2023-08-21 13:15:44
Astronomers have found the possible “brother” of a planet orbiting a distant star. The team has detected a cloud of debris that could be sharing the orbit of this planet and that, it is believed, could be the basic components of a new planet in the process of formation or the leftover remains of one already formed. If confirmed, this discovery would be the strongest evidence yet that two planets can share an orbit.
The finding has been made using the ALMA (Atacama Large Millimeter/submillimeter Array), an observatory dependent on the ESO (European Southern Observatory) and other entities.
“Two decades ago, it was theoretically predicted that pairs of planets of similar mass could share the same orbit around their star, the so-called Trojan or co-orbital planets. For the first time, we have found evidence in favor of this idea”, says Olga Balsalobre-Ruza, a student at the Center for Astrobiology (CAB) in Madrid, Spain, who led the study.
Trojans, smaller bodies in the same orbit as a planet, are common in our own solar system, the most famous example being Jupiter’s Trojan asteroids, more than 12,000 rocky bodies that are in the same orbit around the Sun as the giant gaseous. When asteroids orbiting Jupiter were first discovered, they were named after the heroes of the Trojan War, giving rise to the name Trojans for these objects.
It has been predicted that Trojans, and particularly Trojan planets, could also exist around a star other than our Sun, but the evidence is scant. Until now, exotrojans (Trojan planets outside our solar system) have been like unicorns: theory allows them to exist, but no one has ever detected them, as Jorge Lillo-Box, a researcher at the Center for Astrobiology and co-author of the study, points out.
The international team of scientists of which Balsalobre-Ruza and Lillo-Box are part used ALMA to find the strongest observational evidence to date that Trojan planets could exist in the PDS 70 system. This young star is known to harbor two planets Jupiter-like giants PDS 70b and PDS 70c. By analyzing archival ALMA observations of this system, the team detected a cloud of debris at the location of PDS 70b’s orbit where Trojans are expected to exist.
The Trojans occupy so-called Lagrange zones, two extended regions in a planet’s orbit where the combined gravitational pull of the star and the planet can trap material. Studying these two regions of PDS 70b’s orbit, astronomers detected a faint signal from one of them, indicating that a debris cloud with a mass up to about twice that of our Moon could reside there.
The team believes that this cloud of debris could point to an existing Trojan world in this system or to a planet in the process of forming. “Who could imagine two worlds that share the length of the year and the basic conditions of habitability? Our work is the first proof that this type of world could exist”, says Balsalobre-Ruza. “We can imagine that a planet can share its orbit with thousands of asteroids like in the case of Jupiter, but it is amazing to me that planets can share the same orbit.”
This image, taken with ALMA, shows the young planetary system PDS 70, located almost 400 light-years from Earth. The system has a star at its center, around which the planet PDS 70 b (highlighted with a solid yellow circle) orbits. In the same orbit as PDS 70b, indicated by a solid yellow ellipse, astronomers have detected a cloud of debris (circled by a yellow dashed line) that could be the building blocks of a new planet in the process of formation or the remains of leftovers of one already formed. The ring-shaped structure that dominates the image is a circumstellar disk of material, from which planets are forming. In fact, there is another planet in this system: PDS 70c, which is located at 3 o’clock just off the inner edge of the disk. (Image: ALMA (ESO/NAOJ/NRAO)/Balsalobre-Ruza et al. CC BY 4.0)
“Our research is a first step to search for coorbital planets very early in their formation,” says co-author Nuria Huélamo, principal investigator at the Center for Astrobiology. “It opens up new questions about the formation of Trojans, how they evolve and how frequent they are in different planetary systems,” adds Itziar De Gregorio-Monsalvo, Director of the ESO Office of Science in Chile, who also contributed to this research.
To fully confirm their detection, the team will have to wait until after 2026, when they use ALMA, to see if both PDS 70b and its sister debris cloud move significantly together in their orbit around the star. “This would be a breakthrough in the field of exoplanets,” says Balsalobre-Ruza.
“The future of this topic is very exciting and we look forward to the expanded capabilities of ALMA, planned for 2030, which will dramatically improve the array’s ability to characterize Trojans on many other stars,” concludes De Gregorio-Monsalvo.
The study is titled “Tentative co-orbital submillimeter emission within the Lagrangian region L5 of the protoplanet PDS 70 b”. And it has been published in the academic journal Astronomy & Astrophysics. (Source: IT. CC BY 4.0)
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