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View Full Version : The popular artistic depictions of hot planets



m1omg
2010-Nov-06, 11:51 AM
Why are hot planets, for example the well known Hot Jupiters, almost always depicted like Jupiter with a faint dark reddish glow? Even the colder ones are already as hot as glowing embers in a fire, the average ones are as hot as a candle flame (1100 degrees Celsius) and the hottest ones are hotter than a blast furnace or a propane torch, having the temperatures more close to that of a cooler incandescent light bulb filament (around 2000 degrees Celsius) or an M class star for example http://en.wikipedia.org/wiki/WASP-12b or http://en.wikipedia.org/wiki/HD_149026_b , and consider that just a few kilometers below the surface the heat will get much worse.

Depictions like this http://en.wikipedia.org/wiki/File:HD149026b_nasa.jpg or http://upload.wikimedia.org/wikipedia/commons/e/ef/51_Pegasi_b_v3.jpg are not accurate. These planets look more like some embers at 700 degrees than 1500-2000 degrees. A planet that is the same temperature as L-M class star is not going to look like a faint ember, it is going to look like an L-M class star. Even a common hot Jupiter is going to glow bright reddish/yellowish white, just like a candle flame or molten iron in a blast furnace does. Yes, many Hot Jupiters were measured to be dark. Dark as in, absorbing radiation, not being black. They are going to glow brightly from the heat they recieve + internal heat, and there is also the reflected light. Even at almost zero albedo, HD 149026 b still recieves around 1500x as much sunlight as Earth and its star is going to look 30x as bigger on the sky as our Sun from the Earth ( I used http://web.archive.org/web/20030218125318/www.geocities.com/Area51/Corridor/8611/mseqstar.htm to calculate this), so even if the planet reflected 99 percent of the light into space it is still going to be blindingly bright, it is not going to just absorb everything, and even if it did, it would be white hot at these temperatures from radiated light.

2000 degrees is "red" only from light year distances, remember, even a light bulb is whitish even through it is much smaller than a hot Jupiter.

So, the proper depiction of a hot Jupiter would be basically - like a ball of flames travelling at supersonic speeds for common hot Jupiter on the nightside, like a incandescent bulb on the nightside for hottest Jupiters, and blindingly bright on the dayside, this is probably the closest depiction to this that I've seen http://www.oklo.org/wp-content/images/hd149026b.gif , it also comes with a nice article on this topic http://oklo.org/2005/12/05/i-wear-my-sunglasses-at-night/ an excerpt "The dayside, blindingly illuminated by the scorching proximity of the star, is roughly 500 times brighter than desert sand dunes on a midsummer day. In order to look at the illuminated side of the planet at all, you need extremely dark wraparound sunglasses, or better yet, an eyeshield made from #10 welders glass (where #14 welder’s glass is recommended for those who stare at the sun).". Even here, the darkside is still a bit too faint IMHO, considering it is still going to be as hot in many cases as a candle or even a natural gas flame.

The commonly depicted Jupiter cloud bands are unrealistic too IMHO. It is safe to assume that any hot Jupiter around a F-M class star is going to be tidally locked, so the atmospheric circulation is probably going to look more lke this http://www.extrasolar.net/planettour.asp?StarCatId=&PlanetId=3 http://www.universetoday.com/76303/the-strange-warm-spot-of-upsilon-andromedae-b/ http://www.sciencedaily.com/releases/2007/05/070509145605.htm .

In other words, in my opinion, depicting hot Jupiters looking like they are colder than a T class brown dwarf is misleading.

Also, wouldn't very hot Jupiters have plasma even on their "surfaces" or at least a few km below? Considering that the material ion the surface of a "cool" M class is already plasma, wouldn't it mean that really hot Jupiters would have granulation, eruptions etc.?

eburacum45
2010-Nov-06, 01:23 PM
The Oklo image http://www.oklo.org/wp-content/images/hd149026b.gif is probably very realistic, if you could adjust your vision so that details can be seen on the 'dark' side. However if you were to adjust your vision so that details could be seen on the day side (by using very dark goggles, say), then the night side would look quite dim. It is all a matter of contrast.

The Oklo image is also good because it shows a realistic pattern of circulation. Even though these planets are tidally locked, they do rotate quite rapidly for their size because of the shortness of their year. So their atmospheres will be turbulent, slightly banded and very chaotic, not just with a simple hot-spot as shown in the Extrasolar Visions image.

I don't know about the possibility of plasma in these planets- depth and pressure need to be taken into consideration, not just temperature.

m1omg
2010-Nov-06, 02:34 PM
Thanks for an answer, I agree that the Oklo image is probably the most realistic that I've seen, still, the night side seems a bit dim, it can depend through, for example upsilon Andromedae b's nightside is 1000 degrees cooler than its dayside (it is still hot as the surface of Venus through so no "ice caps" of water clouds on the nightside, but an emberlike glow) http://news.sciencemag.org/sciencenow/2006/10/13-02.html, but on HD 189733 b the temperatures are distributed basically evently, except for a hot spot that is cca 300 degrees hotter than most of the planet http://en.wikipedia.org/wiki/File:Ssc2007-09a_medium.jpg .

Is there a bigger version of the Oklo image btw? It would make an awesome PC desktop wallpaper.

And about the plasma issue well, above 2000 degrees I think gas is plasma no? Even a candle flame is partially a plasma, at much lower temperatures. If faint red dwarfs are made of plasma (all stars are or no?), then why couldn't very hot planets? Anyways, doesn't even Jupiter have plasma very deep? Plus, plasma can be very rarified but also dense as we can see on stars (inner layers of the Sun vs. photosphere vs. corona - but everything there is plasma), and I guess the strong Jovian magnetic fields and the strong stellar winds at those distances from their suns can ionize gas very much, making the gas giant to be made of plasma (and I guess the evaporating exospheres of gas giants like Osiris aka HD 209458 b are plasmatic even through they don't have to have plasma on the surface, there is even an possibility that the evaporating atmosphere will become trapped inside the magnetic field of the planet, stopping the mass loss, basically creating a "corona" of plasma [AFAIK ionised gas = plasma] around the planet).

Hungry4info
2010-Nov-06, 11:38 PM
Is there a bigger version of the Oklo image btw? It would make an awesome PC desktop wallpaper.

Somwhat larger version:
http://c2431622.cdn.cloudfiles.rackspacecloud.com/wp-content/uploads/2008/10/2005-0703core-full.jpg You can blow it up of course.

And I firmly agree, the best rendition of a hot Jupiter I've yet seen.

Romanus
2010-Nov-07, 08:31 PM
How the night side would look depends, IMO, how you're viewing the planet as a whole. If you're looking at this hot jupiter in half-phase, the enormous contrast between the light and dark sides will probably make the night side look very dark, by the same principle as sunspots. As the phase angle increases, the brightness of the dark side would increase as well.

Rapid circulation of the atmosphere could have some interesting effects...it's worth speculating whether (looking dead at the dark side) of the planet whether the "early evening" side of the disk would be noticeably brighter than the "early morning" side, even with supersonic winds.