Many conspiracy theories, old and new, fantasize about a planet orbiting Earth behind the Sun. While we know this is not true, the way planetary orbits work allows multiple celestial bodies to share the same orbit under certain conditions. Now, astronomers have found the first instance in another solar system.
The PDS 70 star system is very young and we know for sure that it has two planets called PDS 70b and PDS 70c. Located 400 light-years away, both planets are believed to be gas giants like Jupiter. In the same orbit as PDS 70b, astronomers have discovered a large cloud of debris, a possible indication of a forming planet or remnants of an already formed planet.
Lead author Olga Balsalobre-Ruza, a student at the Center for Astrobiology in Madrid, said in a statement: “Twenty years ago it was theoretically predicted that pairs of planets of similar mass could share the same orbit around their star, called Trojan or co-orbiting planets. “This is the first time we have found evidence to support this idea.”
Trojan asteroids are rocky bodies in orbit with a planet. Jupiter has more than 4800 Trojan asteroids divided into two groups, one before the gas giant and the other following it, while Earth also has two. Jupiter is located 60 degrees in front and behind the planet at L4 and L5 in the same orbit. The debris cloud in the PDS 70 system is also in one of these Trojan regions, and astronomers believe they’ve observed a type of exotrovia situation where an object twice the size of the Moon is formed in this orbital configuration.
Co-author Jorge Lillo-Box, a senior researcher at the Center for Astrobiology, added, “Exotroria [Trojan planets outside the Solar System] have been like unicorns until now: theories allowed them to exist, but no one had been able to detect them.”
The masses of the two potential objects in this system appear to be very different, and their orbits are thought to be roughly the distance between Uranus and the Sun. But the existence of smaller planets orbiting closer to their stars could open up a whole new spectrum of possibilities for what kinds of planets (and perhaps life forms) might exist there.
Balsalobre-Ruza “Who can imagine two worlds sharing the duration of the year and the habitable conditions? Our work is the first proof that such a world can exist,” he explains. “We can imagine that a planet could share its orbit with thousands of asteroids, as in the case of Jupiter, but the fact that planets can share the same orbit is mind-blowing to me.”
If confirmed, this will be the strongest evidence yet that the two planets can share the same orbit. However, we are still in the early stages of investigations. The candidate exoplanet was discovered in archival data from the Atacama Large Millimeter/submillimeter Order (ALMA), and more can be found in past and future observations.
The study has been published in Astronomy & Astrophysics.
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