Discovery and exploration of the Solar System
Encyclopedia
For many thousands of years, civilizations, with a few notable exceptions, did not recognize the existence of the Solar System
. It was believed the Earth to be stationary at the centre of the universe
and categorically different from the divine or ethereal objects that moved through the sky. While the Indian mathematician-astronomer Aryabhata
and the Greek philosopher Aristarchus of Samos
had speculated on a heliocentric reordering of the cosmos, Nicolaus Copernicus
first developed a mathematically predictive heliocentric system. His 17th-century successors Galileo Galilei
, Johannes Kepler
, and Isaac Newton
developed an understanding of physics
which led to the gradual acceptance of the idea that the Earth moves round the Sun and that the planets are governed by the same physical laws that governed the Earth. In more recent times, this led to the investigation of geological phenomena such as mountains and craters and seasonal meteorological phenomena such as clouds, dust storms and ice caps on the other planets.
The first exploration of the Solar System was conducted by telescope
, when astronomers
first began to map those objects too faint to be seen with the naked eye.
Galileo Galilei
was the first to discover physical details about the individual bodies of the Solar System. He discovered that the Moon
was cratered, that the Sun was marked with sunspots, and that Jupiter had four satellites in orbit around it. Christiaan Huygens followed on from Galileo's discoveries by discovering Saturn's moon Titan
and the shape of the rings of Saturn
. Giovanni Domenico Cassini
later discovered four more moons of Saturn
, the Cassini division in Saturn's rings.
Edmond Halley
realised in 1705 that repeated sightings of a comet were recording the same object, returning regularly once every 75–76 years. This was the first evidence that anything other than the planets orbited the Sun. Around this time (1704), the term "Solar System" first appeared in English.
In 1781, William Herschel
was looking for binary star
s in the constellation of Taurus
when he observed what he thought was a new comet. Its orbit revealed that it was a new planet, Uranus, the first ever discovered.
Giuseppe Piazzi
discovered Ceres in 1801, a small world between Mars and Jupiter that initially was considered a new planet. However, subsequent discoveries of thousands of other small worlds in the same region led to their eventual reclassification as asteroid
s.
By 1846, discrepancies in the orbit of Uranus led many to suspect a large planet must be tugging at it from farther out. Urbain Le Verrier's calculations eventually led to the discovery of Neptune. The excess perihelion precession of Mercury
's orbit led Le Verrier to postulate the intra-Mercurian planet Vulcan
in 1859, but that would turn out to be an irrelevant thesis
.
While it is debatable when the Solar System was truly "discovered," three 19th century observations determined its nature and place in the universe beyond reasonable doubt. First, in 1838, Friedrich Bessel
successfully measured a stellar parallax
, an apparent shift in the position of a star created by the Earth's motion around the Sun. This was not only the first direct, experimental proof of heliocentrism, but also revealed, for the first time, the vast distance between our Solar System and the stars. Then, in 1859, Robert Bunsen
and Gustav Kirchhoff
, using the newly invented spectroscope, examined the spectral signature of the Sun and discovered that it was composed of the same elements as existed on Earth, establishing for the first time a physical link between the Earth and the heavens. Then, Father Angelo Secchi
compared the spectral signature of the Sun with those of other stars, and found them virtually identical. The realisation that the Sun was a star led to the hypothesis that other stars could have systems of their own, though this was not to be proven for nearly 140 years.
Further apparent discrepancies in the orbits of the outer planets led Percival Lowell
to conclude that yet another planet, "Planet X
", must lie beyond Neptune. After his death, his Lowell Observatory
conducted a search which ultimately led to Clyde Tombaugh
's discovery of Pluto
in 1930. Pluto was, however, found to be too small to have disrupted the orbits of the outer planets, and its discovery was therefore coincidental. Like Ceres, it was initially considered to be a planet, but after the discovery of many other similarly sized objects in its vicinity it was reclassified in 2006 as a dwarf planet
by the IAU.
In 1992, the first evidence of a planetary system
other than our own was discovered, orbiting the pulsar
PSR B1257+12
. Three years later, 51 Pegasi b
, the first extrasolar planet
around a Sunlike star, was discovered. As of 2008, 221 extrasolar systems have been found.
Also in 1992, astronomers David C. Jewitt
of the University of Hawaii
and Jane Luu
of the Massachusetts Institute of Technology
discovered . This object proved to be the first of a new population, which became known as the Kuiper belt
; an icy analogue to the asteroid belt of which such objects as Pluto and Charon were deemed a part.
