Mysterious star system sees five alien planets orbit in 'harmonic' pattern

Rob Waugh
·3-min read
The system boasts six exoplanets and that all but the one closest to the star are locked in a rare rhythm as they move in their orbits (ESO)
The system boasts six exoplanets and that all but the one closest to the star are locked in a rare rhythm as they move in their orbits (ESO)

Astronomers have spotted a star system in which five planets orbit a central star in a strange, but precise, harmony.

The weird find could throw light on how planets, including those in our own solar system, formed and evolved, the University of Warwick researchers said.

There are six planets in system TOI-178, orbiting a star some 200 light-years away in the constellation of Sculptor.

All but the one closest to the star are locked in a highly-precise cosmic dance as they move in their orbits.

There are patterns that repeat themselves as the planets go around the star, with some planets aligning every few orbits.

The research was published in the journal Astronomy and Astrophysics.

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Edward Bryant, a PhD student in the department of physics at the University of Warwick, said: “The exciting aspect of this system is that five of the planets are interacting with each other.

“Over the next few years, we will be able to monitor the effect these interactions have on the orbits of the planets, which will allow us to place precise constraints on the masses and orbits of these planets.”

The discovery was made using a combination of telescopes, including the University of Warwick-operated Next-Generation Transit Survey (NGTS).

Bryant said: “This future study of the system could even reveal the presence of additional planets. The NGTS facility is very well-suited to undertake this future monitoring.”

Scientists have spotted similar patterns in the orbits of three of Jupiter’s moons: Io, Europa and Ganymede.

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Io, the closest of the three to Jupiter, completes four full orbits around Jupiter for every orbit that Ganymede, the furthest away, makes, and two full orbits for every orbit Europa makes.

But the pattern of the planets in the TOI-178 system is much more complicated, the researchers said.

While the second planet from the star (the first in the resonance chain) completes 18 orbits, the third planet from the start (second in the chain) completes nine orbits, and so on.

The scientists initially only found five planets in the system, but by following this resonant rhythm they calculated where in its orbit an additional planet would be when they next had a window to observe the system.

This dance of resonant planets provides clues about the system’s past.

“The orbits in this system are very well-ordered, which tells us that this system has evolved quite gently since its birth,” said co-author Yann Alibert, from the University of Bern.

If the system had been significantly disturbed earlier in its life, for example by a giant impact, this fragile configuration of orbits would not have survived.

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