# What would the scientific explanation be for an energy source that can last 130,000 years?

I am playing with the idea of an alien ship landing on earth 130,000 years ago. Over time it's covered up with water and sediments and is eventually discovered in modern day.

It contains numerous hibernation chambers for aliens hence it would need an energy source to moderate and run the chambers. Scientifically how could a single energy source or battery last all that time?

• You have two issues here: the actual energy source, and the durability of the generator and consumer(s) of that energy. The latter is the bigger problem, IMO. – Zeiss Ikon May 10 at 14:11
• In this case, assume that the chambers were designed to last and preserve its users indefinitely. – Luke Duffy May 10 at 14:15
• Note, “Lasts a really long time” is not the same as “Never runs out”. – RBarryYoung May 11 at 14:18
• – Clockwork May 11 at 16:49
• To answer the question in the title... The sun is a pretty powerful energy source and it's lasted orders of magnitude more than 130k years! – Hearth May 12 at 3:53

### Neutrinovoltaic panels

We can generate pseudo-never-ending power from all sorts of particles impacting all sorts of surfaces. Starting with the most common - visible light photons. Earth-made photo-voltaic panels (aka - solar panels) can last 20+ years, turning photons to power for as long as the panels are in the sun, slowly degrading from UV exposure and hail impacts.

If we crank up the craftsmanship and keep the hail away, photo-voltaic panels should be able to last a long time. Cranking the craftsmanship is just a factor of the story telling - how well made was your alien ship? If the thing is still standing after 130,000 years, I'm guessing they're pretty good, so if the ship had solar panels, and it ever saw sun - they'd probably still work too!

Unfortunately, your ship isn't in direct sunlight, so we have to abandon photons and move to another particle.

You could use betavoltaic panels if you're near radiation. These are a real thing earthlings can make and can used to power low power device for long periods of time by converting beta radiation into power.

Alpha voltaic pannels are also a thing - we can use Alpha particles to generate power.

Gamma voltaic devices are also a thing, we can use gamma particles to generate power.

I think you see where this is going: Humans already have Alpha, Beta, Gamma, and visible light powered generators. You just need to find a particle that can get all the way down to the ship without wasting any energy hitting pesky dirt or water.

Neutrinos are your answer - they travel through basically everything, except the specially made panels on the ship, designed for exactly this purpose, which have been receiving power from the sun for a few hours every day when the planets rotation lines the panels up with the sun and they receive several kW of Neutrinos.

Copying some maths from PcMan:

7e10 solar neutrinos per cm2 per second. Most of these are from p+p fusion, thus 400keV. So 0.004486Joule per second per cm2. That's a small but respectable 44.9 watt per square meter.

You can tweak how much power the ship actually gets by varying the panel sizes, ship location, and ship orientation until the numbers make sense. (Optimal alignment is panels perpendicular to the ecliptic plane) If the ship has, say, 30 square meters of panels, that's a little under 1.5kW of power at peak alignment, but its probably following a sine wave up to its peak. If used to charge some capacitors that last the "night" it's able to put out a constant say 100 watts. That is not enough to power the computer or sensors or anything more than a few faint emergency lights, but definitely enough to keep the already frozen crew in insulated pods frozen for another 24 hours in emergency preservation mode.

It makes sense to include a power source like this. If I'm freezing myself for long distance space travel. I'd want to know that if the reactor scrammed and the backup generator ran out of fuel, there was another backup power source that work almost anywhere and wasn't going to kill me if in shadow.

• Just to nit-pick -- gamma radiation is photons, just with very high energy/short wavelength. – Zeiss Ikon May 10 at 14:39
• I was also considering catching solar neutrinos and turning them into energy, but gave up on finding the numbers to do a back-of-the-envelope calculation of how much energy it would actually be possible to generate that way. Is your "several kW" number based on anything? – Philipp May 10 at 14:48
• @Philipp Gut instinct, googling the eV of these particles, what-if.xkcd.com/73, and a partially educated guess. – Ash May 10 at 14:50
• @Philipp 7e10 solar neutrinos per cm2 per second. Most of these are from p+p fusion, thus 400keV. So 0.004486Joule per second per cm2. That's a small but respectable 44.9 watt per square meter. Now you just have to figure out how to catch them! – PcMan May 10 at 16:00
• This might even explain how the ship got found. There are no known materials that effectively stop neutrinos, right? We do research by sending them straight to the earth, and they always come out for measuring on the other end, except if we send between these two stations... what could possible be in between them that's blocking the unblockable? – Erik May 11 at 9:01

A black hole with mass of 3.6 million tonnes has a lifetime of 130000 years and will emit $$2 \cdot 10^{13}$$ W. Slightly increase the mass and you can prolong the lifetime as you please.