Mike Brown
, Chad Trujillo
and David Rabinowitz
announced the discovery of Eris
in 2005, a scattered disc
object larger than Pluto and the largest object discovered in orbit round the Sun since Neptune.
Since the start of the Space Age
, a great deal of exploration has been performed by robotic spacecraft
missions that have been organized and executed by various space agencies.
All planets in the Solar System have now been visited to varying degrees by spacecraft launched from Earth. Through these unmanned missions, humans have been able to get close-up photographs of all the planets and, in the case of landers
, perform tests of the soils and atmosphere
s of some.
The first artificial object sent into space was the Soviet satellite Sputnik 1
, launched in 1957, which successfully orbited the Earth until January 4 the following year. The American probe Explorer 6
, launched in 1959, was the first satellite to image the Earth from space.
, which sped past the Moon in 1959. Originally meant to impact with the Moon, it instead missed its target and became the first artificial object to orbit the Sun. Mariner 2
was the first probe to fly by another planet, Venus, in 1962. The first successful flyby of Mars was made by Mariner 4
in 1965. Mariner 10
first passed Mercury
in 1974.
The first probe to explore the outer planets was Pioneer 10
, which flew by Jupiter in 1973. Pioneer 11
was the first to visit Saturn, in 1979. The Voyager
probes performed a grand tour of the outer planets following their launch in 1977, with both probes passing Jupiter in 1979 and Saturn in 1980 – 1981. Voyager 2
then went on to make close approaches to Uranus in 1986 and Neptune in 1989. The Voyager probes are now far beyond Neptune's orbit, and are on course to find and study the termination shock, heliosheath, and heliopause. According to NASA
, both Voyager probes have encountered the termination shock at a distance of approximately 93 AU from the Sun.
The first flyby of a comet occurred in 1985, when the International Cometary Explorer
(ICE) passed by the comet Giacobini-Zinner
, while the first flybys of asteroids were conducted by the Galileo space probe, which imaged both 951 Gaspra
(in 1991) and 243 Ida
(in 1993) on its way to Jupiter
.
No Kuiper belt object has yet been visited by a spacecraft. Launched on January 19, 2006, the New Horizons
probe is currently en route to becoming the first man-made spacecraft to explore this area. This unmanned mission is scheduled to fly by Pluto in July 2015. Should it prove feasible, the mission will then be extended to observe a number of other Kuiper belt objects.
), followed by Mars in 1971 (Mariner 9
), Venus in 1975 (Venera 9
), Jupiter in 1995 (Galileo), the asteroid 433 Eros
in 2000 (NEAR Shoemaker
), Saturn in 2004 (Cassini–Huygens), and Mercury in 2011 (MESSENGER
). The Dawn spacecraft is currently set to orbit the asteroid Vesta
in 2011 and the dwarf planet Ceres in 2015.
The first probe to land on another Solar System body
was the Soviet
Luna 2
probe, which impacted the Moon in 1959. Since then, increasingly distant planets have been reached, with probes landing on or impacting the surfaces of Venus in 1966 (Venera 3
), Mars in 1971 (Mars 3
, although a fully successful landing didn't occur until Viking 1
in 1976), the asteroid 433 Eros
in 2001 (NEAR Shoemaker
), and Saturn's moon Titan
(Huygens
) and the comet Tempel 1 (Deep Impact) in 2005. The Galileo orbiter also dropped a probe into Jupiter's atmosphere in 1995; since Jupiter has no physical surface, it was destroyed by increasing temperature and pressure as it descended.
To date, only two worlds in the Solar System, the Moon and Mars, have been visited by mobile rovers
. The first rover to visit another celestial body was the Soviet Lunokhod 1
, which landed on the Moon in 1970. The first to visit another planet was Sojourner, which travelled 500 metres across the surface of Mars in 1997. The only manned rover to visit another world was NASA's Lunar rover
, which travelled with Apollos 15
, 16
and 17
between 1971 and 1972.
) and to orbit the Earth was Yuri Gagarin
, a Soviet cosmonaut who was launched in Vostok 1
on April 12, 1961. The first man to walk on the surface of another Solar System body was Neil Armstrong
, who stepped onto the Moon
on July 21, 1969 during the Apollo 11
mission; five more Moon landings occurred through 1972. The United States' Space Shuttle
, which debuted in 1981, is the only reusable spacecraft to successfully make multiple orbital flights. The five shuttles that have been built have flown a total of 121 missions, with two of the craft destroyed in accidents. The first orbital space station
to host more than one crew was NASA
's Skylab
, which successfully held three crews from 1973 to 1974. The first true human settlement in space was the Soviet space station Mir
, which was continuously occupied for close to ten years, from 1989 to 1999. It was decommissioned in 2001, and its successor, the International Space Station
, has maintained a continuous human presence in space since then. In 2004, SpaceShipOne became the first privately funded vehicle to reach space on a suborbital flight. That year, U.S. President George W. Bush
announced the Vision for Space Exploration
, which called for a replacement for the aging Shuttle, a return to the Moon and, ultimately, a manned mission to Mars.
