WDiscovery 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.The Solar System — our Sun's system of planets, moons, and smaller debris — is humankind's cosmic backyard. Small by factors of millions compared to interstellar distances, the spaces between the planets are daunting, but technologically surmountable.
WThe exploration of Io, Jupiter's innermost Galilean and third-largest moon, began with its discovery in 1610 and continues today with Earth-based observations and visits by spacecraft to the Jupiter system. Italian astronomer Galileo Galilei was the first to record an observation of Io on January 8, 1610, though Simon Marius may have also observed Io at around the same time. During the 17th century, observations of Io and the other Galilean satellites helped with the measurement of longitude by map makers and surveyors, with validation of Kepler's Third Law of planetary motion, and with measurement of the speed of light. Based on ephemerides produced by astronomer Giovanni Cassini and others, Pierre-Simon Laplace created a mathematical theory to explain the resonant orbits of three of Jupiter's moons, Io, Europa, and Ganymede. This resonance was later found to have a profound effect on the geologies of these moons. Improved telescope technology in the late 19th and 20th centuries allowed astronomers to resolve large-scale surface features on Io as well as to estimate its diameter and mass.
WThe planet Mars has been explored remotely by spacecraft. Probes sent from Earth, beginning in the late 20th century, have yielded a large increase in knowledge about the Martian system, focused primarily on understanding its geology and habitability potential. Engineering interplanetary journeys is complicated and the exploration of Mars has experienced a high failure rate, especially the early attempts. Roughly sixty percent of all spacecraft destined for Mars failed before completing their missions and some failed before their observations could begin. Some missions have met with unexpected success, such as the twin Mars Exploration Rovers, Spirit and Opportunity which operated for years beyond their specification.
WThe exploration of Mercury has a minor role in the space interests of the world. It is the least explored inner planet. As of 2015, the Mariner 10 and MESSENGER missions have been the only missions that have made close observations of Mercury. MESSENGER made three flybys before entering orbit around Mercury. A third mission to Mercury, BepiColombo, a joint mission between the Japan Aerospace Exploration Agency (JAXA) and the European Space Agency, is to include two probes. MESSENGER and BepiColombo are intended to gather complementary data to help scientists understand many of the mysteries discovered by Mariner 10's flybys.
WThe exploration of Neptune has only begun with one spacecraft, Voyager 2 in 1989. As of July 2020, there are no approved future missions to visit the Neptunian system. NASA, ESA, and independent academic groups have proposed future scientific missions to visit Neptune. Some mission plans are still active, while others have been abandoned or put on hold.
WThe exploration of Pluto began with the arrival of the New Horizons probe in July 2015, though proposals for such a mission had been studied for many decades. There are no plans as yet for a follow-up mission, though follow-up concepts have been studied.
WThe exploration of Saturn has been solely performed by crewless probes. Three missions were flybys, which formed an extended foundation of knowledge about the system. The Cassini–Huygens spacecraft, launched in 1997, was in orbit from 2004 to 2017.
WThe physical exploration of the Moon began when Luna 2, a space probe launched by the Soviet Union, made an impact on the surface of the Moon on September 14, 1959. Prior to that the only available means of exploration had been observation from Earth. The invention of the optical telescope brought about the first leap in the quality of lunar observations. Galileo Galilei is generally credited as the first person to use a telescope for astronomical purposes; having made his own telescope in 1609, the mountains and craters on the lunar surface were among his first observations using it.
WThe exploration of Uranus has, to date, been solely through telescopes and a lone probe by NASA's Voyager 2 spacecraft, which made its closest approach to Uranus on January 24, 1986. Voyager 2 discovered 10 moons, studied the planet's cold atmosphere, and examined its ring system, discovering two new rings. It also imaged Uranus' five large moons, revealing that their surfaces are covered with impact craters and canyons.
WThe history of scientific thought about the formation and evolution of the Solar System begins with the Copernican Revolution. The first recorded use of the term "Solar System" dates from 1704.
WInterplanetary 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.
WObservations of the planet Venus include those in antiquity, telescopic observations, and from visiting spacecraft. Spacecraft have performed various flybys, orbits, and landings on Venus, including balloon probes that floated in the atmosphere of Venus. Study of the planet is aided by its relatively close proximity to the Earth, compared to other planets, but the surface of Venus is obscured by an atmosphere opaque to visible light.
WThis is a list of active space probes which have escaped Earth orbit. It includes lunar space probes, but does not include space probes orbiting at the Sun–Earth Lagrangian points. A craft is deemed "active" if it is still able to transmit usable data to Earth.
WA sample-return mission is a spacecraft mission to collect and return samples from an extraterrestrial location to Earth for analysis. Sample-return missions may bring back merely atoms and molecules or a deposit of complex compounds such as loose material ("soil") and rocks. These samples may be obtained in a number of ways, such as soil and rock excavation or a collector array used for capturing particles of solar wind or cometary debris.
WThe timeline of discovery of Solar System planets and their natural satellites charts the progress of the discovery of new bodies over history. Each object is listed in chronological order of its discovery, identified through its various designations, and the discoverer(s) listed.
WThis is a timeline of Solar System exploration ordered by date of spacecraft launch. It includes:All spacecraft that have left Earth orbit for the purposes of Solar System exploration, including lunar probes. A small number of pioneering or notable Earth-orbiting craft.