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An international research team of astronomers and astrophysicists were originally trying to find and study pulsars with the Kepler space telescope and the Kitt Peak Earth observatory in Arizona. However, the team got more than they bargained for. Later last week, they detected a star with a unusual pulsating rate: intervallic modulations, which occurred every 5.76 and 8.23 hours, caused the star to faintly flicker. Upon further studying, the team found out that these modulations were not produced by the star, and that is when they discovered two earth-sized exoplanets rotating around a red giant star well within its outer envelopes of gas.
“Having migrated so close, they probably plunged deep into the star’s envelope during the red giant phase, but survived,” says Stéphane Charpinet, who is the leader of the team and an astronomer at the University of Toulouse in France.
Before this finding, scientists in general assumed that planets engulfed by a red giant’s outer layers would be incinerated, and it is believed that this is to happen to the Earth since the Sun is fated to become a red giant. Now that these two exoplanets have been discovered, though, it seems that planets are able to endure stars’ transition to a red giant.
The star in question is named KIC 05807616 (also KOI 55, with “KOI” being the acronym for “Kepler Object of Interest”), formerly a main sequence star on the Hertzsprung-Russell Diagram, like our Sun. The two exoplanets, KOI 55-01 and KOI 55-02, revolve around KIC 05807616 less than approximately 900,000 kilometers and approximately one million kilometers, orbiting KIC 05807616 closer than Mercury orbits the Sun. They have the radii of .76 and .87 times the Earth’s respectively, making them the smallest exoplanets detected thus far.
According to another member of the team, Elizabeth ‘Betsy’ Green, an associate astronomer at the University of Arizona’s Steward Observatory, “The friction with the star’s envelope also strips the gaseous and liquid layers off the planet, leaving behind only some part of the solid core, scorched but still there.” This would account for KOI 55-01 and KOI 55-02′s small sizes.
The research team studied KIC 05807616 and found out that it had been transitioning to become a typical red giant, but since the nuclear reactions began occurring in the outer shells rather than in the core, it expanded, shedding its outer layers and jettisoning much of its mass. Due to the fact that KOI 55-01 and KOI 55-02 orbit KIC 05807616 closer than Mercury orbits the Sun, they may have may have helped KIC 05807616 with its transition, causing it to lose mass more rapidly by stripping its outer shells of gas.
The exoplanets ultimately affected KIC 05807616 enough to become a subdwarf B, which, entirely stripped of its outer layers, has the core of a red giant and the luminosity of a main sequence star, but smaller in mass. Upon finishing their research, the team concluded that planets can affect stellar evolution. “We think this is the first documented case of planets influencing a star’s evolution,” Charpinet states.
“We thought we had a pretty good understanding of what solar systems were like as long as we only knew one – ours,” says Green. “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.”