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
. It was believed the Earth to be stationary at the centre of the universe
Universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...
and categorically different from the divine or ethereal objects that moved through the sky. While the Indian mathematician-astronomer Aryabhata
Aryabhata
Aryabhata was the first in the line of great mathematician-astronomers from the classical age of Indian mathematics and Indian astronomy...
and the Greek philosopher Aristarchus of Samos
Aristarchus of Samos
Aristarchus, or more correctly Aristarchos , was a Greek astronomer and mathematician, born on the island of Samos, in Greece. He presented the first known heliocentric model of the solar system, placing the Sun, not the Earth, at the center of the known universe...
had speculated on a heliocentric reordering of the cosmos, Nicolaus Copernicus
Nicolaus Copernicus
Nicolaus Copernicus was a Renaissance astronomer and the first person to formulate a comprehensive heliocentric cosmology which displaced the Earth from the center of the universe....
first developed a mathematically predictive heliocentric system. His 17th-century successors Galileo Galilei
Galileo Galilei
Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...
, Johannes Kepler
Johannes Kepler
Johannes Kepler was a German mathematician, astronomer and astrologer. A key figure in the 17th century scientific revolution, he is best known for his eponymous laws of planetary motion, codified by later astronomers, based on his works Astronomia nova, Harmonices Mundi, and Epitome of Copernican...
, and Isaac Newton
Isaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...
developed an understanding of physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
which led to the gradual acceptance of the idea that the Earth moves round the Sun and that the planets are governed by the same physical laws that governed the Earth. In more recent times, this led to the investigation of geological phenomena such as mountains and craters and seasonal meteorological phenomena such as clouds, dust storms and ice caps on the other planets.
Antiquity and first observations
Telescopic observations
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
, when astronomers
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
first began to map those objects too faint to be seen with the naked eye.
Galileo Galilei
Galileo Galilei
Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...
was the first to discover physical details about the individual bodies of the Solar System. He discovered that the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
was cratered, that the Sun was marked with sunspots, and that Jupiter had four satellites in orbit around it. Christiaan Huygens followed on from Galileo's discoveries by discovering Saturn's moon Titan
Titan (moon)
Titan , or Saturn VI, is the largest moon of Saturn, the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found....
and the shape of the rings of Saturn
Rings of Saturn
The rings of Saturn are the most extensive planetary ring system of any planet in the Solar System. They consist of countless small particles, ranging in size from micrometres to metres, that form clumps that in turn orbit about Saturn...
. Giovanni Domenico Cassini
Giovanni Domenico Cassini
This article is about the Italian-born astronomer. For his French-born great-grandson, see Jean-Dominique Cassini.Giovanni Domenico Cassini was an Italian/French mathematician, astronomer, engineer, and astrologer...
later discovered four more moons of Saturn
Sidera Lodoicea
Sidera Lodoicea is the name given by the astronomer Giovanni Domenico Cassini to the four moons of Saturn discovered by him in the years 1671, 1672, and 1684 and published in his Découverte de deux nouvelles planètes autour de Saturne in 1673 and in the Journal des sçavans in 1686...
, the Cassini division in Saturn's rings.
Edmond Halley
Edmond Halley FRS was an English astronomer, geophysicist, mathematician, meteorologist, and physicist who is best known for computing the orbit of the eponymous Halley's Comet. He was the second Astronomer Royal in Britain, following in the footsteps of John Flamsteed.-Biography and career:Halley...
realised in 1705 that repeated sightings of a comet were recording the same object, returning regularly once every 75–76 years. This was the first evidence that anything other than the planets orbited the Sun. Around this time (1704), the term "Solar System" first appeared in English.
In 1781, William Herschel
William Herschel
Sir Frederick William Herschel, KH, FRS, German: Friedrich Wilhelm Herschel was a German-born British astronomer, technical expert, and composer. Born in Hanover, Wilhelm first followed his father into the Military Band of Hanover, but emigrated to Britain at age 19...
was looking for binary star
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
s in the constellation of Taurus
Taurus (constellation)
Taurus is one of the constellations of the zodiac. Its name is a Latin word meaning 'bull', and its astrological symbol is a stylized bull's head:...
when he observed what he thought was a new comet. Its orbit revealed that it was a new planet, Uranus, the first ever discovered.
