How could an organism reach escape velocity using only biological means?

Question

The species in question that can survive in the vacuum of space for extended periods of time (say months). They can feed on stellar radiation and have an innate sense of orbital dynamics. They come from a planet with several moons and they frequently travel from the planet to the moons and back, and occasionally venture out to other planets. The planet has similar gravity to Earth.

Moving in space seems somewhat plausible. They could use thin membranes as solar sails and bladders of gas for maneuvering.

How do they get into orbit?

I'm looking for a mechanism that is primarily biological rather than technological. I recognize that the line is fuzzy, so the main criteria I'm looking for is that one of these animals could make it happen purely of their own means, without assistance from any others. Beavers can make a lodge, but each one can do it by their own power without reliance on the work of other beavers, so I'd count this as biological. Bees making a hive takes a lot of bees to do and no single bee can reasonably do it by itself; this, I'd classify as the lowest threshold of technological. A human making fire with a bow drill that they can make themselves out of materials in nature is grey area; they need knowledge passed on by other people, but otherwise can do it of their own means.

If the planet needs to be substantially less massive that Earth to make this possible, that's an option, but the closer to Earth's gravity, the better.

Clarifications:

• The organism should be big enough to be visible unaided, but beyond that is whatever size makes this plausible.
• The entire organism does not need to make it into space (and it seems unlikely that this would happen). All that needs to happen is an egg, seed, or larva capable of growing a new organism makes it into space.
• A given member of this species does not need to make this trip multiple times in a lifetime, and the trip to space could definitely be part of a very specific lifecycle phase (like Salmon spawning, only much more extreme).
• The organism does not need to be an animal. If there's going to be a lot of photosynthesizing or if it would need to have a large stationary component, it could be a plant.

Answer 1

Bordering on plagiarism, borrowing from Larry Niven's stage trees the creatures while immobile while landed could have further adaptations to its canopy to allow its foliage to fold away at launch, then deploy again in a way to act as a solar sail.

It could even exist as an ocean living organism that launches from the water. There are any number of possibilities from the basic idea.

Answer 2

Nice, you know your shortcomings, nice definition of what passes and what's not.

While it probably possible to imagine a creature which can do as you want - hop from a gravity well to space periodically, doubt it can do it frequently however, as even few times is somewhat an achievement.

We may probably imagine them being able to produce carbon nanotubes natively, as part of their tissue, 100GPa tensile strength and thus being able to accumulate required energy over time and then use atmosphere gas and (or) water to propel themselfs like a typical rocket. Or even rocketfuel, without cryo to it, and be in essence a rocket.

However it probably just a good(or not, taste preferences) handwavium

More realistically, on the border of handwavium it can be a part of some maturity metamorphosis, when a bigger body shoots out its part(s) in to the space. There are real proposals of gun like solutions which should be capable to shoot a ton or so in to space, and it looks viable. But sure mass of the gun and mass of a projectile - one is much bigger than another, but there is a certain simplicity to installation, it just long, km's long.

• km size organisms are not common, but some forests are one tree actually(or something close to that), so not impossible. So some photosyntetic organism, without necessity to move that much, maybe, but not only.

And those guys, which are shot to orbit, they do not travel that much of the orbit of the planet, they hunt for those spores to grow, and that this bigger ground body lives by itself long enough to shoot many of those projectiles, with nanotubes and such it may endure more than one shot, plus healing, and other ways, etc. Projectiles, those shoots, are some sort of spore witn a shell, so as it is food for those in orbit, so as it can become some sort of parasite, which sticks to already grown thing in an attempt to consume it, and some times it just kills kessler syndrome like or just by a collision.

So when they grow enough, those who survived it all and were in luck they may choose to get to higher orbits, to avoid being shot by a parasite thing or collide with others, and maybe later they evolve in something which travels a little bit more.

Ecosystem of those wont't be so chil, as you seems anticipate, it will be harsh bloody massacre in slowmo over 1000's of years, a blood bath from which rare surviviors will emerge and wander off. The thing will evolve sloow, but it can be engineered.

So situtation can be quite complex. So easier it is to handwave the first option. So while it is not impossible to imagine such thing, hard to anticipate it to evolve, but who knows who knows, and I guess there is a chance to make such thing to be.

PS more like comment answersince I can't comment due wb javascript updates.

