Transiting rocky planet detected

[Kullat Nunu]

ESA: COROT discovers smallest exoplanet yet, with a surface to walk on (http://www.esa.int/esaCP/SEM7G6XPXPF_index_0.html)

About 330 exoplanets have been discovered so far, most of which are gas giants with characteristics similar to Jupiter and Neptune.

The new find, COROT-Exo-7b, is different: its diameter is less than twice that of Earth and it orbits its star once every 20 hours. It is located very close to its parent star, and has a high temperature, between 1000 and 1500°C. Astronomers detected the new planet as it transited its parent star, dimming the light from the star as it passed in front of it.

So it is extremely hot, but terrestrial. Or a hot ocean planet. But definitely not a gas giant.

[Ilya]

A "super-Mercury"?

[NEOWatcher]

"Surface to walk on" is definitely a stretch, but at least they didn't go down the normal "Earthlike" or "Super Earth" route.

They compare the findings with the majority gas giant discoveries, but how does it compare with the more recent smaller rocky planets? Is the determination of the size the big story here?

And once again, scientists are puzzled. No, puzzled means that there's enough data to contradict previous findings. It does not mean they don't know yet.

[Kullat Nunu]

"Surface to walk on" is definitely a stretch, but at least they didn't go down the normal "Earthlike" or "Super Earth" route.

Well, it is a super-Earth... :eh:

They compare the findings with the majority gas giant discoveries, but how does it compare with the more recent smaller rocky planets? Is the determination of the size the big story here?

Well, it could have been a very low-massive hot Neptune. The biggest news (or actually not news for those who have listened the rumors) is that finally an exoplanet that is not a gas giant has been detected using the transit method.

[Tom Mazanec]

Could it be chthonian?

[NEOWatcher]

Well, it is a super-Earth... :eh:
Based on what? Is there even an accepted definition?

My criteria is as follows:
To be considered an x-Earth, the exoplanet must have more in common to Earth than it does with other planets in our solar system based on what we can determine from that planet.

In this case, there seems to be plenty of planets that have more in common to the discovery than our own.

Well, it could have been a very low-massive hot Neptune.
Thus; reinforcing my definition. ;)

The biggest news (or actually not news for those who have listened the rumors) is that finally an exoplanet that is not a gas giant has been detected using the transit method.
Ok; that's what I was wondering. So, even though this is not the first rocky planet, it is the first using transit?

[Kullat Nunu]

I am totally fed up with planetary definitions... People call super-Earths planets that are more massive than the Earth but lack the thick gaseous envelope that hot Neptunes have. And yes, it is the first transiting terrestrial exoplanet. Or it could be a so-called ocean planet, or a core of Neptune-type ice giant with considerable amount of water and ice. Some planets, like the pulsar planets of PSR1257+12 and the couple microlensing planets have almost certainly hard surfaces, but we don't know how big in size they actually are.

[timb]

I am totally fed up with planetary definitions... People call super-Earths planets that are more massive than the Earth but lack the thick gaseous envelope that hot Neptunes have.


Actually the term is routinely used for any exoplanet whose minimum mass is less than 10 Earths. That leads to cynicism.


And yes, it is the first transiting terrestrial exoplanet. Or it could be a so-called ocean planet, or a core of Neptune-type ice giant with considerable amount of water and ice. Some planets, like the pulsar planets of PSR1257+12 and the couple microlensing planets have almost certainly hard surfaces, but we don't know how big in size they actually are.

I doubt that this (http://exoplanet.eu/planet.php?p1=CoRoT-Exo-7&p2=b) is any sort of ocean or ice world. Using a rough luminosity of 0.6 for the K0 host the irradiance is about 2,000 S giving a blackbody temperature of about 1675K. The mass is reported as 11 ME. The radius reported on exoplanet.eu (0.13 RJ) is smaller than that reported in the Exoplanets mailing list (1.75-2 RE). Either way the planet is considerably denser than Earth. A body with a substantial water content would not be so dense and would probably have evaporated.

