Colonization of Mercury
Similarity to the Moon 
Like the Earth's Moon, Mercury does not have any significant atmosphere. It is close to the Sun and rotates slowly with a very small tilt of its axis. The lack of an atmosphere also means the lack of heat transfer by convection from any near-by hot objects. However, thermal protection of colonists and sensitive equipment would still require shielding from the intense solar radiation that reaches Mercury's surface and from the infrared radiation of any very hot region of Mercury's surface and insulation from heat conducted through the ground from any very hot surrounding ground. Hot areas can be avoided by moving to remain in the neighborhood of the terminator. Because of the similarity to Earth's moon, any colonization of Mercury might be performed with the same general technology, approach and equipment as a colonization of the Moon. Bruce Murray referred to Mercury as "A Mini-Earth in Moon's Clothing". Unlike the Moon however, Mercury has the additional advantage of a magnetic field protecting it from cosmic rays and solar storms, and a larger surface gravity of about 0.38 g, nearly equal to that of Mars.
Ice in polar craters 
Due primarily to its proximity to the Sun, the surface of Mercury can reach 700 K (427 °C, 800 °F) near the equator, hot enough to melt lead. However, temperatures at the polar regions are much colder (< 273 K (0 °C) ) and there may even be deposits of ice inside permanently shaded craters.  The polar areas do not experience the extreme daily variation in temperature seen on more equatorial areas of Mercury's surface.
Solar energy 
Being the closest planet to the Sun, Mercury has vast amounts of solar power available. Its solar constant is 6.3-14.5 kW/m², on average 6.5 times that of Earth or the Moon. Because the tilt of its axis of rotation relative to its orbit is so low, approximately 0.01 degrees, there is also the possibility of so-called peaks of eternal light, similar to those of the Moon—high points located at the poles of the planet that are continuously radiated by the Sun. Even if they do not exist, it is possible that they could be constructed artificially.
Valuable resources 
There are predictions that Mercury's soil may contain large amounts of helium-3, which could become an important source of clean nuclear fusion energy on Earth and a driver for the future economy of the Solar System. However, Mercury's magnetic field could have prevented helium-3 from reaching the surface.
Mercury is also theorized to have a crust rich in iron and magnesium silicates, with the highest concentrations of many valuable minerals of any surface in the Solar System, in highly concentrated ores.
Geologist Stephen Gillett has suggested this will make Mercury an ideal place to build solar sails, which could launch as folded up "chunks" by mass driver from Mercury's surface. Once in space the solar sails would deploy. Since Mercury's solar constant is 6.5 times higher than Earth's, energy for the mass driver should be easy to come by, and solar sails near Mercury would have 6.5 times the thrust they do near Earth. This could make Mercury an ideal place to acquire materials useful in building hardware to send to (and terraform) Venus.
Considerable gravity 
Mercury is larger than the Moon, with a diameter of 4879 km versus 3476 km, and has a higher density due to its large iron core. As a result, gravity on the surface of Mercury is 0.377 g, more than twice that of the Moon (0.1654 g) and very close to the surface gravity on Mars. Since there is evidence of human health problems associated with extended exposure to low gravity, from this point of view, Mercury might be more attractive for long-term human habitation than the Moon.
The lack of any substantial atmosphere, close proximity to the Sun and long solar days (176 Earth days) would all lead to significant challenges for any future human settlement. There probably exists water ice at the poles, but some of the elements needed for life do not exist on the planet. These would have to be imported.
Mercury is also deep in the Sun's gravitational potential well, requiring a larger velocity change (delta V) to travel to and from Mercury than is needed for other planets, although, in the past, gravity assist orbits using Venus have been used to reach Mercury. However, entering orbit around Mercury and landing on the surface would take 6 years with current propulsion methods. Solar sails and mass drivers may assist in transportation in the future, but are not viable options at present.
Fictional depictions 
See also 
- Bruce Murray and Ronald Greeley, "Earthlike Planets: Surfaces of Mercury, Venus, Earth, Moon, Mars", W. H. Freeman, 1981, ISBN 0-7167-1148-6
- Ice on Mercury
- Mercury Fact Sheet
- Analog, September 1986
- Eric H. Christiansen and W. Kenneth Hamblin, "Exploring the Planets", 2nd ed.; Prentice Hall, 1995, p. 133
- Stephen L. Gillett, "Mining the Moon", Analog, Nov. 1983
- Stanley Schmidt and Robert Zubrin, eds., "Islands in the Sky: Bold New Ideas for Colonizing Space"; Wiley, 1996, p. 71-84
- A Mercury Colony? An exposition of the case for colonizing Mercury in preference to other planets (specifically in preference to Mars), by physicist Jim Shifflett.