PPS

• "can be a part of some maturity metamorphosis" whichever way you do it (gun or rocket) it necessarily loses a large portion of its mass with every ascent into orbit and beyond .. so one way or another whatever method is chosen it can probably be viewed as this to some degree, it's going to require a long growth period to replace the parts used for each launch whichever way you go .. if the OP was using a smaller gravity well things could be different. – @Pelinore

About how long it takes to recharge. Due the size, photosyntesis is the most likely as an option, not necessarly the only one, especially if we talk about artificial creature, but for evolved one it is a most likely option.

In earth conditions, 100x100m plot of land can bring about 2 tonnes of fuel, in form of grass itself, so if we wanna some juice from them it will be less. So, the thing grows some sort of "limbs" getting 2t of fuel per season is optimistic scenario. And so for "just" 2000t (Falcon level, not exact number, with just 5-10t payload to obit) it will take 1000 years of milking that 1ha plot of land. Sure it takes less time to grow bigger, and 1x1km may spedup things to a decade or few(there is time required to collect energy to grow those limbs over that bigger area)

All in all it decades between recharges, not a thing to do at wimp, unless it is some from of gray goo and it more tuned to this kinds of things, which can be if it designed.

PPPS speeds and feeds of patch/"limbs"/energy collector growing

• "100x100m plot of land can bring about 2 tonnes of fuel" Hmm 🤔 perhaps we might consider a fungus, or something that shares some of its characteristics, this one covers 5.5 km subsurface with its Mycelium – @Pelinore

Growing a patch takes some time. If we take grass as our example, then it grows about 1g of dry material per meter per day, there is root system as well which also should be grown, let's say it almost the same size/mass as what is on the top. And full grown system is about 400g per m2

• grass is used in the answer, and elswehere in the post, only to estimate potencial of speed of growth or speed of producing useful chemicals("fuel"), just because I know some numbers about it, but by itself it not necessarly a best syste, however one of many possible solutions it may as well just look as an regular grass patch, but it does not mean it is your regular grass patch, or that it should look like one in other cases. But less stuff one has tk grow faster things go.

speeds and feeds

If we take our grass model as studu case then close to a best speeds case, speed of growth, how much it covers, doubles each year/season (not a strict calculation, but some approximation), then if it starts with 1m2 then it covers 1ha in 13-14 seasons, 1km2 - in 20 seasons, 100km2 - in 26 seasons. Exponencial growth rate, and artificial system can do that.

Real grass patch probably grows more linearly, like proportional to circumference/perimiter of the patch - so it more like linear speed 1m per season, and 1ha is then in 50 seasons, 1km2 in 500 seasons.

• real plants use seeds as well, to speedup, which are carried by wind or animals or..

So depends on strategy, and abilities of that organism its time to expand the means of collecting energy something in between those numbers.

And depending on how much fuel it needs and speed of growth it will have some typical size as optimim between the speed of expansion to collect more energy and energy flow due time of that expansion.

I mean that it all depends on events whjch have place in the system, for cases when we optimize it for time, there is an optimum between how much to invest in system which collects energy, and how much energy to extract after that. It typical EROEI, almost a definition of it, and specifics of what is actually optimal, is not an easy question, but at least it easy to say that be huge huge huge humongous big is not neccessarly a best strategy for all cases. But something up to around 1km2 may be a reasonable number.

types of plants moss, grass, bushes, trees

As for which plants to model after, all those 4 categories have their advantages and disadvantages in this situation, and it depends on climate and environment. Trees are good to extract stuf from depths, but they are expensive energy wise per square meters(poor EROEI). Moss is cheap energy wise to cover surface(good EROEI) but poor at extraction of water from depths so it grows in naturally moist environments. Grass and bushes are somewhat in between.

Each of those potencially can create root system, but some horizontal tree like structures look like an solution in this case which nature and skme designs could take, as it needs channels of considerable sizes to collect stuff in a central location. Maybe more like lianes, on the ground. Just interconnected regular root structure won't do the job as it has other goals. (Tree roots have the goal to gather stuff to a central location - so it a good model)

So as layout it may look like a mold from a top(or like a tree leaf), as strucutre elements it lianes(big diameter closer to collecting point, branching out like in a leaf), grass bushes as main energy collectin element. And its size pretty much unlimited, and only limited time how long it it sufficient for it to collect what it needs.

But it just one of the potencial options, there is some variety of what kind of shapes it can potencially take to solve energy collecting problem.

Parasitic properties to solve the problem, liane like, looks like a good strategy in the case, if there are forests to exploit, etc. That all is a deeper level of speculation.

Consider things only on energy level, to a certain point is a lesser speculation, or if we skip which specific shape a solution takes then it is close to be not a speculation, because we rely on conservating of energy law, physics and such things.