[timb]

Comparing this planet's mass and radius with the Fig.4 and Fig.5 curves in MASS-RADIUS RELATIONSHIPS FOR SOLID EXOPLANETS (arXiv:0707:2895), the 1.75-2 RE figure is consistent with an Earth-like composition or even a planet with about 20% water and a larger iron core than Earth, while the 0.13 RJ figure is consistent with a solid iron planet. These curves are for a "cold" planet. If this planet had an external water layer it would surely have a thick steam atmosphere which would expand the transit radius.

[Manchurian Taikonaut]

With all that de-classification of Pluto in 2006 I was wondering why doesn't NASA start a planetary rating system like you see in Star Trek movies. Fox and other news groups were running stories about Corot bagging an "Earth-Like Planet" (http://www.foxnews.com/story/0,2933,487485,00.html). If we had a CaptainKirk style rating system, M-class, class-D etc wouldn't this avoid much of the confusion?

[NEOWatcher]

With all that de-classification of Pluto in 2006 I was wondering why doesn't NASA start a planetary rating system like you see in Star Trek movies.
Even if they did, how much pull does NASA really have on the research being done? I have no clue, but I would imagine the IAU has a much bigger representation of planetary research definitions than NASA.

Fox and other news groups were running stories about Corot bagging an "Earth-Like Planet" (http://www.foxnews.com/story/0,2933,487485,00.html).
Some of it is the wording of the press release from the research, then magnified by the news groups.
Researchers want to make thier story interesting with some catch phrase or attempt at sounding like normal folk, then the media runs with it.
If we had a CaptainKirk style rating system, M-class, class-D etc wouldn't this avoid much of the confusion?
I agree a rating system would be good, but the general public would just say "what does that mean?"
It would give the media a way go come up with a standard filler chart that they can pull out of a drawer to go along with a story.

[timb]

Fox and other news groups were running stories about Corot bagging an "Earth-Like Planet" (http://www.foxnews.com/story/0,2933,487485,00.html).

"The claim that it is the 'smallest exoplanet' found to date is not correct," said planet-formation theorist Alan Boss of the Carnegie Institution of Washington. "It is the smallest mass exoplanet found to date that transits, but other hot super-Earths have been found that do not transit but have lower masses."

Odd that a "planet-formation theorist" doesn't know the difference between size and mass.

The internal structure of COROT-Exo-7b particularly puzzles scientists, as they are unsure whether it is an "ocean planet," a kind of planet whose existence has never been proved so far.

In theory, such planets would initially be covered partially in ice, and they would later drift toward their star, with the ice melting to cover it in liquid.

I wonder if these "scientists" have heard of the critical temperature (http://en.wikipedia.org/wiki/Critical_temperature)? There would be no liquid water on a planet with a temperature over 1000˚C.

[Drunk Vegan]

If we had a CaptainKirk style rating system, M-class, class-D etc wouldn't this avoid much of the confusion?

I agree a rating system would be good, but the general public would just say "what does that mean?"
It would give the media a way go come up with a standard filler chart that they can pull out of a drawer to go along with a story.

I'm sure that could be easily handled by just entering it like:

"The newly discovered planet, a Class M, orbits a star 457 lightyears from Earth. Class M indicates a planet with a temperature above 1000 degrees, orbiting at the distance that Mercury orbits our own sun, or closer."

And just give the planet in our own solar system that is the closest analogue for reference. So a Class V for Venus-type planet, one with a high greenhouse effect. Class M for Mercury, close in and hot. Class J for Jovian, etc.

This would also encourage the people producing these titles to not be so lazy with the headlines, since there would be 9 different classifications, including moons, 10, including dwarf planets.

I think the problem is the ignorance of the reporters - the only two types of planets they are aware of, it appears, is "gas giant" and "Earthlike."

[timb]

And just give the planet in our own solar system that is the closest analogue for reference. So a Class V for Venus-type planet, one with a high greenhouse effect. Class M for Mercury, close in and hot. Class J for Jovian, etc.

