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Assume a plant was engineered to cope with a wide range of different environments, and to have seeds that were capable of traveling through and surviving both the depths of space and re-entry into atmosphere. Given this assumption then you can see these plants would slowly (much slower than light speed of course) spread throughout the galaxy.

The problem though is gravity wells, how would the planets get their seeds into orbit with sufficient escape velocity to reach other planets or better yet other solar systems? Is it even possible for a purely biological process unguided by intelligence (other than that which designed the planets in the first place) to do this?

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    $\begingroup$ Though not directly related, this excellent answer is a relevant read. $\endgroup$ – overactor Feb 26 '15 at 12:16
  • $\begingroup$ Even if a plant could get out of a gravity well and survive in space, the chances of it ever arriving on any habbitable planet considering the vast distance of space and the presence of solar winds which would likely push the seeds away from solar systems. $\endgroup$ – Vulcronos Feb 26 '15 at 18:00
  • $\begingroup$ There is an absolutely incredible answer to this question implied in the last sentence of Preston & Child's The Ice Limit, but I don't have time now to write a complete answer. In brief, the seeds have to be incredibly tough and once germinated they must have to create billions of additional seeds. Then they pollinate themselves back into space when their host planet's sun goes nova. $\endgroup$ – Henry Taylor Feb 27 '15 at 22:12
  • $\begingroup$ In a sufficiently violent system impact debris are a perfectly normal way for material to flit around a system. Over the long term this could transfer a lot of material across several star systems -- but that's OK for plants, they don't mind waiting so much. $\endgroup$ – zxq9 Feb 28 '15 at 4:46
  • $\begingroup$ In Larry Niven's Known Space books there is a thing called a Stage Tree. Genetically engineered as a solid rocket booster with a seed pod as it's payload. $\endgroup$ – Mr. Smythe Mar 29 '16 at 14:30

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How much energy do we need?

Well, the escape velocity of the Earth is $11,180 m/s$. To accelerate 1 gram to this speed, you need:

$$\frac{mv^{2}}{2}$$ $$\frac{1g\times (11,180m/s)^{2}}{2} = 62.5kJ$$

To find out how we could possibly generate that kind of energy, the heat of combustion of methane is $55.5kJ/g$. It seems like this might not be as far fetched as it would seem at first glance. (Though I would suggest that your seeds are made of handwavium to explain why it survives the explosion and the air resistance it would face)

What's the evolutionary advantage of intermediate steps?

I think the first step isn't too terribly unlikely. Imagine a plant that produces seeds and then explodes when it's ready, thus spreading its seeds over a larger area. You could even say that the underground parts of the plant survives the explosion and grows back in a few years. Now imagine that this plant looks a bit like another plant that the local fauna likes to munch on. And that, when you apply too much pressure to this plant when it's ripe, it explodes. This would result in most of the seeds flying off as usual. Some seeds would hit the animal though. And if these seeds have enough kinetic energy, they might even kill that animal. This ensures that the seeds have plenty of food when growing into plants themselves. As a side effect, some seeds could be shot straight up. I'm not quite sure how to justify the step from seeds flying fast enough to reliably kill an animal to them flying fast enough to escape the gravitational pull of the earth (let alone the solar system). Some wild suggestion that pop into my head are a weapon race with an animal that develops thicker and thicker skin and the idea that if you explode hard enough,you might kill some animals standing a few meters (or kilometers) away as well.

What is the benefit in the end?

I think this is where it falls flat, If you somehow manage to reach escape velocity and against all odds actually hit another planet and this planet is capable of harboring life, you still only have one plant (correction, one seed) in an ecosystem it is very likely not at all adapted to thrive in. Hardly a big advantage over other other plants.

Luckily as the writer you can just decree that two nearby planets (or a planet and its moon) just so happen to have similar ecosystems.

