I was wondering what the physical characteristics/traits are that would make an alien race perfectly adapted to exploring space.
Assuming this race does not have FTL, but could reach potentially 0.8C, I would guess that a fairly long lived species is one trait.
What other biological traits would help them?
EDIT I have removed the planetary traits section of my original post, as I agree with @JanDoggen that it makes the question much broader.
They would need to be able to live without breathing anything, for sure.
Their muscles and bones would have to be exempt from atrophy, because you aren't using your bones much in space so they would tend to thin out. If their muscles never atrophy, then they probably aren't growing much muscle regularly either, so they must have some mechanism for movement other than human-style sinews which contract. Maybe they move by means of some kind of magnetism (the way electric 3-phase motors and solenoids do). Or maybe they move by filling pouches with fluid to expand them (kindof like pneumatics, but with pouches). Or maybe they move by popping little round nodes to convex or concave, (like a venus fly trap). Or maybe they move by altering their crystal structure to produce little pieces that stick out and then come back in on various parts of their body (I don't know of anything that does that).
They need to get their energy from somewhere, so I'm thinking starlight is abundant enough in space that they can use that. But absorbing light means that you aren't getting very much energy very often (especially while you're on a planet with a dense atmosphere). So they need to have the ability to store a lot of energy long term, only expending what they use. So maybe on a planet with an atmosphere which doesn't allow any sunlight through, they can only be on the planet for a few weeks before they start running out of energy.
But if your creatures are organic then it's likely that they grow physically during their lives. Hydrogen is abundant in space, so a good race that eats should be able to eat just about anything with hydrogen in it, and then internally transmute that into helium, and then carbon. This implies that they have nuclear fusion reactions going on in their bellies, so they will need to do that in very small amounts at a time to maintain their physical existence safely. They'll have very warm internal body temperatures during whatever phase in their life they want to grow (maybe they grow as long as they're alive, maybe they choose to grow whenever they have time for it). Since they need to be able to handle very cold external temperatures, I'm thinking they must have a well insulating exoskeleton, and since they are using hydrogen to grow it means they'll shed their exoskeleton on a regular basis as they grow.
Standing upright on two legs is good for a being which is well adapted to one single planet with a very specific gravity. A race which is able to travel to any other planet, and handle the wide variety of gravitational pulls on those planets, would have numerous short legs, or no legs. Short legs are harder to break, and easier to push yourself up on, and if you have more than four of them then you can stand on some while you move others. The race would need a flexible body, too, to handle various terrains. So with the exoskeleton, maybe a segmented body like a millipede (but it doesn't have to be long like a millipede). It doesn't make much sense for a race adapted to the maximum possible planets to have wings, because they depend on gasses being around to push against.
The size of the race is effectively arbitrary; no matter how big you make them, there will always be a bigger race out there somewhere. If you make them too small, though, then it could get hard to manage production of energy eventually. A small race has some advantages related to their ability to keep food for a long time, etc.. They could survive for a long time on a small cash of food.
A hardcore surviving species should have tons of kids in one gestation cycle and be ok with many of them dying, but expect each one of them to share its food with the pack (think cockroaches). However, since this race is adapted to minimizing energy use and storing it long term, it might make sense for them to have few babies and work hard storing up energy to produce each one, like people do. You'll have to decide if you want them to gestate their babies internally, or externally in eggs -- and that might depend on how they get around space and their social structure. Maybe they shoot their eggs into space at random and the eggs hatch and colonize nearby planets, or maybe they keep their babies close and teach them the culture of their parents.
Anyway, this post is getting long. I hope it helps!
A digital life form. A life form that has evolved past the need of a biological body to survive AKA reached the technological singularity.
They can be uploaded and downloaded from any robotic or biological body purpose built. They can be backed up, restored, copied and even merged should something happen. They don't need air or food and can exist in virtual worlds while travelling the vast distances between physical worlds. They aren't affected by the ravages of time and can exist on worlds that would kill any biological life.
They are the perfect space faring life form.
I would say that one of the most valuable traits for such a race would be to have the means to modify their own physical traits. It could be an innate ability that would allow them to evolve necessary physical traits to survive an environment they have entered including Space itself, or by means of gene manipulation to give themselves those traits depending upon the technological advancement of such a race.
Example: Increase bone density and related attributes to explore a planet with high gravity. Decrease metabolism rate while in space travel to endure long travel time while using minimal resources etc.
