Interplanetary spaceflight or interplanetary travel is the crewed or uncrewed travel between stars and planets, usually within a single planetary system. In practice, spaceflights of this type are confined to travel between the planets of the Solar System. Uncrewed space probes have flown to all the planets in the Solar System as well as to dwarf planets Pluto and Ceres, and several asteroids. Orbiters and landers return more information than fly-by missions. Crewed flights have landed on the Moon and have been planned, from time to time, for Mars and Venus. While many scientists appreciate the knowledge value that uncrewed flights provide, the value of crewed missions is more controversial. Science fiction writers propose a number of benefits, including the mining of asteroids, access to solar power, and room for colonization in the event of an Earth catastrophe.
Robert Zubrin is an American aerospace engineer, author, and advocate for human exploration of Mars. He and his colleague at Martin Marietta, David Baker, were the driving force behind Mars Direct, a proposal in a 1990 research paper intended to produce significant reductions in the cost and complexity of such a mission. The key idea was to use the Martian atmosphere to produce oxygen, water, and rocket propellant for the surface stay and return journey. A modified version of the plan was subsequently adopted by NASA as their "design reference mission". He questions the delay and cost-to-benefit ratio of first establishing a base or outpost on an asteroid or another Apollo program-like return to the Moon, as neither would be able to provide all of its own oxygen, water, or energy; these resources are producible on Mars, and he expects people would be there thereafter.
Space colonization is a form of permanent human habitation and exploitation of natural resources off the planet Earth.
Terraforming or terraformation is the hypothetical process of deliberately modifying the atmosphere, temperature, surface topography or ecology of a planet, moon, or other body to be similar to the environment of Earth to make it habitable by Earth-like life.
The Case for Mars: The Plan to Settle the Red Planet and Why We Must is a nonfiction science book by Robert Zubrin, first published in 1996, and revised and updated in 2011.
The Millennial Project: Colonizing the Galaxy in Eight Easy Steps by Marshall T. Savage is a book in the field of exploratory engineering that gives a series of concrete stages the author believes will lead to interstellar colonization. Many specific scientific and engineering details are presented, as are numerous issues involved in space colonization.
Planetary protection is a guiding principle in the design of an interplanetary mission, aiming to prevent biological contamination of both the target celestial body and the Earth in the case of sample-return missions. Planetary protection reflects both the unknown nature of the space environment and the desire of the scientific community to preserve the pristine nature of celestial bodies until they can be studied in detail.
The hypothetical colonization of Mars has received interest from public space agencies and private corporations, and has received extensive treatment in science fiction writing, film, and art.
Many parts of the outer Solar System have been considered for possible future colonization. Most of the larger moons of the outer planets contain water ice, liquid water, and organic compounds that might be useful for sustaining human life.
Asteroids, including those in the asteroid belt have been suggested as a possible site of human colonization. Some of the driving forces behind this effort to colonize asteroids include the survival of humanity, as well as economic incentives associated with asteroid mining. The process of colonizing asteroids does have many obstacles that must be overcome for human habitation, including transportation distance, lack of gravity, temperature, radiation, and psychological issues.
Saturn’s largest moon Titan is one of several candidates for possible future colonization of the outer Solar System.
The terraforming of Mars is a hypothetical procedure that would consist of a planetary engineering project or concurrent projects, with the goal of transforming the planet from one hostile to terrestrial life to one that can sustainably host humans and other lifeforms free of protection or mediation. The process would presumably involve the rehabilitation of the planet's extant climate, atmosphere, and surface through a variety of resource-intensive initiatives, and the installation of a novel ecological system or systems.
The terraforming of Venus is the hypothetical process of engineering the global environment of the planet Venus in such a way as to make it suitable for human habitation. Terraforming Venus was first proposed in a scholarly context by the astronomer Carl Sagan in 1961, although fictional treatments, such as The Big Rain of The Psychotechnic League by novelist Poul Anderson, preceded it. Adjustments to the existing environment of Venus to support human life would require at least three major changes to the planet's atmosphere:
- Reducing Venus' surface temperature of 737 K
- Eliminating most of the planet's dense 9.2 MPa (91 atm) carbon dioxide and sulfur dioxide atmosphere via removal or conversion to some other form
- The addition of breathable oxygen to the atmosphere.
Christopher P. McKay is a planetary scientist at NASA Ames Research Center, studying planetary atmospheres, astrobiology, and terraforming. McKay majored in physics at Florida Atlantic University, where he also studied mechanical engineering, graduating in 1975, and received his PhD in astrogeophysics from the University of Colorado in 1982.
The ethics of terraforming has constituted a philosophical debate within biology, ecology, and environmental ethics as to whether terraforming other worlds is an ethical endeavor.
The following outline is provided as an overview of and topical guide to space exploration:
Freeman Dyson has proposed that trans-Neptunian objects, rather than planets, are the major potential habitat of life in space. Several hundred billion to trillion comet-like ice-rich bodies exist outside the orbit of Neptune, in the Kuiper belt and Inner and Outer Oort cloud. These may contain all the ingredients for life, including significant amounts of deuterium and helium-3. Since Dyson's proposal, the number of trans-Neptunian objects known has increased greatly.
Space trade is interplanetary or interstellar trade. Plans and ideas on how trade functions have been published by Futurists and pundits since the 1960s, though science fiction writers have been envisioning such trade for several more decades.
Deep space exploration is the branch of astronomy, astronautics and space technology that is involved with exploring the distant regions of outer space. However, there is little consensus on the meaning of "distant" regions. In some contexts, it is used to refer to interstellar space. The International Telecommunication Union defines "deep space" to start at a distance of 2 million km from the Earth's surface. NASA's Deep Space Network has variously used criteria of 16,000 to 32,000 km from Earth. Physical exploration of space is conducted both by human spaceflights and by robotic spacecraft.
Martyn J. Fogg is a British physicist and geologist, an expert on terraforming.