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    $\begingroup$ This does not take into account the tyranny of the rocket equation however, and if you try to launch it at that speed directly, the seed is likely to be obliterated by air resistance. $\endgroup$ – March Ho Feb 26 '15 at 14:16
  • $\begingroup$ @MarchHo, good point, I've added a small note about it. $\endgroup$ – overactor Feb 26 '15 at 14:32
  • $\begingroup$ You nailed it when you mentioned " evolutionary advantage of intermediate steps". Without that, such migration cannot evolve in a natural way. You were just too scared to say "no way". $\endgroup$ – Peter M. Feb 26 '15 at 17:23
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    $\begingroup$ Who says it has to be Earth? Maybe it's on a planet with lower gravity. Maybe it's on two planets that revolve around each other. If the seeds can bounce back and forth between the planets, that seems like a huge evolutionary advantage. And if some seeds happen to escape into deep-space... $\endgroup$ – BlueRaja - Danny Pflughoeft Feb 26 '15 at 17:39
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    $\begingroup$ This is very creative. Maybe the plants also have some evolutionary pressure to jump between continents? Perhaps due to a harsh seasonal cycle the continents become uninhabitable in regular intervals. If the seasonal cycle has been steadily speeding up and the continents slowly spreading we could have intermediate steps and slowly evolve rocket seeds. $\endgroup$ – Praxeolitic Feb 27 '15 at 2:55
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No

Space has to be a natural force in order for plants to use it. Plants do use wind or water simply because it is here

Using water, air, or other animals (either on fur or via digestive system) will get you somewhere even if you are not aiming

Space is hard.

To get somewhere, you have to always aim

Even if you could evolve mechanism strong enough to shoot your seeds to a speed of escape velocity, there is nothing granting you, that such seed will eventually end up somewhere.

Space is empty.

Getting from planet A to planet B is feat of engineering, because everything is constantly moving and rotating. And everything happens relatively fast. Not to mention that your seed would have to be extra durable to survive planetary re-entry (you have no engines to break, do not forget). So your seed would theoretically enter other planet at speed 11.2 km/s (25, 200 miles/hr or 40 320 km/h or almost 3 Mach). You would need really durable seed to survive that.

Space does not support life. Neither do planets.

Look at our Solar system. There are 9 Planets - Yes, I refuse to put Pluto out - and the only planet where we 100% know is supporting life is ... You guessed it, the Earth.

Suppose your plant could survive on Mars, Titan and Europa. There are 189 targets to hit in solar system (not counting the asteroids). So the probability of hitting something supporting life is 1.5 percent. Good luck

Long story short: Without changing universe to the ground, your idea is not feasible

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    $\begingroup$ Plenty of plants in our planet release thousands or even millions of seeds knowing that only some of them will find a fertile home. So if you throw enough millions or billions of seeds into space then eventually some of them will hit Titan, or Mars, or Europa. We've found asteroids from Mars on Earth for example... $\endgroup$ – Tim B Feb 26 '15 at 13:01
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    $\begingroup$ I had the same idea as you are suggesting. But still, I am pretty damn sure that even if you release billion seeds randomly into space, the chance of actually hitting something is near to impossible. My 1.5 percent is in case when you already know you are going to hit something $\endgroup$ – Pavel Janicek Feb 26 '15 at 13:05
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    $\begingroup$ But the seeds are frozen so they have time, plenty of time :) $\endgroup$ – Tim B Feb 26 '15 at 13:33
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    $\begingroup$ @TimB If the seed just flew out in straight lines in random directions from earth, about 1 in 33 billion would hit mars. If I'm not mistaken. $\endgroup$ – overactor Feb 26 '15 at 14:12
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    $\begingroup$ A plant would have to launch literally trillions of seeds for one to have any reasonable chance to find another planet habitable to it, and why would a plant have evolved to do that? $\endgroup$ – Monty Wild Feb 27 '15 at 1:36
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A lot of the answers seem to be focusing on the amount of energy required to launch a seed to escape velocity. However there is another possibility to consider. Light gasses such as hydrogen and helium naturally escape from the Earth's atmosphere all the time without needing any sort of explosions. A combination of the lighter than air nature of these gasses and the average speed of individual molecules in these gasses contribute to this.