Giuseppe Piazzi
Giuseppe Piazzi
Giuseppe Piazzi was an Italian Catholic priest of the Theatine order, mathematician, and astronomer. He was born in Ponte in Valtellina, and died in Naples. He established an observatory at Palermo, now the Osservatorio Astronomico di Palermo – Giuseppe S...
discovered Ceres in 1801, a small world between Mars and Jupiter that initially was considered a new planet. However, subsequent discoveries of thousands of other small worlds in the same region led to their eventual reclassification as asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s.
By 1846, discrepancies in the orbit of Uranus led many to suspect a large planet must be tugging at it from farther out. Urbain Le Verrier's calculations eventually led to the discovery of Neptune. The excess perihelion precession of Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
's orbit led Le Verrier to postulate the intra-Mercurian planet Vulcan
Vulcan (hypothetical planet)
Vulcan was a small planet proposed to exist in an orbit between Mercury and the Sun. In an attempt to explain peculiarities of Mercury's orbit, in the 19th-century French mathematician Urbain Jean Joseph Le Verrier hypothesized that they were the result of another planet, which he named Vulcan...
in 1859, but that would turn out to be an irrelevant thesis
Ignoratio elenchi
Ignoratio elenchi is the informal fallacy of presenting an argument that may in itself be valid, but does not address the issue in question...
.
While it is debatable when the Solar System was truly "discovered," three 19th century observations determined its nature and place in the universe beyond reasonable doubt. First, in 1838, Friedrich Bessel
Friedrich Bessel
-References:* John Frederick William Herschel, A brief notice of the life, researches, and discoveries of Friedrich Wilhelm Bessel, London: Barclay, 1847 -External links:...
successfully measured a stellar parallax
Stellar parallax
Stellar parallax is the effect of parallax on distant stars in astronomy. It is parallax on an interstellar scale, and it can be used to determine the distance of Earth to another star directly with accurate astrometry...
, an apparent shift in the position of a star created by the Earth's motion around the Sun. This was not only the first direct, experimental proof of heliocentrism, but also revealed, for the first time, the vast distance between our Solar System and the stars. Then, in 1859, Robert Bunsen
Robert Bunsen
Robert Wilhelm Eberhard Bunsen was a German chemist. He investigated emission spectra of heated elements, and discovered caesium and rubidium with Gustav Kirchhoff. Bunsen developed several gas-analytical methods, was a pioneer in photochemistry, and did early work in the field of organoarsenic...
and Gustav Kirchhoff
Gustav Kirchhoff
Gustav Robert Kirchhoff was a German physicist who contributed to the fundamental understanding of electrical circuits, spectroscopy, and the emission of black-body radiation by heated objects...
, using the newly invented spectroscope, examined the spectral signature of the Sun and discovered that it was composed of the same elements as existed on Earth, establishing for the first time a physical link between the Earth and the heavens. Then, Father Angelo Secchi
Angelo Secchi
-External links:...
compared the spectral signature of the Sun with those of other stars, and found them virtually identical. The realisation that the Sun was a star led to the hypothesis that other stars could have systems of their own, though this was not to be proven for nearly 140 years.
Further apparent discrepancies in the orbits of the outer planets led Percival Lowell
Percival Lowell
Percival Lawrence Lowell was a businessman, author, mathematician, and astronomer who fueled speculation that there were canals on Mars, founded the Lowell Observatory in Flagstaff, Arizona, and formed the beginning of the effort that led to the discovery of Pluto 14 years after his death...
to conclude that yet another planet, "Planet X
Planet X
Following the discovery of the planet Neptune in 1846, there was considerable speculation that another planet might exist beyond its orbit. The search began in the mid-19th century but culminated at the start of the 20th with Percival Lowell's quest for Planet X...
", must lie beyond Neptune. After his death, his Lowell Observatory
Lowell Observatory
Lowell Observatory is an astronomical observatory in Flagstaff, Arizona. Lowell Observatory was established in 1894, placing it among the oldest observatories in the United States, and was designated a National Historic Landmark in 1965....
conducted a search which ultimately led to Clyde Tombaugh
Clyde Tombaugh
Clyde William Tombaugh was an American astronomer. Although he is best known for discovering the dwarf planet Pluto in 1930, the first object to be discovered in what would later be identified as the Kuiper Belt, Tombaugh also discovered many asteroids; he also called for serious scientific...
