This is for a book. An ancient, badly damaged, base has been found in the asteroid belt. The base has been open to the vacuum of space, although a large proportion of the base is within the body of the asteroid and not on the surface, so has been protected from solar radiations and micro-meteor impacts.

I wanted the protagonists to discover remains in the base that will allow them to get a rough age but I don't know the limits of carbon dating or if it would even be possible, given the overall conditions caused by a hard vacuum. I don't know if carbon dating is a viable option and, if it isn't, does another another field of science offer a plausible way of getting to the age of the base?

Note - The base is tens of millions of years old and the majority of it is buried deep under the surface of the asteroid.

The technology basis for the protagonist is roughly fifty years advanced from current day earth. Two major changes are hydrogen-based power units have replaced all fossil fuels and inter-solar system travel is viable but only just starting using ships powered by EM Drives.

The technology basis for the base builders is highly advanced; viable interstellar travel capabilities, for example.

Not sure I understand the reasons for this being put on hold as it would appear to fit in to the "Effects of events or world elements, including biology, technology and magic, on specific aspects of that world's societies, cultures, and environment" caveat of the exchanges rules.

Can you please explain what I am misunderstanding ?

  • Edited for spelling, clarity and on hold clarification.
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    $\begingroup$ Carbon dating is applicable only for organic material of terrestrial origin. It works by determining the ratio between the amount of carbon isotopes present in the sample to be dated; by assuming that originally the ratio was the same as in Earth's atmosphere the age of the sample can be calculated. (Massive oversimplification.) It cannot possibly work for an object of alien origin, because we don't know what the ratio between carbon isotopes was originally. And any way it has a hard limit at about 50 thousand years before present, because for older samples there is not enough C-14 to measure. $\endgroup$
    – AlexP
    Commented Nov 14, 2017 at 11:26
  • 2
    $\begingroup$ worldbuilding.stackexchange.com/help/on-topic: How to achieve a specified effect in a defined world, including by the use of biology, technology or magic, while maintaining in-universe consistency. Is this not what OP is looking for? I suppose the question could move to astronomy stack if it must be actual science. If fictional or newly invented methods are allowed this has to be here. Vote to reopen. $\endgroup$
    – Willk
    Commented Nov 14, 2017 at 15:15
  • 1
    $\begingroup$ I keep hoping that questions like this will be deemed on topic because they strike me as perfect. Why have a science tag, a hard science tag, or a reality check tag if the only on topic questions revolve around mythical creatures or the physics of a tidally locked planet? Clearly the poster is attempting to build a world. I also vote to reopen, and to review what WBSE should be about. $\endgroup$
    – SFWriter
    Commented Nov 14, 2017 at 16:08
  • $\begingroup$ Reopen. Archeology on sth. that would be on-topic (like an asteroid colony) is certainly also perfectly within our subject. Where else? $\endgroup$
    – Karl
    Commented Nov 14, 2017 at 19:05
  • $\begingroup$ Maybe one of the close voters could throw a bone to Gawainuk and suggest how this might be modified to warrant reopening. @L.Dutch? $\endgroup$
    – Willk
    Commented Nov 15, 2017 at 17:50

6 Answers 6


Extra-solar and extra-terrestrial material is very hard to date, which works for you

To elaborate on @Gawainuk's comment: all radiometric dating (*) of objects hinges on that you have a good estimate — a "baseline" — of how radioactive a material was when that material was "fixed" in the object.

On Earth this is comparatively "easy". But out in space, this can become really tricky, especially so if the material has its origins outside our solar system. Further complicating this is that ionizing cosmic radiation affects how radioactive materials are, adding a significant count of radiation that messes up the baseline. On Earth our atmosphere decreases this effect significantly, but it is still significant enough that we must consider it.

For your purposes, what your protagonists can do is to compare material found deep inside the base, that can be concluded had its origins on the surface of the same asteroid. A simple geological and then chemical analysis can conclude this with ease. They then do a radiometric comparison with surface material that stayed exposed to cosmic radiation, with the material that was deep inside, and thus shielded. With this your protagonists can get a ballpark figure of the age of the base that puts them within one or two magnitudes of its true age, i.e. "My best guess says this is between 10 and 100 million years old, my worst at 5 to 500 million".

(*) Carbon dating is one of several ways of performing radiometric dating. There are other substances apart from carbon we can do this on, providing different time scales, ranging from decades to billions of years


Carbon dating is problematic, as you need to know level of Carbon 14 in the atmosphere at the time the animal or plant you are studying died. But there are other radiometric dating methods which might work.

The simplest thing would perhaps be if they found a machine similar to a radioisotope thermoelectric generator, which is a device that uses a radioactive substance to create electricity. It is today used to power interplanetary probes, among other things.

If the protagonists find a device powered by say plutonium-238, they can look at the ratio of plutonium, uranium and lead to infer the number of years since the plutonium was refined. This is similar to uranium-lead dating which is a dating method that can determine the age of rocks that are from a million year old to several billion.

The base may also have a derelict nuclear reactor, similar to that of nuclear-powered submarines today. You can have the protagonists do a similar analysis here.

