1st known 'Trojan' planets discovered locked in the exact same orbit around a star

It's possible that a distant planet the size of Jupiter is carrying the fragments of a smaller planet.

Two sister planets locked to the same orbit around the same star are the first indication of the extremely uncommon "Trojan" planets, according to astronomers.

A Jupiter-sized planet and a cloud of junk, which may be the fragments of a dead planet or the assembling pieces of one yet to be formed, are the prospective co-orbiting planets, which are around the young star PDS 70 some 370 light-years distant.

The finding will be the first ever identification of Trojan planets if researchers can verify that the debris cloud is traveling along the same orbital path as the large planet. On Wednesday, July 19, the researchers published their findings in the journal Astronomy and Astrophysics.

Two decades ago, it was theorized that pairs of planets with comparable masses may circle their star in a similar manner, known as Trojan or co-orbital planets. We have discovered proof for that theory for the first time, according to the main author Olga Balsalobre-Ruza, a graduate student at the Center for Astrobiology (CAB) in Madrid, Spain.

The Greeks and Trojans (the opposing sides of the legendary Trojan War in Homer's Iliad) were divided into two asteroid clusters that were discovered around Jupiter based on their proximity to the gas giant's gravitationally stable Lagrange points, giving rise to the name Trojan planets.

A solar system's Lagrange points are locations where the gravitational pulls of a star and an orbiting planet balance out an object's orbital motion, locking it so that it moves in lock-step with the planet.

Not just asteroids, but planets that develop at the same moment can also get imprisoned on the same orbital path by Lagrange points. However, despite astronomers' calculations predicting that up to 42 Earth-sized planets may theoretically fit into a single orbit, Trojan planets have not yet been discovered due to Trojan orbits' long-term instability and the incapability of present observatories to see them.

The researchers employed the Atacama Large Millimeter/submillimeter Array (ALMA), a collection of 66 sub-radio range telescopes in Chile's Atacama Desert, to search for indications of Trojans hiding out in space. Since very cold pockets of gas and dust frequently emit millimeter and submillimeter light, this is the ideal wavelength to look for planets in their first or terminal phases of motion.

The PDS 70 system is home to two monster planets the size of Jupiter. The scientists discovered a weak signal by enlarging one of the Lagrange points that belonged to the planet PDS 70b. The signal came from a debris cloud, which meant that PDS 70b was being followed by a mass that was nearly twice the size of the moon.

"Who could think of two worlds with the same yearly cycle and inhabitable conditions? The first proof that a world like this may exist comes from our work, according to Balsalobre-Ruza. "It is mind-blowing to me that planets could share the same orbit," one person said. "We can imagine that a planet could share its orbit with thousands of asteroids, as in the case of Jupiter."

To validate their discovery, the researchers will have to wait until 2026. The subsequent window then appears, allowing the user to see if PDS 70b and the associated Trojan have relocated together. The researchers will have achieved success if it is discovered that the planets have behaved in this way.

According to co-author Itziar De Gregorio-Monsalvo, head of the Office for Science at the European Southern Observatory in Chile, "Our research is a first step to look for co-orbital planets very early in their formation." "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 characterize Trojans in many other stars."