However, he tweeted the name of his new megaspaceship will not be the Mars Colonial Transport it will be the interplanetary transport system. Elon plans to go beyond Mars to the entire solar system.
Mars isn't the solar system's only marginally habitable world for would-be new world colonists. The Moon, Venus, the asteroid Ceres, Titan and Callisto all have some advantages that could allow for colonies to subsist. Musk now seems to be suggesting that some of these more distant destinations, especially moons around Jupiter and Saturn, might be reachable with the Interplanetary Transport System.
Turns out MCT can go well beyond Mars, so will need a new name…— Elon Musk (@elonmusk) September 17, 2016
Fellow multi-billionaire and rocket company owner Jeff Bezos of Amazon has also been talking about solar system colonization
Oceans trapped under ice appear to be pretty common in the solar system and one of them, on a small moon of Saturn’s, appears to be quite hot. Scientists reported evidence for hydrothermal vents on the Saturnian moon Enceladus, with temperatures of its rocky core surpassing 194 degrees Fahrenheit (90 degrees Celsius) in spots. The discovery, if confirmed, would make Enceladus the only place other than Earth where such chemical reactions between rock and heated water are known to be occurring today — and for many scientists, it would make Enceladus a most promising place to look for life.
Any place with liquid water is a candidate for microbial extraterrestrial life. Mars, Titan, Europa, Ceres, Enceladus, and Ganymede have the presence of water ice and speculation that life may exists there. There are now six candidate locations for liquid water in solar system other than Earth.
The Journal of Geophysical Research: Space Physics, another team reported signs of another under-ice ocean, on Ganymede, the largest of Jupiter’s moons. Scientists are already convinced that there is a large ocean, also covered by ice, on another Jovian moon, Europa. NASA’s Galileo spacecraft had also found hints of hidden water on Ganymede and on another of Jupiter’s moons, Callisto.
Journal of Geophysical Review - The search for a subsurface ocean in Ganymede with Hubble Space Telescope observations of its auroral ovals
Europa is estimated to have twice the amount of water as Earth.
Scientists have long suspected that there was an ocean of liquid water on Ganymede — the largest moon in the solar system, at about 3,273 miles (5,268 kilometers) across — has an ocean of liquid water beneath its surface. The Galileo probe measured Ganymede's magnetic field in 2002, providing some data supporting the theory that the moon has an ocean. It is estimated that Ganymede has more water than Earth.
Liquid water moons of gas giants and in asteroid belts could be common outside our solar system as well. The most common of the thousands of exoplanets that have been identified are gas giants.
Enceladus could have a 10 kilometer thick liquid water Ocean under 30-40 kilometers of ice.
Water appears to make up about 40 percent of Ceres' volume.
Water on Mars exists today almost exclusively as ice, with a small amount present in the atmosphere as vapor. The only place where water ice is visible at the surface is at the north polar ice cap. Abundant water ice is also present beneath the permanent carbon dioxide ice cap at the Martian south pole and in the shallow subsurface at more temperate latitudes. More than five million cubic kilometers of ice have been identified at or near the surface of modern Mars, enough to cover the whole planet to a depth of 35 meters. Even more ice is likely to be locked away in the deep subsurface.
Some liquid water may occur transiently on the Martian surface today but only under certain conditions.
The case for Titan
Titan is suggested as a target for colonization, because it is the only moon in the Solar System to have a dense atmosphere and is rich in carbon-bearing compounds. Robert Zubrin identified Titan as possessing an abundance of all the elements necessary to support life, making Titan perhaps the most advantageous locale in the outer Solar System for colonization, and saying "In certain ways, Titan is the most hospitable extraterrestrial world within our solar system for human colonization".
1. Titan has a lot of water ice.
2. Titan has 100 times the hydrocarbons as the Earth. Liquid methane lakes the size of the Great Lakes on Earth. Regular combustion engines or fuel cells could be run on the liquid methane.
3. Titan has an atmosphere that protects against radiation.
hydrosphere of earth 1.5×10^18 short tons
deuterium 2.5X10^13 tons
Solid core fission rockets would have enough thrust to weight ratio be able to mine Saturn's atmostphere.
Titan orbits Saturn once every 15 days and 22 hours. Like the Moon, and many of the satellites of the gas giants, its rotational period is identical to its orbital period; Titan is thus tidally locked in synchronous rotation with Saturn, and always shows one face to the planet.
Robert Zubrin identified Saturn, Uranus and Neptune as "the Persian Gulf of the Solar System", as the largest sources of deuterium and helium-3 to drive the pending fusion economy, with Saturn the most important and most valuable of the three, because of its relative proximity, low radiation, and excellent system of moons.
Titan has an atmospheric pressure one and a half times that of Earth. This means that the interior air pressure of landing craft and habitats could be set equal or close to the exterior pressure, reducing the difficulty and complexity of structural engineering for landing craft and habitats compared with low or zero pressure environments such as on the Moon, Mars, or the asteroids. The thick atmosphere would also make radiation a non-issue, unlike on the Moon, Mars, or the asteroids.
Titan has a surface gravity of 0.138 g, slightly less than that of the Moon. Managing long-term effects of low gravity on human health would therefore be a significant issue for long-term occupation of Titan, more so than on Mars.
There is a NASA Institute for Advanced Concepts has a study of a submarine for exploring a hydrocarbon liquid lake on Titan.