's discovery of Pluto
Pluto
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...
in 1930. Pluto was, however, found to be too small to have disrupted the orbits of the outer planets, and its discovery was therefore coincidental. Like Ceres, it was initially considered to be a planet, but after the discovery of many other similarly sized objects in its vicinity it was reclassified in 2006 as a dwarf planet
Dwarf planet
A dwarf planet, as defined by the International Astronomical Union , is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite...
by the IAU.
In 1992, the first evidence of a planetary system
Planetary system
A planetary system consists of the various non-stellar objects orbiting a star such as planets, dwarf planets , asteroids, meteoroids, comets, and cosmic dust...
other than our own was discovered, orbiting the pulsar
Pulsar
A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...
PSR B1257+12
PSR B1257+12
PSR B1257+12, sometimes abbreviated as PSR 1257+12, is a pulsar located roughly 2000 light-years from the Sun. In 2007, it was confirmed that three extrasolar planets orbit the pulsar.- Pulsar :...
. Three years later, 51 Pegasi b
51 Pegasi b
51 Pegasi b , sometimes though unofficially named Bellerophon, is an extrasolar planet approximately 50 light-years away in the constellation of Pegasus...
, the first extrasolar planet
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
around a Sunlike star, was discovered. As of 2008, 221 extrasolar systems have been found.
Also in 1992, astronomers David C. Jewitt
David C. Jewitt
David C. Jewitt is a professor of astronomy formerly at the University of Hawaii Institute for Astronomy, now at UCLA. He was born in 1958 in England, and is a 1979 graduate of the University of London. Jewitt received an M.Sc. and a Ph.D. in astronomy at the California Institute of Technology in...
of the University of Hawaii
University of Hawaii
The University of Hawaii System, formally the University of Hawaii and popularly known as UH, is a public, co-educational college and university system that confers associate, bachelor, master, and doctoral degrees through three university campuses, seven community college campuses, an employment...
and Jane Luu
Jane Luu
-Early life:Luu was born in 1963 in South Vietnam to a father who worked as a translator for the U.S. Army. Her father taught her French as a child, beginning her lifelong love of languages....
of the Massachusetts Institute of Technology
Massachusetts Institute of Technology
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...
discovered . This object proved to be the first of a new population, which became known as the Kuiper belt
Kuiper belt
The Kuiper belt , sometimes called the Edgeworth–Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 50 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive...
; an icy analogue to the asteroid belt of which such objects as Pluto and Charon were deemed a part.
Mike Brown
Michael E. Brown
Michael E. Brown has been a professor of planetary astronomy at the California Institute of Technology since 2003....
, Chad Trujillo
Chad Trujillo
Chadwick A. "Chad" Trujillo is an astronomer and the co-discoverer of the dwarf planet Eris.Trujillo works with computer software and has examined the orbits of the numerous trans-Neptunian objects , which is the outer area of the solar system that he specialized in. In late August 2005, it was...
and David Rabinowitz
David L. Rabinowitz
David Lincoln Rabinowitz is a researcher at Yale University. He has built CCD cameras and software for the detection of near-Earth asteroids and Kuiper Belt Objects, and his research has helped reduce the assumed number of near-Earth asteroids by half, from 1,000-2,000 to 500-1,000 He has also...
announced the discovery of Eris
Eris (dwarf planet)
Eris, formal designation 136199 Eris, is the most massive known dwarf planet in the Solar System and the ninth most massive body known to orbit the Sun directly...
in 2005, a scattered disc
Scattered disc
The scattered disc is a distant region of the Solar System that is sparsely populated by icy minor planets, a subset of the broader family of trans-Neptunian objects. The scattered-disc objects have orbital eccentricities ranging as high as 0.8, inclinations as high as 40°, and perihelia greater...
object larger than Pluto and the largest object discovered in orbit round the Sun since Neptune.
Observations by spacecraft
Space Age
The Space Age is a time period encompassing the activities related to the Space Race, space exploration, space technology, and the cultural developments influenced by these events. The Space Age is generally considered to have begun with Sputnik...
, a great deal of exploration has been performed by robotic spacecraft
Robotic spacecraft
A robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...
missions that have been organized and executed by various space agencies.