This suggests an alternate possibility. Perhaps you have a plant which grows a seed which is a large balloon-like structure filled with hydrogen gas. Better still, not just a single seed but thousands or millions of tiny seeds. It is not unreasonable to expect a plant to evolve which can split water into hydrogen and oxygen, venting the oxygen to the atmosphere and slowing filling a balloon-like cavity with the hydrogen as it grows bigger. At a certain time in its growth cycle the seed balloon would be released and float through the atmosphere to a new location. The natural course of evolution would of course dictate that most of the time the balloon would release its seeds before ever leaving the atmosphere, but sometimes this would not be the case. Perhaps the mechanism which regulated when the seed balloon separated occasionally was faulty and it continued to grow and accumulate an excess of hydrogen until its excess buoyancy exceeded the tensile strength of the vine it was attached to. There are many possibilities.

Once this seed had cleared the atmosphere it could continue to float into space. Perhaps the vacuum of space would degrade the skin of the balloon and eventually it would pop, ejecting various seed pods in all different directions, some of which would eventually reach another planet.

Now as far as re-entry it is easy to imagine something like dandelions, where re-entry would be slow and gentle due to the seeds having something like a parachute preventing them from falling too quickly.

Update: Doing a bit more research on this, it appears that the issue of the balloon making it out of the atmosphere can be overcome if the plant-material can stretch enough to allow the balloon to expand a great deal so as to allow the interior pressure to continue to exceed the (tenuous) external pressure. In addition, at a high enough altitude, the solar wind and possible interactions with the planet's magnetic fields could provide an assist, with the enlarged surface area of the balloon capturing the solar wind like a sail to propel it away from the sun and out of Earth's gravity well. So having the balloon actually pop due to pressure wouldn't be beneficial, instead this should occur due to a slow natural breakdown of the organic material after an extended exposure to space - perhaps in the atmosphere this breakdown would occur due to passing through storms or over longer periods of time, creating a lengthy gestation period of many year similar to cicadas.

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    $\begingroup$ I can't really see how the balloon would reach space: it can only ascend while the atmosphere is dense enough, which is true only up to a certain altitude. $\endgroup$ – Maxime Lucas Feb 26 '15 at 17:07
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    $\begingroup$ @skysurf3000 Definitely easier to do in the context of worldbuilding. However, since Hydrogen gas by itself can escape into space, it seems the only thing preventing a container of hydrogen from doing the same thing is the fact that it's contained... this is where I was thinking the balloon exploding might help. $\endgroup$ – Michael Feb 26 '15 at 17:21
  • $\begingroup$ But the balloon will likely explode in the uppermost atmosphere -- still well within the grasp of the planet's gravity. The seeds would get launched outward a little from the explosion, then start coming back down toward the planet, or maybe achieve a slowly-decaying orbit at best :( $\endgroup$ – Doktor J Feb 26 '15 at 21:22
  • $\begingroup$ @DoktorJ Possibly. But if the shape of the balloon is pointed at the top, it might have enough upward momentum to make it out of the atmosphere before it actually pops. $\endgroup$ – Michael Feb 26 '15 at 23:45
  • $\begingroup$ A balloon cannot reach escape velocity. They are not anti-gravity: balloons only rise to the level where their buoyancy equals the surrounding atmosphere, not above it. As far as hydrogen escaping - a hydrogen atom has such negligible weight that it is irrelevant. $\endgroup$ – pluckedkiwi Feb 27 '15 at 14:10
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It would have to be engineered in.

Imagine this scenario: In corner A, we have a variable red dwarf star, with a predictable cyclical flare-up period, in that every x * 100 years it intensifies its activity pattern for a few centuries (perhaps due to the influence of some stellar companion, not gonna bother with those physics). Orbiting this flaring star we have two planets in a tidal lock with the star, each with a potential eye-of-sauron-style hot starside, cold night-side, but with a solid life-belt on each. During the star's normal activity, the Planet A is nice and tree-habitable and Planet B is too cold. During the flareups, the star's radiation would sterilize A, while B warms up to be nice and habitable.

