Tal­mu­dic Exo­bi­ol­ogy Re­dux

We re­cently asked this Tal­mu­dic Ques­tion as our TQ #71 :

As NASA's hot­shot exo­bi­ol­o­gist, you are asked to de­sign an Earth satel­lite sys­tem in which some organism(s) can live ac­tively (i.e.. no spores) for mil­len­nia. How would you go about it? Spec­ify an or­bit of your choice.

Source

Ami Bachar replied:

I would take a clean coca cola bot­tle, fill it half with soil and half with sea wa­ter, and make sure it stays liq­uid for the next 1000 years. "Every­thing is every­where and the en­vi­ron­ment se­lects" (Mar­t­i­nus Bei­jer­inck) + "life is what hap­pens to you while you're busy mak­ing other plans" (John Lennon). If it is well closed and noth­ing es­cape from the bot­tle than there should be enough of every­thing needed to sus­tain life for much longer than a mil­len­nia.

To which I (Elio) replied: The sim­plic­ity of your pro­posal wins out over all the com­plex schemes that I had dreamt up. Good for you!

It turns out that I jumped the gun. It's not so sim­ple, as fel­low blog­ger Rus­sell Neches in­sight­fully pointed out.

by Rus­sell Neches

Feel­ing a bit giddy with sleep de­pri­va­tion (and the first suc­cess­ful run on our lab's new se­quenc­ing ma­chine), I de­cided to take a crack at Tal­mu­dic Ques­tion #71:

As NASA's hot­shot exo­bi­ol­o­gist, you are asked to de­sign an Earth satel­lite sys­tem in which some organism(s) can live ac­tively (i.e., no spores) for mil­len­nia. How would you go about it? Spec­ify an or­bit of your choice.

Ami Bachar gamely sug­gested en­trust­ing a cargo of sea­wa­ter and dirt to a Coca Cola bot­tle, and lob­bing it into or­bit. I liked this idea so much that I couldn't re­sist em­broi­der­ing it.

This is a fas­ci­nat­ing idea. Could you cre­ate the happy con­di­tions we en­joy here on the sur­face of this planet, but with­out the planet? Could you do it with­out cheat­ing with mov­ing parts, power sources, or other un-planet-like fea­tures? For­tu­nately, the au­di­ence we're try­ing to please are mi­crobes, who aren't as finicky as as­tro­nauts.

The first prob­lem is that Coke has never, to my knowl­edge, de­signed bot­tles that will stop hard UV ra­di­a­tion, X‑rays, or rel­a­tivis­tic pro­tons. Such a bot­tle would never make it past the prod­uct safety laws, even those from Coke's early days. The glass would need to be doped with a dou­ble-hand­ful of lead to stop at least some of the UV and X‑rays, and per­haps some low‑Z metal like beryl­lium (which is pos­si­bly more toxic than lead) to slow so­lar par­ti­cles be­fore they reach our pre­cious mud. Oth­er­wise, dur­ing a so­lar storm, the bot­tle could be ster­il­ized by Bremsstrahlung ra­di­a­tion. Even thus en­hanced be­yond bev­er­age con­tainer spec­i­fi­ca­tions, the glass prob­a­bly wouldn't do nearly as good a job as the ozone layer and the Earth's mag­netic field. Good thing mi­crobes are tough.

The next prob­lem to worry about is tem­per­a­ture. An ob­ject in a shady spot on the moon will cool to ‑153 °C, and in a sunny spot will heat to 107 °C. The Earth's av­er­age tem­per­a­ture is about 13 °C. How hot would it get in­side the bot­tle? The key to the puz­zle is the Ste­fan-Boltz­mann Law:

I = σT⁴

where the con­stant σ is called, nat­u­rally, the Ste­fan-Boltz­mann con­stant, T is the tem­per­a­ture of the sun's pho­to­s­phere (about 6000 Kelvin), and I is the power emit­ted per square me­ter. Us­ing the Ste­fan-Boltz­mann law, we can cal­cu­late that the sun's sur­face emits 7.3×10⁷ watts per square me­ter. Mul­ti­plied by the to­tal sur­face area of the sun, that's 3.9×10²⁶ watts. This en­ergy spreads out more-or-less uni­formly through space in all di­rec­tions. When you spread it over a 96-mil­lion-mile ra­dius sphere, you get 1367 watts per square me­ter. This num­ber is Earth's so­lar con­stant (S₀).

