Kamikaze planet says "fuck you" to star

[TithonusSyndrome]

Really, honestly better than any movie

WASHINGTON – Astronomers have found what appears to be a gigantic suicidal planet.

The odd, fiery planet is so close to its star and so large that it is triggering tremendous plasma tides on the star. Those powerful tides are in turn warping the planet's zippy less-than-a-day orbit around its star.

The result: an ever-closer tango of death, with the planet eventually spiraling into the star.

It's a slow death. The planet WASP-18b has maybe a million years to live, said planet discoverer Coel Hellier, a professor of astrophysics at the Keele University in England. Hellier's report on the suicidal planet is in Thursday's issue of the journal Nature.

"It's causing its own destruction by creating these tides," Hellier said.

The star is called WASP-18 and the planet is WASP-18b because of the Wide Angle Search for Planets team that found them.

The planet circles a star that is in the constellation Phoenix and is about 325 light-years away from Earth, which means it is in our galactic neighborhood. A light-year is about 5.8 trillion miles.

The planet is 1.9 million miles from its star, 1/50th of the distance between Earth and the sun, our star. And because of that the temperature is about 3,800 degrees.

Its size — 10 times bigger than Jupiter — and its proximity to its star make it likely to die, Hellier said.

Think of how the distant moon pulls Earth's oceans to form twice-daily tides. The effect the odd planet has on its star is thousands of times stronger, Hellier said. The star's tidal bulge of plasma may extend hundreds of miles, he said.

Like most planets outside our solar system, this planet was not seen directly by a telescope. Astronomers found it by seeing dips in light from the star every time the planet came between the star and Earth.

So far astronomers have found more than 370 planets outside the solar system. This one is "yet another weird one in the exoplanet menagerie," said planet specialist Alan Boss of the Carnegie Institution of Washington.

It's so unusual to find a suicidal planet that University of Maryland astronomer Douglas Hamilton questioned whether there was another explanation. While it is likely that this is a suicidal planet, Hamilton said it is also possible that some basic physics calculations that all astronomers rely on could be dead wrong.

The answer will become apparent in less than a decade if the planet seems to be further in a death spiral, he said.

Plasma tides! Giant burning planets! Not half bad stuff to find while you're planet hunting.

[Simon_Jester]

I'd like to get some clarification on Hamilton's comment...

[Oskuro]

Less than a day orbit? While flaming and causing plasma tides? Quite a sight.

[Dark Flame]

How do the plasma tides affect the planet's orbit?

[Dave]

How do the plasma tides affect the planet's orbit?

I'm guessing that the mass of the planet causes it to pull some of the star's surface both along with it and out behind it. The energy to do so has to come from somewhere, namely, out of the energy represented by the planet's current orbit. Eventually it will lose enough energy that it will come too close to the star and be destroyed.

[Exonerate]

I'm no astrophysicist, but I thought that current star formation theory was that when you got a critical mass, stuff would collapse upon itself, triggering fusion and creating a star if conditions were right, or just a planet if they weren't. So how did the planet manage to get this close to the star? Did it form further away and just drift closer over billions of years or is there another mechanism to explain this?

[dragon]

Well perhaps it got hit my a large asteroid or meteor and that changed its orbit velocity enough that it fell into a tighter spiral.

[RedImperator]

I'm no astrophysicist, but I thought that current star formation theory was that when you got a critical mass, stuff would collapse upon itself, triggering fusion and creating a star if conditions were right, or just a planet if they weren't. So how did the planet manage to get this close to the star? Did it form further away and just drift closer over billions of years or is there another mechanism to explain this?

It's probably a young solar system where the planets which formed in unstable orbits haven't all been ejected, consumed by the parent star, or collided with another planet. The reason our solar system has eight planets in nice, stable, near-circular orbits is because all the other ones were destroyed or ejected. We're probably observing the same process here.

[starslayer]

I'm guessing that the mass of the planet causes it to pull some of the star's surface both along with it and out behind it. The energy to do so has to come from somewhere, namely, out of the energy represented by the planet's current orbit. Eventually it will lose enough energy that it will come too close to the star and be destroyed.

You are correct in that the star's tidal bulge will tend to lag the planet due basically to friction type forces in the star; because it does so, there is now a gravitational force pulling ever so slightly backward on the planet. This is what causes the planet to spiral in, not conservation of energy. IOW, think of Netwon's 3rd Law: A force is always felt by two objects in opposite directions (this is what is really meant by the "action, reaction" stuff). Because the tidal bulge lags the planet, the planet tugs it forward, and in response is tugged backward by the star. This backward tug causes the planet to lose orbital momentum, and it spirals in, circular orbit or not.

It's probably a young solar system where the planets which formed in unstable orbits haven't all been ejected, consumed by the parent star, or collided with another planet. The reason our solar system has eight planets in nice, stable, near-circular orbits is because all the other ones were destroyed or ejected. We're probably observing the same process here.

The leading hypothesis for the formation of most hot Jupiters goes like this: Gas giants can probably only form further out from the star, both to allow for the large rocky core to form (which would need to be several times Earth's mass), and then to accrete appreciable amounts of gas, as the star's radiation pressure is strong enough further in to blow away most of the gas and dust. Once they have formed, if the disk is dense enough, drag from the disk will cause them to spiral in, sometimes as far as this one has. You are correct in that this is a very young system.

Edited for clarity.

[ArmorPierce]

How do the plasma tides affect the planet's orbit?

The same way that Earth's tide effects the moon.