This would also encourage the people producing these titles to not be so lazy with the headlines, since there would be 9 different classifications, including moons, 10, inc...

Your proposal is anthropocentric, and would provide inadequate categories to describe the known exoplanets and would be unable to accommodate cases where we lack knowledge. Hot Jupiters are a class that does not exist in the solar system (to describe them as either Mercury analogs or Jupiter analogs is clearly inadequate). Similarly warm Jupiters, hot Neptunes etc. What do you call a 10 ME planet of unknown radius and composition in an Earth-like orbit? OTOH why are separate categories needed for Neptune-like and Uranus-like planets?

I suggest a three symbol code, with the first symbol coding the irradiance equivalent distance from the host, the second the mass, and the third the type/composition. I ordered the symbols in that way because if we know anything about an exoplanet it is the orbit, then we constrain the mass, and finally we may discover something about its type. Here are some rough bounds for the semi-major axis categories (which are really blackbody temperature categories).


Category Bound Notes
Very hot <0.1AU
Hot <0.7AU
warm <1.5AU a generous HZ
cool <2.7AU bounded by the snowline
cold <30AU
very cold >30AU maybe redundant


For mass the solar planets provide better coverage than for temperature:


superjovian >2 MJ
jovian >0.5 MJ
saturnian >50 ME
neptunian >10 ME
superearth >2 ME
terran >0.3 ME
martian >0.03 ME
submartian <0.03 ME


Composition could be classified as


gas Jupiter, Saturn
gas-ice Neptune, Uranus
ice-rock Ganymede, hypothetical ocean planets
rock Earth etc


though that's not really adequate. You'd probably want different subcategories of ice-rock and rock to describe the atmosphere, or maybe a fourth symbol.

You could attempt to condense all the information into one symbol, but with only six orbit categories, eight mass and four composition categories (almost certainly inadequate), you would need 192 different symbols, and you'd need extra symbols for the under-determined cases.

[NEOWatcher]

I'm sure that could be easily handled by just entering it like:
Yes, that was intent of the "pull out of the drawer chart" comment. The reporter doesn't need to understand what it is, but can just print the chart, or one entry from the chart.
I think the problem is the ignorance of the reporters - the only two types of planets they are aware of, it appears, is "gas giant" and "Earthlike."
Yes; ignorance partly due to lazyness. Why try to dig to find out what it means when you can just highlight a quote to get the headline?

I can see from the discussion that agreeing on a classification method looks to be a bigger problem than Pluto.

[Eckelston]

With all that de-classification of Pluto in 2006 I was wondering why doesn't NASA start a planetary rating system like you see in Star Trek movies. Fox and other news groups were running stories about Corot bagging an "Earth-Like Planet" (http://www.foxnews.com/story/0,2933,487485,00.html). If we had a CaptainKirk style rating system, M-class, class-D etc wouldn't this avoid much of the confusion?

A good classification system relies on a good understanding of the underlying population. Otherwise you run the risk of putting similar objects into different categories or worse: fundamentally different ones into the same one. This is fine of course if you are willing to tweak or completely redesign your system as you learn more about the population but that didn't work out too well with solar system objects.

[Fiery Phoenix]

I hope the IAU has read this thread!

[timb]

A good classification system relies on a good understanding of the underlying population. Otherwise you run the risk of putting similar objects into different categories or worse: fundamentally different ones into the same one. This is fine of course if you are willing to tweak or completely redesign your system as you learn more about the population but that didn't work out too well with solar system objects.

The population is fairly well understood in terms of mass, radius and orbital parameters. We're pretty sure we know what planets can be made of too (rock, ice, gasses, honest-to-god metals). A system based on placing the planet into broad categories on each of these axes (with a narrower category in each corresponding to earth-like worlds) should be fairly robust. This could be represented as a numerical code. Earth would be a "364", in terms of categories I floated.

[KaiYeves]

"The newly discovered planet, a Class M, orbits a star 457 lightyears from Earth. Class M indicates a planet with a temperature above 1000 degrees, orbiting at the distance that Mercury orbits our own sun, or closer."

