Bizarre ‘inside-out’ solar system that shouldn’t exist discovered
Scientists have discovered something that they previously thought wasn’t possible – an ‘inside out’ star system.
When you line all the planets in our solar system up, the four closest to the sun are rocky and the four furthest are giant gassy balls.
This pattern – rock then gas – isn’t unique to us and has been seen countless times in other star systems.
Yet an international team of scientists has discovered that 116.27 light-years away from us is an interstellar system that is the other way around.
LHS 1903 is a star orbited by three planets, the closest being a rocky one with two gas worlds close by.
The researchers, led by Thomas Wilson from the University of Warwick, found a fourth planet circling LHS 1903, but it was rocky rather than gassy.
Wilson tells Metro: ‘This system really opens up what a star system should look like.
‘Before our study, we thought that smaller planets were only in the inner system and larger planets were further away.
‘But now LHS 1903 breaks this thinking and unveils that a whole wide range of systems could be out there for us to discover.’
Why is this star system inside-out?
Stars are constantly hurling out solar radiation, which can easily strip away a planet’s atmosphere, leaving it barren. Take Mercury, for example.
Further out, however, the atmosphere can safely wrap around a planet and form gas giants, like Saturn or Uranus.
Despite being a red dwarf, so named because these small stars emit reddish light, LHS 1903 still spews enough radiation to shear its planets.
So, how did the outermost planet in the system get so rocky? Why isn’t it gassy?
Wilson and his team’s observations, published in Science, suggest that the fourth planet may have had its atmosphere torn off, or it never formed one.
‘What we think happened was that the planet closest to the star was born first, and then the second furthest was formed, and then the third and fourth,’ explains Wilson, a process called inside-out planet formation.
‘This means that these alien worlds would have been born at different times and in different environments.
‘This is a big deal because it would mean that planets in the same star system look different because of where and when they were formed.’
To demonstrate how, well, strange this is, Wilson says to picture how different Earth would be if our solar system were inside out.
‘Jupiter and Saturn would gravitationally throw around the other planets, either out of the system, into each other, or into the sun,’ he says.
‘If Earth survived this, it’ll likely be very far from the Sun and so very cold.’
How did scientists discover this?
The team spotted this out-of-place planetary system using the European Space Agency’s CHaracterising ExOPlanet Satellite (Cheops).
Thousands of exoplanets – planets orbiting other stars – have been discovered over the years. It’s Cheops’ job not to find new ones, but help us understand the ones we already know about.
The space agency’s project scientist, Max Guenther, says that figuring out if a planet is rocky or gassy is harder than it sounds for astronomers.
The picture right at the top of the story certainly isn’t what they see when they peek through their telescopes.
‘You can compare it to the body mass index, or BMI,’ Guehtner says.
‘You measure a human in terms of size and mass but once you start to draw and describe the person, they become a person.
‘What you see in the images is an interpretation of the actual measurements.’
These measures come from a method of observation called transmission spectroscopy, also called the blink method.
‘Cheops is no different from a smartphone camera – just way more expensive and stable,’ Guehtner says.
‘If you take a photo on a cloud-free night, you’ll see white dots on a black background. That’s the same pictures that we’re taking.’
By taking a few photos of the same patch of sky every 30 seconds or so, scientists can see if these tiny, smeared pixels flicker at all.
If they do, there’s a good chance a planet just drifted by, called a transit blip. ‘Sometimes it’ll be a change of just 1% of light,’ Guehtner says.
When light from LHS 1903 shines through a planet’s atmosphere, some gases filter the starlight. For a brief moment, astronomers can see clues about the planet’s chemical makeup.
Experts can also guess the mass of a planet by observing the gravitational tug – or wobble – that it exerts on its star as it orbits.
With all this BMI-grade data, astronomers can calculate whether planets are rocky, like Earth, or fluffy, like clouds.
One day, we think every interstellar system has rocky planets in the front, gas giants in the back. The next day, they can be anything but.
But when it comes to science, being proven wrong is one of the ‘best outcomes’ scientists can hope for.
‘It doesn’t mean that everything is wrong,’ Guehtner adds, ‘it just means it was too simplistic because we had limited data so far.’
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