Classification of extrasolar planets?

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Classification of extrasolar planets?

Post by NuclearVacuum on 4th September 2009, 9:30 pm

I am very knit picky, I love to classify things into categories. I wanted to know if anybody has heard of any attempt to make an official classification system of exoplanets. If there isn't, I think I will introduce my proposal.

For the past year, I have been working on an expanded version of Sudarsky's system. I believe I am close to being done, but recently I have been hitting road blocks. I know I am going to get complains on my classification proposal, but I want your help in perfecting it.

http://nuclearvacuum.wikia.com/wiki/Planetary_classification

Here is the link to my home page. Please check it out and give me your comment.

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Re: Classification of extrasolar planets?

Post by Sirius_Alpha on 5th September 2009, 9:20 am

At quick glance, I am not sure pulsar planets deserve their own category.

Your inclusion of Mercury, Venus, Earth, Mars, and Neptune, are in my opinion, taking the Sudarsky scheme out of context. It's only meant to describe gas planet atmosphere chemistry. Gas planet atmospheres will be quite different from terrestrial planet atmospheres. While I understand that you have a mass-category, it seems to me to sort of break down for sub-Jovians when the Sudarsky scheme is still included.

A water-cloud Jovian and Earth would be given the same numeral, but these planets are vastly different.

Neptunes can either be terrestrial planets (rocky) or jovian planets (gaseous).

Neptune's are believed to be a category of their own, with interior structures dominated by ices. Thus, they're also called "ice giants", just as Jovians are "gas giants" (because their interiors are dominated by gases. A 15 Earth-mass superEarth, though with Neptunian mass, isn't an ice giant, so it's somewhat of a misnomer to throw it in with the "Neptunes" category.

Besides, cores that accrete this much mass usually go on to be gas giants early on in the formation of the solar system. Ice giants seem to form later.

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Re: Classification of extrasolar planets?

Post by NuclearVacuum on 5th September 2009, 10:31 am

Hm... I am so confused. I've always though of the Sudarsky system as more of a temperature measurement over atmospheric composition. I know the atmosphere of a class II planet would differ greatly from Earth, but I consider them similar on the ideals of orbital position of their parent star.

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Re: Classification of extrasolar planets?

Post by Lazarus on 5th September 2009, 6:33 pm

Sulphuric acid clouds don't really work for a gas giant.

Terrestrial planets are oxygen-rich, gas giants are hydrogen rich. Sulphur in gas giants tends to be in compounds based on hydrogen sulphide (e.g. the ammonium hydrogen sulphide cloud deck of Jupiter), rather than compounds based on sulphur dioxide (e.g. sulphuric acid, like the clouds of Venus).

I have no idea why the concept of a gas giant covered in sulphuric acid clouds is such a popular one, but the reasoning behind the concept is flawed. The atmosphere of Venus is nothing like the atmosphere of a gas giant.
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Re: Classification of extrasolar planets?

Post by Stalker on 6th September 2009, 6:11 am

I said that hot jupiters also has spectral classes as stars, but with "p" behind (Mp, Lp may be Tp and Yp).This can be interessant for you.

When in the classification of Sudarsky, I find that it is exceeded by observations.
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Re: Classification of extrasolar planets?

Post by Lazarus on 6th September 2009, 7:18 am

Well it doesn't seem that Sudarsky is too useful for the hot Jupiters. The evidence suggests that hot Jupiters have extremely low albedos, the classification pM/pL divides planets with stratospheres (that are inefficient at redistributing heat to the dark side of the planet) and planets without them (with hot night sides)...

Unfortunately we don't have many windows into what goes on between 1000K and 150K... the T/Y transition hasn't yet been conclusively identified.
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Re: Classification of extrasolar planets?

Post by NuclearVacuum on 6th September 2009, 10:25 am

Lazarus wrote:Sulphuric acid clouds don't really work for a gas giant.

Terrestrial planets are oxygen-rich, gas giants are hydrogen rich. Sulphur in gas giants tends to be in compounds based on hydrogen sulphide (e.g. the ammonium hydrogen sulphide cloud deck of Jupiter), rather than compounds based on sulphur dioxide (e.g. sulphuric acid, like the clouds of Venus).

I have no idea why the concept of a gas giant covered in sulphuric acid clouds is such a popular one, but the reasoning behind the concept is flawed. The atmosphere of Venus is nothing like the atmosphere of a gas giant.