Edit: A generator using Americum-241 makes for more straightforward dating, see discussion below

  • $\begingroup$ Plutonium-238 has a half-life of 88 years. This base is supposed to be 10 000 000+ years old. This means at least 100 000 half-lives (divisions by 2) have passed. This translates to 30 000 magnitudes (divisions by 10). Considering that the number of atoms in the universe is approximately 10 to the power of 81, in other words 81 magnitudes, we have to conclude that even if the entire universe had consisted of Pu-238 when this base was created, all that material would now have decayed, many times over, down to the last atom. :) $\endgroup$
    – MichaelK
    Commented Nov 14, 2017 at 12:03
  • $\begingroup$ @MichaelK: Plutonium-238 decays into Uranium-234 on its way to lead. Uranium-234 has a half-life of 246 000 years, meaning there will be about 10^12 atoms of lead for each atom of Uranium-234. This is about the same ratio as that of Carbon-14 to other carbon atoms in the atmosphere, so should be well within the limits of analysis. $\endgroup$
    – Abulafia
    Commented Nov 14, 2017 at 13:18
  • $\begingroup$ Ah, that works well then! :) $\endgroup$
    – MichaelK
    Commented Nov 14, 2017 at 13:20
  • $\begingroup$ @MichaelK: A more "pedagogical" sceanario would be a thermoelectric generator using Americum-241. (real-world generator) While having a short half-life, it decays into Neptunium-237, which has a half-life of 2 million years. $\endgroup$
    – Abulafia
    Commented Nov 14, 2017 at 13:26
  • $\begingroup$ Baseline for carbon-14 is not the problem. Half-life is. Half-life of 5700 years means that about 60,000 years is the limit of its usefulness for radiometric dating. So using it on a base which is tens of millions of years old just isn't going to work. $\endgroup$ Commented Feb 3, 2019 at 2:17

Date the base by accumulation of solar wind particles.

The solar wind moves out from the sun and hits everything in the solar system. Our magnetosphere and atmosphere deflect most of the fast moving charged particles. In places like the moon without that protection, fast moving particles hit and accumulate. In this article they examined accumulations of neon isotopes deposited by the solar wind on the moon and on a spacecraft.


For the last 4 billion years, energetic solar particles have bombarded the Moon. But studies of these particles in rocks brought back by the Apollo astronauts have mystified scientists.

That is because the ratio of two isotopes of neon have varied according to depth in the rocks, with comparatively more neon-22 than neon-20 at lower depths. That suggested that counter to theory, the Sun had once been significantly more active than it is today, shooting out higher energy particles that could travel farther into the rocks.

Now, Ansgar Grimberg at the Swiss Federal Institute of Technology (ETH) in Zurich, and colleagues have resolved the conundrum.

They used nitric acid to strip away layers of a specially made metallic glass that had been exposed to the solar wind for 27 months on the Genesis spacecraft, which crashed to Earth in 2004.

When they measured the neon distribution in the exposed solar wind samples, they found the top layer had considerably higher proportions of neon-20 than observed in the lunar samples, while the underlying layers were similar to those seen in the Moon rocks.

That suggests that erosion from micrometeorites and space particles removed some of the original neon from the top surface of all lunar rocks.

More importantly, it also shows that the solar wind alone – not any extra activity on the Sun – can explain the puzzling neon variations in the Moon rocks, with the heavier neon-22 simply implanting itself more deeply than neon-20.

The sun ejects lots of particles including massive ones like xenon. Any number of different stable elements could be used and it makes sense to use more than one. One can extrapolate from the above article that the more massive the particle, the deeper it goes when it hits that makes sense as the massive particles have more kinetic energy. The base will have particles implanted in it no matter how deep. If it is very deep it will be more massive particles than light ones, but they will be there. Given a known rate of particle deposition by the solar wind you can calculate the age of the base by the amount of particles which have been deposited there by the solar wind.


How about if an artifact is found that dates the base. Something like a calendar left by the occupants of the base and one of your characters puzzles out how to read it. Maybe something related to position of the stars relative to the solar system or something.


One option is to use meteorite impacts

miteorite dating is usually used to date large impact basins and other planetary structures. It tends to use impacts caused by large objects of tens to hundreds of meters or more in diameter, but there is no reason why this technique shouldn’t be extended to micrometeorites on any surface.

Over thousands of years meteorites would cause a roughening of surfaces in general and pitting in places. Depending on the size of the surface installation and the exact amount of time, a few larger impacts might be seen that were capable of making holes in the outer structural material.

Statistical analysis of the size distribution of such micro craters could provide an estimate of the age of the installation assuming that the structure would have been installed impact free from new materials. The background level of expected impacts could be discovered from examining the surface of the asteroid that was not covered by the base or other nearby planetary bodies using traditional techniques as well as radioisotope dating.


There are a large number of problems with this scenario. First things first Carbon-14 Dating tops out at around 50,000 years. Second Carbon-14 dating relies on the fact that Earth has a steady rate of Carbon-14 creation and terrestrial creatures have a predictable rate of carbon uptake, thus dates in the nuclear age are skewed by fallout from atmospheric testing. Thirdly exposure to vacuum has some strange and unpredictable effects on organic material that would be hard to factor in. Fourth, any radiological dating will be "messed up beyond all recognition" (that's a technical term) by exposure to cosmic radiation outside the shielding of a thick atmosphere and strong magnetosphere.

So that's things you can't easily use, you can possibly use the rate of decay of the construction materials in vacuum as a benchmark for the age of the site since that will be fairly uniform, for a given material.


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