And just give the planet in our own solar system that is the closest analogue for reference. So a Class V for Venus-type planet, one with a high greenhouse effect. Class M for Mercury, close in and hot. Class J for Jovian, etc.
But if worlds like Mercury are class M, what would the code for planets like Mars be? Class A for Ares?

[Eckelston]

The population is fairly well understood in terms of mass, radius and orbital parameters.

By population I mean the population of all extrasolar planets not just the ones that have been discovered so far. And that population is by no means well understood. All we have is a tiny and extremely biased sample.

We're pretty sure we know what planets can be made of too (rock, ice, gasses, honest-to-god metals).

Or a combination of these, like Earth. Which combinations are allowed, which ones are common or rare is not well understood, as far as I know. Same goes for most other characteristics.

A system based on placing the planet into broad categories on each of these axes [...] should be fairly robust. This could be represented as a numerical code. Earth would be a "364", in terms of categories I floated.

This sounds like a grid to me. Sure, you can cover any parameter space with this but I still don't see how this improves understanding or organizes our knowledge efficiently.

[Kullat Nunu]

I hope the IAU has read this thread!

Eh, we didn't have enough planet definition threads already? Looks like we have now an analogue of Godwin's Law in astronomy. Every thread turns at some point into a "What is a planet?" argument.

[eburacum45]

A three-part classification system sounds very sensible to me. Your three parameters would be mass, composition, and temperature.

The composition parameter would probably be the most variable, encompassing gas giants, gas and ice worlds with a range of different possible ices; mantle-rich worlds with a range of possible mantle materials, and metal-rich core worlds (and admixtures between all these classes).

I think this is the way forward; a tri-partite naming system should work for most purposes. I've been struggling towards such a tri-partite taxonomy recently, adapting John Dollan's science-fictional Planet Classification List so that it has three distinct categories, as shown here, an attempt to divide gas giants up into separate categories
http://eg.orionsarm.com/xcms.php?r=oaeg-view-article&egart_uid=4682f9dc86875
A typical gas giant may be classified using both size and temperature types to create a subtype, so the full classification might be Meso-EuJovian Subtype(This is the full classification for Jupiter) or Meso-HyperthermalJovian Subtype (the full classification for Hat-P-1B)

[eburacum45]

Eh, we didn't have enough planet definition threads already? Looks like we have now an analogue of Godwin's Law in astronomy. Every thread turns at some point into a "What is a planet?" argument. Well, I think we are talking more about a detailed taxonomy here, making fine distinctions between various observed and hypothetical exoplanets. One day (hopefully) such a system could be both necessary and an interesting field of study in its own right.

[timb]

This sounds like a grid to me. Sure, you can cover any parameter space with this but I still don't see how this improves understanding or organizes our knowledge efficiently.

It doesn't do either. The proposal was for a system for compactly naming what sort of planet a planet was.

[timb]

A three-part classification system sounds very sensible to me. Your three parameters would be mass, composition, and temperature.


The radius parameter is not practically redundant, because typically we will know it well before we know the composition. In fact the composition will most commonly be a guess informed by the mass and radius. So I don't think it is safe to omit it. Even when mass, composition, and temperature are known the radius could vary, eg with age. Young gas giants contract considerably. There's also a distinction to be made between true temperature, which at the moment we rarely know, and temperature inferred from irradiance.

The composition parameter would probably be the most variable, encompassing gas giants, gas and ice worlds with a range of different possible ices; mantle-rich worlds with a range of possible mantle materials, and metal-rich core worlds (and admixtures between all these classes).


Most of these distinctions will be unobservable for a long time. For now the most remote observations give us is mass, radius, temperature, and maybe some idea of what the outermost layer is made of, and usually less. Later we will be able to tell whether a planet has an optically thick or thin atmosphere, and later still make out something of the surface features. Once a planet has more than two major components there's no way to determine their ratios from these measurements. For example, if a planet with a known mass and radius has a metal core, a rock inner mantle and an ice outer mantle, you can produce the same parameters by, for example, compositions that are mostly rock and ones that are mostly metal and ice.


