My idea is an planet that is one living organism wrapped all around an rocky foundation. It orbits an sun of one solar mass, and has an Earthlike radius. Its albedo is about 20%, so it gets 1098.4 W/m^2 of usable energy, which equates to 2.80X10^17 W of energy. It uses photosynthesis to produce glucose, and synthesizes nitrates to use for amino acids from its atmosphere, as well as recycling its waste. Its photosynthesis is 26% efficient, so 7.28X10^16 J of energy is stored as glucose every second, and every mole of glucose stores 2.88 MJ of energy. That means that every second, 25.3X10^10 mol of glucose are produced, and every second, an equivalent amount is used. The amount of energy it uses in a day is equivalent to 6.29X10^21 J, or 1.50X10^18 kcal, which means that its mass is 5.97*10^21 kg. It has its own atmosphere, which it uses to be able to produce the biochemical reactions it needs to survive, and complex systems to live.

It reproduces by creating 70-kg spores that can survive the vacuum of space, as well as atmospheric reentry, and fires them out at 50 km/s every now and then. Once a spore lands on a planet and absorbs water, it begins to grow until it envelops the entire surface, and begins growing outwards once that is done. It has many long, thin, strong villi that work to optimize surface area for biochemical reactions and light capture, and they work to thermoregulate, seeing that due to internal reactions releasing 64% of their energy as heat, it produces 4.66*10^16 W of heat. The villi can be kilometers tall, and have pockets of hot air that reduce their density, and keep them afloat on the massive ocean that the organism uses. Antibodies break down any organic matter that comes in contact with the surface, preventing infections by pathogens and giving an input of nutrients. Can my living planet exist, with our known models of biology, physics, and chemistry? Why or why not?

For example, how thick can it grow before it becomes too large to support its own weight? And, how much area would it need to stay at an internal temperature of 37 degrees Celsius?

  • $\begingroup$ I would say it isn’t, as it is planet sized, I would recommend asking: Is this living planet plausible? $\endgroup$
    – user84509
    Commented Apr 13, 2021 at 20:58
  • 1
    $\begingroup$ It doesn't cover every aspect of your question, but How big would an amorphous blob have to be to toss part of itself into orbit? is quite similar and my answer there covers why your reproduction method won't work. $\endgroup$
    – Rob Watts
    Commented Apr 13, 2021 at 21:10
  • $\begingroup$ More or less plausible, even naturally evolved one. Some aspect more some aspect less plausible. but elephant in the room the organism itself, so nothing to worry about, hardest part is handwaved already. Firts two answers present atm are weak $\endgroup$
    – MolbOrg
    Commented Apr 14, 2021 at 1:53
  • $\begingroup$ Your projectile seeding is going to be a problem for any planet as big as mars, let alone something the size of Earth, reaching escape velocity is going to be the problem // plausibility becomes less implausible if you downgrade this to a living asteroid or small moon // that aside John Varley has pretty much already done this with his Gaea trilogy, you're just scaling it up to planet size, or trying to // so maybe check out how he rationalised it first & then go from there. $\endgroup$
    – Pelinore
    Commented Apr 15, 2021 at 22:19

2 Answers 2


Efficiency numbers are off

Plants are .1% to 4% efficient at turning incoming energy into plant. So your 26% is much too generous. These numbers are from plant efficiencies for the whole biofuel thing. Granted the life prior to the living planet could have evolved higher efficiency which was then incorporated.

How would exoplanet seeding evolve?

Evolution happens over many, many generations. A generation that takes hundreds of million years is just not going to happen. There are plants that have pods that launch seeds at high velocities. But to get seeds that can reach solar system escape velocities, tolerate being frozen for 100M years, to then survive reentry. Evolution does not form novel structures from nothing. This stretches plausibility to beyond breaking.

Immune systems don't work that way.

Antibodies break down any organic matter that comes in contact with the surface, preventing infections by pathogens and giving an input of nutrients.

Antibodies just stick to their target, sometimes interfering with function. That is it. Other systems grab the marked target and destroy. But how does the organism determine what is:

  • Self (don't attack)
  • Offspring/ parent ( does it eat the offspring or parent)?
  • Don't care (food/nutrient, )

That is, what is other that is not counter productive to attack. If it is too aggressive all food will be rejected. Very easy for a hyper destructive organism to be come self destructive.

Your living planet is a mono-culture extreme.

How will it handle a rapidly evolving bacteria or fungus? On it's home planet there will be bacteria and viruses that have co-evolved with it. What about prions? cancer?

What portion is plausible.

Plants that span continental regions and large are plausible. There are organism that span hundreds to thousands of acres.

I suppose it could be created/engineered by an insane society that welcomed that they would be killed by their creation.

  • $\begingroup$ autoimmune aspect is good, the rest can be be improved $\endgroup$
    – MolbOrg
    Commented Apr 14, 2021 at 1:50

No, it is not realistic

First of all, 50 km/s is ridiculously fast. If you assume an unrealistically fast acceleration of 100g (far more than a human could reasonably survive) it will still take 50 seconds to get up to speed, during which time it will travel $\frac{1}{2}at^2=125000$ meters. Thanks to the $t^2$ component of that equation, having a more reasonable, slower acceleration will require an even greater distance. In other words, there is absolutely no way to "fire something out" at 50 km/s. It has to be a rocket, and a organic rocket seems very implausible.

Second, 50 km/s is ridiculously slow in astronomical terms. The escape velocity of the Sun from the orbit of the Earth is 42 km/s (source), so it would leave the solar system at a hard max of 8 km/s. That in turn means it takes at least 37,000 years to travel a single lightyear, and >100,000 years to travel to the closest star systems. It would have to be completely inert in order to survive that distance, and that means no course corrections or being able to repair damage due to interstellar radiation.

You could still make an interesting story with this organism as a premise, but just realize that it is in no way realistic.

  • $\begingroup$ Why u compare it to a human? It may be a bunch of cells suspended as tissue or independant cells in some slime/water. Nothing significant will happen with such a seed form for that time, not even talking about cases which can be hardened for all that. And sure it does not have to be a rocket, but that a different subject, one of the nonrocket launch systems, not sure if it has mentioning on wiki. $\endgroup$
    – MolbOrg
    Commented Apr 14, 2021 at 1:43
  • $\begingroup$ @MolbOrg comparing to a human is useful for making an abstract number feel a little more real. It's also an indication that anything sensitive (such as DNA or whatever the organism uses as an equivalent) is likely going to be damaged by that degree of acceleration. $\endgroup$
    – Rob Watts
    Commented Apr 14, 2021 at 3:16
  • $\begingroup$ Humans do survieve 80g acceleration, how about that as a shocker, lol, here, I put too much attencion on lungs, but experiments are more interesting. U never used a centrifuge for purposes of biology research, or else u won't even dream to go so far and bold to say about destruction of DNA, 100g is not enoug to do anything to cells besides precipitation. Useful g's are measured in 1000's and more 1-30 kG. And u have destroy cells before that, to get their guts, those numbers won't do that work fo you. So comparison is misleading at best. $\endgroup$
    – MolbOrg
    Commented Apr 14, 2021 at 9:26
  • $\begingroup$ But your another answer u reffer is good, does not reach perfection, as an example 10% increase of speed of sound due compressin of water at something around 4000bar, just to begjn with, another aspects I didn't read that question, but applied for here it is enough if you capable to launch few miligrams once in a while. But it does conduct perception of certain problems, so a good answer. $\endgroup$
    – MolbOrg
    Commented Apr 14, 2021 at 9:38

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