Astronomers find evidence of two planets sharing the same orbit around a star

Could two similar worlds orbit the same star, side by side? A new study appears to have discovered just that.

By Iain Todd

Published: Wednesday, 19 July 2023 at 12:00 am

Astronomers have discovered strong evidence of two planets sharing the same orbit around a star.

A new study reveals the detection of a cloud of debris sharing another planet’s orbit.

This could be the building blocks of a new planet, or the remnants of one already formed.

If confirmed, it would be the first time that the ‘sibling’ of a planet orbiting a distant star has ever been seen.

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Image showing planetary system PDS 70, with a star at its centre. Highlighted in a yellow circle is planet PDS 70b, and highlighted in a dotted yellow circle is a potential Trojan planet sharing the same orbit. Credit: ALMA (ESO/NAOJ/NRAO) /Balsalobre-Ruza et al.

The discovery adds further evidence to the existence of so-called Trojan planets, or co-orbital planets, which is when pairs of planets of similar mass share the same orbit around their host star.

A similar example can be found in our own Solar System in the Trojan asteroids of Jupiter, which are more than 12,000 rocky bodies that share Jupiter’s orbit around our Sun.

But finding a Trojan planet has so far proven difficult.

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An artist’s impression of the Trojan asteroids, which share the same orbital path around the Sun as gas giant Jupiter. Credit: NASA/JPL-Caltech

A team of astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) in the Atacama Desert of Chile observed the PDS 70 system, which is a star 400 lightyears away known to host two Jupiter-like planets called PDS 70b and PDS 70c.

They spotted a cloud of debris at the location in PDS 70b’s orbit where Trojans are thought to exist.

Studying the Lagrangian zones – regions in a planet’s orbit where gravitational equilibrium between the planet and host star can trap cosmic material – around PDS 70’s orbit, the astronomers found evidence of a cloud of debris.

That debris has a mass up to about twice that of Earth’s Moon, and may well be evidence of a Trojan planet sharing the same orbit around the host star.