All planets in the Solar System have now been visited to varying degrees by spacecraft launched from Earth. Through these unmanned missions, humans have been able to get close-up photographs of all the planets and, in the case of landers
Lander (spacecraft)
A lander is a spacecraft which descends toward and comes to rest on the surface of an astronomical body. For bodies with atmospheres, the landing is called atmospheric reentry and the lander descends as a re-entry vehicle...
, perform tests of the soils and atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
s of some.
The first artificial object sent into space was the Soviet satellite Sputnik 1
Sputnik 1
Sputnik 1 ) was the first artificial satellite to be put into Earth's orbit. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957. The unanticipated announcement of Sputnik 1s success precipitated the Sputnik crisis in the United States and ignited the Space...
, launched in 1957, which successfully orbited the Earth until January 4 the following year. The American probe Explorer 6
Explorer 6
Explorer 6 was a United States satellite launched on August 7, 1959. It was a small, spheroidal satellite designed to study trapped radiation of various energies, galactic cosmic rays, geomagnetism, radio propagation in the upper atmosphere, and the flux of micrometeorites...
, launched in 1959, was the first satellite to image the Earth from space.
Flybys
The first successful probe to fly by another Solar System body was Luna 1Luna 1
Luna 1 , first known as First Cosmic Ship, then known as Mechta was the first spacecraft to reach the vicinity of the Moon and the first of the Luna program of Soviet automatic interplanetary stations successfully launched in the direction of the Moon.While traveling through the outer Van Allen...
, which sped past the Moon in 1959. Originally meant to impact with the Moon, it instead missed its target and became the first artificial object to orbit the Sun. Mariner 2
Mariner 2
Mariner 2 , an American space probe to Venus, was the first space probe to conduct a successful planetary encounter . The first successful spacecraft in the NASA Mariner program, it was a simplified version of the Block I spacecraft of the Ranger program and an exact copy of Mariner 1...
was the first probe to fly by another planet, Venus, in 1962. The first successful flyby of Mars was made by Mariner 4
Mariner 4
Mariner 4 was the fourth in a series of spacecraft, launched on November 28, 1964, intended for planetary exploration in a flyby mode and performed the first successful flyby of the planet Mars, returning the first pictures of the Martian surface...
in 1965. Mariner 10
Mariner 10
Mariner 10 was an American robotic space probe launched by NASA on November 3, 1973, to fly by the planets Mercury and Venus. It was launched approximately two years after Mariner 9 and was the last spacecraft in the Mariner program...
first passed Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
in 1974.
Pioneer 10
Pioneer 10 is a 258-kilogram robotic space probe that completed the first interplanetary mission to Jupiter, and became the first spacecraft to achieve escape velocity from the Solar System. The project was managed by the NASA Ames Research Center and the contract for the construction of the...
, which flew by Jupiter in 1973. Pioneer 11
Pioneer 11
Pioneer 11 is a 259-kilogram robotic space probe launched by NASA on April 6, 1973 to study the asteroid belt, the environment around Jupiter and Saturn, solar wind, cosmic rays, and eventually the far reaches of the solar system and heliosphere...
was the first to visit Saturn, in 1979. The Voyager
Voyager program
The Voyager program is a U.S program that launched two unmanned space missions, scientific probes Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable planetary alignment of the late 1970s...
probes performed a grand tour of the outer planets following their launch in 1977, with both probes passing Jupiter in 1979 and Saturn in 1980 – 1981. Voyager 2
Voyager 2
The Voyager 2 spacecraft is a 722-kilogram space probe launched by NASA on August 20, 1977 to study the outer Solar System and eventually interstellar space...
then went on to make close approaches to Uranus in 1986 and Neptune in 1989. The Voyager probes are now far beyond Neptune's orbit, and are on course to find and study the termination shock, heliosheath, and heliopause. According to NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
, both Voyager probes have encountered the termination shock at a distance of approximately 93 AU from the Sun.
The first flyby of a comet occurred in 1985, when the International Cometary Explorer
International Cometary Explorer
The International Cometary Explorer spacecraft was originally known as International Sun/Earth Explorer 3 satellite, launched August 12, 1978. It was part of the ISEE international cooperative program between NASA and ESRO/ESA to study the interaction between the Earth's magnetic field and the...
(ICE) passed by the comet Giacobini-Zinner
21P/Giacobini-Zinner
Comet Giacobini–Zinner is a periodic comet in our solar system.It was discovered by Michel Giacobini from , who observed the comet in the constellation of Aquarius on December 20, 1900...