I think this is the way forward; a tri-partite naming system should work for most purposes. I've been struggling towards such a tri-partite taxonomy recently, adapting John Dollan's science-fictional Planet Classification List so that it has three distinct categories, as shown here, an attempt to divide gas giants up into separate categories
http://eg.orionsarm.com/xcms.php?r=oaeg-view-article&egart_uid=4682f9dc86875

You seem to contradict yourself by first saying gas giants are from 0.2 MJ to 13 MJ, and then considering gas giants as small as 0.03 MJ. I think that Neptune-like planets could be considered separately as ice giants, given that they are only about 15% "gas" and mostly "ice" (quoted words in the astronomical sense). They are much denser than "gas" dominated bodies of the same mass (cf Neptune and Saturn). You've also got the problem of what to call large core gas giants that could be more than 50% "metals" (some hot jupiters may be in this class).

Your temperature classes roughly correspond to mine, so I generally agree with them. :) Tying them to their implications for the atmosphere of a Jupiter-analog is interesting but problematic. Will you have a different set of temperature bands for Venus-like planets, Earth-like planets, Neptune-like planets etc? they all have different atmospheres which would respond to different irradiances in different ways. That would seem very complex and ad hoc. My preference was to base the levels on points of general astrophysical, exobiological or distributional interest. Such as the snow line, the limits of the HZ for an earth-like planet, and the cluster of planets in "hot" orbits.

[eburacum45]

You seem to contradict yourself by first saying gas giants are from 0.2 MJ to 13 MJ, and then considering gas giants as small as 0.03 MJ. The smaller ones might be better described as 'gas dwarfs' or 'gaseous terrestrials'. I think such objects might exist, although there are none in our system. Planets almost entirely made of hydrogen and helium, but with terrestrial mass, might exist, especially around very metal poor stars. Other gases may also be possible- like the speculative CO planets discussed recently. I think that Neptune-like planets could be considered separately as ice giants, given that they are only about 15% "gas" and mostly "ice" (quoted words in the astronomical sense). Yes; a sensible suggestion. On the other hand, some planets in this mass range might have little water or comparable ices, so would have interiors more closely resembling Jupiter- with liquid and metallic hydrogen layers instead. Would they count as ice giants?

[timb]

The smaller ones might be better described as 'gas dwarfs' or 'gaseous terrestrials'. I think such objects might exist, although there are none in our system. Planets almost entirely made of hydrogen and helium, but with terrestrial mass, might exist, especially around very metal poor stars. Other gases may also be possible- like the speculative CO planets discussed recently. Yes; a sensible suggestion. On the other hand, some planets in this mass range might have little water or comparable ices, so would have interiors more closely resembling Jupiter- with liquid and metallic hydrogen layers instead. Would they count as ice giants?

No, they wouldn't. Gas dwarves? Gas subgiants? Personally I'm sick of this dwarf/giant terminology and hence my suggestion of mass bands labelled with numbers. Current formation theories predict a core of at least 10 ME so very small gas planets shouldn't exist because pure gas needs to be much more massive than that to collapse from a disk into a planet (around 7 MJ, from memory). I wouldn't worry too much about accomodating speculative planets and planets which currently accepted theories say shouldn't exist. If you have categories that provide full coverage for each dimension (mass, size etc) then there will always be a slot for a new planet, however strange it may be. Individual planets may have their peculiarities that aren't adequately described by the classification system, but the point of the system isn't to precisely describe every conceivable planet but to provide a quick characterization of the great majority of planets.

[eburacum45]

Well, one category that you might usefully add to your composition list is 'core'; once we start seeing transits of terrestrial planets in detail we might be able to distinguish planets with high core fractions.

