For the first time, ‘sister’ planets orbiting the same orbit are discovered

Astronomers have discovered a “sister” planet orbiting a young star that orbits a Jupiter-like planet. This discovery is also considered an important milestone. Because although the existence of such an orbital system is theoretically accepted, no evidence based on observation has been obtained before. In addition, it is thought that the information to be obtained can answer questions about the formation of planets.

Planets sharing the same orbit discovered

Researchers used the Atacama Large Millimeter/Submillimeter Telescope Array ALMA in Chile to observe the PDS 70 system, located 370 light-years away in the constellation Centaurus. It is not the first time that the PDS 70 system has been discovered, as it was already known that two Jupiter-like planets exist in this system, known as “PDS 70b” and “PDS 70c”. However, follow-up observations have detected a cloud of debris orbiting the Jupiter-like planet “PDS 70b,” representing a new planet that is either actively forming or has already formed.

“Twenty years ago, it was predicted that pairs of similar-mass planets, called “Trojan horses” or “co-orbiting planets,” could share orbits around their stars. For the first time, we found evidence in favor of this idea,” said Olga Balsalobre-Ruza, lead author of the study at the Center for Astrobiology in Madrid.

“Trojans” in the Solar System

Although the observation made is a first for the Trojan planet, scientists are actually familiar with such situations from the Solar System. The most famous example of this is the Trojan asteroids, a family of more than 12,000 rocky bodies that accompany Jupiter on its orbital journey around the Sun. This inspired scientists that a similar event could occur in orbit of other stars.

Twice the mass of the moon

During observations of the planetary system, the research team noticed a cloud of debris in PDS 70b’s orbit at a point where Trojans could exist. The findings pointed to a debris cloud about twice the mass of the Moon, which could be a Trojan planet or a planet in formation.

Discovered in 2018, exoplanet PDS 70b has three Jupiter masses and takes more than 119 years to complete one orbit around its star, according to NASA. To confirm their observations and the discovery of sister planets, the researchers will have to wait until after 2026, when they can use ALMA to see how far PDS 70b and the debris cloud have traveled in its long orbital period around the star.