Then apply the HandyWavy$$^{TM}$$ stack to convert the Hawking radiation emitted by the black hole into usable energy.

Don't forget to put into the balance also the maintenance and repair robots and their energy needs.

• And heavily handwave cooling... A 20 TW heat source anywhere on Earth would be the wonder of wonders. – AlexP May 10 at 16:27
• @AlexP actually no need for cooling, the handywave magtainment 6000 (magnetic containment) field converts your usual waste heat output to electrical energy at 99.9999% efficiency - assuming they have one, because how else are they containing the blackhole in a spaceship? – TCooper May 11 at 1:16
• @TCooper but you can't just tell that excess electrical power to patiently wait till you need it. Just as with powerful heat source the electricity must go somewhere. – Dmitri Urbanowicz May 11 at 11:32
• @TCooper: Better be sure your handywave Second Law compensators don't break down. – Michael Seifert May 11 at 15:42
• @DmitriUrbanowicz Exactly, it's converted to cover the electric cost in maintaining the magnetic containment field. Basically just turn the energy on itself to contain it indefinitely - tis the nature of a handywave device to almost break the laws of physics after all – TCooper May 11 at 17:02

Geothermal power.

The ship has extended a long and durable metal spike down 20 km into the upper mantle. Heat is conducted up this spike to the ship, where it powers a Stirling engline on the temperature differential between the mantle and the cool waters where the ship is.

The ship came to rest in a place where the mantle was close enough to the surface to access. This was on purpose - the ship scouted for such areas before landing. This ship is purpose built to maintain the hibernation chambers using geothermal power.

• Over a span of 130,000 years, I'd be concerned about earthquakes or other geological activity damaging the spike. – GrumpyYoungMan May 10 at 23:20
• @GrumpyYoungMan: Including corrosion of the spike or even deposition of waterbourne or steambourne minerals encasing the spike, reducing its thermal properties. – Fred May 11 at 5:44
• Instead of just one long metal spike, I would put in a factory that slowly mines the area around it for ore and extracts metal to craft into more metal spikes to drop down over time. The whole system should be self-sustaining in order to accommodate for the fact that the original spike will corrode over time. So some of the energy gained from the spike should be devoted to the life support systems, and the rest to making sure it can continue acquire more energy to last over the eons. – Darrel Hoffman May 11 at 13:31
• @GrumpyYoungMan if the ship has a maintenance system that should not be an issue, very little actually movement happens from earthquakes unless you fall on a faultline – John May 12 at 0:48

You could use RTG, just as humans do for some of our spaceships. Only you need to select radioisotope which would last longer. Humans have used up to Americium-241, which has half-life of 432 years, but they could use radioisotopes with longer half-life, for example thorium-230 which has half-life of about 75 thousand years. But your power requirements should probably be modest to be running from such long-lasting power source (or have a lots of it).

If you need larger power surge capabilities though, you would use RTG to charge up a supercapacitor, which could then provide much bigger power at once - but would need long time to recharge again.

• I love this idea! I think the half-life of thorium-230 is actually 75 thousand years—perfect for this application. – Vectornaut May 11 at 12:55
• Here's an Insect template you can use to calculate the power per mass for initial decays of a given isotope: decay_energy / (atomic_number * 1.661e-27 kg) * log(2) / half_life -> kW / Mg – Vectornaut May 11 at 13:14
• And here's a nice table of radioactive isotopes, which includes half-life and decay energy. (Each energy comes with an I number, which I think tells you what fraction of decays have that energy.) – Vectornaut May 11 at 13:20
• Thorium-230 is a great choice, because it does a high-energy alpha decay to radium-226, which quickly does another high-energy alpha decay. Overall, if I've calculated correctly, it should give off over a kilowatt per ton. ((0.763*4.687 + 0.234*4.620) + (0.944*4.784 + 0.0555*4.601)) MeV / (230 * 1.661e-27 kg) * log(2) / (7.538e4 years) -> kW / Mg – Vectornaut May 11 at 13:21
• If it's to last over 100,000 years, you might be better starting with U-234, which decays to Th-230 with a 244,500 year half life. This will increase the energy yield by 10%, but reduces the power to 1/3 of that for Th-230. You will have to take into account the degrading of the thermopiles, both through alpha-bombardment and old-age – CSM May 11 at 15:28

## Antimatter Batteries

I think anti matter fits your use-case well.

## Benefits of Antimatter

1. Very simple to moderate the amount of draw, low minimum power threshold

Your energy extraction is directly proportional to the amount of mass you input into the system. Many other power systems like Fusion, Fission, or Hawking Radiation all have minimum output thresholds or require a minimum amount of energy to self-sustain.

If you don't want power out of an antimatter battery, you just don't input mass - so it has a minimum energy generation of 0, in principle.

