Worlds For Man - Part 1 - Mercury

"Worlds for Man - Mercury"

(c) 2007, 2011 by Jordan S. Bassior

Little Mercury, the smallest of the currently-official eight planets, is notable for her density (second densest world in the Solar System) and proximity to the Sun. Mercury is an airless rockball, superficially similar to Luna, which has been stripped of her volatiles by heating and of some of her lighter solids by impacts. The result is a dense and refractory planet, rich in heavy elements but poor in many lighter ones.

Mercury is primarily of economic interest for three reasons. The first is that it is probably the richest of all Solar worlds in terms of readily accessible metals, radioactives and other heavy elements (1). The second is that it (like Luna) probably has significant deposits of tri-helium on its surface (2). The third is that Mercury is bathed in solar energy, and is furthermore a good base from which to construct and deploy close-in orbiting Solar energy collectors (3): energy may also be drawn from Mercury's passage through the Sun's magnetic field.

In the Near-Term, colonization of Mercury will focus on prospecting and mining. Mercurian ores can be easily (4) refined  using the abundant energy, launched up the shallow gravitational well, and then dispatched elsewhere in the System. Though Mercury is deep within the Sun's gravity well, the total delta vee required to get elsewhere in the system from the surface of Mercury is still smaller than that required to do so from the surface of the Earth (5). One disadvantage is that a space elevator isn't practical: Mercury rotates on its axis far too slowly for that.

Despite Mercury's proximity to the Sun, it is in some ways a surprisingly friendly target for early colonization. To begin with, Mercury has a magnetic field strong enough to ward off the Solar wind, so colonists need not worry about being bombarded with charged particles. There are four good sources of energy: solar radiation, solar magnetic, fissionables, and fusibles. Though the dayside is hot, some polar regions are in perpetual shade, and the rotation is slow enough that ground vehicles could easily remain in the night side or twilight zone (important for prospectors!).

Like Luna, there are probably ice deposits at the poles, providing a small but vital source of water, hydrogen and oxygen for a starting colony.  Unlike Luna, the ice deposits probably exist only at the poles, so at some point water would need to be imported.  Hydrogen might also be extracted by magnetic scoop from the solar wind, providing a source of fuel for fusion reactors.

We may thus envision Near-Term colonies being placed in the polar regions, with a webbing of solar-magnetism power receptors and electric train lines running from pole to pole. Prospectors would venture forth from the polar colonies, probably in large tracked or balloon-tired wheeled all terrain vehicles, endeavoring to remain near the Terminator or Twilight Zone. To maximize their exploration in the limited available time, each sapient prospector (6) would command a fleet of roving drones. Almost all of this infrastructure would be easily constructable from local materials.

The poles themselves would become increasingly crowded, owing to the difficulties of permanent settlements elsewhere on the planet. Direct launches and landings might well be made at the poles, because Mercury is small and very slow-rotating, and hence the delta vee advantages of equatorial operations would be small compared to the disadvantages of the extreme temperature variations. To the poles would come imports of volatiles and lighter solids; from the poles would depart shipments of heavy metals, radioactives and rare earths for the Outer System.

Mercury is also, as I mentioned in the previous chapter, ideally positioned as a base for operations designed to extract Solar energy. Eventually, there would be frequent launches of material to construct close-in Solar power satellites.

There would in general be a high proportion of robots to organics, because the cost of constructing robots would be relatively low. Mercury would be one of the first worlds in the System to have a large robotic population (another such world would be Venus, considered in the next part). By the end of this period some of them would be sapient.

Mid-Term development would largely continue on the same terms. The web of rail and power stations would spread over the Mercurian surface. Permanent settlement of the temperate and equatorial zones would begin, fed by growing population and new technologies that would enable excess dayside heat to be conducted to and radiated from the nightside. These new towns would be mostly underground, to avoid the thermal stresses at the surface, and would be connected by ultrafast underground maglev railways.

Most of the prospecting work would have been completed and most of the surface resources taken. Mines would now burrow deep into the crust, and begin tapping the mantle. Hermeothermal (6) energy might be employed as a cheap alternative to nuclear reactors.

The initial work of Solar materials extraction would be based from Mercury: the first vast electromagnetic coils would have been drawn from Mercurian metals, though in time that operation would become self-supporting. Almost certainly a lot of the plant would be owned by Mercurians.

The Mercurians themselves, both organic and inorganic, might have engineered themselves to better suit their world. Thermal and hard-radiation tolerance would be obvious design goals. For humaniform organics, part of this might take the classic pulp SF approach of extremely dark skin, and possibly third eyelids to protect against glare (7).

Terraforming is also a possibility. Sunshades could be deployed to lower the insolation on the dayside (this implies that solar power production moves offworld) and mirrors used to provide it to the nightside; iceteroids crashed to supply volatiles, including both atmosphere and hydrosphere. Mercury would probably always be a hot desert world by human standards, but in this period it might become shirtsleeves-habitable, especially to the Mercurians themselves.