Enter Deidre Skye, xenobiologist and ecopoet extraordinaire, with the full resources of her Kardashev II Culture-share at her fingertips. Her stellar white pines, besides being fantastically beautiful, have a set of heliotropic & heliometric mechanisms that detect the early warnings of an impending flare-up (while on planet A), decades in advance. This triggers a strange kind of hoarding behavior, whereby the oldest pines with the strongest root systems start to grow to an impressive size, while hydrazine accumulates in the cold safe confines of the deep root system. The fertilized acorns (or whatever the heck pines produce) are placed in these strange solid pods, with metallic buildup and a ridiculously low friction quotient. The whole tree turns into a giant hyperorbital cannon. Each time the fuel accumulation process is complete, the tree fires the pod out into space, in a direction determined by the season and the current location of the star in the sky.

Cocooned in its protective shell, the acorn-whatever survives the insane acceleration of launch, and if the launch is successful, is placed on a Hohmann transfer orbit to planet B. With luck, some of the seeds land in the soon-to-be-habitable zone of Planet B. During the flare-up, these seeds grow like crazy into their adult forms, and instantly start to accumulate reserves for the reseeding of Planet A, since the flareups only last for a century or so.

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Getting into Space Once your seed is in space for a long period of time (aka. is not in a suborbital trajectory), there are very few obstacles to it exploring the whole galaxy. Indeed, given enough with time, gravitational perturbations from asteroids or moons (or even planets and stars at bigger scales) can increase (or decrease) its velocity, thus its orbit. If you are lucky enough (which basically means "if you have a huge number of seeds), there is no obstacle to one seed leaving the solar system.

The main thing getting in the way of that occurs at the very beginning: from the ground, it is impossible to launch something into a stable orbit. That means that you have to not go through a stable orbit but instead go straight to escape velocity. Let's make some calculations. I'll assume your seeds weight 1g.

  • from Earth, the seed needs around 5x10^4J of kinetic energy to get to escape velocity. That is the energy liberated by around 12g of TNT (according to WolframAlpha). That doesn't seem much, but: (1) all that energy needs to be delivered upwards (as opposed to "in every direction" as is usually the case with TNT) and (2) your seed will be slowed down by the atmosphere. That means Earth is a no-go.
  • from something like Titan or Europa however, escape velocity is much smaller: around 2000J, that is .5g of TNT or the energy obtained by burning 0.07g of ethanol. I think that a plant might be engineered to trigger something like that. You still need a bit more energy in order to account of the atmospheric drag, but if you are lucky enough and get helped by a geyser (which seems to exist on Europa), it may work.

Surviving in space Space is empty and cold, and we are talking about a 1g seed. Solar panels or any form of energy seems a bit far-fetched. So the seed has to go through a sort of hibernation, similar to the one that can experience some extremophiles. AFAIK, we don't know of any specie that is able to survive a long-term journey into space.

Landing The good thing about spending a lot of time in space is that gravity starts to add up. What I mean is that it is possible that your seed will meet an asteroid along the way and be progressively embedded into it. Maybe it could protect it during the landing as a heat shield?

Natural Selection Now, why would a plant choose to propulse its seeds as far away as possible. Well there is one big advantage: it enables the plant to expand its territory. There are already a number of mechanism to make sure that the seeds do not end up too close to the morther-tree (getting animals to eat them, give them winglets and hope for a good wind...). And propulsion might be an other one. Moreover the plants could start by sending seeds on suborbital trajectories. This has a double advantage:

  • It fills the gap between "sending the seed 5 meters away" and "sending it on an interplanetary trajectory".
  • It explains why the seeds had to evolve to be able to survive in space.

In the end, I think the answer is yes, given enough time, but it seems complicated if you start from Earth. A smaller planet may be a better starting point.

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    $\begingroup$ There are a lot of things that could combine to help the plants and seeds. A smaller planet, of course. This also generally implies a thinner atmosphere, and it could have (relatively) higher mountains, giving the plants a better starting point and less air resistance. A faster rotation could help, too. Also, the arrangement of nearby planets in the solar system could increase the chances of the seeds landing somewhere. $\endgroup$ – KSmarts Feb 26 '15 at 16:06
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Overactor hit upon many of the factors but I don't find his answer complete.