Specific solution it is a design work, and it can take multiple shapes, and is more subjective, to what people think is more viable or less viable.

All in all - all kinds of specific solutiins can be reasinably imagined in this case, and which one is better realy depends on an environment, to which we have no knowledge about.

Answer 3

A planet might have a mountain (or a few) that extends far above its atmosphere. Or many; with atmosphere being something that exists in valleys. Creatures may have started climbing high to get away from air-breathing predators. And so evolved various forms that can go without air for a very long time, and also harvest energy from solar or other radiation. Eventually, such creatures reached the mountain tops.

Wings are useless high above the atmosphere, but they may fly in a bottle-rocket fashion expelling gas and liquid. Useful to get away from an anaerobic predator, or for flying off a steep mountain to land far away. Extreme variants could expel 90% of their mass, to go as far and fast as possible. For this is an arms race, and the predators may have evolved the same trick. The best fliers survive.

Now, if a small moon has a very eccentric orbit, perhaps it occationally get near enough that its gravity picks up such flying animals. At first, they simply used this to go further away and land on other continents. Eventually, they learned to stay in orbit, safe from predation for a while. Maybe they can take off from the small moon too; low gravity and it might have edible minerals like water ice.

Answer 4

Your planet has a 1 hour day

You may have heard that most rocket launches happen close to the equator - that's because a lot of the work to get up to escape velocity is done by the Earth's rotation (about 1/24th). If Earth spun just under 24 times faster, anything "stationary" on the surface of the equator would be just below escape velocity. Your creatures can reach escape velocity by travelling to the equator and jumping.

Of course, this raises its own problems. The atmosphere would also be at escape velocity, so would be stripped away (though fortunately your creatures have some capability to survive that - I wonder why that is?). But also, any perturbation of the surface of the planet would cause surface material to fly out into space and the planet would start losing mass - we probably can't actually get to escape velocity.

To get the last little hurdle, your creatures follow a three step process:

Wait for an eccentric moon orbit

Your creatures have an innate understanding of orbital mechanics. So they can predict when one of those moons is about to come close to your planet - lending it's own gravity to assist any attempts to escape the planet's velocity (effectively reducing the escape velocity temporarily).

Get higher

You mentioned building dams, but there's another animal that builds structures - spiders. Only instead of making a web with a high tensile strength material, your creatures make a spire with a high transverse strength material - effectively making a small space elevator.

Flatulate

A by-product of making the spire-silk is gas. The creatures store this gas until they are at the peak of their spire, the moon is just overhead, and they let it all out.

Answer 5

Riding the atmospheric electricity

The planet has exceptionally high levels of atmospheric electricity due to combination of strong magnetic field and strong star wind. (Or maybe there's a magnetar neutron star nearby.) So living organisms evolved to electrically charge seeds, then whole bodies, to spread themselves long distances. The higher, the better, and over billions of years this means adaptation to stratospheric vacuum and cosmic rays. On top of thunderstorms there are electric fields strong enough to accelerate dust to escape velocity. The creatures are much larger than dust though, but still very lightweight. Most of their bodies consist of very long carbon nanotubes and they resemble hair balls. The hair holds immense electric charge required for interplanetary launch by a storm. In space the hair is discharged, pulled closer and doubles as shielding against harsh environment. When landing on another moon/planet it is used as ablative heat shield and needs to be regrown.

It all requires some way to manage electric charge of their whole body in vacuum, this means using ion beams or cathode rays. I don't think these are beyond the reach of biology. Or it is for them a primitive technology, like fire is for us.

Answer 6

The Creature is lighter than air

These creatures are born with a pollon-like airtight capsule structure within which they can withstand the extremes of space. When it is time to move on to another planet, they pump out as much air as possible from their capsule until there is a high vacuam inside their body. Terrestrial organs such as the pumping organ are discarded, and off it flies! 🚀 By the time it reaches atmospheric altitudes with air density matching its effective density, solar winds are strong enough to carry it. Besides periodic revival (for purposes as DNA replication to prevent irreversible mutations from accumulating), the organism ceases all chemical activity by radiating nearly all its heat away until it is just a few uK above 0. When it enters a hospitable planet, it revives for good, fills up with air, floats around until it reproduces, and then repeats the process.

Answer 7

The energy budgets of interplanetary travel on reasonably short time lines are insanely large.

