There’s been a lot of exoplanet news lately! Part of that is due to the American Astronomical Society meeting recently — in fact, there was so much I wrote four articles just from that (Part 1, Part 2, and Part 3, and Part 4). This next story wasn’t released at the meeting, yet may honestly be the most mind-blowing of them all.
Astronomers have found what appears to be a planet literally boiling away from the blast-furnace heat of its star.
Holy cosmic oxyacetylene torch!
There’s a bit of a back story here. The star, KIC 12557548, is about 1500 light years away, and is one of many thousands being observed by the orbiting Kepler Observatory (KIC stands for Kepler Input Catalog, a list of stars under Kepler’s watchful eye). The observatory stares at one spot in the sky, looking for stars whose brightness dips periodically. There can be many causes of such behavior, one of which is the presence of planets orbiting the star and blocking the light from it as they pass in front of it. This is called a transit, and has proven to be wildly successful; hundreds of planets have been discovered this way.
What the authors of this new study are saying is that they see a periodic dip in the brightness of KIC 12557548 every 15.685 hours. Yes, hours. The star is a bit smaller and cooler than the Sun (a K star with about 0.7 times the mass of the Sun, if you want specifics), but even so, the planet must orbit the star a mere 1.5 million kilometers (900,000 miles) from its surface — that’s less than four times the distance of the Moon from the Earth!
That’s close. You’d expect the planet to be cooking… and you’d be right. It’s probably somewhere around 2000°C (3600°F).
Usually, with most planets, the amount of light blocked as the planet passes in front of the star is the same every time. That makes sense, because the planet itself isn’t changing. But not for KIC 12557548. What they saw was that every transit was different. Sometimes more than 1% of the light is blocked, sometimes they detect no dimming at all at the appointed time. That’s really weird.
They looked at and eliminated a few different scenarios, but the fact that the planet is that close to the star really leaves just one idea: a rocky world, probably half the diameter of Earth, being vaporized by the heat of its parent star*.