The Earth ab­sorbs a disk of this sun­light (πr²), but the en­ergy is spread over the sur­face of a sphere (4πr²), so the av­er­age amount of en­ergy falling on a square me­ter of the Earth is one quar­ter of the so­lar con­stant, or 342 watts per square me­ter. A Coke bot­tle isn't a sphere, but it's also not made out of thick lead/beryllium glass ei­ther. This is a very spe­cial Coke bot­tle.

About 30% of the light that reaches the sur­face is re­flected back into space (this is called albedo, which as­tronomers spend a fair amount of time wor­ry­ing about). The albedo re­duces the en­ergy avail­able for heat­ing to 240 watts per square me­ter. Us­ing the Ste­fan-Boltz­man Law, this gives us a tem­per­a­ture of 255K, or ‑18 °C. This is the Earth's av­er­age equi­lib­rium ra­di­at­ing tem­per­a­ture, which it for­tu­nately never reaches, thanks to our won­der­ful at­mos­phere. Don't let any­one tell you that the green­house ef­fect is a bad thing! All things in mod­er­a­tion, of course.

In the Earth's at­mos­phere, wa­ter va­por, car­bon diox­ide and methane are opaque to in­frared, but trans­par­ent to vis­i­ble light. A great deal of sun­light comes down as vis­i­ble light, heats up the ground, and gets re-ra­di­ated by in­frared. Be­cause of these green­house gasses, some of this in­frared heats up the at­mos­phere, which then re-ra­di­ates both into space and back at the ground. (Ac­tual gar­den green­houses do not work this way at all; they sim­ply block heat losses from con­vec­tion by trap­ping the air in­side.)

This ex­tra ra­di­a­tion from the at­mos­phere heats up the ground, which then re-ra­di­ates a bit more. This ex­tra heat leads, of course, to more re-ra­di­a­tion from the ground, which also warms the at­mos­phere. It's a cute lit­tle prob­lem; each time you go around, you throw half the heat into space, half the heat back at the ground, and you get a geo­met­ric se­ries that con­verges at 2. If the Earth's at­mos­phere were a per­fect green­house, the av­er­age tem­per­a­ture would be 58°C.

Go­ing back to the Coke bot­tle, we can choose a tem­per­a­ture be­tween ‑18 °C and 58 °C by set­ting the strength of the green­house ef­fect. We'll be care­ful to choose mud of the right color to ap­prox­i­mate the Earth's albedo. To do the job of Earth's green­house gasses, we can use an op­ti­cal in­frared fil­ter, like the ones used in dig­i­tal cam­eras. The bot­tle would need to be triple walled to min­i­mize heat loss from con­duc­tion, with the mid­dle wall act­ing as the fil­ter.

One of the fea­tures of our planet that has al­lowed life to keep its foothold here de­spite an un­sta­ble cli­mate is that our planet has a nice va­ri­ety of tem­per­a­ture zones. When the planet warms, the tem­per­ate zones march to­ward the poles, and when the planet cools, they march to­ward the equa­tor. The Earth owes this fea­ture to its size and its cur­va­ture. Even if the bot­tle were a sphere ro­tat­ing about an axis, like a minia­ture model of the Earth, the heat con­duc­tion in the mud would keep it at ba­si­cally the same tem­per­a­ture through­out, de­spite get­ting more ra­di­a­tion at its "equa­tor."

To set up a tem­per­a­ture gra­di­ent, we'll need some kind of heat flow through the mud, from a source to a sync. All we need to do is dial up the green­house ef­fect, and add a sync. Let­ting heat "leak" out of the bot­tle from a spe­cific place is easy; just add a bit of metal that sticks through the lay­ers of the bot­tle, with a lit­tle heat sync dan­gling out into space. With­out a source of heat, the heat sync would tend to­ward ‑18 °C. You could think of this as the bot­tle cap.

This would help en­cour­age eco­log­i­cally dis­tinct bands, which would help pre­serve and gen­er­ate di­ver­sity. This would be im­por­tant for keep­ing things go­ing as con­di­tions changed.

Af­ter all this, the ex­per­i­ment prob­a­bly wouldn't last a thou­sand years. What makes the Earth so won­der­ful is that it has a lot of semi-sep­a­rated com­part­ments and a lot of big gra­di­ents. Con­di­tions change con­stantly and some­times cat­a­stroph­i­cally, but there is al­ways a com­fort­able place some­where.