Earth's escape velocity is 11 km/s. Every kg of matter we push out of the Earth's gravity well is 60,000,000 J of energy. 1 kg of fat is 37,000,000 J; rocket fuel is in that same range, as that is basically what practical chemical energy can store.

To convert stored energy to kinetic and not lose it all to atmospheric friction, you have to get out of the atmosphere rapidly, which means burning the initial stored energy fast, and probably starting high. Even if you lose a small amount to atmospheric friction, you'll still lose a bunch to entropy.

This means for every kg of stuff you get out of escape velocity, you have to burn significantly more than 1 kg of stored chemical energy to do it. In turn, this means that whatever you eject out of the atmosphere is a small component of whatever sent it up.

You can shave off a good bit of that kinetic energy by only reaching orbit instead of escape velocity. But that doesn't help as much as you might want if you want to reach another celestial body; the moon is about 400,000 km up, and reaching it requires almost as much energy as escaping the Earth's pull entirely. Getting there quickly also requires more energy than getting there slowly.

...

Now, we could imaging bypassing the chemical energy problem. Imagine a planet with nuclear based metabolisms. Creatures have evolved to build reactors. The first creatures that did so "built" breeder reactors, which "polluted" the biosphere with waste products. This would first cause a massive extinction event, like the oxygen crisis on Earth did, but eventually creatures would adapt to this new energy source.

After a time, the waste products would become food for other creatures. Biology would flow from uranium breeder reactor plants, whose waste products would feed herbavores, and then the herbavores would be consumed be carnivores in turn.

Cold-reactor animals use the passive radioactivity of materials to provide energy over time. Hot-reactor animals cause cascades and have to actively moderate their nuclear metabolism.

With the higher energy densities of a nuclear metabolism, making creatures capable of flying to space becomes more practical (if you consider animals who evolve nuclear reactors "practical").

The planet these creatures evolve on would have a higher metal content in its crust, and extremely exotic and toxic biology.

But natural uranium has an energy density of 700,000,000,000 J/kg, many many times that of chemical storage. Orders of magnitude of energy forgive a multitude of sins.

I am imagining a large blimp type creature with a reactor gut. It splits hydrogen and oxygen to inflate its bladder, and recombines it to descend. Heat pumps evolve to improve its reactor efficiency. Metals are used to build structures that biology doesn't deal with well, like high radiation, and are maintained by biological expendable "cells". Insulation in the form of foamy metal, and eventually vacuum chambers, develop to allow for higher heat gradients. This is exploited by heat pumps to eventually evolve cryonic storage, which improves the creatures ability to use oxygen and hydrogen.

Rockets for high-altitude maneuvering, where the air is thin, start to develop; if you can go higher than your predators, you are safe. High-altitude is used by "pregnant" blimp-creatures to grow a child away from predators and food sources; the predators follow, possibly evolved over millions of years from the same blimp-creatures who fled the out performed predators.

An arms race continues. Thrusting yourself into low orbit becomes a solution, no longer able to use the blimp for lift, but that doesn't matter as maintaining orbit becomes cheap. Ram jets, that pick up what atmosphere there is, concentrate it, heat it up by the reactor, and expel it out the back are used to reach orbit; rockets to stabilize.

As food is nuclear fuel, these low orbit creatures are a food source. Predators evolve to eat them, pushing the orbital biosphere further out.

Answer 8

How could a creature reach escape velocity using only biological means?

Not practically. On earth escape velocity is 11.2 km/s, or over 25,000 mph. This is so far beyond anything that a biological entity can do I think I can confidently say it is not reasonable. This is also ignoring the atmosphere, which will make it much harder in more ways than one.

You can reduce the size of the planet, for example Mars escape velocity is "only" 5.03 km/s, and mercury 4.3, but these are in the same order of magnitude and really do not help enough.

The way it is theorised to happen is that meteorite impacts throw up matter from one planet that would achieve enough velocity to escape to another planet. This could have happened to bring life from Mars to Earth.

Answer 9

Slow and steady...

Earth's gravity (aka, acceleration) is 9.807 m/s². To make a point, if you have an acceleration away from the earth of 9.807000...0001 m/s², you will eventually escape Earth's gravity. Said another way, if you have enough fuel to consistently travel, oh, let's say one mm/hr away from the Earth, you'll eventually escape it. Example: the ISS orbits 400km above the Earth. It'll take 45,662.1 years to do it... but if your fuel and supplies can hold out that long, you'd get there because your acceleration was in excess of gravity.

