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 report published in Science, scientists reveal their finding of a unique planet far too huge for its sun. The findings question everything we know about how planets and their solar systems form — also, 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 research. “Our present theories of planet formation have problems accounting for what we’re witnessing.”
The enormous planet is 13 times as large as the Earth — about the same as Neptune. But what’s unusual 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 represents the first time scientists have identified such a large planet around such a small star. Ultra-cool stars are famously the coldest and least massive stars in the Universe.
Existing scientific theories indicate that stars arise from huge clouds of dust and gas. And, when they’ve finished, what remains in the discs around the star turns into planets. But LHS 3154 doesn’t have enough mass to produce a planet as huge as this one, according to the scientists – requiring them to re-examine what they know.
In reality, according to the scientists’ estimates, the dust-to-mass and dust-to-gas ratios around the young star would need to have been 10 times higher than the model suggests for the planet to be so big.
The researchers discovered the odd pair when they were searching for planets having liquid water on their surface. This would make them potentially livable for life.
These planets are easier to find when they’re orbiting ultracool stars. That’s because the low temperature generally suggests the planet is closer – resulting in a more visible signal for the astronomical spectrograph used to hunt for them.
“Think about it like the star is a campfire. The more the fire cools down, the closer you’ll need to come to that fire to be 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 identify it by noticing a very small shift in the color of the star’s spectrum or light as it is tugged on by an orbiting planet.”