Jupiter and Corot-exo-3b are about the same size, but Corot-exo-3b is much, much more massive. Image Credit: ESA

Dense Exoplanet Creates Classification Calamity

6 Oct , 2008

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Given all the fervor over the definition of Pluto (planet? dwarf planet? snowball?), let’s hope the debate over the discovery of a planet that lies in an equally hazy area of classification is a little calmer. The COROT satellite recently discovered an extrasolar planet named Corot-exo-3b. It’s quite a curiosity as far as exoplanets are concerned, and its characteristics – such as a density twice that of lead – may force astronomers to rethink the distinction between massive planets and low-mass brown dwarfs.

Corot-exo-3b is orbiting close to its star, and takes 4 days and 6 hours to complete one orbit. For comparison, Mercury orbits the Sun every 88 days. It’s also roughly the same size as Jupiter, but far more dense, totaling a whopping 21.6 times Jupiter’s mass. This makes classification of the object a bit tricky.

“COROT-exo-3b might turn out to be a rare object found by sheer luck. But it might just be a member of a new-found family of very massive planets that encircle stars more massive than our Sun. We’re now beginning to think that the more massive the star, the more massive the planet,” said Dr Francois Bouchy, from the Institut d’Astrophysique de Paris (IAP), a member of the team that discovered the object.

Because of its extreme density, Corot-exo-3b lies in the shady area of classification between planet and brown dwarf. Brown dwarfs are massive bodies (between about 13 and 80 times the mass of Jupiter) that don’t make the cut for fusing hydrogen in their cores – and thus don’t shine in optical wavelengths – yet are much more massive that what is normally classified as a planet. Brown dwarfs can fuse deuterium even at lower masses (above 13 Jupiter masses), and lithium in masses above 65 that of Jupiter.

Planets generally form out of a disk of dust and gas that surrounds the early star they orbit, and then are pulled in closer due to friction with the debris that lies in their orbit. The close orbit and very short orbital period of Corot-exo-3b was likely caused by this effect.

The COROT satellite initially discovered the planet by measuring the change in the brightness of the host star as the planet passes in front of it. As the planet moves in front of the star, it slightly darkens the visible light, and then the star brightens once again as the planet moves behind it. The bigger the planet, the more it will darken the light coming from the star. The pull of a planet as it moves around its star can also redshift or blueshift the light coming from the star, and this shift can give information as to the mass of the planet.

Follow-up observations of the planet were done by a collaboration of scientists from around the world, led by Dr. Magali Deleuil from the Laboratoire d’Astrophysique de Marseille (LAM). Their results will be published in the journal Astronomy and Astrophysics.

Author’s note: Due to technical errors in the original posting of this article, the original was removed from UT, but the link may still show up in your feed reader. Be assured that this corrected version is the real, much more accurate one.

Source: ESA


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mandydax
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mandydax
October 6, 2008 9:49 PM

Didn’t I read on here somewhere that planets aren’t able to get much larger volume-wise than Jupiter? The reason is that as more material collects to add to the planet’s mass, it increases the gravity and further compresses the core material. Not until mass sufficient for fusion is achieved is there any force opposing gravity other than the electromagnetic force keeping the individual atoms from fusing, at which point the release of energy from the fusion into the material tends to expand the planet into a star. I think that was how the hypothesis went.

mandydax
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mandydax
October 6, 2008 10:01 PM

Ah, yes! andy commented exactly what I was thinking of over at Bad Astronomy.

pantzov
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pantzov
October 6, 2008 4:22 PM

“…We’re now beginning to think that the more massive the star, the more massive the planet…”

ummm… excuse me? i’m going to go out on a limb and predict that this will be disproven smile

this object is fascinating. there are several things that it could turn out to be. we need to find more of them to conduct further research.

sps
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sps
October 6, 2008 4:41 PM

agreed

Kevin F.
Member
October 6, 2008 4:48 PM

Failed star? Captured neutron star/white dwarf/brown dwarf?

j.h.wegener
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j.h.wegener
October 6, 2008 4:51 PM

Why should planets have much in common at all? Perhaps to discuss “planets” as if it is one sort of object can be compared to label all water animals “fish” or all flying animals “birds”. Perhaps “planets” only have central stars in common?

