Astronomers recently had a groundbreaking discovery – they spotted two exoplanets that could be sharing the same orbit! While not unusual for other celestial bodies, this is the first time such behavior has been spotted in planets. And what’s more, they even took the first-ever photo of the phenomenon.
The team of researchers used a ground-based array called the Atacama Large Millimeter/submillimeter Array (ALMA). They investigated the system around star PDS 70, located 400 light-years away from the Earth. The system has two known exoplanets orbiting it, called PDS 70 b and PDS 70 c. And when they analyzed the archival ALMA observations of this system, the team spotted a cloud of debris at the location in PDS 70b’s orbit where so-called “Trojans ” are expected to exist.
What are Trojans?
As the team explains in the statement, “Trojans [are] rocky bodies in the same orbit as a planet.” As I mentioned, they’re not s uncommon with other celestial objects. They are also common in our own Solar System and the most famous example is the Trojan asteroids of Jupiter. These Trojans are over 12,000 rocky bodies in the same orbit around the Sun as Jupiter! In fact, Trojan asteroids even exist within the Earth’s orbit.
What makes these planets so special?
As I mentioned, this is the first time ever that we may have evidence of two planets sharing the same orbit. “Exotrojans [Trojan planets outside the Solar System] have so far been like unicorns: they are allowed to exist by theory but no one has ever detected them,” Jorge Lillo-Box, a senior researcher at the Centre for Astrobiology in Madrid.
The researchers published their findings in the journal Astronomy & Physics. “Two decades ago it was predicted in theory that pairs of planets of similar mass may share the same orbit around their star, the so-called Trojan or co-orbital planets,” says Olga Balsalobre-Ruza, a student at the Centre for Astrobiology and the paper’s lead author. “For the first time, we have found evidence in favour of that idea.”
Trojans are found in special areas along a planet’s path where the gravity of the planet and its star work together to capture things like rocks and dust. Scientists were examining two such areas in the orbit of a planet called PDS 70b. In one of these areas, they found a weak signal that suggests there could be a huge pile of debris, weighing about twice as much as our Moon, trapped there.
The team believes this cloud of debris could point to an existing Trojan world in this system or a planet in the process of forming. “Who could imagine two worlds that share the duration of the year and the habitability conditions? Our work is the first evidence that this kind of world could exist,” Balsalobre-Ruza says. “We can imagine that a planet can share its orbit with thousands of asteroids as in the case of Jupiter, but it is mind blowing to me that planets could share the same orbit.”
Future plans
“Our research is a first step to look for co-orbital planets very early in their formation,” says co-author Nuria Huélamo, a senior researcher at the Centre for Astrobiology. Itziar De Gregorio-Monsalvo, ESO Head of the Office for Science in Chile, who also contributed to this research, adds: “It opens up new questions on the formation of Trojans, how they evolve and how frequent they are in different planetary systems.”
The team plans to use ALMA again after 2026 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.
[via Digital Trends; image credits: ALMA (ESO/NAOJ/NRAO) /Balsalobre-Ruza et al.]
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