At Home in Mercury
Table of contents
After the banker
When
a banker jumps out of a window, jump after him — that's where the money
is.
Maximilien Robespierre
We do not yet know how many other planets in our galaxy might be made suitable for our most valued forms of life, much less how many might sate our lust for colonisation, but within our solar system, there is just one Earth. Most of our other solar system bodies could hardly suit any self-supporting population, and those for which any form of colonisation would be conceivable at all, would be absolutely dependent on trade with major colonies, and in particular with Earth.
As for the other planets in our solar system, there is no-short-term prospect of colonising the four giants, though some of their moons might hold promise. Some of the larger members of the asteroid belt, such as Ceres, might turn out to be of value, but Luna, Mars, Pluto, and Venus have little to offer pioneers in the short term. We cannot dismiss them permanently, but, as planetary engineering projects, they present formidable challenges. For one thing, all of them this side of Venus tend to be poor in renewable energy.
Mercury however, may be more valuable — a little torrid of course, but that can be overcome if the engineering challenges look surmountable. If Mercury turns out to be merely mineable, automated machinery could suffice, but in the longer term, the planet might offer immense wealth, even for a resident human population.
Let us think about it. . .
Why and wherefore?
"Because
it is there"
George Mallory
Mallory in his brief day had drive, but there was little material point to tackling Mount Everest. In considering tackling Mercury however, I urge some decidedly promising material incentives, and part of the reason that I give might be expressed as: "Because of where it is ".
Other parts might include "Because of what it is", or: "Because of how it behaves".
For much of my life it had been thought that Mercury kept one face to the sun, and accordingly that one face was appallingly hot and the dark face might be the coldest place in the solar system. It now is known however, that the planet is unusual in its rotation and orbit, with a day length that varies, but generally exceeds its year length.
In almost perverse contrast its irregularities however, Mercury's axis of rotation has only a slight inclination to its ecliptic, only a fraction of a degree, so that its poles are not exposed to much solar radiation. Earth's axial inclination is roughly a hundred times greater.
The orbit of Mercury is unusually eccentric, and is at an unusually large angle to the solar system elliptic. This eccentricity must expose its crust to unusually large periodic stresses and tidal bulge. Accordingly, parts of the planet, particularly near the equator, might be geologically or seismically unstable, but of course, we know frustratingly little about Mercury; it hides a great deal in plain sight. Our ignorance must complicate the life of any engineer interested in plans for building on, or mining into, the planet, but other facts might actually bear gifts — Greek gifts perhaps, but gifts all the same. For example, hundreds of millions of years of consistent patterns of deformation, heating, and cooling, might have led to creation or concentration of interesting or valuable objects or materials.
We just do not yet know.
Be all that as it may, the promises that Mercury might hold could generally be categorised as: residential, mineral, industrial, and astronautic.
I don't take the residential aspects very seriously; certainly a Mercury crammed to the suburbs with offices and residences seems unrewarding. But some population would be necessary for dealing with other items, even if only to keep an eye on the AI robots. More on that later.
Mercury's mineral reserves are necessarily speculative, both in quantity and quality and even in relevance, because not many minerals would be worth exporting across space, but it seems that Mercury's crust (plus mantle, to the extent that there is any mantle) is disproportionately thin and the core is complex.
Given that solar power would be inexhaustible for our next few billion years or so, and that the intensity of solar radiation at Mercury's orbit is generally more than five times greater than at Earth's orbit, and more like ten times greater than at Earth's sea level, and that Mercury's gravity is just over one third of Earth gravity, very deep tunnelling should be cheap enough to be rewarding. Mining for siderophile metals such as the platinum group, especially iridium, might be profitable. At the same time, the crust might be rich in valuable lithophiles, in particular thorium, uranium, and rare earths. The fissionables might be of special interest as sources of power for colonies and projects more distant from the sun.
Such lithophiles might be rewarding as by‑products of the production of water from bombarding silicates with solar wind protons.
