An exoplanet that is narrowly avoiding a fiery death has been discovered far out in space, with one theory of its survival mimicking one from a George Lucas movie.
Baekdu (8 UMi), a star located around 520 light years from Earth, is in the final death throes of its life, having expanded massively outwards as its stellar core collapses.
Despite having inflated to an estimated 1.5 times the distance between the star and its planet, which should have engulfed it, scientists have discovered that it is still there, as explained in a study published in the journal Nature on June 28.
The planet is named 8 UMi b, or Halla, and is a Jupiter-like gas giant orbiting the red giant star at a distance around half that between the Earth and our sun. The study cites three possible theories why Halla hasn't been obliterated, one of which is straight out of Star Wars: Episode IV—A New Hope, released in 1977.
The world of Tatooine—best known as Luke Skywalker's home planet—is part of a fictional binary system.
The release explained: "Another theory for the planet's survival is that it never faced the danger of engulfment. Similar to the famous planet Tatooine from Star Wars, which orbits two suns, the team believes the host star Baekdu may have originally been two stars.
"A merger of these two stars may have prevented any one of them from expanding sufficiently large enough to engulf the planet."
The incredible discovery has led the astronomers to rethink how expanding stars can affect their solar systems.
"Planetary engulfment has catastrophic consequences for either the planet or the star itself—or both. The fact that Halla has managed to persist in the immediate vicinity of a giant star that would have otherwise engulfed it highlights the planet as an extraordinary survivor," Marc Hon, a NASA Hubble Fellow at the University of Hawaii Institute of Astronomy (UH IfA) and lead author of the study, said in a statement.
Stars stay alive through a balance between the massive gravity of its mass pressing inwards and the outwards push of the thermonuclear fusion occurring within, converting hydrogen to helium. As stars like our own sun die, they run out of hydrogen fuel, causing the core to collapse inwards, which raises the internal temperature of the star and ignites a shell of hydrogen burning around the core. This causes the outer layers of the star to billow outwards rapidly and the star becomes a red giant, the European Space Agency explains.
Our own sun is expected to die in this manner, and it is forecast to expand up to the orbit of Mars, engulfing ourselves, the red planet, Mercury and Venus.
Red giants reach such high temperatures that helium starts to fuse in the core to form carbon. If the star is large enough, it will eventually explode as a supernova, but if not, it will gradually shrink back down, becoming a white dwarf.
Baekdu's dying expansion is estimated to stretch out to around 1.5 times larger than Halla's orbit. However, NASA's Transiting Exoplanet Survey Satellite data showed that Baekdu is burning helium in its core, indicating that it had already expanded enormously into a red giant star.
This means that Halla somehow survived the expansion.
"Together, these observations confirmed the existence of the planet, leaving us with the compelling question of how the planet actually survived," UH IfA astronomer Daniel Huber, second author of the study, said in the statement. "The observations from multiple telescopes on Maunakea was critical in this process." Maunakea is one of the main observatories on the island of Hawaii.
In the paper, the authors theorize how Halla could have made its lucky escape.
One theory suggests that Baekdu may once have been a binary star system, like that of the planet Tatooine. In this scenario, Baekdu may have resulted from the merging of the two stars, stopping the star from growing as large as it might have if it had only been a single star.
"Most stars are in binary systems, but we don't yet fully grasp how planets may form around them. Therefore, it's plausible that more planets may actually exist around highly evolved stars thanks to binary interactions," explained Hon.
Another suggestion is as Halla being a hot Jupiter-type planet, it may have gotten closer to the star since its expansion, entering the region that would have been engulfed.
A third theory is that Halla is simply a very new planet, having only formed after the star shrank back after expanding, or forming from the gas cloud made by two stars merging, if Baekdu was indeed once a binary system.
Due to the difference between this solar system and our own, it's very unlikely that Earth will have a similar escape in the final days of our sun. However, it is nothing to lose sleep over, as the sun is expected to carry on happily burning for at least another 4 to 5 billion years.
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Jess Thomson is a Newsweek Science Reporter based in London UK. Her focus is reporting on science, technology and healthcare. ... Read more
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