Astronomical puzzle
The planet that survived: Researchers puzzle how exoplanet Halla escaped starfire
Illustration of an exoplanet orbiting its star. How Halla survived the fire of his sun in the constellation Lesser Bears is debatable
© Imago Images
Halla should no longer exist – its own sun should have swallowed the exoplanet. Actually. But he is still there. Scientists are now trying to figure out how this is possible.
The 520 light-years away ExoplanetPlanet 8 UMi b should actually no longer exist. The sun he orbited all his life should have eaten him up – like dying stars do. But for some reason 8 UMi b refused to burst into flames. “Life after death”, headlined the Keck Observatory in Hawaii, whose employees discovered the cosmic miracle.
Bloated Death: When Stars Die
The researchers later renamed the distant chunk in the Ursa Minor constellation, which Korean astronomers discovered in 2015, for obvious reasons: They named it Halla – after the highest mountain in South Korea. It belongs to the class of “Hot Jupiters”: Exoplanets whose mass corresponds at least to the largest planet in our solar system, but have a significantly higher surface temperature.
“Halla is a kind of forbidden planet,” NASA researcher Marc Hon of the University of Hawaii at Manoa told the New York Times. Hon is part of the research team investigating the event this week in the US journal “Nature” published.
What makes Halla so “forbidden” is its very existence. After all, his sun should have extinguished him. When stars run out of fuel and reach the end of their lives, they swell up tremendously. In the process, these red giants swallow the planets in their orbit – one after the other. It has long been suspected that stars take their companions with them to their deaths and has recently been directly proven for the first time.
Exactly this fate should have overtaken Halla. Using NASA’s Transiting Exoplanet Survey Satellite, astronomers found that the host star Baekdu was already burning helium. This is exactly what stars do only after they have completely used up their hydrogen supply, which they use to carry out nuclear fusion. A helium-dodging star like Baekdu is literally in prolonged death throes—so it would have to have already absorbed nearby planets. And Halla was close enough: the exoplanet orbits its host star at a distance of around 69 million kilometers, roughly half the distance between the Earth and the Sun.
Planetary Survival Theories
“We just don’t think Halla could have survived being absorbed by an expanding red giant star,” astronomer study co-author Daniel Huber told CNN. “This planet should no longer exist today!” believes his colleague Hon. Naturally, the question arises: why does it do it after all? Why wasn’t Halla grilled? Scientists have several theories about this. Two of that:
- Double Happiness: On the one hand, it is possible that the exoplanet orbited not one, but two stars a long time ago – like the desert planet Tatooine in Star Wars. Today’s host star Baekdu may have formed through the merger of its predecessors. In this original binary star system, a smaller white dwarf would have collided with an expanding red giant. That, in turn, would have ended the “big brother’s” expansion prematurely – and saved Halla from a fiery end.
- Second Generation Planet: Another explanation: Halla was never in danger, he wasn’t even there when things should have gotten tight. The exoplanet could exist not in spite of the stellar bloating, but because of it. In this theory, Halla was born in the gas cloud created when the binary stars collided. Halla would be a second-generation descendant, so to speak.
In any case, the Halla proves that planets can exist in the most unlikely of places.
Our sun could also swallow up the earth one day
However, Halla is not over the hill. Baekdu, about 1.6 times the mass of our Sun, will one day expand. “This planet may have escaped death once, but it’s unlikely to live on once the star expands,” explains Hon.
Nasa engineering
The expensive look at the stars is worth it: 15 everyday technologies that would not exist without space travel
Incidentally, this fate also awaits our earth. But don’t worry: there’s still time, an estimated five billion years. Our Sun is, so to speak, in its mid-life crisis. But in the end it will expand to a hundred times its current size – and probably swallow our homeland.
Sources: “space.com“; “New York Times“; CNN; “Science News“