, while the first flybys of asteroids were conducted by the Galileo space probe, which imaged both 951 Gaspra
951 Gaspra
951 Gaspra is an S-type asteroid that orbits very close to the inner edge of the asteroid belt. Gaspra was the first asteroid ever to be closely approached when it was visited by the Galileo spacecraft, which flew by on its way to Jupiter on 29 October 1991.-Characteristics:Apart from a multitude...
(in 1991) and 243 Ida
243 Ida
243 Ida is an asteroid in the Koronis family of the asteroid belt. It was discovered on 29 September 1884 by Johann Palisa and named after a nymph from Greek mythology. Later telescopic observations categorized Ida as an S-type asteroid, the most numerous type in the inner asteroid belt. On 28...
(in 1993) on its way to Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
.
No Kuiper belt object has yet been visited by a spacecraft. Launched on January 19, 2006, the New Horizons
New Horizons
New Horizons is a NASA robotic spacecraft mission currently en route to the dwarf planet Pluto. It is expected to be the first spacecraft to fly by and study Pluto and its moons, Charon, Nix, Hydra and S/2011 P 1. Its estimated arrival date at the Pluto-Charon system is July 14th, 2015...
probe is currently en route to becoming the first man-made spacecraft to explore this area. This unmanned mission is scheduled to fly by Pluto in July 2015. Should it prove feasible, the mission will then be extended to observe a number of other Kuiper belt objects.
Orbiters, rovers and landers
In 1966, the Moon became the first Solar System body beyond Earth to be orbited by an artificial satellite (Luna 10Luna 10
Luna 10 was a Luna program, robotic spacecraft mission, also called Lunik 10.The Luna 10 spacecraft was launched towards the Moon from an Earth orbiting platform on March 31, 1966. It was the first artificial satellite of the Moon...
), followed by Mars in 1971 (Mariner 9
Mariner 9
Mariner 9 was a NASA space orbiter that helped in the exploration of Mars and was part of the Mariner program. Mariner 9 was launched toward Mars on May 30, 1971 from Cape Canaveral Air Force Station and reached the planet on November 13 of the same year, becoming the first spacecraft to orbit...
), Venus in 1975 (Venera 9
Venera 9
Venera 9 was a USSR unmanned space mission to Venus. It consisted of an orbiter and a lander. It was launched on June 8, 1975 02:38:00 UTC and weighed 4,936 kg...
), Jupiter in 1995 (Galileo), the asteroid 433 Eros
433 Eros
433 Eros is a near-Earth asteroid discovered in 1898, and the first asteroid to be orbited by a probe . It is an S-type asteroid approximately 34.4×11.2×11.2 km in size, the second-largest NEA after 1036 Ganymed, and belongs to the Amor group.Eros is a Mars-crosser asteroid, the first known...
in 2000 (NEAR Shoemaker
NEAR Shoemaker
The Near Earth Asteroid Rendezvous - Shoemaker , renamed after its 1996 launch in honor of planetary scientist Eugene M. Shoemaker, was a robotic space probe designed by the Johns Hopkins University Applied Physics Laboratory for NASA to study the near-Earth asteroid Eros from close orbit over a...
), Saturn in 2004 (Cassini–Huygens), and Mercury in 2011 (MESSENGER
MESSENGER
The MErcury Surface, Space ENvironment, GEochemistry and Ranging space probe is a robotic NASA spacecraft in orbit around the planet Mercury. The spacecraft was launched aboard a Delta II rocket in August 2004 to study the chemical composition, geology, and magnetic field of Mercury...
). The Dawn spacecraft is currently set to orbit the asteroid Vesta
4 Vesta
Vesta, formally designated 4 Vesta, is one of the largest asteroids, with a mean diameter of about . It was discovered by Heinrich Wilhelm Olbers on March 29, 1807, and is named after the Roman virgin goddess of home and hearth, Vesta....
in 2011 and the dwarf planet Ceres in 2015.
The first probe to land on another Solar System body
Landings on other planets
This is a list of all spacecraft landings on other planets and bodies in the solar system, including soft landings and both intended and unintended hard impacts...
was the Soviet
Soviet space program
The Soviet space program is the rocketry and space exploration programs conducted by the former Union of Soviet Socialist Republics from the 1930s until its dissolution in 1991...
Luna 2
Luna 2
Luna 2 was the second of the Soviet Union's Luna programme spacecraft launched to the Moon. It was the first spacecraft to reach the surface of the Moon...
probe, which impacted the Moon in 1959. Since then, increasingly distant planets have been reached, with probes landing on or impacting the surfaces of Venus in 1966 (Venera 3
Venera 3
Venera 3 was a Venera program space probe that was built and launched by the Soviet Union to explore the surface of Venus. It was launched on November 16, 1965 at 04:19 UTC from Baikonur, Kazakhstan....
