APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

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APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by APOD Robot » Wed Sep 20, 2023 4:05 am

Image Methane Discovered on Distant Exoplanet

Explanation: Where else might life exist? One of humanity's great outstanding questions, locating planets where extrasolar life might survive took a step forward in 2019 with the discovery of a significant amount of water vapor in the atmosphere of distant exoplanet K2-18b. The planet and its parent star, K2-18, lie about 124 light years away toward the constellation of the Lion (Leo). The exoplanet is significantly larger and more massive than our Earth, but orbits in the habitable zone of its home star. K2-18, although more red than our Sun, shines in K2-18b's sky with a brightness similar to the Sun in Earth's sky. The 2019 discovery of atmospheric water was made in data from three space telescopes: Hubble, Spitzer, and Kepler, by noting the absorption of water-vapor colors when the planet moved in front of the star. Now in 2023, further observations by the Webb Space Telescope in infrared light have uncovered evidence of other life-indicating molecules -- including methane. The featured illustration imagines exoplanet K2-18b on the far right orbited by a moon (center), which together orbit a red dwarf star depicted on the lower left.

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Javachip3

Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by Javachip3 » Wed Sep 20, 2023 9:37 am

On the dark (night) side of the planet, there are some small faint red lights. Are these meant to be molten lava, or ... cities?

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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by Guest » Wed Sep 20, 2023 9:42 am

While I find the search for life very intriguing, I really don’t care much for these kinds of scifi-like illustrations. Any of the images obtained by a telescope would have been better than this fantasy.

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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by Guest » Wed Sep 20, 2023 11:22 am

picture of the day is not a picture.

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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by johnnydeep » Wed Sep 20, 2023 12:20 pm

Guest wrote: Wed Sep 20, 2023 11:22 am picture of the day is not a picture.
Sure it is. It's not a photo, but it's definitely a picture. After all, this is "Astronomy Picture of the Day", not "Astronomy Photo of the Day".

And I like this picture just fine.
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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by AVAO » Wed Sep 20, 2023 3:14 pm

Guest wrote: Wed Sep 20, 2023 9:42 am While I find the search for life very intriguing, I really don’t care much for these kinds of scifi-like illustrations. Any of the images obtained by a telescope would have been better than this fantasy.
Well. I basically agree with you on that. You can see the "true" APOD image below.
It is remarkable that several tracers in the spectrum of this exoplanet indicate chemical compounds that could come directly or indirectly from living beings. Methane alone is not the deciding factor here, as Titan with its methane lakes would be anything but life-friendly.

Image
Credit: NASA, CSA, ESA, J. Olmstead (STScI), N. Madhusudhan (Cambridge University)

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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by johnnydeep » Wed Sep 20, 2023 3:46 pm

So which is the more accurate human eye depiction, this APOD or the image from Wikipedia?

k2-18b.jpg
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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by johnnydeep » Wed Sep 20, 2023 3:49 pm

Javachip3 wrote: Wed Sep 20, 2023 9:37 am On the dark (night) side of the planet, there are some small faint red lights. Are these meant to be molten lava, or ... cities?
Well spotted! Cities lit with red lights could indeed be appropriate for a species that evolved with a red dwarf in the sky!
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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by Chris Peterson » Wed Sep 20, 2023 4:07 pm

johnnydeep wrote: Wed Sep 20, 2023 3:46 pm So which is the more accurate human eye depiction, this APOD or the image from Wikipedia?

k2-18b.jpg
I'd definitely go with the one on the right. Red dwarfs are not red, any more than our sun is green. Their spectra may peak in the red and IR, but that's quite different. The image on the left looks like a carbon star! To our eyes, red dwarfs look whitish-orange. And from inside the system, the star would likely look close to white to our eyes, and a water planet is basically blue... even when illuminated with very warm white sunlight.
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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by johnnydeep » Wed Sep 20, 2023 4:17 pm

Chris Peterson wrote: Wed Sep 20, 2023 4:07 pm
johnnydeep wrote: Wed Sep 20, 2023 3:46 pm So which is the more accurate human eye depiction, this APOD or the image from Wikipedia?