Industrial activities would have to be at advanced levels, because
only the highest-valued products would be worth exporting against the
gravitational gradient of the sun. With practically free energy and hardly any
atmosphere, many processes, such as extraction of He‑3 from solar wind, should
be cheap compared to working in space or on Earth. I have discussed some aspects
of He‑3 collection at:
https://fullduplexjonrichfield.blogspot.com/2011/01/one-theme-that-occurs-frequently-among.html
Astronautic services would be minor in comparison, but facilities on and around Mercury would be uniquely sited for continuous observation of the sun and as a reference beacon for navigation and communication.
Patently Mercury offers potential assets and resources on a vast scale; as far as I can tell, no other site in the solar system can rival them, except possibly in the Kuiper belt and the core of Earth; and those are speculative and possibly impracticable to access profitably.
So let us now consider the associated options and obstacles.
The worst obstacles
Well! some will say, in this case we
have only submitted to the nature of things.
The nature of things is, I admit, a
sturdy adversary.
Edmund Burke
I am quite sure that the obstacles that spring most obviously to mind are physical realities such as sultry nearness to the sun, and the costly navigational difficulties of travelling so deeply into the sun's gravity well, and returning from it, bearing minerals and other physical rewards.
In fact, sturdy though those adversaries surely are, I regard them as minor in comparison to less obvious items.
As things stand, I regard the most immediate of the obstacles as being our current ignorance of the nature of Mercury. We have learnt more about the planet than all we ever knew about it in even the recent past, but that still is not even nearly enough.
To begin with, we do not yet know much about Mercury's surface, even though we recently have obtained some pretty impressive photography. And what we see so far is challenging, to put it mildly; that surface looks like a planetary rubble pile, and we do not yet understand all the structures, not in detail anyway. We do not yet know how stable Mercury is, either superficially or seismically, or how hard the material is, or how useful it might be for building structures, or how difficult to drill or excavate.
We do not yet know how disruptive the tidal effects of Mercury's annual asymmetric journey round the sun may be, but the intensity of the stresses that they apply should be something like ten or twenty times as great as anything that Earth experiences from our solar and lunar tides.
Given the absence of a liquid ocean, such tidal forces might not seem impressive, but they should be sufficient to distort the planet's crust and liquid core quite severely — and that could have all sorts of temperature and tectonic effects. Quakes might be more frequent and more intense than we are used to. Internal heating of the planet's material by tidal stretching and relaxing, might rival the intensity of solar heating of the planet. They also might create local concentrations of valuable materials.
Quakes also might be the reason for Mercury's fragmented rocky surface, and if so, the engineering of structures on or within the surface, whether roads or tunnels or dwellings, might be more difficult than we would prefer.
Then again, especially because of the almost complete lack of atmosphere, day and night temperatures would differ hugely: freezing cold and baking heat for successive periods of something like 1000 hours at a time — each continuous period of heat or cold would exceed 80 Earth-days. During such nights, cold could be collected at the surface and pumped down to underground reservoirs. In turn, during the long, hot days, heat could be stored in other reservoirs. Such reservoirs could be used as the basis for temperature regulation. It also could be the basis for energy storage; Mercury offers enormous amounts of free energy, partly direct solar energy, partly by regular cycling of temperatures from hot to very cold.
I suspect, but cannot be sure, that Mercury in its orbit near the sun would be rather more subject to meteoroid collisions than most bodies, but such as they are, the collisions should tend to be energetic; the relative speeds of local meteoroids so close to the sun, would tend to be high.
What we really need, apart from more artificial satellites around Mercury, is a number of Mercury landers that could report back on impacts, and on seismic, chemical, and geological conditions; before we can predict the practicality of mining and construction in or on the planet. We still do not know how much water is frozen into the poles for example, if any.
Obviously, if we cannot rely on the stability of Mercurian topography, construction would be problematic, and if we cannot rely on the presence of large, tempting, mineral masses, mining would be a poor prospect. For example, if Mercurian accretion simply amassed its crustal materials at random, mining Mercury might be no more rewarding than mining waste landfills on Earth.
On Earth our geology has largely been sorted and modified by water and by tectonic activity, which have led to the creation of many of our ore bodies. Mercury has had nothing of the kind, but all the same, evidence suggests that its crust spent millions of years in a stable state of melt, possibly of repeated states of that type. That would suggest opportunities for the formation and segregation of possibly valuable ores on a massive scale.