But what if we run with your solar sail idea? Using this uber-cool explanation of solar sails we discover that if we assume that the creature doesn't need food (e.g., let's assume a portion of the sunlight is used to keep the creature alive), then the creature could be the size of a bird and eventually leave orbit.

It will take a honking long time... but it would make it!

The problem is easily stated as, if you have enough fuel (sunlight) and time (food/energy), then you can always justify a creature biologically leaving the planet and traveling between them.

Your problem isn't "can I travel in space biologically?" Your problem is, "does my creature design allow it enough food/energy to survive the time required for the trip?"

Now, if we want the creature to be (*ahem*) realistic, then we need to worry about the fact that its sails won't be perfectly reflective, it needs food and water, etc.

But I like the idea better than flatulence that creates an initial velocity of hundreds of thousands of km/hr....

Answer 10

Examining the ecosystem of the "creature" could help define the lifecycle and metabolic processes of the species.

It must have a planetary phase, presumably where most of the metabolizing happens. A phase where it escapes the orbit of a planet. A phase where it crosses the vacuum of space. And a phase of reentry into atmospheres or landing on other orbital objects.

These different environments are so extreme, in temperature variation, chemical composition, radiation levels, and gravitational forces, I imagine the creature would have to go through pretty dramatic changes during a very long life cycle. Different stages in the life cycle may resemble plant or fungal life more than terrestrial animal life.

The planetary phase: Adult

• Probably the most metabolically intensive phase.
• Chemically, what does the organism need for its metabolic processes?
• Probably survives best on smaller rocky bodies. Escaping the gravity well of larger gaseous planets poses more complications.
• This may be the most active phase (or phases) of the organisms lifecycle, akin to a frenzy of mating and feeding and storing up the energy it needs for escaping orbit and the long cold journey through the vacuum.
• This phase of intensive feeding may also be one of the core drivers in their ecosystem which pushed the evolution of travel between rocky bodies in space.

The escape phase: Larval

• After the creature has mated, reproduced and metabolized a colossal amount of energy it would enter the escape phase.
• It could be imagined that individuals in this species have the ability to leave orbit on their own. Maybe they have some mechanism like the hypertrophied claw of a pistol shrimp that blasts them out of the gravity well into space. This would require a much larger, more complicated organism.
• Another option is the mass ejection of offspring all at once at some point in the lifecycle of the organism. The organism may use naturally occurring volcanic activity to launch spores into space. Or like some plants use ballochory (ballistic seed dispersal) the organism may create eruptions of its own, producing volatile gases under pressure which result in a mass ejection of seeds or spores.

The vacuum phase: Nymph

• I like the image of the organism using large organic solar sails in the vacuum of space. This may be more animal, with sensory organs for detecting the infrared signature or gravitational field of small rocky bodies hundreds of thousands or millions of kilometers away. Or it may be more like a seed with a large sail on the solar wind.
• Is the interplanetary or interstellar? The requirements placed on the organism change by significant orders of magnitude depending on what the volume of it's theoretical environment is. If the organism travels between rocky bodies within a single solar system this requires exponentially less energy than if the organism is also escaping the gravity well of the local star for interstellar travel. The scale of metabolism required changes dramatically.
• It would take years or even decades to travel between planets within a system (a chemical rocket would make the trip from earth to mars in maybe 7 months but, the organism would have to survive longer, more unpredictable journeys). To travel between stars may take centuries or millennium.
• To have a viable chance of seeding other rocky bodies within a solar system with offspring that can survive the diverse and extreme conditions would require millions of seeds or spores or offspring to survive the escape phase. Trillions of offspring would be needed to have a viable chance of covering the huge volume of even our own solar neighborhood in the local bubble.

The reentry phase: Encysted or Cocoon

• Once the nymph or seed became caught in another gravity well and began spiraling towards reentry, I imagine it would have to become encysted or form some sort of protective shell.
• If it survived reentry into an atmosphere or striking some rocky body without any atmosphere then, I imagine the majority of cysts would still perish. The ecological window the organism can survive in would already be unimaginably wide but, can't be infinite. Even within our own solar system the diversity of the environments on rocky planets and moons is extreme. If the organism can survive and grow after splashing down into one of Titans lakes of liquid methane, I can't imagine it would have a very high survival rate in the dense atmosphere of Venus where it may be more than 400 degrees Celsius.

Answer 11

Atmospheric mountains

First of all, you don't need escape velocity. You need to be able to get to the Lagrange points between the planet and the moons. This already simplifies the matter a lot, but you still require insane amounts of energy to get there.

