Largest Known Rocky Planet 40 Times Larger Than Earth Found Orbiting a Sun-Like Star 730 Light Years Away

A big, dense, and bizarre planet is seen 730 light-years away. Astronomers said that they have never seen any planet like it before, neither from the Solar System nor afar.

This roasted world is known as TOI-849b, the most massive rocky planet ever observed equivalent to over 40 Earth worth of material crammed inside it. Surprisingly, planet TOI-849b's large size suggests that it should be a gas giant like the Jupiter, yet it seems it has no atmosphere.

David Armstrong, an exoplanet researcher at the University of Warwick and study lead author, told the journal Nature, via email, that it is challenging for a planet to be as massive and dense as TOI-849b without becoming a gas giant.

"Something in that standard process went wrong," said Armstrong. Along with his colleagues, they believe that the rocky world is the exposed core of a giant planet that should have been bigger than Jupiter.

Scientists have called this new rocky planet weird and unsure of what it could be telling them.

Bizarre Largest Rocky Planet

Over the past decade, astronomers have spotted thousands of exoplanets among the galaxy's star fields. Most of them fall into categories such as "hot Jupiters" or a big, gassy planet on tight orbits, and some are classified as "super-Earths," rocky planets bigger than Earth but smaller than Neptune.

But TOI-849b is neither of these categories.

Spotted by NASA's Transiting Exoplanet Survey Satellite (TESS), used for planet-hunting, this equipment is searching for 200,000 of the nearest and brightest stars. It discovered TOI-849b when the planet crossed its star's face and briefly blotted out a hint of starlight.

According to the National Geographic, the alien world revolves around its star every 18 hours, which means that its surface temperature could be at 2,800 degrees Fahrenheit or 1,538 degrees Fahrenheit.

Furthermore, TESS observations also showed that the planet is 3.4 times as wide as Earth and 85% as wide as Neptune. This makes its size unusual, given its proximity to its star. Astronomers have only observed hot Jupiters and super-Earths in tight orbits until now, but nothing as bizarre as this planet.

"There really are no planets of that mass there," says Jonathan Fortney, director of the Other Worlds Laboratory at the University of California Santa Cruz.

But while the planet is roughly as wide as Neptune, observation from the HARPS instrument reveals that it is at least twice as massive.

The Core of a Gas Giant

TOI-849b's odd properties suggest that it could probably be the core of a gas giant planet that should have grown more massive than Jupiter. Gas giants in the Solar System are thought to have dense cores, although nothing comes close to TOI-849b.

Based on current planet formation theories, worlds grow from small seeds of rock and ice planted from a swirling gas and dust surrounding newborn stars. Planets such as Earth, amass a small amount of material and remain small, while some gather more gas hence becoming giant gas planets, like Jupiter and Saturn.

One possibility why TOI-849b has cleared a gap around its star is because it ran out of material to collect, and stalled. Or this massive planet could have been a huge planet that somehow lost its atmosphere because it was too close to its star.

The third possible explanation is that cataclysms during the planet's early years both bulked up TOI-849b's core and stripped away its atmosphere.