There is no chemical explosive powerful enough to throw a seed off an Earthlike planet. This doesn't really matter, though, because you can't push any reasonable-sized seed through a terrestrial atmosphere with a single launch impulse anyway.

However, rockets could do the job. Why would a plant develop a rocket? It's on a world with no weather and no animals, it lacks any other means to disperse seeds. It would be an extremely unlikely evolutionary step but not utterly impossible if the core of the plant was an energy-storage chemical capable of self-combustion. Once you have even a crude rocket it could evolve from there.

Alternately, it could be an engineered plant. Think of the stage trees of Larry Niven's universe. A long-extinct race of biological engineers created a plant that good specimens could be used as strap-on boosters for rocket launching.

Now, combine that with a very small seed with a sail--it could be boosted to the stars by the solar wind. Incredibly slow but not impossible.

Edit: Another version of this comes to mind: The rocket launches a seed pod, once the pod is above the atmosphere it separates into two parts--the rear one being a hydrogen bomb. The seeds would have to be very radiation resistant.

The advantage of this approach is that you don't need anything like as powerful a rocket to do it, the plant doesn't need to be nearly as perfect.

A nuke would most certainly require it to be an engineered species. We do isotope separation by means of things that proceed faster for lighter isotopes, there's no reason a plant engineered to do so couldn't separate the uranium out. The hard part would be separating out the deuterium--the separator can't very well have hydrogen in it's makeup and hydrogen is one of the big components of a plant.

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  • $\begingroup$ The only problem is that a sail-seed would be blown away from all stars. $\endgroup$ – Monty Wild Feb 27 '15 at 1:33
  • $\begingroup$ @MontyWild The sail wouldn't be nearly as durable as the seed. The seed gets up to interstellar velocity, the sail decays with time, by the time it reaches another star system it's just a seed and won't be pushed away. $\endgroup$ – Loren Pechtel Feb 27 '15 at 3:02
  • $\begingroup$ Actually a certain amount of pushed away is desirable as you approach the new system to slow you down a bit :) $\endgroup$ – Tim B Feb 27 '15 at 9:01
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The plant would need to evolve for these qualities:

  • High conversion rate of CO2 to oxygen compared to its mass
  • Photosynthesis with very high efficiency (absorbed light vs. generated calories)
  • Able to grow in confined space with minimal soil
  • Able to grow in microgravity
  • Either large yield of edible fruits with high nutritious value or being nutritious itself and very high growth rate.

It would then be the ideal plant for a spacefaring species to use as a hydroculture on board of their space ships and colonies on other planets. They would take it wherever they travel and spread it with them around the galaxy.

Does this answer sound like a cop-out? Then please keep in mind that there are quite a lot of plant species which depend on animals to spread their seeds.

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I'm not sure why so many assume the plant would emulate the human method of getting to space.

It'd be much easier to use the hydrogen from photosynthesis to fill a membrane and float a seed pod to the edge of space. Air density does the work.

From there, release microscopic seeds to catch some solarwinds. Floating that high would certainly be beneficial to dispersing around a planet, leaving orbit might just be an incidental and advantageous accident.

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  • $\begingroup$ At the edge of space you're still deep in the gravity well of earth. All our satellites are outside the atmosphere, but it'd still take a vast amount of energy to achieve escape velocity. $\endgroup$ – Sobrique Feb 26 '15 at 20:54
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    $\begingroup$ @Sobrique It's a microscopic seed, vast amount of energy may be an overstatement. $\endgroup$ – Samuel Feb 26 '15 at 21:12
  • $\begingroup$ Balloons cannot reach escape velocity. A hydrogen balloon may reach very high in the atmosphere, but it will never leave it. While microscopic organisms may float in the atmosphere, they will not just spontaneously float up in a vacuum (no air currents to ride). Even if you could get to the outermost edge of the atmosphere, you are still deep within the gravity well. $\endgroup$ – pluckedkiwi Feb 27 '15 at 14:15
  • $\begingroup$ @pluckedkiwi The balloon doesn't need to reach escape velocity, you may be misunderstanding what that means. This won't work on Earth. I'm not suggesting floating into vacuum. $\endgroup$ – Samuel Feb 27 '15 at 14:29
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I think it's worth mentioning "stage trees" here. These are in Larry Niven's "Known Space" series ( http://aliens.wikia.com/wiki/Stage_Tree_(Known_Space) ), plants that grow into solid-fuel rockets to spread their seeds. Most of the time they develop into a single-stage rocket that only delivers the seeds elsewhere on the same planet, but can, if they grow from particularly resource-rich soil, grow into a multi-stage form that can get their seed pod to escape velocity.