Long-Term development would probably see core-tapping to extract rich concentrations of heavy elements. Mercurian geology (hermeology) would be brought completely under sapient control. Specialized races of animals or even sapients might be created to swim in the core and seek out especially valuable swirls of metals (8).

Solar operations would have long since become independent of Mercury, and with the availability of vast amounts of hydrogen, deuterium, tritium and trihelium from the Sun and the gas giants, the heyday of Mercury's importance as an energy-production center would be past. But Mercury would still make a good base for spacecraft construction, and despite its depth in the Sun's gravity well might become a launching station for the faster kinds of koopcruisers (9), oortcruisers (10), and starships.

Thus, the smallest terrestrial planet of the Solar System would be firmly connected to the longest-term future of Mankind.

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Notes:

(1) - Earth is slightly denser and eighteen times more massive than Mercury, so Earth has in absolute terms far more heavy metals.  But Earth has also two and half times the gravity of Mercury, meaning that a mine of given structural strength can sink two and a half times as deep into Mercury as Earth.  Our deepest Earthly mines are about 4 miles down:  we could sink shafts 10 miles deep into Mercury.

The area-volume relationship also helps.  Mercury has a full one-seventh the surface area, and almost half the land surface area of the Earth, which means that the volume of accessible crust is roughly the same barring seafloor mining on Earth, and even with seafloor mining, a much larger percentage of Mercury's mass is within 10 miles of the surface than the percentage of Earth's mass within 2.5 miles of the surface.

Add to this that Mercury is, as far as we know, virgin for mining.  The easily-accessible surface deposits which, on Earth, were played-out decades, centuries or even millennia ago, would on Mercury be simply lying there for the exploitation.  The first century or two of Mercurian mining might hence be very profitable, as one wouldn't even need to go down that deep to strike rich lodes.

And Mercury has almost certainly been differentiated by geological processes, meaning that rich lodes would in fact be found.  Unlike smaller and colder bodies, Mercury had a molten core at least in the past, and possibly in the present, mixing, re-mixing, and thus concentrating valuable metals.  Mercury is likely to be the location of future metals rushes.

(2) - Both Mercurian and Lunarian tri-helium is sprayed into the regolith by the solar wind.  Logically Mercury, which is three times closer to the Sun than Luna, should have richer deposits of tri-helium than Luna.  On the other hand, that same Solar radiation might knock the tri-helium loose again, and once loose it would be lost due to the low Mercurian gravity.  On the gripping hand, Mercury's gravity is greater than Luna's.  So the issue is complex, but some tri-helium is almost certainly there.

(3) - Remember the close-in Solar power arrays proposed in the Near-Term for colonization of the Sun?  The materials needed to build these arrays need to come from somewhere.  Earth is relatively far away and Venus is a very hostile environment for factory and launcher construction and operations.  Mercury is the closest planet and will be, once we become accustomed to the extreme insolation and delve out underground bases for the crews, a relatively safe place from which to operate.

(4) - Assuming a background of experience in low-gravity, vacuum-environment, solar-flare endangered mining operations.  Obviously, the early decades of such operations might be plagued by fatal and costly accidents, as is the case in the early decades of any new resource extraction technology.

(5) - Though the Solar gravitational well is deeper than the Earth's, an object on the surface of Mercury is already in orbit around the Sun, and hence if it can achieve Mercury's escape velocity can then use a continuous low-thrust system such as an ion drive to spiral outward.  Mercury's escape velocity is only 4.25 km per sec, as opposed to the 11.2 km/sec required to escape from the Earth.

(6) - By analogy with "geothermal."

(7) - Barring at least Mercury-orbital sunshades, the surface of Mercury would obviously be too hot for our kind of life, even if such life were modified to be able to operate in vacuum without spacesuits.  On the other hand, orbital sunshades are not a very advanced technology, and the infrastructure to deploy such would be created in the process of creating the infrastructure to deploy Solar-orbital power collectors.  And, even if one is wearing a spacesuit or living in a hab, heat- and radiation-tolerance would allow one improved survival abilities in a crisis, where one might want to turn the air conditioning down or operate for extensive periods on the surface with no radiation shielding save that of one's suit.

(8) - Implying a high-temperature silicon or even exotic materials-based biochemistry, of course.

(9) - Koopcruisers ("Kuiper Belt Cruisers") would be longer-ranged ships than ordinary interplanetary vessels, designed and provisioned for flights across average distances of 10's of AU, rather than the AU's common in the System proper. The difference between an Outer System IPV and a Koopcruiser would be of course a vague one.

(10) - Oortcruisers ("Oort Cloud Cruisers") would be very long range space ships, designed and provisioned for flights across average distances of 100's of AU. Sufficiently long-range oortcruisers would essentially be short-ranged starships.