Once upon a time, there was a planet that was too big for its tiny sun. And it threw science into chaos…
No, this isn’t a fairy tale: a giant among dwarfs has been discovered – but in space, in a solar system far from our own.
In a new paper published in Science, scientists reveal their discovery of a rare planet far too big for its sun. The findings challenge everything we know about how planets and their solar systems form – plus, how scientists model them.
“An object like the one we discovered is likely extremely rare, so detecting it has been really exciting,” said Megan Delamer, an astronomy graduate student at Penn State, USA, and co-author on the paper. “Our current theories of planet formation have trouble accounting for what we’re seeing.”
The giant planet is 13 times as massive as the Earth – about the same as Neptune. But what’s weird is that the ultra-cool star that it’s orbiting (known catchily as LHS 3154) is nine times less massive than our Sun. That makes the mass ratio of the planet to its star more than 100 times the one between Earth and our Sun.
The discovery marks the first time scientists have found such a giant planet orbiting such a small star. In fact, ultra-cool stars are famously the coldest and least massive stars in the Universe.
Existing scientific theories say that stars form from vast clouds of dust and gas. And, when they’ve finished, what remains in the discs orbiting the star develops into planets. But LHS 3154 doesn’t have enough mass to make a planet as massive as this one, according to the scientists – forcing them to re-examine what they know.
In fact, according to the scientists’ calculations, the dust-to-mass and dust-to-gas ratios around the developing star would need to have been 10 times higher than the model shows for the planet to be so massive.
The team discovered the unusual pair when they were searching for planets with liquid water on their surface. This would make them potentially habitable for life.
These planets are easier to find when they’re orbiting ultracool stars. That’s because the low temperature often means the planet is closer – resulting in a more detectable signal for the astronomical spectrograph used to search for them.
“Think about it like the star is a campfire. The more the fire cools down, the closer you’ll need to get to that fire to stay warm,” said Suvrath Mahadevan, Professor of Astronomy and Astrophysics at Penn State and co-author of the paper.
“The same is true for planets. If the star is colder, then a planet will need to be closer to that star if it is going to be warm enough to contain liquid water. If a planet has a close enough orbit to its ultracool star, we can detect it by seeing a very subtle change in the colour of the star’s spectra or light as it is tugged on by an orbiting planet.”
Read more:
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