‘Mind-blowing’ discovery suggests distant planet may not be alone

There is a planet, 369 light-years from Earth, slowly orbiting its star.

It is a gas giant, three times the size of Jupiter. And it may not be alone.

Astronomers have found evidence to suggest that a second ‘sibling’ planet may be sharing its orbit – the first of its kind.

The researchers detected a cloud of debris that might be sharing this planet’s orbit, which could be the building blocks of a new planet or the remnants of one already formed.

The discovery would be the strongest evidence yet that two exoplanets – planets outside our solar system – can share one orbit, if it is confirmed.

‘Two decades ago it was predicted in theory that pairs of planets of similar mass may share the same orbit around their star, the so-called Trojan or co-orbital planets,’ said Olga Balsalobre-Ruza, who led the paper published in Astronomy & Astrophysics.

‘For the first time, we have found evidence in favour of that idea.’

The PhD student at the Centre for Astrobiology in Madrid, Spain, added: ‘Who could imagine two worlds that share the duration of the year and the habitability conditions? Our work is the first evidence that this kind of world could exist.

‘We can imagine that a planet can share its orbit with thousands of asteroids as in the case of Jupiter, but it is mind blowing to me that planets could share the same orbit.’

Trojans – rocky bodies in the same orbit as a planet – are common in our own solar system, with the most famous example being the Trojan asteroids of Jupiter.

These are more than 12,000 rocky bodies that are in the same orbit around the sun as the gas giant.

While astronomers have predicted that Trojans could also exist around a star other than our Sun, there has been little evidence to support this.

‘Exotrojans [Trojan planets outside the solar system] have so far been like unicorns – they are allowed to exist by theory but no-one has ever detected them,’ says co-author Jorge Lillo-Box, a senior researcher at the Centre for Astrobiology.

Using the Atacama Large Millimeter/submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner, scientists say they have found the strongest observational evidence yet that Trojan planets could exist – in the PDS 70 system.

This young star is host to two giant, Jupiter-like planets, PDS 70b and PDS 70c.

By analysing archival ALMA observations, the scientists spotted a cloud of debris at the location in PDS 70b’s orbit where Trojans are expected to exist.

According to the researchers, this cloud of debris could point to an existing Trojan world in the system, or a planet in the process of forming.

PDS 70b, discovered in 2018, takes 119.2 years to complete on orbit of its star.

To fully confirm their detection, the team will need to wait until after 2026, when they will aim to use ALMA to see if both PDS 70b and its sibling cloud of debris move significantly along their orbit together around the star.

‘This would be a breakthrough in the exoplanetary field,’ Olga Balsalobre-Ruza concluded.

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