Maybe you can blame me for that. Venus is my favorite planet of them all, and when I read about sulfur giants, I fell in love with them. Plus the fact that I hate change, so its going to be a long time before I can think of them as impossible.

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Re: Classification of extrasolar planets?

Post by NuclearVacuum on 6th September 2009, 10:27 am

Stalker wrote:I said that hot jupiters also has spectral classes as stars, but with "p" behind (Mp, Lp may be Tp and Yp).This can be interessant for you.

When in the classification of Sudarsky, I find that it is exceeded by observations.

That actually seems like a really good idea. But since we currently can't see the spectrum of an exoplanet, this idea seems to be for future understandings. I am trying to make a system that can explain planets by what we already know.

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Re: Classification of extrasolar planets?

Post by Sirius_Alpha on 6th September 2009, 10:39 am

Yeah, and not to mention Venus (at least in some wavelengths) looks like a gas planet in appearance. But alas, it's very different. I'm sure a few gas planets out there really do look like Venus. Saturn's not too far away. Though both differ dramatically in chemistry of course.

Ultimately, I think that chemistry is the key to any planetary classification scheme for gas planets. This will mean that we won't be for sure what sorts of planets we're observing until we obtain spectra. For terrestrial planets, the issue will probably be very convoluted, for terrestrial planets will probably be extremely diverse and will probably fit more on a continuum than a classification scheme. Maybe once terrestrial exoplanet spectra are gained frequently enough, some patterns will emerge.


Stalker wrote:That actually seems like a really good idea. But since we currently can't see the spectrum of an exoplanet, this idea seems to be for future understandings. I am trying to make a system that can explain planets by what we already know.

If I recall correctly, we only have spectra for HD 209458 b and HD 189733 b. Aside from the obvious abundance of H and He, there's...

HD 209458 b atmosphere:
Sodium (2001), oxygen (2004), carbon (2004), water vapour (2007).

HD 189733 b atmosphere:
Sodium (2007), haze (2007), Methane (2008), Water vapour (2008), Carbon dioxide (2008), Carbon Monoxide (2008)

(If I am missing anything please tell me!)

So we can see that these two planets are quite different at least as far as what has been detected so far. Not really a lot of information on which to build much of a classification scheme.

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Re: Classification of extrasolar planets?

Post by NuclearVacuum on 6th September 2009, 12:43 pm

Wait, they know what the atmosphere is made of? I knew they found atmospheres, but I had no idea they knew what they had in them. Wow!

But anyway, this still complies with my earlier statement. We only know 2 planets (out of the over 300). I'm not good with percentages, but that would be something like we could have a spectral classification on 1% of the planets. I was referring to the ideal of making a system on the information known on every planet (mass and distance for example).

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Re: Classification of extrasolar planets?

Post by Lazarus on 6th September 2009, 1:58 pm

One question to ask is whether any classifications naturally emerge out of the observations... the pM/pL split for hot Jupiters has already been mentioned.

Looking at the plot for radial-velocity planets of log mass against log period, it seems there are two main "clumps": one centred at roughly 3 days, one at >200 days. Roughly speaking these are the hot Jupiters and the eccentric Jupiters. Interestingly, the low mass tail of the hot Jupiters (extending down to the hot Neptunes) stays to the long period side of 2 days. Intermediate period Jupiters are rare.

There are other indications of distinct populations in the known extrasolar planets as well. Rossiter-McLaughlin effect measurements suggest two groups of hot Jupiters: the more common ones with very low inclinations to the stellar equator, and a second, randomly oriented population.

(incidentally Fomalhaut b is probably quite a warm planet thanks to internal heating - it doesn't really fall into the Neptune-like temperature regime)
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Re: Classification of extrasolar planets?

Post by NuclearVacuum on 6th September 2009, 6:00 pm

Has anybody really coined the term "cold Jupiter" before. Because I have been thinking of a new classification that could include hot planets (short, close, and hot orbits) and cold planets (long, far, and cold orbits). Simple and easy to remember. Razz

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Re: Classification of extrasolar planets?

Post by Stalker on 7th September 2009, 2:10 am

I have a question: have the planets of type Neptune the same characteristics as Jupiters of the same temperature?
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Re: Classification of extrasolar planets?

Post by Sirius_Alpha on 7th September 2009, 7:59 am

I would suspect that the answer is "no" due to their slightly different atmospheric compositions (assuming Uranus and Neptune are typical of such worlds). Eager to see Gliese 436 b's spectrum Smile

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