[ExI] Red Tides of Neptune?

[The Avantguardian]

---Stuart wrote:
>>Compare the pictures.
  
>> http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=2565
>> http://en.wikipedia.org/wiki/Image:Coccolithophore_bloom.jpg

--- Amara Graps <amara at amara.com> wrote:

> Stuart: You'll need to dig up the color table for those images
> (suggestion:
> go to the 2003 Icarus paper to which that the PR refers. Planetary
> data is usually spectrally coded, so that green represents a
> wavelength
> region. I doubt that green corresponds to what you are accustomed to
> seeing in visual wavelengths.

You were right, Amara. The HST picture is falsely colored. I followed
your suggestion and looked up the color table. The color table is as
follows: blue=467nm (visible blue), green=673nm (visible red),
red=850nm-1000nm (invisible IR). So I read the paper and  and fooled
around with the pictures in photoshop looking at the RGB channel
intensities for various pixels on the picture. For the most part,
Stormovsky et. al. were right the overall albedo of Neptune is
increasing. That is on average, Neptune is growing brighter for all
three wavelengths that they tested.

However they don't talk much about local irregularities one of which is
the falsely green-colored belt at ~60 degrees S latitude. Now the green
channel intensity is a measure of the amount of red light being
reflected from Neptune. Most places on the planet look falsesly colored
shades of blue. This is because blue light, red light, and IR light is
being reflected back into space at various intensities.

This means that there will be subtle areas in the false color map of
magenta (deficit of green channel) and cyan (deficit of red channel)
mixed in with the blue channel to form the aquamarine of the overall
picture. There will also be bright white areas corresponding to
reflection of all three wavelengths balancing the all three of the RGB
channels. Cirrus type ice crystal clouds tend to do that on earth too
which is why the look so bright from space.
 
What this means is that the "green belt" is actually a red belt where
almost all of the blue and IR is being absorbed by something while red
light is reflected. Now most plants on earth are green because the
chlorophylls (A & B) absorb light roughly in the 450 nm and 650 nm
regions. The spectral region between these absorption maxima are "waste
light" and are thus reflected. So the fact that the "green belt" is
actually red, rules out normal cholorphyll-based photosynthesis and
green plants/green algae since their cholorphyll would absorb the red.
Bacterial chlorophylls are different a different story however, in that
they absorb light in the 800nm-1000nm region.

Furthermore microbes are incredibly diverse in their arsenal of
survival genes. Many like the red algae and purple bacteria use
carotenoids as a "light antenna" to absorb longer wavengths and
transfer the energy to chlorophyll. A common example of this is the red
tide phenomenon which is a bloom of dinoflagellates or other red algae.

Take the genus of bacteria called Rhodobacter.
http://www.nature.com/emboj/journal/v18/n3/full/7591488a.html
They can facultatively use carotene and bacteriochloryphyll to
anaerobically perform photosynthesis in anoxic environments. Their
absorptions peak right around blue 470nm and infrared 890nm. See figure
2.  

Rhodobacter has an unusually broad range of metabolism. The most
studied species Rhodobacter sphaeroides, possesses a very versatile
metabolism which include heterotrophy (eating organic matter)
photosynthesis (eating light), lithotrophy (eating non-organic matter),
and is a facultative breather. It has both aerobic and anaerobic
respiration and can live with or without oxygen. It can also fix
nitrogen and synthesize tetrapyrroles, chlorophylls, heme, and vitamin
B12. It's like the SUV of bacteria.

Furthermore there is a related species called Rhodospirillum centenum
that forms cysts. Cysts are almost as hardy as the endospores but are
larger and consist of a "four-pack" of bacterial cells.
http://www.bio.indiana.edu/~bauerlab/cystformation.html

Yet another related species is Rhodoferax antarcticus. It is a
psychrophile an extremophile that loves the cold. It can grow at O
degrees celsius.
http://www.science.siu.edu/microbiology/extremophiles/grant_proposal.html

So taking your suggestion didn't eliminate the possibility of the red
belt being a bacterial bloom on Neptune, but it did narrow down the
number of possible species. Of course there could be another
explanation why a narrow belt in the southern hemisphere of Neptune
would reflect red light but absorb blue and infra-red. At the very
least there seems to be some interesting chemistry going on in a
strangely localized area of the planet. I am completely open to other
explanations. Anyone got any?



Stuart LaForge
alt email: stuart"AT"ucla.edu

"Life is the sum of all your choices."  
Albert Camus


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