"Getting into orbit"

Getting into orbit is a tough job. As the creator of XKCD tells us: "The reason it's hard to get to orbit isn't that space is high up. It's hard to get to orbit because you have to go so fast."

Getting into space then is 'easy'. Even an airplane has done it. The difficulty is staying there. Imagine you have a mountain or special balloon that goes to the edge of the thermosphere:

Now if you throw something it'll just fall down to the Earth.

What you need to do is throw it hard enough that the curve of throwing will go around the Earth:

On Earth this takes about 8km/s, or 28800km/h or 17895,5 mph. Even starting at the edge of space without wind resistance is a tough task. Even high speed meglev trains in near vacuum tunnels, so practically no friction, are thought to go 'only' 1000km/h. The hyperloops a a bit faster with an expected 1200km/h, but still well short of the mark. Even at a theoretical best of 8000km/h we're still way short. However, we don't need to get into orbit. We can do the simpler task of just getting off Earth and reaching the Lagrange point. If the moon(s) are in the right position, it's just straight up. If you reach the Lagrange point between the celestial bodies you have reached a form of equilibrium, allowing for your own solutions of navigating space.

Getting to a Lagrange point

Getting to a Lagrange point is just straight up, but not easier. The Lagrange point L1 between Earth and the moon is 1.5 million kilometers away. If you are at the edge of the Thermosphere you're only 800km away from the surface with about 8,8m/s gravitational pull instead of 9,8. That means you're still going to have to fight a rounded 1.5 million kilometers of slowly reducing gravitational pull to get to the L1 point.

A big problem of rocketry is taking fuel with you. You have a payload. You make a rocket with fuel and find that you now have an extra rocket with fuel to take with you. So you extend the rocket and add more fuel. But you just added more rocket and fuel, so you need to add more...

Luckily this does end with a fuel with high energy density. If the density is high enough you have more thrust power per weight of the fuel than the fuel itself weights. Yet here is one of the problems. A creature needs to feed on energy to survive. Next it needs to add absurd amounts extra to produce many times it's body weight (depending on the energy density of the fuel) as fuel. This needs to be stored safely for a certain duration of time and eventually into something that can direct and ignite the fuel. Iirc they often use a secondary fuel to supply oxygen for a good and powerful burn, meaning you need two kinds of containers.

Suffice to say that eventually you need a lot of energy and materials to get to L1 even from the edge of space. It doesn't matter if you use magnets, fuel or telekinesis. The power to get a positive speed away from Earth all the way to L1 needs to come from somewhere and is a lot.

The only option to achieve enough energy in any plausible way is that it's a tiny, tiny creature. That means that if the conditions are right it can gain a lot of energy from the environment, like bacteria in hay have an abundance of energy around them that they can start spontaneous fires. A large size creature like a human simply can't do this by any plausible means and survive. Though I have to say it isn't impossible for biology to create high density fuels inside them, it seems a bit out of reach as well.

How to make it as plausible as possible?

To make it as plausible as possible we can do a few things. The climb out of the atmosphere is the hardest part, as you need to also content with the air friction. Having a less thick atmosphere will help a great deal, both in depth and density. If it is thin enough you can have a mountain reach part or even all of the way. That way the climb can be done in steps instead of all at once. Spreading this effort for going high into the atmosphere will already help a great deal. Alternatively you can have the creature use something like a weather balloon. They can reach up to 120km in Earth atmosphere. The problem of balloons however is that they can't really go out of the atmosphere. At best they can skim the edge, like a ship on water, but this would be extremely difficult.

A thinner atmosphere would also be a reason for the creature to exist. It is closer to space, with a more abundant or stable food source if it goes outside the planet's atmosphere.

A less dense planet with a lot less gravity will obviously also work.

To gather enough energy it would need to be small to take advantage of unexpected high densities of energy that can be gathered and processed if needed. A problem is that it would need to move the energy relatively further than a bigger creature if you want to climb a mountain for example.

Maybe it would be better to not travel the system and stay closer to Earth. Go up that mountain jutting just out the thin atmosphere and bask in the rays of the sun. Or have it be a weather balloon creature that skims through the high, thin layers of air. With little protection of the outside layers they should be bombarded by the interstellar radiation. Each is more plausible than making high grade rocket fuel and launching into space.

But last and not least, you could have these creatures be in an asteroid field. They could feed on the debris and use ice for oxygen, among other things. As the gravity of the asteroids is already minimal and no atmosphere to speak of they can easily escape it, extending their tendons to sail through the massive asteroid belt and collect interstellar radiation.