k2-18b.jpg
I'd definitely go with the one on the right. Red dwarfs are not red, any more than our sun is green. Their spectra may peak in the red and IR, but that's quite different. The image on the left looks like a carbon star! To our eyes, red dwarfs look whitish-orange. And from inside the system, the star would likely look close to white to our eyes, and a water planet is basically blue... even when illuminated with very warm white sunlight.
Thanks. I know you'd be sure to reply. :ssmile:
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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by Ann » Wed Sep 20, 2023 5:05 pm

Chris Peterson wrote: Wed Sep 20, 2023 4:07 pm
johnnydeep wrote: Wed Sep 20, 2023 3:46 pm So which is the more accurate human eye depiction, this APOD or the image from Wikipedia?

k2-18b.jpg
I'd definitely go with the one on the right. Red dwarfs are not red, any more than our sun is green. Their spectra may peak in the red and IR, but that's quite different. The image on the left looks like a carbon star! To our eyes, red dwarfs look whitish-orange. And from inside the system, the star would likely look close to white to our eyes, and a water planet is basically blue... even when illuminated with very warm white sunlight.
I agree that an M-type star would look mostly white to our eyes, if it had been our Sun. But I don't agree that the Earth would have been blue planet if it had been orbiting an M-type dwarf.

There are two ways of defining the color blue. There is the objective way, which has to do with measuring wavelengths. I would define wavelengths between 475 and 440 nm as "objectively blue", although you could certainly argue about the exact span of wavelengths.

But to us humans, "blue" is what our brains actually tell us is what we think of as "blue". And that is a subjective matter. A stunningly perfect demonstration of how much our brains can be fooled was the actual color of a famous striped dress. Was the dress white and gold or blue and black?


Well, it turns out that the dress was in fact blue and black. My point is that our brains can be fooled. So if the Earth had orbited a red dwarf star, which produced very little light between 440 and 475 nm, we might still "see blue" in the world we lived in.

My point is that there would be very little actual blue light. And that would make an objective difference.

I recommend this question and answer from Quora:

Quora wrote:

Q: What colour sky would you observe from a planet around a dwarf star such as TRAPPIST-1?

A: First of all, note that while TRAPPIST-1 (henceforth referred to as T-1) is an extremely cool red star, it’s still about 2600 Kelvins, which isn’t that much cooler than an incandescent light bulb filament. It would certainly appear reddish, but not the deep red color that artists tend to give red stars.

But it’s what you don’t see that’s important. According to this calculator, T-1 only emits about 4% of its light in the visible portion of the spectrum, a miniscule 0.05% in the ultraviolet, and everything else in the infrared (microwaves, x-rays, etc. are negligible). Of the visible light, 9.3% is in the violet to blue range, 30% is in the blue-green-yellow range, and 60% is in the yellow-orange-red range.

By comparison, the sun emits 28% of its light in the visible spectrum, 9.4% in the UV, and the remaining 62.5% in the infrared. Of the visible light, 34% is violet-to-blue, 35% is blue-green-yellow, and 32% is yellow-orange-red.

Now, let’s think about what we’d see if we were getting the same total irradiance from T-1 as Earth does from the sun, which is close to T-1d (which gets 114% of Earth’s irradiance). First, the visible light would be seven times dimmer in total, comparable to a cloudy day even with clear skies. If you were a bird or some other creature that could see Ultraviolet, you’d really notice: there would be less than 1% of the available ultraviolet radiation that the sun produces. Incidentally, this means that getting a sunburn on one of T-1’s planets would probably be impossible. It might even mean you could look directly at the star without hurting your eyes, because UV does a lot more damage than visible or especially infrared light.

If you dove underwater, you’d also notice a big change: even in crystal-clear water it would very quickly become dark. This is because of the relatively lack of blue-violet light, which travels through water MUCH more easily than yellow or red light.

But what about the sky? Well, if the atmosphere is relatively earthlike, then Rayleigh scattering will scatter blue light more effectively, but there’s less of it. With blue light being so much less abundant, the sky might actually end up having a grey or yellow color! It would also be relatively dark. However, more dense atmospheres create more scattering and a paler sky, while less dense atmospheres create a darker sky, to the limit where with no atmosphere at all it’s black.

