What effect would liquid sulfur oceans, sulfur dioxide in the atmosphere have on visibility, sound propagation and other environmental information?
EDIT: I eventually managed to find the absorption spectra of SO2 online - it absorbs in the ultraviolet range only, not in the visible light range, so the only factor affecting light transmitting through the atmosphere will be the level of sulfur vapor humidity. Sections of the question have been struck out or added (in bold) to reflect this.
Question: I'm having trouble (after lots of googling and reading) finding information on the physical properties that the atmosphere and oceans would have - specifically, the penetration of light and transmittance of sound through the atmosphere and seas.
The only relevant information I found was from Freitas' famed Xenology book, which said of atmospheric sulfur vapor "At 1 atm pressure, blue light is cut to below human eye visibility in less than half a meter, and the red is gone in fifty meters. So if the partial pressures of [sulfur vapor] exceed perhaps 0.001-0.01 atm, no light of any color will be able to reach the surface of the planet from the outside"
I couldn't find anything for sulfur dioxide in the air (see edit at top) or liquid sulfur.
My specific questions are:
-
What will the lighting conditions be like?
- What would the effect of sulfur vapor humidity in the air be on visibility? Specifically, what partial pressure of vapour seems reasonable? (I can approximate from the quote above from Freitas)
How far will light penetrate through the sea?
How much light will reach the surface?-
What wavelengths will penetrate the atmosphere? (presumably only the yellow color of the liquid sulfur's own color would penetrate through the sea itself for any appreciable distance)
How far and how well will sound travel through the sea?
How effective would detection of electric fields be in a sulfur sea? (E.g. for prey detection, as in sharks)
I don't need super accurate answers; ballpark figures in terms of comparisons to earth atmosphere and oceans would be fine - e.g. that light penetration at 1 meter depth in the sulfur sea would be equivalent to 1km in the earth's oceans.
The species of focus (which I expect I will have other questions about later) lives around the ocean surface - just below the surface in shallow waters, at the surface, and on coastal land areas, so I need this information to check that the creature's design - senses, communication methods etc - are ball-park plausible. E.g. I don't want to write about how they use echolocation or an electric sense to find prey if it turns out that they would only be effective at a range of millimeters.
I am aiming for a situation where enough light reaches the surface of the planet for photosynthesis to be reasonable (this doesn't have to be earth-like - more efficient pigments than chlorophyll are handwavable), and where light penetrates through the ocean at least far enough to make monochromatic vision useful for communication/close navigation. For sound, echolocation and vocal communication in the oceans (conversation style in a social animal, not cross-ocean whale song) would be nice but not a deal breaker. Shark-like electrosense is just a possibility I'm exploring - if it's feasible life would evolve a way to exploit it.
Background: The planet is (probably - see below) tidally-locked, with a bright-side surface temperature range of approximately 120°C to 170°C. At these temperature ranges, sulfur is liquid - light yellow and relatively thin up to about 157°C, and then dark red and viscous (but less dense) above that. Rivers and oceans will be mostly the yellow form, with dark red viscous patches floating on top at the hottest ocean areas, dark red viscous rivers and lakes on the hottest land masses, and interesting lava-lamp like effects over underwater hot vents or lava flows.
Due to wind currents blowing warm air to the dark side, and ocean currents circulating eastwards around the planet (due to coriolis forces), the dark side temperatures are not too far below (sulfur's) freezing point (113°C). There are thus large regions of solid sulfur 'ice,' but also regions where sulfur remains liquid.
The atmosphere contains sulfur dioxide, and some fluorine compounds (for biological reasons), and probably (but the precise details are not very important) carbon monoxide, carbon dioxide and nitrogen or other gases. The atmosphere will contain sulfur vapor also, due to the liquid sulfur oceans. The atmosphere does not need to be very dense - tidally locked planets can maintain fairly warm dark side temperatures with a relatively thin atmosphere and ocean circulation, and I can handwave it a bit with the very potent greenhouse capability of some fluorine compounds
The planet is host to carbon-based life where plants photosynthesize by absorbing SO2, storing the O, and releasing S. Animals eat the oxygen-containing plant tissues, 'inhale' sulfur, and exhale SO2. Proteins etc are fluorocarbon based, but this is a behind-the-scenes detail.
"Probably tidally locked:" the idea of tidal locking was initially just a way to create areas which would have low humidity (since sulfur vapor strongly absorbs light) yet were near/over oceans: (relatively) steady dry winds blowing over land from the dark side to the light side. I do quite like the idea but am not averse to changing it if it doesn't actually give me the situation I want.