The stage trees were genetically engineered as rocket boosters, but later went feral and spread themselves several light years (over many billions of years).

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This might become feasible if many assumed restrictions are lifted, most importantly - that this isn't Earth.

  1. Gravity and atmosphere density - the 'plant' would need to depend more on soil/fluids than on gases, but it would get around the problems of drag, escape velocity and reentry.
  2. Definition of 'world' - perhaps, rather than the planet itself, the habitable environment is its planetary ring system. The individual moonlets, etc, would then be the equivalent of continents and islands, and collisions/fragmetnations would be frequent. Also, the organism may then have entire chunks of rock to detonate, asuming it can process the minerals.
  3. The plant may be very different than what we may associate with the term - possibly using a different process than photosynthesis.
  4. Scale - considering the failure rate of 'unaimed' space travel, you'd need orders of magnitude more time and resources (space volume, mostly) than you probably meant. But then, the Universe is old.
  5. Symbiosis: the plant may be capable of this on its own, but the development of the process is not feasible without aid from non-plant organisms. The internal 'caretakers' may add aiming capability, or fashion MIRVs and thrusters ejecting depleted debris rather than spores.

I envision depleted central areas inside bubbles of the organism using 'nets' to gather and connect accumulated rock chunks, with different strategies for growth and dealing with competition (note that integration is likely); and then progression to space invaders aiming to use all mineral resources in creation of Dyson rings and more ships.


An interesting idea, though likely not what you're looking for.

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Depends on what you start on. Earth, I think is very unlikely other than maybe by accident, Large impact shoots plant material into space and it some how travels and survives landing on another planet.

The more likely scenario IMO would be a plant (engineered as you say) living on small planetoids or asteroids. Something already designed for the harsh environment of space with little resources. It could then be able to 'shoot' its spoor into space much easier, maybe with a hard case nut, and the seed doesn't germinate unless it hits something hard or has it burned off by reentry. The idea of course would be in general to move in solar system but some might reach another system after many 1000's of years (maybe millions).

EDT: Colony organisms (like lichen) or self cloning would be necessary for a lone 'seed' to be successful when it germinates.

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I base this on the assumption that we are aiming for having any kind of plant life on planets far away that do not currently harbour life (not necessarily spreading Earth's life).

To describe an upper bound of the method, I'll look at it from a high level perspective, refering to the other answers for the "technical details".
Based on this, I will show that - depending on various unknown estimates - the method of sending germs may not be worth it - because nature is faster:

The idea is doing that by spreading life from earth to other planets, using some kind of suitable germs. The germs do not use propulsion, and are send out in random directions.

Based on other answers, I assume it would require a very huge, even astronomical number of germs:

So, we hope to create one or more plants during the next couple of billion years.

We need a large number of germs to expect even a single one point at a suitable planet. But very few of these will end up on the surface of the planet and be still alive (and that's already assuming they stay fresh for a billions of years.)

All in all, that will be expensive. But let's assume we have "suitable funding".
So, we can plan to use all resources of the earth to produce and send germs.

Now we could, in principle, calculate a probability of succeeding, assuming we go to that limit.

Now, the interesting point: I suspect that it may be more probable that live develops by independent evolution on the planets.
Of course, the probability of life starting from molecules is hard to tell, but, for some definition of "succeeding" above, we could compare to find out whether nature may succed way before us.

