A rare six-planet solar system, unchanged for billions of years, has been discovered 100 light-years from Earth.
The planets are all ‘sub-Neptunes’, meaning they are smaller than our Neptune, and could be rocky with an atmosphere and water like Earth – something needed for alien life to evolve.
The system’s central star, HD110067, has been perplexing astronomers for years, ever since Nasa’s exoplanet-hunting telescope TESS first spotted signs of a possible orbiting planet.
TESS, or Transiting Exoplanet Survey Satellite, first detected dips in the star’s brightness in 2020, suggesting that one or possibly two planets were orbiting it – blocking part of the light as they passed between the star and TESS.
The original analysis suggested one of these took just 5.64 Earth days to orbit the star, with the other in an unknown orbit.
However, further analysis suggested there may in fact be four planets, changing the whole landscape of the solar system.
To help unravel the planetary puzzle, Dr Rafael Luque of the University of Chicago and scientists across the world – including those from the University of Warwick – joined the investigation.
Using date from the European Space Agency’s (ESA) CHaracterising ExOPlanet Satellite (CHEOPS), they discovered there were in fact six planets, with three dancing around in a mesmerising pattern known as ‘orbital resonance’, which helped explain the star’s bizarre behaviour.
The phenomenon occurs when two or more planets’ orbits are different lengths but still in sync. For example, the second planet in the system takes almost exactly one and a half times as long to orbit the star as the innermost planet, and the third planet takes one and a half times the second.
This ‘perfectly synchronised waltz’ means for each three orbits of one planet, the next orbits twice.
This orbital resonance is rare in star systems, with planets circling stars easily thrown off course, such as from the gravity of a massive planet, a close encounter with a passing star or even a major impact.
‘We think only about one per cent of all systems stay in resonance,’ said Dr Luque, explaining why HD110067 is special and invites further study. ‘It shows us the pristine configuration of a planetary system that has survived untouched.’
Not only that, but the orbital resonance of the three inner planets allowed researchers to discover three more.
‘By establishing this pattern of planet orbits, we were able to predict other orbits of planets we hadn’t yet detected,’ said Dr Thomas Wilson, from the University of Warwick’s physics department.
‘From this we lined up previously unexplained dips in starlight observed by CHEOPS and discovered three additional planets with longer orbits. This was only possible with the crucial CHEOPS data.’
The new system is the brightest discovered with four or more planets, but this does have impacts on whether or not life could evolve.
‘All of these planets have large atmospheres – similar to Uranus or Neptune – which makes them perfect for observation with JWST,’ said Dr Wilson.
‘It would be fascinating to test if these planets are rocky like Earth or Venus but with larger atmospheres. However, they are all much hotter than Earth, 170-530 degrees Celsius, which would make it very difficult for life to exist.’
However, that doesn’t mean alien life within the system is completely ruled out.
‘That being said, obtaining JWST observations of the atmospheres of these planets will tell us if any of them do have water,’ he added. ‘Also, while we’ve discovered six planets, there could still be more planets in this system at colder temperatures that are closer to the habitable zone of the system.’
The study is published in the journal Nature.
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