, by then, we will know if these two exoplanets are really sharing the same orbit around a star.
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