Just days after the first Earth-sized exoplanets were discovered, we find two more planets that are even smaller – but they weren’t always like that. These pint-sized worlds are remnants of gas giants, the lone survivors of a dead star.
The star KIC 05807616 was once much like our own Sun. Not big enough to go supernova, the star started expanding outwards once its fuel ran out, ballooning up into a red gent as much as a hundred times its original diameter. This fate awaits the Sun five billion years from now, and its final expansion will almost certainly vaporize Mercury, Venus, Earth, and possibly Mars. Nothing should be able to survive this sort of extreme stellar blast furnace.
At least, that’s what astronomers always assumed. But an international team of astronomers have actually detected two planets in very close orbits around KIC 05807616. These planets, known as KOI 55.01 and KOI 55.02, are even smaller than those discovered around Kepler-20, clocking in at just 76% and 87% the size of Earth. The two planets have a couple of the closest orbits around a star we’ve ever seen, at just 5.76 and 8.23 hours, or 0.016 and 0.02 times the distance Mercury orbits our Sun. That makes their average temperatures around 16,000 degrees Fahrenheit.
What’s remarkable is that KIC 05807616 has already shed its outer envelope of stellar material, meaning it’s now much smaller than it was during its period of red giant expansion. Considering how close KOI 55.01 and KOI 55.02 are to the star, that means they must have once been inside the expanding red giant…and yet, somehow, they survived being vaporized. This is the first time we’ve seen any indication a planet can survive being inside a red giant.
This solar system also provides the first clear proof that planets can shape the evolution of their star. As these planets plunged deep into the red giant’s envelope, their presence helped strip atmosphere off the star and fling it into space. At the same time, the incredible heat of the red giant stripped away all the gas and liquid layers of the planets, so that only the dense solid core remained to eventually take up orbit. The astronomers say this is the first indisputable evidence of planets actually directing the course of their star’s development.
So does this mean Earth has a chance to survive its fiery execution? Unfortunately, the odds are still against it. The astronomers suspect these planets are actually the charred husks of gas giants, possibly once as large as Jupiter and Saturn. These planets plunged deep inside the red giant’s envelope, either because they had a very close orbit to begin with or because they were dislodged from a more distant orbit by the red giant’s gravity. If it’s the latter, then we might be looking at the future of our own gas giants, which could similarly dive inside the Sun when it goes red giant.
That said, the presence of these planets so close around a red giant was a hugely unexpected find, and these current explanations can only be considered a best guess. There’s clearly a lot we don’t know about the dying days of a solar system – and it’s just possible we’ve just observed a way Earth itself might survive its vaporization. Either way, considering they actually dived inside a star and survived, I think it’s safe to declare KOI 55.01 and KOI 55.02 the two most badass planets in the cosmos. I think the scientific community will get behind me on that one.
Via Nature. Illustration by Stéphane Charpinet/Institut de Recherche en Astrophysique et Planétologie in Toulouse, France.