According to the same Quora answer, however, the planet (or planets?) would look bluish, because
Sadly, due to the dearth of visible light and the planet’s likely blue color (meaning the most common light, red, would be absorbed more)
I don't understand why a planet would look blue because it was illuminated by a reddish sun in a way that made the most common light, red, to be absorbed more. Why would red light be absorbed more to make the planet look blue?

Anyway, this is my point. If we lived on a planet orbiting a red dwarf star, our daytime skies would be darker and less blue than they are here on Earth.


However, I also found this illustration of red dwarf star Trappist-1 and its mostly bluish-looking planets. Does anyone care to explain why most of the planets would look so blue?


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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by Chris Peterson » Wed Sep 20, 2023 5:14 pm

Ann wrote: Wed Sep 20, 2023 5:05 pm
Chris Peterson wrote: Wed Sep 20, 2023 4:07 pm
johnnydeep wrote: Wed Sep 20, 2023 3:46 pm So which is the more accurate human eye depiction, this APOD or the image from Wikipedia?

k2-18b.jpg
I'd definitely go with the one on the right. Red dwarfs are not red, any more than our sun is green. Their spectra may peak in the red and IR, but that's quite different. The image on the left looks like a carbon star! To our eyes, red dwarfs look whitish-orange. And from inside the system, the star would likely look close to white to our eyes, and a water planet is basically blue... even when illuminated with very warm white sunlight.
I agree that an M-type star would look mostly white to our eyes, if it had been our Sun. But I don't agree that the Earth would have been blue planet if it had been orbiting an M-type dwarf.

There are two ways of defining the color blue. There is the objective way, which has to do with measuring wavelengths. I would define wavelengths between 475 and 440 nm as "objectively blue", although you could certainly argue about the exact span of wavelengths.

But to us humans, "blue" is what our brains actually tell us is what we think of as "blue". And that is a subjective matter. A stunningly perfect demonstration of how much our brains can be fooled was the actual color of a famous striped dress. Was the dress white and gold or blue and black?


Well, it turns out that the dress was in fact blue and black. My point is that our brains can be fooled. So if the Earth had orbited a red dwarf star, which produced very little light between 440 and 475 nm, we might still "see blue" in the world we lived in.

My point is that there would be very little actual blue light. And that would make an objective difference.

I recommend this question and answer from Quora:

Quora wrote:

Q: What colour sky would you observe from a planet around a dwarf star such as TRAPPIST-1?

A: First of all, note that while TRAPPIST-1 (henceforth referred to as T-1) is an extremely cool red star, it’s still about 2600 Kelvins, which isn’t that much cooler than an incandescent light bulb filament. It would certainly appear reddish, but not the deep red color that artists tend to give red stars.

But it’s what you don’t see that’s important. According to this calculator, T-1 only emits about 4% of its light in the visible portion of the spectrum, a miniscule 0.05% in the ultraviolet, and everything else in the infrared (microwaves, x-rays, etc. are negligible). Of the visible light, 9.3% is in the violet to blue range, 30% is in the blue-green-yellow range, and 60% is in the yellow-orange-red range.

By comparison, the sun emits 28% of its light in the visible spectrum, 9.4% in the UV, and the remaining 62.5% in the infrared. Of the visible light, 34% is violet-to-blue, 35% is blue-green-yellow, and 32% is yellow-orange-red.

Now, let’s think about what we’d see if we were getting the same total irradiance from T-1 as Earth does from the sun, which is close to T-1d (which gets 114% of Earth’s irradiance). First, the visible light would be seven times dimmer in total, comparable to a cloudy day even with clear skies. If you were a bird or some other creature that could see Ultraviolet, you’d really notice: there would be less than 1% of the available ultraviolet radiation that the sun produces. Incidentally, this means that getting a sunburn on one of T-1’s planets would probably be impossible. It might even mean you could look directly at the star without hurting your eyes, because UV does a lot more damage than visible or especially infrared light.