The fine details of composition will probably need close-up examination- but very large telescope arrays should tell us a lot beforehand. I think we might be in for some surpises- I remember how bizarre and diverse the moons of Jupiter seemed when they were first imaged. Before Voyager, no-one knew how diverse these worlds could be.
Looking at the table of cosmic abundances of elements, we can see that neon is a very common element, and so is magnesium. Carbon monoxide is more common as a compound in the universe than water. Should we expect to see these compounds and elements in more abundance in other systems? Some of them. perhaps. But labelling them as 'ice' or 'rock' or 'core' will do for observations at a distance.

[timb]

Well, one category that you might usefully add to your composition list is 'core'; once we start seeing transits of terrestrial planets in detail we might be able to distinguish planets with high core fractions.

The fine details of composition will probably need close-up examination- but very large telescope arrays should tell us a lot beforehand. I think we might be in for some surpises- I remember how bizarre and diverse the moons of Jupiter seemed when they were first imaged. Before Voyager, no-one knew how diverse these worlds could be.
Looking at the table of cosmic abundances of elements, we can see that neon is a very common element, and so is magnesium. Carbon monoxide is more common as a compound in the universe than water. Should we expect to see these compounds and elements in more abundance in other systems? Some of them. perhaps. But labelling them as 'ice' or 'rock' or 'core' will do for observations at a distance.

Neon and CO both have much lower boiling points than water, and I don't believe that CO is more common than water.

[eburacum45]

If all planetary systems have roughly the same composition as ours, then yes, water will be much more common than CO, but as an interstellar molecule, CO seems to be more common than water.
From here
http://www.astronomynotes.com/ismnotes/s3.htm
Different types of atoms can combine in the coldest regions of space (around 10 K) to make molecules. The cold molecules are detected in the radio band. Most of the molecules are hydrogen molecules (H2) and carbon monoxide (CO).

So far, water has been detected in the atmospheres of several exoplanets, - this is not true of carbon monoxide, so probably CO is less common in planetary systems. I think we might have to look for special cases to see planets with high CO components- for instance systems which have formed from clouds with lots of CO.

Neon is another problem; I would expect it to boil off less easily than helium, so it should be present in gas giants at approximately the cosmic abundance- but in our system it isn't. Any world that has enough gravity to retain helium should retain neon- that may mean that in other systems neon is more common, and we are an exception, or it may mean that all systems lose neon by the same process.

[timb]

If all planetary systems have roughly the same composition as ours, then yes, water will be much more common than CO, but as an interstellar molecule, CO seems to be more common than water.
From here
http://www.astronomynotes.com/ismnotes/s3.htm



What you quoted does not imply that carbon monoxide is more common than water. Why would prevalance in the interstellar medium be of relevance to planet formation? The conditions of planet formation are much hotter and denser. If you are sure there are planets made of almost pure carbon monoxide or neon, go ahead and include them as special categories in your classification scheme. I wouldn't want to be associated with it.

[eburacum45]

I'm not sure that either exist at all. However the possibility of CO planets was discussed in a previous thread, mostly because of an article in New Scientist which mentions them.
image here
http://space.newscientist.com/data/images/ns/cms/dn12685/dn12685-2_600.jpg
They would seem to resemble waterworlds more than gas giants in density, so in the astronomical jargon CO would probably count as an 'ice' rather than a gas.

Do pure CO worlds exist? I don't know. Neon worlds seem even less likely. Something seems to have removed neon from our solar system during formation; that might happen everywhere (or it might not).

As an aside, the astronomical terms 'gas, ice, and rock' are described on this page
http://space.y2u.co.uk/Astronomy_Gas_Giant_Planet.htm
The rather misleading term has caught on because planetary scientists typically use 'rock', 'gas', and 'ice' as shorthands for classes of elements and compounds commonly found as planetary constituents, irrespective of what phase they appear in. In the outer solar system, hydrogen and helium are "gases"; water, methane, and ammonia are "ices"; and silicates are rock. When deep planetary interiors are considered, it may not be far off to say that, by "ice" astronomers mean oxygen and carbon, by "rock" they mean silicon, and by "gas" they mean hydrogen and helium. I would add that the term 'core' is also used to distinguish the heavy, iron-rich cores of worlds like Earth and Mercury, and planets with large cores could theoretically be noticeably denser than planets with small or absent cores.

