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A strange planetary system has left scientists baffled – as it appears to be ‘inside out’.
The system includes four planets around a cool faint red dwarf star, which scientists have named LHS 1903.
Usually, planets closest to a star are rocky, while those further away are gaseous.
For example, here in our own Solar System, Mercury and Mars are rocky, while Jupiter and Neptune are gaseous.
However, experts from the University of Warwick were amazed to discover that the new system breaks this convention.
While the planets begin with a rocky planet followed by two gas worlds, the outermost planet is rocky.
‘This strange disorder makes it a unique inside–out system,’ said Dr Thomas Wilson, first author of the study.
‘Rocky planets don’t usually form far away from their home star, on the outside of the gaseous worlds.’
Normally, the planets closest to a star are rocky, because solar radiation sweeps away their gaseous atmospheres, leaving dense, solid cores behind.
Planets in the further reaches of a system are able to hold on to their gaseous atmospheres.
In their new study, the team used the European Space Agency’s Cheops satellite to study the system, and spotted a rocky planet on the fringes.
Initially, the researchers theorised that the rocky and gaseous planets may have swapped places, or that the rocky planet lost its atmosphere in a collision.
However, they soon ruled these out.
Instead, they found evidence that the planets did not form at the same time, but formed one after another, from the inner to the outermost planet.
‘By the time this final outer planet formed, the system may have already run out of gas, which is considered vital for planet formation,’ Dr Wilson explained.
‘Yet here is a small, rocky world, defying expectations.
‘It seems that we have found first evidence for a planet that formed in a gas-depleted environment.’
What remains unclear is if this strange inside out system is a one-off, or if there are others out there.
‘Much about how planets form and evolve is still a mystery,’ said Maximilian Günther, Cheops project scientist at ESA.
‘Finding clues like this one for solving this puzzle is precisely what CHEOPS set out to do.’