Of course, containment fields etc. will still have some kind of 'vampire draw', but as a percentage of overall output it should be much lower than competing alternatives.

1. Extremely high energy density

As a fuel source, it's nigh impossible to beat antimatter. If you want mass -> energy conversion of any kind, this would be how to get it done, as the energy contained by your reaction mass is equal to MC^2. It's difficult to quantify the energy demands of your space ship, but a gram of antimatter could power LA for about 2 years, give or take.

1. Mechanical simplicity

To trigger a reaction that generates energy, just touch the anti-hydrogen. Although containment fields are non-trivial to engineer, this is actually pretty simple - it's just a magnetic cage in a vacuum chamber. It could be completely solid-state, in principle. The hard part about generating power from anti matter is just getting antimatter in the first place, but your magic aliens have obviously solved that problem already.

1. Completely self-contained

An antimatter power generation system does not require any external force operating on it to produce power - it doesn't need to get hit by photons or neutrinos, experience significant gravitational interactions, etc. This means it can continue to operate anywhere, under any conditions, as long as the reactive mass doesn't run out. As a side benefit, because it's totally self-contained, it can also be nigh undetectable (with adequate shielding). A power source that reacts to external inputs such as a gravity wave generator or even Neutrino voltaic panels would leave a trace of some kind as it stole energy from it's environment, whereas this system would leave only waste heat.

## Drawbacks of Antimatter

There are, of course, some problems with this solution that may render it unsuitable for your story.

1. Minimum mass

You need an amount of reactant mass equal to, well, E/C^2. So depending on total 'E' expenditures for 130 millenia, that could be quite substantial.

1. Exhaustible

Your power source is a really great battery, but it's just a battery. It can run dry. Eventually.

1. Requires maintenance

This is not a drawback unique to antimatter, as it applies to all possible power generation options, but it is something to think about.

Entropy exists.

You can't escape it.

Everything, and I do mean everything, degrades to some extent over time. You can't run a constant current through a wire and expect it to stay pristine - you will need something to replace power conduits, electromagnets, etc. Even assuming exotic materials that mankind has never seen, 130,000 years is simply too long for something to exist without experiencing wear and tear.

Your ship will require some system or robotic staff that is capable, in principle, of replacing and retrofitting any individual component of the ship. Given advanced future tech like molecular printing and/or atomic forges, it's not inconceivable that a perfect (or near enough perfect over the course of this timeframe) repair crew could exist - but you'd need to have one, and it'd need to be active periodically to affect repairs.

• Drawback: the energy output is in the form of gamma rays which IIRC are hazardous to living beings as well as highly penetrating, making it difficult to shield against, and difficult to capture for extracting energy. – GrumpyYoungMan May 10 at 23:26
• @GrumpyYoungMan If you're going to extract energy from the annihilation reaction you sort of have to capture the radiation, otherwise you just kind of annihlated some matter, which is a VERY FUN way to spend a wednesday afternoon, but kind of useless as a generator. – Iron Gremlin May 10 at 23:29
• Two things: 1.) Any energy source will be detected because at some point you are getting heat out of the ship. Converting natural radioactivity to power is going to be the hardest if not impossible to notice - how can you know that "rock" X first absorbed gamma rays, converted them to electricity and then heated up; vs the same without electricity step. 2.) I think you should put energy density in the answer: 9e16 J/kg. Times 2 if ordinary matter is "free". So 1MW constant power consumption requires only about 25 kg for this amount of time = negligible. – Zizy Archer May 11 at 8:16
• @ZizyArcher re: 1 - This is correct, but it's also a law of thermodynamics, so it applies to all options equally thus it's something of a moot point. I'll be less absolute in my language but I don't think it qualifies as a refutation of the general assertion. re : 2 Thanks, will do. – Iron Gremlin May 11 at 15:03
• downside you have to burn a lot of that energy just containing the antimatter. – John May 12 at 0:46

A fairly small mass of antimatter, with a suitable (left as an exercise) conversion system, will keep a long time (assuming the magnetic bottle and vacuum hold) and provide energy enough to run minimal systems for that kind of time period.

Which begs the question why anyone would design a ship with that kind of endurance. Even though we build submarines that can go years without refueling, mission duration is typically six months because that's the limit on consumable supplies the boat can carry (frozen foods and ingredients for on-board cooking are the main limits).

One potential out is if the hibernation capsules require very minimal power compared with normal ship operation; for instance, if they have insulation capable of holding, say, liquid nitrogen for centuries without external input, the onboard power systems and refrigeration only need to remove the tiny residual heat leakage. That would allow a ship capable of a few years' voyage to rest this way for tens of thousands of years in an emergency situation.