Note as well that the term 'rock' tends to be used for silicates in our system - however magnesium is almost as abundant on a cosmic scale as silicon, so magnesium minerals (olivine, for instance) could make up a large portion of many worlds out there (olivine contains silicon too, of course).

[timb]

I'm not sure that either exist at all. However the possibility of CO planets was discussed in a previous thread, mostly because of an article in New Scientist which mentions them.
image here
http://space.newscientist.com/data/images/ns/cms/dn12685/dn12685-2_600.jpg
They would seem to resemble waterworlds more than gas giants in density, so in the astronomical jargon CO would probably count as an 'ice' rather than a gas.


Obviously CO is an ice. So are CO2 and cyanogen. Any simple chemical made from any two of H, C, O and N is an ice in this context as far as I am concerned.


Do pure CO worlds exist? I don't know. Neon worlds seem even less likely. Something seems to have removed neon from our solar system during formation; that might happen everywhere (or it might not).

As an aside, the astronomical terms 'gas, ice, and rock' are described on this page
http://space.y2u.co.uk/Astronomy_Gas_Giant_Planet.htm
I would add that the term 'core' is also used to distinguish the heavy, iron-rich cores of worlds like Earth and Mercury, and planets with large cores could theoretically be noticeably denser than planets with small or absent cores.


True. You can also see "metal" used for this, which is slightly confusing because metal has already been (mis)used in another sense by astronomers.

Note as well that the term 'rock' tends to be used for silicates in our system - however magnesium is almost as abundant on a cosmic scale as silicon, so magnesium minerals (olivine, for instance) could make up a large portion of many worlds out there (olivine contains silicon too, of course).

There's no shortage of dolomite, magnesite, brucite, carnallite, talc, and olivine in the Earth's crust and they are universally regarded as "rock". Magnesium is a large-ish proportion of the mass of the Earth.

[Tom Mazanec]

Bump.
I will repeat my question of Feb 3. Is this a chthonian planet? Can I at least get a yes, no or maybe?

[eburacum45]

There have been a couple of different estimates for radius, so far, ranging from 9300km (approx) to 12700 km (approx). If the smaller figure is correct (and assuming the mass estimate is correct too) then this is a very debse planet, dense enough to be a chthonian world, a former gas giant with its atmosphere stripped away..
http://en.wikipedia.org/wiki/Chthonian_planet
But it might not be hot enough to be such a world, so perhaps for some reason it simply formed with very little atmosphere.

The most commonly quoted radius is approx 10800 km; that is not quite so dense, so the planet might have quite a respectable atmosphere and/or shell of water-ice.

[timb]

Bump.
I will repeat my question of Feb 3. Is this a chthonian planet? Can I at least get a yes, no or maybe?

If you studied you might be able to contribute yourself, one day.

[Tom Mazanec]

I have an OLD BS in astronomy (1980). I occasionally answer a question if I see one I can answer. But true aastronomers are on this board (at least better than me) and I do prefer to learn here. I hope that my questions are at least interesting.

[eburacum45]

Just to clarify- I'm certainly not an astronomer, this is just a hobby for me. Anything I say should be treated as the mutterings of an interested layman.

[Christopher Ferro]

I never heard of chthonian planets. I don't even know how to pronouce the word "chthonian." It looks very Star Trek alien-ish to me.

CJSF

[eburacum45]

Actually it is from the ancient Greek; chthonian means "of the earth", with a subtext of "out of hell". These hypothetical planets are very hot and supposedly have very high gravities, making them hellish places indeed.

COROT-Exo-7b is hot, but to be honest I'd expect a real chthonian world to be hotter still.

I don't know if I'm right or not, but I pronounce the word "ker-thown-ian". I've asked my wife, who studied greek for a while, and she thinks that's not too far off.