Again, if Mercurian crustal rock proves to be too stubborn, mining it might be unpractical. Also, if we do not know the thickness and uniformity of the planetary crust, we cannot tell how deep to dig, or where to look for the most valuable rewards.
Mining the core might be another matter.
Clearly, until we have explored such factors and their implications, proposals for colonisation or exploitation would be pure speculation.
Real Estate
In the light of the challenges to survival on Mercury, most foreseeable colonisation probably would be off‑planet at first, say in spacecraft chasing its wandering L2 point. I discuss some incentives for exploiting that region in another essay, in which I propose the extraction of Helium-3, should that ever become worthwhile. Craft in that station also would be valuable as space beacons for astronautic and astronomic purposes. Whether it would be of value for residential and industrial functions in space, I cannot predict.
Accordingly, I do not discuss that option at any length. There is however, scope for discussion of both surface and subsurface real estate. Furthermore, surface installations for harvesting solar wind would be almost as good as harvesting it in space around Mercury.
Surface real estate
One field of interest is the slowness of Mercury's rotation, combined with its low gravity. Even at its equator one could remain on the night side or in twilight at a jog trot: less than 4 kilometres per hour. If there were a requirement for such a mobile structure to keep in, or out of, the sun it would need only very modest smoothing of the way for large vehicles, or even mobile cities, to remain in desired locations relative to the sun.
Of course, the equator is the worst case. At latitudes of 60 degrees the speed would be only half as great, and at 75 degrees about one quarter. At such high latitudes however, it probably would be more practical to build sintered rubble walls behind which stationary structures could shelter from the sun, and on which to mount photoelectric panels.
Even closer to the equator, where fixed structures were required for whatever reason, special roofing designs could support power panels and create comfortable living temperatures beneath. Alternatively, if the nature of the substrate lent itself to such structures, whole cities could be constructed in tunnels deeper than a few metres below the surface. That would be more than sufficient for protection from heat, cold, minor meteoroidal impacts and harmful radiation. Even on the surface, weather, in the sense we encounter it on Earth, would not be a significant problem.
A major, and enduring, hazard would be the surrounding vacuum if the residential structure were ruptured by seismic or other disturbances, but appropriate precautions should be practical in the design of the building modules.
Much of the illumination in such cities could be direct sunlight and all the power for digging and smelting the building material would be solar.
That refers to problems of the midday sun, but midnight would be another matter. It would present interesting engineering challenges to know how far to rely on stored heat after sunset, rather than electricity supply from cables encircling the planet and distributing power from hot regions to cold.
If we ever decrease the day length till Mercury keeps just one face turned to the sun, that would change matters of course. It would create new problems, such as creating permanently roasting and freezing faces, but improve the stability of the terrain and building structures. On balance however, I incline not to interfere with the rotation, but cannot predict what our descendents of say a few hundred years into the future would wish to achieve.
Subsurface resources
Tunnel cities would start as a sort of hybrid surface-and-subsurface real estate. By the time that they amounted to anything like real cities, they undoubtedly would be subsurface.
For more detail on the form and function of buildings, we would need a great deal more information on the nature of Mercurian geology. At present we have very little idea of which minerals of practical interest might occur in its shallower depths. If no shallow materials proved attractive, then it would be necessary to explore the planet's core. We really have very little idea of the nature of the top few hundreds of metres of the Mercurian surface. It might be largely a hard, silica-rich material, difficult to work or dig, but also might be variously fractured basalt-like stuff.
To mend such deficiencies in our knowledge is easier said than done, even though Mercury's crust is only a fraction of Earth's crust, and its gravity a fraction of Earth's gravity. In contrast, the metallic core material is pretty certain to be very valuable indeed, both in bulk and in its minor components, but, to put it charitably, it is at present doubtful whether it would be valuable enough to justify extraction and export to off-planet destinations. In fact, as I write, I am quite convinced that not only in terms of our current needs and capabilities, but also in our foreseeable future, there is no question of anything of the kind becoming practicable, let alone profitable in the next several centuries.
"Then why discuss it at all?" Homo ephemerens demands.