If you dove underwater, you’d also notice a big change: even in crystal-clear water it would very quickly become dark. This is because of the relatively lack of blue-violet light, which travels through water MUCH more easily than yellow or red light.

But what about the sky? Well, if the atmosphere is relatively earthlike, then Rayleigh scattering will scatter blue light more effectively, but there’s less of it. With blue light being so much less abundant, the sky might actually end up having a grey or yellow color! It would also be relatively dark. However, more dense atmospheres create more scattering and a paler sky, while less dense atmospheres create a darker sky, to the limit where with no atmosphere at all it’s black.

According to the same Quora answer, however, the planet (or planets?) would look bluish, because
Sadly, due to the dearth of visible light and the planet’s likely blue color (meaning the most common light, red, would be absorbed more)
I don't understand why a planet would look blue because it was illuminated by a reddish sun in a way that made the most common light, red, to be absorbed more. Why would red light be absorbed more to make the planet look blue?

Anyway, this is my point. If we lived on a planet orbiting a red dwarf star, our daytime skies would be darker and less blue than they are here on Earth.


However, I also found this illustration of red dwarf star Trappist-1 and its mostly bluish-looking planets. Does anyone care to explain why most of the planets would look so blue?


Ann
4% is a lot, given our eyes' logarithmic response. We see over many orders of magnitude... 4% is not even 2 orders. A decently lit room at night is "dark" in the context of the analysis above, yet most of us don't notice it seeming any darker than daylight unless we can compare them back and forth. And as was noted, a red dwarf has a similar spectrum to an incandescent light bulb... and the last time I noticed it, we see blue just fine in a room lit with incandescent light bulbs.
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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by Roy » Wed Sep 20, 2023 5:23 pm

Interesting speculation. Based on some Fraunhofer absorption lines that maybe have come from a planet. In our solar system we have four gas giants, one water world, one dry world with vanished atmosphere, and one gas midget with dense carbon dioxide atmosphere, surface temperature of melting lead, rotating slowly retrograde. Plus a number of rocks. So, the odds are about one in seven, based on our sample. Not so bad- we just have to look at more stars.

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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by Ann » Wed Sep 20, 2023 6:54 pm

Chris Peterson wrote: Wed Sep 20, 2023 5:14 pm
4% is a lot, given our eyes' logarithmic response. We see over many orders of magnitude... 4% is not even 2 orders. A decently lit room at night is "dark" in the context of the analysis above, yet most of us don't notice it seeming any darker than daylight unless we can compare them back and forth. And as was noted, a red dwarf has a similar spectrum to an incandescent light bulb... and the last time I noticed it, we see blue just fine in a room lit with incandescent light bulbs.
We certainly see blue in a room lit with incandescent light bulbs. But to me, blue objects are a lot more dull and a lot less vivid than when the same blue objects are seen in daylight. I don't know about the rest of you, but I am constantly aware of the yellow hue of the illumination in a room lit with incandescent light, or on streets lit with streetlamps.


There is no way that daylight can look "objectively the same" on a planet under a red dwarf star as on a planet under an early G-type star.

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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by Ann » Wed Sep 20, 2023 7:18 pm

I was in Copenhagen last Friday and happened upon a small pavilion called "Poetic daylight". The pavilion contained three small rooms which let in a huge amount of light. The first room was brightly lit up with this color, ███, and I was overwhelmed by the sensation of the color of the soft light of the blue sky. The next room was suffused with a soft yellow light, something like this: ███. Again I was overwhelmed by the feeling of the room being illuminated by the color of direct sunlight with little or no contribution from the blue sky.

The light in the last room was white, ███. You can guess why. It was illuminated both by the Sun and by the blue sky.

I found it very interesting.