Jorge
Guest
October 6, 2008 5:09 PM

Well, if we define the upper boundary of “planet” as the mass at which deuterium fusion becomes possible, then there’s little doubt that this object is indeed a brown dwarf.

The only difficulty this poses is to those that think there is a fundamental difference in the way planets and stars form. Since I’ve never bought that one, I’m cool. That object It’s a fascinating brown dwarf, as far as I’m concerned. And I can’t help wondering what kinds of extreme processes would take place deep inside exo-3b. Twice as dense as lead is an average density of the whole BD: deep inside it, density would probably be a LOT larger. The mind boggles.

Peter
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Peter
October 6, 2008 5:23 PM

The article doesn’t mention heat output. Is there an indication of some fusion? What does it appear as in infrared? I think we’ll find a lot of these as we look more closely at known stars. They probably will end up as the “other” type of solar system.

Andrew
Member
Andrew
October 6, 2008 7:33 PM

I doubt that the people observing the planet have found much more information than that presented here.

I’m guessing that the planet in question just happens to have a whole lot more metal in it’s core than Jupiter has, but is otherwise still a gas giant.

cfkin
Member
cfkin
October 6, 2008 8:03 PM

RE: “What does it appear in the infrared?”

With a four day orbital period It’s probably much to close to its star to image with anything we have now.

leafguy
Member
October 6, 2008 9:41 PM

Hmm methinks we could have a rather large solid planet here, likely a huge iron core.

Its possible to be a brown dwarf, but a neutron star is not an option, since an object the size of the earth likely contains more mass than our sun.

Im sticking with huge terrestrial planet, or small brown dwarf

Louis
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Louis
October 7, 2008 7:20 AM

4 days and 6 hours!!! wow!! even faster than Mercury. Is it because it’s in a closer distance or because of the gravitational pull of the star? This is so intriguing!! grin

DestroyAllHumans
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DestroyAllHumans
October 7, 2008 7:26 AM

Why do we assume this thing is a natural object? Other than the fear of being ridiculed by mainstream astronomers who want to keep their jobs, that is.

John Mendenhall
Member
John Mendenhall
October 7, 2008 7:48 AM

Occam’s razor. The chances of it being a natural object are much greater than it being a ‘made’ object, especially since we know of no non-human manufactured objects.. The simplest explanation is probably the correct one.

starman
Member
starman
October 7, 2008 10:26 AM

At twice the density of lead, this is made of Unobtainium.

Dale
Member
Dale
October 7, 2008 10:52 AM

Gas giant planets formed when H and He were still abundant in our solar system. If they grow large enough, they might become a brown dwarf, possibly initiate nuclear fusion. Terrestrial planets like the Earth grew after H and He largely dissipated, which limited their overall mass to what heavy elements (C, O and heavier) were available. If such a terrestrial planet attracted much more of these elements after H and He were gone, its size and gravity would account for the higher density (21 times lead). To me this type of planet is very different from a brown dwarf and could never initiate fusion energy because not sufficient H would be present.

DestroyAllHumans
Guest
DestroyAllHumans
October 7, 2008 11:02 AM

I know it probably is “just” some kind of new planet we haven’t seen before because we have so far to go in our exploration of the Universe.

But I cannot help but retain the feeling that we (or at least astronomers with big scopes0 are staring at artifical objects out there all the time and don’t know it – or are too afraid of ridicule and job loss to even suggest it out loud.

Some day we will grow up, then we’ll be allowed into the Galactic Empire.

Dale
Member
Dale
October 7, 2008 1:30 PM

@DestroyAll. This planet is the size of Jupiter, but 21 times as massive. That’s 6600 Earth masses. Quite an accomplishment for an artificial body.

Heber Rizzo
Guest
October 7, 2008 3:57 PM
What is a planet? A planet, as defined by the International Astronomical Union (IAU), is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals (wikipedia, fine definition). What is a brown dwarf? Brown dwarfs are sub-stellar objects with a mass below that necessary to maintain hydrogen-burning nuclear fusion reactions in their cores, as do stars on the main sequence, but which have fully convective surfaces and interiors, with no chemical differentiation by depth and, in discussion, that have experienced fusion at some point in their history. (again, a good definition in… Read more »
Heber Rizzo
Guest
October 7, 2008 3:59 PM

…and, of course, excuse me for some little mistakes in my writing; English is not my mother language, and it shows, more often than I would like…

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