Key Takeaways:

  • KELT-11b is a giant exoplanet with surprisingly low density, like styrofoam.
  • It is the third-lowest density planet ever found and orbits a star 320 light-years away.
  • The host star, KELT-11, is nearing the end of its life and will engulf KELT-11b within 100 million years.
  • Astronomers will be able to study KELT-11b’s atmosphere before it is engulfed due to the brightness of its host star.
  • KELT-11b’s existence challenges current scientific understanding and offers a chance to learn more about such inflated planets.

Researchers have discovered a massive exoplanet that is bigger than Jupiter but has a mass far smaller than that of a piece of foam. This unexplained “puffy planet” has a density that is comparable to that of styrofoam.

The discovery team of KELT-11b claims that this “extraordinarily inflated” world is the third-lowest density planet ever found, with a precisely measured mass and radius. This strange, light-weight sphere may provide additional insight into the evolution of such unusual exoplanets. KELT-11b is orbiting a star that is roughly 320 light-years from Earth.

According to astronomer Joshua Pepper of Lehigh University in Pennsylvania, “it is highly inflated, so that while it’s only a fifth as massive as Jupiter, it is nearly 40 percent larger, making it about as dense as styrofoam, with an extraordinarily large atmosphere.”

The exoplanet KELT-11b is unique not only because of its unusual density but also because of the extreme brightness of its host star. The star known as KELT-11 is undergoing a transformation into a red giant, which means that it has begun to burn through its nuclear fuel by combining hydrogen in a shell that surrounds its core.

According to current predictions, KELT-11b will eventually be swallowed by its host star within the next 100 million years as KELT-11’s outer layers expand to swallow the world that resembles Styrofoam.

The planet is in close orbit of its host, KELT-11, and will engulf it in less than five days, so that engulfment will also happen quickly.

However, the intense brightness produced by KELT-11 will allow scientists to learn more about the composition of the planet’s atmosphere before that engulfment occurs.

As KELT-11b transits between the star and Earth during its orbit, the star is actually the brightest visible star in the Southern Hemisphere known to host a transiting planet.

Because the amount of light space telescopes receive from these far-off stars dips slightly as the exoplanet passes in front of them, astronomers frequently find exoplanets through this transit.

However, in the case of KELT-11, the sub-giant’s extreme brightness meant that astronomers utilizing the KELT (Kilodegree Extremely Little Telescope) survey—a pair of robotic telescopes situated in Arizona and South Africa—could hardly distinguish the dip in light brought on by KELT-11b’s transit.

“This discovery was very challenging. The original KELT observations of the star — its light curve — showed only a hint of the transit,” Pepper told Tomasz Nowakowski at Phys.org, when the team first announced their findings prior to peer-review.

“Because the transit is both shallow (a little under 0.3 percent change in brightness) and long, it was very difficult to obtain reliable, complete confirmation observations.”

Following observations ultimately verified the presence of KELT-11b, and now the very intense backlight that complicated its original discovery might aid scientists in determining the makeup of its atmosphere. And that might offer hints as to how this world of Styrofoam became so strangely inflated.

Given its mass and closeness to its host, KELT-11b’s current size is roughly twice that of what scientists can explain, but now that it is known to exist, it presents a fantastic opportunity to learn more about these styrofoam-like planets and what causes them to be both so large and so sparse.

“We think that KELT-11b will be a great test case to help us understand the mechanism that causes inflated planets,” Pepper stated to Phys.org.

“Furthermore, since the host star has evolved onto the sub-giant branch and is reaching the end of its life, we hope that we can study the behaviour of planetary systems at the end-stage of their star’s lifetime.”

The findings are reported in The Astronomical Journal.

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