Deep-Fried Exoplanets Found Circling Dying Star

Epoch Times Staff 

Two Earth-sized planets discovered closely orbiting a hot star 3,900 light-years away may be the remnants of gaseous giants engulfed by the star during its red giant phase, according to new research to be published in Nature on Dec. 22.

Called KOI 55.01 and KOI 55.02, these scorched satellites are the smallest known planets circling an active host star outside our solar system. Their sun, KOI 55 or KIC 05807616, is a subdwarf B star, composed of the exposed core of a red giant that has lost most of its fiery envelope, and burns at about 28,000 Kelvin, or 50,000 degrees Fahrenheit.

“When our sun swells up to become a red giant, it will engulf the Earth,” said study co-author Elizabeth Green at the University of Arizona’s Steward Observatory in a press release. “If a tiny planet like the Earth spends 1 billion years in an environment like that, it will just evaporate.”

“Only planets with masses very much larger than the Earth, like Jupiter or Saturn, could possibly survive.”

The astronomers were using NASA’s Kepler Space Telescope to hunt for pulsating stars, and observe them over long periods of time to measure minute variations in brightness. They can see inside a star’s core using its gravity pulsation modes.

Looking at KOI 55′s pulsations, the researchers noticed that it flickered at one five-thousandth percent of its total brightness every 5.76 and 8.23 hours. They realized this was due to the two small planets passing in front of the star following rapid orbits due to their extreme closeness.

“Planets this close to their star are tidally locked, meaning the same side always faces the star, just like the same face of the moon always faces the Earth,” Green explained. “The day side of Mercury is hot enough to melt lead, so you can imagine the harsh conditions on those two small planets racing around a host star that is five times hotter than our sun at such a close distance.”

As the two planets were immersed inside KOI 55 during its red dwarf phase, they would have plowed through its hot atmosphere, generating friction, and moving closer to the parent star. In the process, the planets would have stripped mass from the star, while also losing their gaseous and liquid layers with only a solid core of iron and other heavy elements remaining.

Known as Chthonian planets, they may be the remnants of ancient gaseous giant planets that could have even triggered the loss of their host star’s envelope due to their proximity.

“We think this is the first documented case of planets influencing a star’s evolution,” said research leader Stephane Charpinet at France’s Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse-CNRS in the release.

“We know of a brown dwarf that possibly did that, but that’s not a planet, and of giants planets around subdwarf B stars, but those are too far away to have had any impact on the evolution of the star itself.”

After centuries of observing the exteriors of stars, astronomers can now see inside stars like these pulsators to better understand how they and their planets evolved.

“We thought we had a pretty good understanding of what solar systems were like as long as we only knew one–ours,” Green concluded. “Now we are discovering a huge variety of solar systems that are nothing like ours, including, for the first time, remnant planets around a stellar core like this one.”