That would be easier to explain in the context of another essay, in which I discuss our prospects for an enhanced status of our species. Interested readers might access it at
https://fullduplexjonrichfield.blogspot.com/2025/08/immortal-imperatives.html
What it amounts to is that at the rate at which the science and technology of biology are progressing, as long as we do not destroy ourselves first, we should be able to increase human longevity to beyond anything reasonably conceivable at present. This would render projects far more long-term than the colonisation of Mercury, not only conceivable, but irresistibly, attractively, profitable. Such projects would be entertaining in their own right, as well as rendering vast volumes of raw material available for levels of civilisation beyond our current imagination.
On such assumptions, I propose some of the following approaches.
Firstly, subsurface cities could extend beneath the surface of Mercury for at least a few kilometres. That would take a few thousand years at least, and would rely on the planet's low gravity. It also would depend on the consistency and temperature of the deep rock. But an established city of that nature should be a lot more comfortable and entertaining than slum-piles on Earth, that we are pleased to call cities at present. It also would demand a lot less than we currently cheerfully inflict on our living planet, in the form of destruction of our biosphere.
So far from the surface, even in a planet as close to the sun as Mercury is, residents, whether human or synthetic, should be safe from most forms of radiation, whether cosmic, solar, or industrial in origin.
At present we have no reason to expect that Mercury has anything resembling a biosphere at all; it might contain inanimate beautiful things that no civilised person would tolerate destroying all the same, so we should not be too complacent; for example, caves in Karst on Earth contain many beautiful crystals and stalactites — but such inanimate things in Mercury would not be nearly so frequent as marvellous living things that we complacently destroy on Earth, and the rarities on Mercury should be easier to avoid and conserve.
Secondly, apart from such cities, we should be able to create super-quarries that could extend down to, or at least near to, the surface of the metallic core of planet Mercury — the real pay dirt.
Two approaches to such an effect suggest themselves. Both are brutal, but which would be more effective, I leave for our descendents to assess.
Opening the coconut
The less imaginative would be to blast a slab off the surface of the planet by steering an otherwise valueless Kuiper belt object, say one with an effective diameter of 20 kilometres, into a rather oblique collision with Mercury, with a trajectory head‑on to the equator of the planet at perihelion. It should be aimed largely to ricochet into space, taking a chunk of crust with it. Suitable technology I discuss in an essay at:
https://fullduplexjonrichfield.blogspot.com/2017/07/kuiperbelt-navigation-and-mining_19.html
Such a collision should strip a huge scab of crust off the planet's shallow core and into space, very likely in the form of a cloud of fragments and vapour. Once the area had cooled off a bit, the scar would be a super-sized quarry into solid metal. It probably would resemble the nickel‑iron meteorites that, though rare, are familiar to us in our day.
All that for a planet-sized chunk of iron and nickel??? Surely not?
Well actually, iron and nickel are valuable in themselves, but, although they might not be worth importing from space in their own right, they are not the only components of such meteorites — metal meteorites and planetary cores also contain valuable quantities of siderophiles such as cobalt and the platinum group, and those might well be worth extracting and transporting if available in sufficient quantities. After peeling of an area of core by an asteroid, or anyway, a Kuiper body, an exposed core like that of Mercury should present opportunities unique within several light years of our Solar system.
One reason why only Homo futurens would be interested, is that it would be a task for centuries to lead up to that single stroke to lay bare an area of Mercury's core. It might take a century or more to find a suitably useless chunk of rock of a suitable size. Such a rock, or block of frozen mud some 20 kilometres across, (if it were metal, we would prefer to use it for its own material, rather thanwaste it as a projectile) would take decades to reach with engineering spacecraft. It would take years of work to equip it for propulsion, and under the influence of nuclear propulsion, it would take centuries to propel and direct it on a trajectory of something between say 20 billion to 100 billion kilometres to Mercury.
Yes, if it worked it would yield huge dividends, but such a project would not be for the short-haul entrepreneur. Only the committed Homo futurens would contemplate such thousand-year projects for a moment.
Pricking the shell
Consider the following alternative to meteoroid collision for working one's way down to below the thin crust‑and‑mantle of a small planet like Mercury: nuclear engineering.