Ob­vi­ously, the ecol­ogy of the Coke bot­tle world not even re­motely re­sem­ble the Earth's. Car­bon cy­cling, phos­pho­rous cy­cling, and ni­tro­gen cy­cling would work com­pletely dif­fer­ently. The reser­voirs of in­or­ganic ma­te­r­ial would be dif­fer­ent, and the path­ways into and out of those reser­voirs would be dif­fer­ent. We would ex­pect very dif­fer­ent dy­nam­ics. My guess is that al­most all of the avail­able in­or­ganic ma­te­ri­als would even­tu­ally be in­cor­po­rated into bio­mass, with only a very small amount made avail­able by se­cre­tions and cells that hap­pened to die. Per­haps this would lead to never-end­ing mi­cro­bial glad­i­a­to­r­ial com­bat, or per­haps it would be a quiet lit­tle gar­den wheel­ing through space. Per­haps you'd end up with noth­ing but cel­lu­lar wreck­age and a gi­ant wad of phage.

Any­way, be­fore at­tempt­ing this ex­per­i­ment, I would strongly rec­om­mend find­ing a way to freeze Richard Lenski for a thou­sand years and thaw him out un­harmed. Some­one is go­ing to get to an­a­lyze the aliquots from the Coke bot­tle. As nice as Richard is, I think he might run over the rest of us with cleats on to be the guy to do it.

Elio: I'd like to thank Aric Mine in Al­bert Colman's lab, as well as Samuel Miller and Genna Pat­ton at the Uni­ver­sity of Chicago, for their sug­ges­tions and cor­rec­tions.

Rus­sell Neches is a mem­ber of the Mi­cro­bi­ol­ogy Grad­u­ate Group, UC Davis.

More from Ami Bachar...

Very well done! and thanks much for ho­n­our­ing my an­swer with a re­ply, it sure is a nice an­swer and one we can learn from. I would like to re­ply with only two points and in any­way say that I fully agree with the above an­swer.

1) I said in the orig­i­nal text "make sure it stays liq­uid for the next 1000 years" and by that I meant that it should be well pro­tected from freez­ing or heat­ing too much. Why would such a thing heat so much dur­ing the com­ing 1000 years I do not know. As far as I was told, space is rather cold. I might be wrong there. In any­way, keep it liq­uid, mean­ing, keep it some­where around room temp.

2) UV is in­deed a good point, al­though I think it will only pen­e­trate to the up­per 0.5mm — so the in­ner mi­crobes should be pro­tected. With re­spect to the pro­ton flux, I do not know much. Around the earth there should be some mag­netic shield for that. Not so sure about the drum sys­tem as well since po­ten­tially you can make the thing or­bit the earth in a way that it ex­pe­ri­ences day-night shifts (it de­pends prob­a­bly on how far the or­bit is from earth. Adding a gra­di­ent screen is a good idea. A Wino­grad­sky col­umn is an up­grade of the bot­tle idea to aug­ment bio­di­ver­sity (al­though I sus­pect most species would be on the in­ner sec­tion where it is dark).

Rus­sell Neches says "pro­vide as many niches as pos­si­ble" and I fully agree. It would def­i­nitely not hurt to have larger niches, e.g., salt wa­ter, fresh wa­ter, soil + wa­ter, soil only of dif­fer­ent kinds, etc. Good call, al­though not as sim­ple as 1 Coca Cola bot­tle — you must ad­mit :). A sys­tem can be VERY com­plex with many many de­vics and gra­di­ents and niches — no doubt, but the ques­tion was to pro­vide a sys­tem that can sus­tain ac­tive or­gan­isms. You can do so with 1$ Bil­lion and you can do it with 1$. Fi­nally, one small ques­tion — I didn't un­der­stand: Why did you say "That prob­a­bly wouldn't work for a thou­sand years ei­ther, but it's get­ting closer"? what is pre­vent­ing from this ecosys­tem with an outer en­ergy source (light) to keep re­cy­cling it­self? Thanks for a good an­swer.

Ami Bachar is a post­doc at the Zucker­berg Inst. for Wa­ter Re­search. Ben-Gu­rion Uni­ver­sity, Is­rael.