• Well, there is no data on the duration of a normal trip for this class of starship, other than it being long, (hence the hibernation chambers capable of lasting 130000 years). Quite possibly, 130000 years is the equivalent of a quick trip to the grocers. If you design a starship for a million year journey, then a 130000 year dip in a pool is barely a footnote. – PcMan May 10 at 15:48
• Or, if you designed it for a journey of a thousand years (reasonable for sub-light travel between nearby stars), this might be a reasonable length of expected emergency endurance (though getting buried in sediment implies little choice of landing site). – Zeiss Ikon May 10 at 16:03
• It's possible they are deliberately waiting on some future state to arise, such as the seemingly unavoidable demise of the human race, or maybe they found planet in the middle of an ice-age and decided to wait for the thaw? – jwdonahue May 10 at 22:56

There's no real free energy BUT maybe the aliens are able to harvest energy from sources that rarely run out:

• Gravity
• Neutrinos
• Magnetic Fields
• Space-Time Waves

The generators must be made of extremely durable materials and the energy conversions must be solid state to avoid corrosion and abrasion.

The hibernation chambers must be extremelly hermetic and must be able to reach 0 reactions inside it using very few energy to keep this state.

• Only two of these are plausible; the other two require motion to extract meaningful energy (unless you want to break physics entirely). – jdunlop May 11 at 22:04

Technitium-99 atomic battery. It has a half life of 211,000 years. This is ultra simple technology that we can produce today. Your aliens keep an atmoic battery on every one of their ships for backup life support. Things go wrong in space; reactors meltdown, generators fail, and engines explode. It could be thousands of years before a rescue ship reaches you, or a hundred thousand years for your momentum to carry you back into a trade lane. When things do go wrong your aliens hunker down in the hibernation pods and wait it out. The atomic batteries are four times as large as they need to be, so that they could power your life support for up to 633,000 years. More than enough time.

Fusion power.

Nuclear fusion can run off water, so a low draw engine could last a huge amount of time, and if they needed more resources they could collect it slowly from ambient water, extracting the precious deuterium.

They could have nanites which drew from local earth resources to help repair any damage and replace broken parts, along with alien technology that made more use of non metal metal subsitutes so they didn't have reliance on special rare materials.

## Possible to engineer for

It is possible to use radio isotopes with comparable half-lives ie half life of 100k years, and a large chunk of it, but that would require pre-planning to be stuck that long. So not plausible. Its possible to have large enough conventional batteries, if it was planned for and the draw low enough.

### Batteries are not the answer

But the point is moot because it seems implausible for people to plan to stuck in a location not of their choosing for 100k+ years, little gain, lots of risk, lots of cost. Unless, perhaps they were deliberately trying to avoid something. That is to say, long term storage is not the answer.

## Low maintenance fusion power system

Best bet in my opinion is just an low maintenance power supply with automated maintenance. With pairs and spare of all the components. This sort of system would be useful in almost all situations.

That is have three primary nuclear fusion power plants, pair and spare. A redundant automated maintenance and repair system. A redundant system that can manufacture more repair units that can repair the power supply and the manufacturing system, and any other shipboard systems such as the hibernation system.

There is available water so fuel can be collected and stored. IF the ship were in space comets, gas giants all have hydrogen for fuel. So lots of fuel.

A fusion power system such as this is good for all around active duty as a space ship. It can be used directly as propulsion system. A high utility system is more plausible then situational what if systems.

### Just that standard ship power plant.

So with fusion and a really good automated maintenance system, it could sustain power very long time. With a maintenance system that due to some chain of events didn't wake anybody.

# The power source is maintained by a swarm of drones

An ant colony is essentially a single organism: an organism with millions of eyes, limbs, and a voracious appetite.

These alien ships are controlled by some kind of shipboard intelligence -- AI or some horrific organic thing -- and all ship functions are performed by drones it controls. Each ship has a variety of drones to handle the variety of jobs on a ship: a small set of large drones for heavy tasks like waiting on the occupants, doing hard engineering, or loading cargo, and a large swarm of tiny drones to handle tasks like interior cleaning, exterior hull repair, or electronics work.

The ship's power source does not normally have an operational lifetime of 130,000 years. But when such a ship finds itself stranded on a planet, it naturally turns its attention to long-term survival -- its own as much as that of the passengers. It has been sending its army of nanomachines into the environment to scavenge for energy and materials.

Over the millennia, this ship has refueled, repaired, upgraded, and finally replaced its power supply many times. No doubt it has invented some truly novel ideas in its desperation. Perhaps in hard times it has even cannibalized a few of its slumbering passengers (or their cryo-beds) when badly-needed elements were in short supply.

The only way for a porchlight to stay on that long is for someone to be inside tending to it. So, make the porchlight be that someone.