Whether it would be faster, better, safer, or cheaper than playing trick potshots with asteroids or comets, would depend on many things, in particular advances in our study of the Kuiper belt, which at present is very poorly known indeed.
This alternative too, is unlikely to appeal to Homo ephemerens, as being too long‑term, but it should be practicable to complete it within a schedule of a century or two.
The nuclear engineering approach would depend on digging down a long way. A great deal of the principle, I discuss in yet another essay at:
https://fullduplexjonrichfield.blogspot.com/2011/01/stop-mucking-with-geothermal.html
The objectives of that essay are different, and the theme refers to a different planet, but some of the considerations are related, and might be helpful to contemplate in some contexts of drilling into Mercury.
This approach is based on drilling one or more holes as many kilometres deep as may be practical, and stacking a number of nuclear weapons at calculated distances in the hole. All the figures I give are thumbsucks, so don't take them too seriously.
A pilot hole, possibly a metre, or perhaps two metres, in diameter, would be necessary for the installation of the bombs. The pilot hole could be drilled by robots wielding lasers or whatever the engineers of the day might recommend; almost certainly different tools would be appropriate at different depths. The hole could be lined with rigid refractory ceramics to permit digging down into near‑molten rock with the help of tunnelling shields, and the depth limitations could be determined by the point where the surrounding rock became too hot or too fluid for maintenance of the hole for installation of the explosive charges.
One could dig a good, large crater by setting off a ten megaton H‑bomb at an optimal depth, but such a crater is relatively wide and shallow, and tends to retain a large volume of material that falls back into the hole. Even a very large single bomb would not dig a very deep hole, because the depth of the crater would be a function of the cube root of the megatonnage of the explosion.
I propose that one could dig a far deeper hole, and place the bombs at successive depths, say 500 metres apart, or whatever distance that preliminary research should recommend, probably starting the detonations from the top down. Blasts in the excavation of the shaft would be detonated at intervals so timed that each blast would anticipate, and avoid interference from, the preceding blast, and would propel the fragments up the shaft as it develops from the preceding blasts.
Doing it that way, each earlier blast would change the surrounding material into a cloud of fines that still would be in suspension when each following blast catches up with it. The resulting succession of blasts would propel the preceding clouds up and out of the hole, creating a comparatively regularly tubular hole, and ejecting practically all the fines out of the resulting tunnel at velocities mainly beyond escape velocity.
Suppose that the hole contained, instead of one 10‑Mt bomb, say twenty 1‑Mt bombs, say half a kilometre apart. The ideal result would be a tubular vertical tunnel some 10 kilometres deep, and 500 metres in diameter.
There would be some residual radioactivity, but most of it by far would be in the cloud ejected harmlessly into space.
Given the lower gravity, those figures might be very much pessimistic, possibly by a factor of 3.
Of course, the bottom of the hole could then be the start of the next interval down, and the sequence could continue until the conditions rendered further blasts unpractical.
When the surrounding rock becomes too yielding to support the full-sized shaft, a smaller shaft can continue further down to the surface of the core by means of refractory lining and tunnelling shield. It would be larger than the pilot shaft down which the bombs had been introduced, because it would be the final mining shaft.
The reason for this dramatic approach is that nothing less is likely to render the outer layer of core accessible. If the bombs can be shown to be unpractical, then we simply would have to wait for a suitable comet or asteroid to be found.
The least intrusive form that the shaft project could take would be to excavate the first two shafts at the poles of the planet, and blast them simultaneously in opposing pairs. However, there could be scope for more shafts to be blasted at lower latitudes, or even on the equator, where the blasting and extraction of material would increase the solar day length. This should be beneficial, because the sun's tidal effects on the structure of the planet could be harmful to engineering projects, especially as the planet gets emptied of its core. Even at low latitudes, tunnel cities down to say, 1000 metres down would be easy to engineer, given that Mercury's gravity is about a third of Earth gravity.
But we may leave such decisions to the engineers of the day.
