Can Earth-sized planets survive their star's expansion?

Dec 21, 2011
This shows two planets that survived the red-giant expansion of their host star. Credit: Illustration by Stéphane Charpinet/Institut de Recherche en Astrophysique et Planétologie in Toulouse, France.

Two Earth-sized planets have been discovered circling a dying star that has passed the red giant stage. Because of their close orbits, the planets must have been engulfed by their star while it swelled up to many times its original size.

This discovery, published in the science journal Nature, may shed new light on the destiny of stellar and planetary systems, including our solar system.

When our nears the end of its life in about 5 billion years, it will swell up to what astronomers call a red giant, an inflated star that has used up most of its fuel. So large will the grow that its fiery outer reaches will swallow the innermost planets of our solar system – Mercury, Venus, and Mars.

Researchers believed that this unimaginable inferno would make short work of any planet caught in it – until now.

This report describes the first discovery of two planets – or remnants thereof – that evidently not only survived being engulfed by their parent star, but also may have helped to strip the star of most of its fiery envelope in the process. The team was led by Stephane Charpinet, an astronomer at the Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse-CNRS, in France.

"When our sun swells up to become a red giant, it will engulf the Earth," said Elizabeth 'Betsy' Green, an associate astronomer at the University of Arizona's Steward Observatory, who participated in the research. "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 two planets, named KOI 55.01 and KOI 55.02, circle their host star in extremely tight orbits. Having migrated so close, they probably plunged deep into the star's envelope during the red giant phase, but survived. In the most plausible configuration, the two bodies would respectively have radii of 0.76 and 0.87 times the Earth radius, making them the smallest planets so far detected around an active star other than our sun.

The host star, KOI 55, is what astronomers call a subdwarf B star: It consists of the exposed core of a red giant that has lost nearly its entire envelope. In fact, the authors write, the planets may have contributed to the increased mass loss necessary for the formation of this type of star.

The authors concluded that may therefore influence the evolution of their parent stars. They pointed out that the planetary system they observed offers a glimpse into the possible future of our own.

The discovery of the two planets came as a surprise because the research team had not set out to find new planets far away from our solar system, but to study pulsating stars. Caused by rhythmic expansions and contractions brought about by pressure and gravitational forces that go along with the thermonuclear fusion process inside the star, such pulsations are a defining feature of many stars.

By studying the pulsations of a star, astronomers can deduce the object's mass, temperature, size and sometimes even its interior structure. This is called asteroseismology.

"Those pulsation frequency patterns are almost like a finger print of a star," Green said. "It's very much like seismology, where one uses earthquake data to learn about the inner composition of the Earth."

To detect the frequencies with which a star pulsates, researchers have to observe it for very long periods of time, sometimes years, in order to measure tiny variations in brightness.

"The brightness variations of a star tell us about its pulsational modes if we can observe enough of them very precisely," Green said. "Let's say there is one pulsational mode every 5859.8 seconds, and there is another one every 9126.39 seconds. There could be lots of stars with rather different properties that could all manage to pulsate at those two frequencies. However, if we can measure 10, or better yet, 50 pulsational modes in one star, then it's possible to use theoretical models to say exactly what the star must be like in order to produce those particular pulsations."

"The only way to do that is to have a telescope sitting in space," she added. "On Earth, we can only observe a star at night. But unless we follow it 24/7, the mathematics give us artifacts. Observing through the atmosphere means that even in the very best of cases we can only detect brightness variations to a ten-thousandth of a percent. But if you've got 50 or a 100 modes going in a star, you need to measure better than that."

For that reason, the team used data obtained from NASA's Kepler Space Telescope for this study.

Unobstructed by the Earth's atmosphere and staring at the same patch of sky throughout its five-year mission, the Kepler Space Telescope sits in a prime spot to detect tiny variations in brightness of stars.

Green had been pursuing a survey to look for hot subdwarf stars in the galactic plane of the Milky Way.

"I had already obtained excellent high-signal to noise spectra of the hot subdwarf B star KOI 55 with our telescopes on Kitt Peak, before Kepler was even launched," she said. "Once Kepler was in and began finding all these pulsational modes, my co-authors at the University of Toulouse and the University of Montreal were able to analyze this star immediately using their state-of-the art computer models."

This was the first time that researchers were able to use gravity pulsation modes, which penetrate into the core of the star, to match subdwarf B star models to learn about their interior structure.

While analyzing KOI 55's pulsations, the team noticed the intriguing presence of two tiny periodic modulations occurring every 5.76 and 8.23 hours that caused the star to flicker ever so slightly, at one five thousandth percent of its overall brightness. They showed that these two frequencies could not have been produced by the star's own internal pulsations.

The only explanation came from the existence two small planets passing in front of the star every 5.76 and 8.23 hours. To complete their orbits so rapidly, KOI 55.01 and KOI 55.02 have to be extremely close to the star, much closer than Mercury is to our sun. On top of that, the sun is a cool star compared to KOI 55, which burns at about 28,000 Kelvin, or 50,000 degrees Fahrenheit.