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Hmm. Others have mentioned the idea of forming a balloon, but it meets the objection that it just gets to the edge of space and pressure changes would likely cause it to burst.

Ok. What if it grows a balloon pod that is smooth and aerodynamic for gaining good upward velocity, and when it's about ready to launch, it boils some chemicals to get a hot thin gas inside. Then it launches up to the edge of space with maybe a little upward velocity left...

... and then it explodes due to lack of pressure, and maybe some of it combusts too. It's shaped to have the explosion/combustion provide a little more upward velocity to part of it...

That would be nowhere near escape velocity for an Earth-like planet...

So what if the upmost-part of the exploded balloon fragment forms a sail shape, to catch the solar wind. This remaining bit of the membrane might be quite light but does gain momentum from solar wind. Plants can sense the direction of sunlight, and adjust themselves to face it, and the structure of the membrane might be able to shape in response to the wind, to catch it, and since it's light and spread out over a relatively wide surface area compared to its mass...

It would also act as a parachute to lightly set it down if it happened to land on a planet with atmosphere.

Maybe that could sail out of a planet's gravity well? I don't know, but I kind of like the idea.

I don't know how or why that would ever get evolved or even engineered, and most of them would just fly out into space and most of them would miss everything.

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Seeds, no way. Spores maybe. I've seem work done in real biology involving bacteria taking rides on hyperbolic comets to other star systems.

Given the numbers involved, I would still consider it rather unlikely. You're not going to make the jump in one step. Spores won't be viable that long as the transit time exceeds DNA decay time. How is your plant gonna live w/ only starlight?

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What about having a planetary crisis as its starting point?

Imagine a civilization with fairly advanced genetic engineering but space-flight capabilities similar to our own. Then, they see a planetoid on a collision course with their own planet - no way to deflect it or change its course, they know they are doomed. Once the planetoid hits, their planet is going to broken up into many, many chunks.

However, someone's pet genetic engineering project was to make a plant that could survive in space on an asteroid. Lo and behold, because of the planetary impact some of these plants wind up on a chunk of the planet that is going to be able to escape the gravity well of that solar system.

As they get farther and farther away from their sun, the metabolism of the plants will slow way down. Occasionally, one of the plants will release their seeds. Thanks to the significantly decreased gravity, it won't be too hard for many of the seeds to leave the now-asteroid. They'll still be in the gravity well of the asteroid, but it won't be too hard for a passing solar system to snag a few. If this asteroid manages to avoid being caught in a solar system itself, then over time it will be able to spread seeds to many solar systems.

If this were to happen earlier in the lifetime of the universe, then I believe planetary collisions would be more common. That would allow the cycle to repeat more frequently - plants surviving on a chunk of a planet that was broken off during a planetary collision. As the number of stray asteroids with plants on them increases, the rate at which these plants can spread will also increase.

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  • $\begingroup$ This is a nice idea, however I think the plants would effectively have to hibernate while in interstellar space... maybe they would activate when approaching a solar system warmed them up, and they would also release spores at that point. $\endgroup$ – Tim B Mar 1 '15 at 10:06
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A seed(as we know it) is only relevant here on planet earth. There is no plausible way any living thing could know how to package a seed for another planet. The only way is sending DNA code.. Which is why all living things are built from DNA code. DNA can survive in the right conditions.. This is probably how life came to our planet. Life on our planet based its structure around carbon. But on another planet the same DNA could use a different host. Life on another planet from the same DNA would look very different.

Also

It appears that a lot of comments on this forum are based around these things happening relatively quickly.. Ideas are being written off because the time scale can't be fathomed. Any travel in space will not happen in a human lifetime or maybe even in the planets life time but the goal would be to create DNA code which could survive indefinitely. And then the possibility of landing in the right environment where it can use resources to continue its progression.

I guess that is why humans are around. We might be able to work out a better way than just leaving it up to nature.. Or maybe we are nature. Of course we are nature. And we are this planets best chance of getting our life to another planet. The only other way would be if this planet was hit by something very large and earth material was launched into space.

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