Empty vessel
Think what could be done if we could make a success of the principle of penetrating the crust (plus any mantle that Mercury might have) for mining purposes. We can expect the gravity of Mercury to increase slightly as we dig down into the crust, until we reach the metal core a few tens of kilometres down, after which the gravity decreases as we dig deeper. Notionally, it would decrease to zero, either as we empty the crust, or reach the centre of the core.
But the core is not infinite. Sooner or later we could expect our descendents to empty it, possibly leaving supporting struts to prevent the planet from collapsing.
It is intriguing to imagine a planetary shell, a practically empty crust, like a coconut shell, say 50 to 100 kilometres thick, and about 4800 kilometres across. In its proportions it would in fact roughly resemble the empty shell of a real coconut.
That however would take a while to achieve, never mind how clever the engineering might be. There will be plenty of time for clever engineering to develop during the project. It would roughly (very roughly, basically a thumbsuck) require the equivalent of extracting an ingot of metal measuring 1000 kilometres thick and wide, and 10000 kilometres long.
A shell like that could not but be precious to a civilisation advanced enough to use it constructively. However, to achieve it would take many thousand years, very likely a few million years. Mind you, it would be a fun thing; resultant gravitation inside the shell would be practically zero.
Furthermore, a shell much thinner than that, suitably treated, should be able to contain an atmosphere at Earth pressure. The engineering would be complex, because the effective gravitation would be theoretically zero inside the shell, but if Homo futurens could not decide on the relevant objectives and measures, Homo would have failed.
"But why bother?", you ask? "After all, our sun inevitably will go red giant and swallow the whole caboodle, won't it?" True, but suppose that to take about five billion years, and suppose our mining to continue for five million years, that would imply our hollow structure to have a useful life of about a thousand times as long as it took to build it (profitably too!), and that implies a useful life as close as a thumbsuck might be to. . . still within a fraction of one percent of five billion years.
For perspective, in terms of thumbsucks, a period of five billion years is about as long as the entire history of life on Earth so far, and about a thousand times longer than the evolutionary history of Homo sapiens so far, and nearly a million times as long as human city civilisation so far, depending on who is counting. In comparison, the most ambitious engineering projects on Earth, throughout history or pre-history, have been pitiful and profitless. Even if the sun chooses to cheat us and blow in one billion years instead of five, that still would be a handsome profit, even though a disappointing one in comparison to five billion.
How humanity would go about achieving such an outcome, is another matter. Hard-nosed as I have been all my life, I do not commit to prediction of detailed future history, but I have discussed some of the principles in an essay at:
https://fullduplexjonrichfield.blogspot.com/2025/08/immortal-imperatives.html
When dealing with projects on such a scale, it is futile to think in terms of the scale of human endeavour of the last two centuries (or even of the days of the erection of ancient monuments such as pyramids and ziggurats millennia ago). No human enterprise in all our history or prehistory, in part or in combination, could stand comparison.
It will demand and imply the emergence of Homo futurens from Homo ephemerens.
For sheer grandeur that is worth striving for.
I regard intelligent hubris as one of the proudest virtues of humanity.
Occupation of the nest
Once we have relatively shapely shafts deep enough for access to valuable material from near to the upper reaches of the planetary core, but before the planetary shell has been hollowed out, there will be plenty of scope for occupation of the walls of those shafts, whether by industrial equipment or even human residence. Such a wall kilometres deep, and half a kilometre in diameter, would present marvellous opportunities on a planet such as Mercury. Once the radioactivity from the explosions, already mostly blown out of the shaft, had decayed enough, a cover over the mouth of the shaft could retain a usable atmosphere. That should not take more than a few decades.
And, if such shafts were dug at each of the poles, their insides would be shielded from the sun, which would be convenient on Mercury.
Another cover could be built across the bottom of the shaft, to protect occupants from the hot, or molten, metal below. That would be necessary to establish liveable conditions above.
In planning excavation blasts on such a scale, the engineering projects might include desirable adjustments of the planet's orbit and rotation. A circular orbit would reduce the tidal stresses created by the sun's gravity. Such an orbit would increase the durability of the engineering works. It similarly might be worth adjusting the day-and year length to match residential requirements optimally; whether to tidally lock the rotation of the planetary shell to keep one face to the sun or not, I cannot decide, so I bequeath the decision to my descendents.
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