Extraterrestrial life, or alien life, is life that originates from another world rather than on Earth. No extraterrestrial life has yet been scientifically conclusively detected. Such life might range from simple forms such as prokaryotes to intelligent beings, possibly bringing forth civilizations that might be far more, or far less, advanced than humans. The Drake equation speculates about the existence of sapient life elsewhere in the universe. The science of extraterrestrial life is known as astrobiology.
An eclipse is an astronomical event which occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three celestial objects is known as a syzygy. An eclipse is the result of either an occultation or a transit. A "deep eclipse" is when a small astronomical object is behind a bigger one.
A planet is a large, rounded astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets by the most restrictive definition of the term: the terrestrial planets Mercury, Venus, Earth, and Mars, and the giant planets Jupiter, Saturn, Uranus, and Neptune. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young protostar orbited by a protoplanetary disk. Planets grow in this disk by the gradual accumulation of material driven by gravity, a process called accretion.
Space colonization is the settlement or colonization of outer space and astronomical bodies. The concept in its broad sense has been applied to any permanent human presence in space, such as a space habitat or other extraterrestrial settlements. It may involve a process of occupation or control for exploitation, such as extraterrestrial mining.
Terraforming or terraformation ("Earth-shaping") 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 for humans to live on.
Emanuel Swedenborg (, Swedish:[ˈsvêːdɛnˌbɔrj] ; born Emanuel Swedberg; was a Swedish polymath; scientist, engineer, astronomer, anatomist, Christian theologian, philosopher, and mystic. He became best known for his book on the afterlife, Heaven and Hell.
The extraterrestrial hypothesis (ETH) proposes that some unidentified flying objects (UFOs) are best explained as being physical spacecraft occupied by extraterrestrial intelligence or non-human aliens, or non-occupied alien probes from other planets visiting Earth. In spite of ardent believers that various UFO sightings are verifiable evidence for the hypothesis, no rigorous analysis has ever concluded as much.
A classical planet is an astronomical object that is visible to the naked eye and moves across the sky and its backdrop of fixed stars. Visible to humans on Earth there are seven classical planets. They are from brightest to dimmest: the Sun, the Moon, Venus, Jupiter, Mars, Mercury and Saturn.
In astronomy, an extraterrestrial sky is a view of outer space from the surface of an astronomical body other than Earth.
The term "exotheology" was coined in the 1960s or early 1970s for the examination of theological issues as they pertain to extraterrestrial intelligence. It is primarily concerned with either conjecture about possible theological beliefs that extraterrestrials might have, or how our own theologies would be influenced by evidence of and/or interaction with extraterrestrials.
Contactees are persons who claim to have experienced contact with extraterrestrials. Some claimed ongoing encounters, while others claimed to have had as few as a single encounter. Evidence is anecdotal in all cases.
Cosmic pluralism, the plurality of worlds, or simply pluralism, describes the belief in numerous "worlds" in addition to Earth, which may harbour extraterrestrial life.
There is evidence that the formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary disk out of which the planets, moons, asteroids, and other small Solar System bodies formed.
Conversations on the Plurality of Worlds is a popular science book by French author Bernard le Bovier de Fontenelle, published in 1686. The book expresses support for cosmic pluralism and discusses the topic of astrobiology. Fontenelle speculated on the existence of Venusians as a distinct species of extraterrestrial life.
Discovery and exploration of the Solar System is observation, visitation, and increase in knowledge and understanding of Earth's "cosmic neighborhood". This includes the Sun, Earth and the Moon, the major planets Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune, their satellites, as well as smaller bodies including comets, asteroids, and dust.
A planetary surface is where the solid or liquid material of certain types of astronomical objects contacts the atmosphere or outer space. Planetary surfaces are found on solid objects of planetary mass, including terrestrial planets, dwarf planets, natural satellites, planetesimals and many other small Solar System bodies (SSSBs). The study of planetary surfaces is a field of planetary geology known as surface geology, but also a focus on a number of fields including planetary cartography, topography, geomorphology, atmospheric sciences, and astronomy. Land is the term given to non-liquid planetary surfaces. The term landing is used to describe the collision of an object with a planetary surface and is usually at a velocity in which the object can remain intact and remain attached.
The following outline is provided as an overview of and topical guide to the Solar System:
Comparative planetary science or comparative planetology is a branch of space science and planetary science in which different natural processes and systems are studied by their effects and phenomena on and between multiple bodies. The planetary processes in question include geology, hydrology, atmospheric physics, and interactions such as impact cratering, space weathering, and magnetospheric physics in the solar wind, and possibly biology, via astrobiology.