"Planets this close to their star are tidally locked," Green said, "meaning the same side always faces the star, just like the same face of the moon always faces the Earth. 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."

The extremely tight orbits are important because they tell the researchers that the planets must have been engulfed when their host stars swelled up into a red giant.

"Having migrated so close, they probably plunged deep into the star's envelope during the red giant phase, but survived," lead author Charpinet said.

"As the star puffs up and engulfs the planet, the planet has to plow through the star's hot atmosphere and that causes friction, sending it spiraling toward the star," Green added. "As it's doing that, it helps strip atmosphere off the star. At the same time, 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."

"We think this is the first documented case of planets influencing a star's evolution," Charpinet said. "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."

"I find it incredibly fascinating that after hundreds of years of being able to only look at the outsides of stars, now we can finally investigate the interiors of a few stars – even if only in these special types of pulsators – and compare that with how we thought evolved," Green said. "We thought we had a pretty good understanding of what solar systems were like as long as we only knew one – ours. Now we are discovering a huge variety of solar systems that are nothing like ours, including, for the first time, remnant around a stellar core like this one."

Explore further: Toothpaste fluorine formed in stars

More information: "A compact system of small planets around a former red-giant star," by S. Charpinet et al., Nature, Dec. 22, 2011

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dtyarbrough
1.2 / 5 (12) Dec 21, 2011
99 of the 99 stable elements boil at temperatures below 5000 degrees Kelvin. How could a planet survive temperatures of 28000 kelvin for millions of years or even 5000 degrees kelvin for that matter. Seems they're not only wrong about the temperature of the sun's corona as demonstrated by comet Lovejoy, they're wrong about the surface temperature as well. My theory predicted this long before these articles. If photons can travel billions of light years without losing significant amounts of energy, imagine photons leaving the solar corona after only 8 minutes if it was even hot enough to boil water. It not just the quality but also the quantity we're talking about.
Pirouette
3 / 5 (6) Dec 21, 2011
""This was the first time that researchers were able to use gravity pulsation modes, which penetrate into the core of the star, to match subdwarf B star models to learn about their interior structure.""

If only this could be done to lay to rest forever Omatumr's "neutron repulsion" hypothesis.
eachus
5 / 5 (7) Dec 21, 2011
99 of the 99 stable elements boil at temperatures below 5000 degrees Kelvin. How could a planet survive temperatures of 28000 kelvin for millions of years or even 5000 degrees kelvin for that matter.


Yes, same mistake as in the case of comet Lovejoy, but not about the temperatures close to the sun or KOI 55. And the knowledge is out there--the tokamak researchers work with it all the time. When you have a solid, either conductor or non-conductor, in contact with a plasma, you get what is usually a wall stabilized arc. A planet moving through a plasma would create those conditions all around it.

The key here is that even in a very low-mass plasma, light--and heat--travels less than an inch before being absorbed and re-radiated. In effect, the planet will look to have a mirror-like surface, and will absorb a miniscule fraction of the heat. Oh, and any matter in the plasma will be carried by magnetic fields around the planet, or comet.
Deesky
4.8 / 5 (14) Dec 21, 2011
My theory predicted this long before these articles. If photons can travel billions of light years without losing significant amounts of energy, imagine photons leaving the solar corona after only 8 minutes if it was even hot enough to boil water.

My theory predicts FTL travel between stars. If unicorns could run faster than the speed of light without getting tired, we could populate the entire universe on horseback.
Isaacsname
5 / 5 (4) Dec 21, 2011
..And I could finally get a pizza in under 30 minutes.

Jazz hands !!
Code_Warrior
3 / 5 (6) Dec 21, 2011
My theory predicted this long before these articles.

Did you publish your prediction anywhere in any form for others to read prior to the discovery of this object? You realize that predictions only count if they are publicly stated prior to supporting evidence being found don't you? What other testable predictions does your theory make that haven't already been discovered?
dtyarbrough
1 / 5 (6) Dec 22, 2011
Code Warrier:
Read http://www.scribd...theories if you are really interested or read some of my comments on previous similar articles
eric96
1 / 5 (2) Dec 22, 2011
The most intriguing question is how big were the planets before they were engulfed? Ten - One Hundred times bigger? They make it sound like the planet withstood the star which is highly unlikely irrelevant of the planets composition; no, the planet merely and barely survived which infers that it was much much bigger prior to.

"The Universe is the manifestation of Everything, therefore it has no beginning nor end in space or time for these are just 2 of the dimensions by which Everything is manifested. There cannot be a theory for the manifestation of Everything for in Everything there are infinite patterns thereby making reduction to an equation impossible. Einstein was wrong. "

Eric Laferriere
bewertow
3.6 / 5 (5) Dec 22, 2011
99 of the 99 stable elements boil at temperatures below 5000 degrees Kelvin. How could a planet survive temperatures of 28000 kelvin for millions of years or even 5000 degrees kelvin for that matter. Seems they're not only wrong about the temperature of the sun's corona as demonstrated by comet Lovejoy, they're wrong about the surface temperature as well. My theory predicted this long before these articles. If photons can travel billions of light years without losing significant amounts of energy, imagine photons leaving the solar corona after only 8 minutes if it was even hot enough to boil water. It not just the quality but also the quantity we're talking about.