I am drawing my idea from the movie 'The Day the Earth Stood Still' in which the visitor arrives in a semi-human state within an organic cocoon or layer and then gradually becomes fully human. If the race doesn't have to steal the DNA as in the movie but be able to modify their bodies to enter a stasis for space travel and evolve back to their desired form once they reach their destination it would mean they have evolved into space faring explorers. While other races which haven't been space faring long will still be relying machines and technology heavily.
Based on the OP's recent comment about technology I am conflicted since the answer could change based on what is considered perfect adaptation - Natural Adaptation to Space Travel? or Technology Augmented Adaptation to Space? Since there is a mention of other races in the galaxy with more advanced technology which could put them at an advantage to invent more ways to adapt to space travel and assuming the 0.8C is attained through technological means and not purely biological.
For biological beings, the difference between living in space and living or working on planets is likely to be about as extreme as the difference between sea creatures living at the bottom of the Marianas Trench and a hummingbird.
For living is free space, a biological organism might choose to become a symbiont, using a "plant" half to collect solar energy (or suitably modified leaves to collect energy at other frequencies) and convert materials into oxygen and carbohydrates or analogous materials. The "animal" portion consumes the oxygen and carbohydrates, and its wastes are fed back into the plant half to continue the cycle. The leaves can also provide temperature control by varying the amount of sap flowing through them, and even provide some limited mobility for solar sailing.
Plant/animal symbiont in orbit
The main issue is the amount of surface area needed to effectively collect and utilize solar energy, plants on Earth typically only use about 1% of the Sun's energy. Even with genetic engineering to increase efficiency, there may be hard thermodynamic limits to how efficient a plant can be.
The actions needed to live and work on the surface are complicated by the massive variables in conditions. Are you prepared to work on the surface of Venus, with an atmospheric pressure of 90 Atm, and a temperature close to the melting point of lead? How about Mars, lacking in Oxygen, protection from Ultraviolet light and hovering near the freezing point of Carbon Dioxide? Jupiter's moon Io has the most active volcanoes in the Solar System, an atmosphere of sulphur compounds and sleeting with hard radiation from Jupiter's magnetic fields, while Titan has a dense atmosphere of nitrogen and hydrocarbons, lakes of methane and is cold enough that ice is as hard as granite.
It is very difficult to imagine a single creature or even machine capable of working in all these environments (and throw in the depths of the Earth's oceans, the microgravity surface or Ceres, the oceans under the ice of Europa or the sun blasted surface of Mercury....).
If your creatures are biological, then they may have developed as symbionts, but use high bandwidth connections to control robotic devices they custom build for each environment while remaining safely in orbit.
Since it's unclear as to whether they may merely drift through space or must actively operate in it, I suggest something like the water bear (tardigrade). There is a fair amount of science fiction that already depicts these as capable of surviving in deep space, due to their cryptobiosis. This state allows them to shrivel up to survive in extremely hostile conditions, but not necessarily live in them.
https://en.m.wikipedia.org/wiki/Tardigrade
If they are able to get into space, and headed in the right direction, they could "hibernate" for the trip, only reviving once they detect livable conditions.
These life forms would need to be a macroscopic extremophile. Capable of operating in atmospheres ranging from hard vacuum to high density corossive.
They would need a hard outer carapice, capable of containing vital organs. They would need fat reserves internal to the carpiace to store energy. They would need a method of storing or replenishing oxygen. Perhaps organs that can store compressed gasses, or potentially a symbotic relationship with bacteria/phytoplankton that can scrub/replenish oxygen.
Their sensory organs would need to be external to the caripace, and expendable. Once they return from a harsh environment, they can grow back. Sensory organs should be able to detect light, heat, radio frequencies, ionizing winds, gravitational forces, and chemicals ie, a sense of smell.
They should have multiple methods of communication, and should have languages based more than one medium: light, pressure(sound), chemical, and/or radio.
Their limbs should be replaceable, and regenerate if lost or damaged, and end in gripping hands/claws. Limbs should be more or less omni-directional, capable of reaching in most directions out from the center pressure vessel.
They should have a method of movement in null gravity, even if that is something as simple as gas-jets.
Basically it this point they would resemble a crab optimized for null-gravity.
I was wondering what the physical characteristics/traits are that would make an alien race perfectly adapted to exploring space.
A virus.
Injected into an asteroid it can travel indefinitely until it impacted the surface of a planet, and if the conditions support life it would grow into a living organism. The virus could just be the way the species packages it's DNA for delivery in a new ecosystem.