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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by orin stepanek » Wed Sep 20, 2023 9:26 pm

ExoplanetJ2_Jabakenji_960.jpg
Exoplanet many times larger than Earth? I don't want to go there; I
weigh enough here on Earth! :lol2:
complifezonewtxt-full.jpg
I take it that the larger the star; the larger the habitable zone! 😋
HTB1wvWmKxSYBuNjSspjq6x73VXay.jpg_q50.jpg
Oh oh; a ferocious lion! :mrgreen:
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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by Chris Peterson » Wed Sep 20, 2023 11:22 pm

Ann wrote: Wed Sep 20, 2023 6:54 pm
Chris Peterson wrote: Wed Sep 20, 2023 5:14 pm
4% is a lot, given our eyes' logarithmic response. We see over many orders of magnitude... 4% is not even 2 orders. A decently lit room at night is "dark" in the context of the analysis above, yet most of us don't notice it seeming any darker than daylight unless we can compare them back and forth. And as was noted, a red dwarf has a similar spectrum to an incandescent light bulb... and the last time I noticed it, we see blue just fine in a room lit with incandescent light bulbs.
We certainly see blue in a room lit with incandescent light bulbs. But to me, blue objects are a lot more dull and a lot less vivid than when the same blue objects are seen in daylight. I don't know about the rest of you, but I am constantly aware of the yellow hue of the illumination in a room lit with incandescent light, or on streets lit with streetlamps.


There is no way that daylight can look "objectively the same" on a planet under a red dwarf star as on a planet under an early G-type star.
Which is fine, because color is fundamentally subjective. I doubt most people would notice any difference between daylight on Earth and daylight on a planet around a red dwarf, because our brains would happily remap our color space into that not-so-different zone.
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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by Ann » Thu Sep 21, 2023 3:31 am

Chris Peterson wrote: Wed Sep 20, 2023 11:22 pm
Ann wrote: Wed Sep 20, 2023 6:54 pm
Chris Peterson wrote: Wed Sep 20, 2023 5:14 pm
4% is a lot, given our eyes' logarithmic response. We see over many orders of magnitude... 4% is not even 2 orders. A decently lit room at night is "dark" in the context of the analysis above, yet most of us don't notice it seeming any darker than daylight unless we can compare them back and forth. And as was noted, a red dwarf has a similar spectrum to an incandescent light bulb... and the last time I noticed it, we see blue just fine in a room lit with incandescent light bulbs.
We certainly see blue in a room lit with incandescent light bulbs. But to me, blue objects are a lot more dull and a lot less vivid than when the same blue objects are seen in daylight. I don't know about the rest of you, but I am constantly aware of the yellow hue of the illumination in a room lit with incandescent light, or on streets lit with streetlamps.


There is no way that daylight can look "objectively the same" on a planet under a red dwarf star as on a planet under an early G-type star.
Which is fine, because color is fundamentally subjective. I doubt most people would notice any difference between daylight on Earth and daylight on a planet around a red dwarf, because our brains would happily remap our color space into that not-so-different zone.
If we were "instantly transported" to a red dwarf planet, I have no doubt we would notice an enormous amount of differences compared with the Earth, where the color of daylight may well be the least of the differences. But it would still be very noticeable.

But I agree with you, of course, that the human brain is extremely adaptable, and certainly when it comes to color perception. If people had to stay on that red dwarf planet for a while, or for the rest of their lives, the color of the daylight on that planet would become as natural to them as the color of artificial illumination is to almost all people is on the Earth.

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Re: APOD: Methane Discovered on Distant Exoplanet (2023 Sep 20)

Post by Ann » Thu Sep 21, 2023 4:00 am

I might add that I asked Qoura about the color and brightness of the daytime sky on Mars vs. the color and brightness of the daytime sky on the Earth. I got an answer that I found deeply unsatisfactory:
Quora wrote:

Q: Is the Mars sky black during the daytime?

A: You'd think that because of the really thin atmosphere of Mars but surprisingly no. Mars actually gets clear blue/orange skies during the day. Or brown if there's a windy day.

Here's a few pictures of a day on Mars:


Well, no way Jose that the second picture gives us a good idea of the color of the daytime sky on Mars! :thumb_down:

I made another search and found two very interesting pictures, where one had been "white-balanced":


Would the sky on a red dwarf planet be any bluer than the non-blue Martian skies shown here? I seriously doubt it (even though the color of the Martian sky is caused by reddish dust in the Martian atmosphere and not by the color of the Sun).

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