This is my first question after a long period of lurking. Apologies if I've gotten the format wrong in any way (too many questions etc) - if I have, let me know and I'll edit
This post was sourced from https://worldbuilding.stackexchange.com/q/70325. It is licensed under CC BY-SA 3.0.
1 answer
How far and how well will sound travel through the sea?
First, we need to figure out exactly what the sea is made out of. You've indicated that it's sulfur, but what kind of sulfur? Lopes & Williams (2005) is an excellent review article on Io that has a section discussing this. They identify different colored sections of Io with different sulfur compounds and allotropes:
- Red: $\text{S}_3$ and $\text{S}_4$, from the breakdown of more complicated sulfur molecules or from condensation of gases containing $\text{S}_2$.
- Yellow: $\text{S}_8$, cyclo-octasulfur.
- Green: Sulfur compounds with contamination by miscellaneous silicates.
- White-grey: $\text{SO}_2$ from crystallization after being deposited by volcanic plumes.
- Black: Silicate-rich areas near hotspots.
We therefore go to octasulfur, $\text{S}_8$, for our oceans. However, classic cyclo-octasulfur is a solid, and melts at around 115°C. The form of octasulfur we need is $\lambda$-sulfur, which is only slightly different (although it is liquid at the temperatures you need; it is generally not a solid form of sulfur).
The speed of sound in a liquid, $c_s$, is easy to determine: $$c_s=\sqrt{\frac{K}{\rho}}$$ where $K$ is the bulk modulus of the liquid and $\rho$ is the density. I was not able to find good measurements of the bulk modulus of $\text{S}_8$ at any temperature, but I did find a study that found the speed of sound at different temperatures, Kozhevnikov et al. (2004). Figure 6 shows some of their results:
They don't present any best-fit curves, but it appears that the results are linear in temperature, with one line valid through 80°C to 160°C and another for 160°C to 200°C. These measurements appear to be for $\text{S}_8$ (presumably $\lambda$-sulfur) and should therefore be perfect for your seas. There is not enough data about sound absorption to determine exactly how it behaves over a wide range of temperatures.
For comparison, the speed of sound in water is approximately 1,500 meters per second, a bit higher than the roughly 1300 meters per second in an $\text{S}_8$ ocean. However, the above results assume that the oceans are extremely pure; as I mentioned above, contamination is extremely likely, and therefore we can't assume that they will be perfectly pure.
How far will light penetrate through the sea?
Let's assume that the Beer-Lambert law is applicable here - which I assume it is. The law states that the intensity, $I$, of light is an exponentially-decaying function of depth: $$I(l)=I_0e^{-l/L}$$ where $I_0=I(0)$ and $L$ is the attenuation length, which determines how quickly the intensity drops off. The attenuation length is the reciprocal of the absorption coefficient, $\alpha$. I found a passing reference which states in its abstract that
The optical absorption coefficient alpha of liquid sulphur has been measured in a wide absorption range from 5.5*10-2 to 2*105 cm-1 at temperatures from 130 to 450 degrees C.
I don't know if the relationship is linear or not (or if this is a form of octasulfur), but it appears to change by seven orders of magnitude within a range of about 300°C. In SI units, this is $5.5\times10^{-4}$ to $2\times10^3\text{ m}^{-1}$. Let's say that the relationship is linear. We then should have a slope of about 3°C/m-1. Therefore, at 170°C, we should find $\alpha\sim120$, and so
$$I(l)=I_0e^{-120l}$$
The above struck-out part is incorrect, as per Tharaib's answer. The coefficient's behavior is distinctly nonlinear with respect to temperature.
How effective would detection of electric fields be in a sulfur sea? (E.g. for prey detection, as in sharks)
Seawater is a decent electrical conductor, because it has free ions; these mean that free electrons can quite easily carry electric currents, and so it is easier for electric fields to permeate the water. For sulfur, things are substantially more complicated. Elemental Sulfur and Sulfur-Rich Compounds I states (page 106) that
under ambient conditions elemental sulfur is one of the best electrical insulators known.
In general, however, sulfur's conductivity rises with temperature, and we are indeed dealing with somewhat high temperatures. Synthetic Methods of Organometallic and Inorganic Chemistry, Volume 4, 1997 confirms that $\alpha$-sulfur is an excellent insulator. However, it, too, states that at high temperatures, sulfur's electrical conductivity (as well as other properties) change suddenly.
I currently cannot get you exact values for $\lambda$-sulfur's electrical conductivity, but it appears that it would be much harder for organisms to sense electric fields in a liquid sulfur ocean.
Answer in progress!
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