You're an idiot. Also, a red giant is much cooler on the surface than the sun. Learn2astrophysics n00b.
bewertow
3.7 / 5 (7) Dec 22, 2011
Code Warrier:
Read http://www.scribd...theories if you are really interested or read some of my comments on previous similar articles


You seem to be suffering from the Dunning-Kruger effect.

http://en.wikiped...r_effect

You are so incompetent that you are incapable of noticing your own incompetence.
Code_Warrior
3.5 / 5 (8) Dec 22, 2011
Code Warrier:
Read http://www.scribd...theories if you are really interested

In your article "Quarks and other crap" you state:
The one true particle is the electron or photon, depending upon whether it is inside or outside of matter. Protons, neutrons, and electrons have no charge, only magnetic fields.

Then, at the end of that paragraph you state:
The field is made up of magnetons, even smaller particles than the electrons,that give the proton, neutron, or electron most of its mass.

Where does the rest of electron mass come from and why don't you consider the magneton to be the one "true" particle?

Then there is this:
Beyond infrared, the electromagnetic spectrum is not made of photons, but consists of waves made up of magnetons. Infrared, visible, untraviolet, xray and gamma rays are made of photons(electrons)

Seems to contradict itself.

I agree with Bewertow's diagnosis. You suffer from the Dunning-Kruger effect.
rubberman
3 / 5 (2) Dec 22, 2011
DYB....I read one of your theories, until you stated that photons decelerrated....it's called "light speed" for a reason. I concur with the above evaluations.

@E96 - There is currently another Physorg article regarding the core of Jupiter undergoing liquification. Check it out. Jupiters core temp. isn't much less than the surface temp. of the star these 2 planets are orbiting. The pressure at it's core is considerably higher than the atmosphere of an expanding red giant so it stands to reason the authors hypothesis regarding these "planets" being stripped down cores of gas giants is correct without even having to venture beyond current knowledge.
dtyarbrough
1.6 / 5 (7) Dec 22, 2011
bewertow: According to wikepedia and other sourses a red giant is 5000 kelvin. Hot enough to melt and boil any element. But that is the very point I am trying to make. If the planets survived, they can not be that hot.
dtyarbrough
1.6 / 5 (7) Dec 22, 2011
Code Warrier: If you read with the intention of understanding, you will find my meaning. Read with the intention of finding typos and you will never understand. I am by no means 100% certain of my theory, only 100% certain that the standard theory is wrong.
dtyarbrough
1.7 / 5 (6) Dec 22, 2011
rubberman: Light speed in a vacuum and light speed in glass, for instance, is two different things. Otherwise there would be no need to specify C as speed of light in a vacuum.
rubberman
4.2 / 5 (5) Dec 22, 2011
Apologies DYB, I over simplified that response. Photons travelling through the interstellar medium cannot remain on the same path without maintaining the same speed. Glass is a refractive/reflective medium, light still travels the same speed through glass, it's direction changes numerous times as it passes through but when it emerges from the glass it is still travelling at the speed of light.
Code_Warrior
3 / 5 (6) Dec 22, 2011
bewertow: According to wikepedia and other sourses a red giant is 5000 kelvin. Hot enough to melt and boil any element. But that is the very point I am trying to make. If the planets survived, they can not be that hot.

dtyarbrough: Have you ever seen a frozen french fry exposed to 350 degree F oil remain uncooked when all the other french fries in the same batch came out crispy? The frozen water in the french fry flashed to steam and formed an insulating layer that severely slowed the flow of heat into the french fry. Given enough time, the fry will get crispy. I suspect something similar happened to these planets. Maybe part of their rocky outer layer boiled, forming an insulating layer contained by the pressure of the red giant's atmosphere, and the atmosphere of the red giant dissipated before the planets got crispy.
Code_Warrior
3 / 5 (6) Dec 22, 2011
Code Warrier: If you read with the intention of understanding, you will find my meaning. Read with the intention of finding typos and you will never understand.

I read with the intention of understanding and asked you a question with 2 parts. Answer it.

I also read many of your other papers. All of your papers contain insults, for example, calling Einstein stupid on repeated occasions.

In "The Problems With Relativity" you do not seem to understand that an observer's perception within their own reference frame does not change. The same observer's perception of another reference frame in relative motion is distorted by an amount given by the equations of relativity. No physical changes take place inside either reference frame, they just appear distorted to each other. Measurements of distorted reference frames will always yield the same speed of light regardless of their relative motion.

Sorry, but claiming that I am just trying to find typos doesn't cut it.