), Mars in 1971 (Mars 3
Mars 3
The Mars 3 was an unmanned space probe of the Mars program, a series of unmanned Mars landers and orbiters launched by the Soviet Union in the early 1970s....
, although a fully successful landing didn't occur until Viking 1
Viking 1
Viking 1 was the first of two spacecraft sent to Mars as part of NASA's Viking program. It was the first spacecraft to successfully land on Mars and perform its mission, and until May 19, 2010 held the record for the second longest Mars surface mission of 6 years and 116 days .- Mission :Following...
in 1976), the asteroid 433 Eros
433 Eros
433 Eros is a near-Earth asteroid discovered in 1898, and the first asteroid to be orbited by a probe . It is an S-type asteroid approximately 34.4×11.2×11.2 km in size, the second-largest NEA after 1036 Ganymed, and belongs to the Amor group.Eros is a Mars-crosser asteroid, the first known...
in 2001 (NEAR Shoemaker
NEAR Shoemaker
The Near Earth Asteroid Rendezvous - Shoemaker , renamed after its 1996 launch in honor of planetary scientist Eugene M. Shoemaker, was a robotic space probe designed by the Johns Hopkins University Applied Physics Laboratory for NASA to study the near-Earth asteroid Eros from close orbit over a...
), and Saturn's moon Titan
Titan (moon)
Titan , or Saturn VI, is the largest moon of Saturn, the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found....
(Huygens
Huygens probe
The Huygens probe was an atmospheric entry probe carried to Saturn's moon Titan as part of the Cassini–Huygens mission. The probe was supplied by the European Space Agency and named after the Dutch 17th century astronomer Christiaan Huygens....
) and the comet Tempel 1 (Deep Impact) in 2005. The Galileo orbiter also dropped a probe into Jupiter's atmosphere in 1995; since Jupiter has no physical surface, it was destroyed by increasing temperature and pressure as it descended.
To date, only two worlds in the Solar System, the Moon and Mars, have been visited by mobile rovers
Rover (space exploration)
A rover is a space exploration vehicle designed to move across the surface of a planet or other astronomical body. Some rovers have been designed to transport members of a human spaceflight crew; others have been partially or fully autonomous robots...
. The first rover to visit another celestial body was the Soviet Lunokhod 1
Lunokhod 1
Lunokhod 1 was the first of two unmanned lunar rovers landed on the Moon by the Soviet Union as part of its Lunokhod program. The spacecraft which carried Lunokhod 1 was named Luna 17...
, which landed on the Moon in 1970. The first to visit another planet was Sojourner, which travelled 500 metres across the surface of Mars in 1997. The only manned rover to visit another world was NASA's Lunar rover
Lunar rover
The Lunar Roving Vehicle or lunar rover was a battery-powered four-wheeled rover used on the Moon in the last three missions of the American Apollo program during 1971 and 1972...
, which travelled with Apollos 15
Apollo 15
Apollo 15 was the ninth manned mission in the American Apollo space program, the fourth to land on the Moon and the eighth successful manned mission. It was the first of what were termed "J missions", long duration stays on the Moon with a greater focus on science than had been possible on previous...
, 16
Apollo 16
Young and Duke served as the backup crew for Apollo 13; Mattingly was slated to be the Apollo 13 command module pilot until being pulled from the mission due to his exposure to rubella through Duke.-Backup crew:...
and 17
Apollo 17
Apollo 17 was the eleventh and final manned mission in the American Apollo space program. Launched at 12:33 a.m. EST on December 7, 1972, with a three-member crew consisting of Commander Eugene Cernan, Command Module Pilot Ronald Evans, and Lunar Module Pilot Harrison Schmitt, Apollo 17 remains the...
between 1971 and 1972.
Manned exploration
Manned exploration of the Solar System is currently confined to Earth's immediate environs. The first human being to reach space (defined as an altitude of over 100 kmKarman line
The Kármán line lies at an altitude of above the Earth's sea level, and is commonly used to define the boundary between the Earth's atmosphere and outer space...
) and to orbit the Earth was Yuri Gagarin
Yuri Gagarin
Yuri Alekseyevich Gagarin was a Soviet pilot and cosmonaut. He was the first human to journey into outer space, when his Vostok spacecraft completed an orbit of the Earth on April 12, 1961....
, a Soviet cosmonaut who was launched in Vostok 1
Vostok 1
Vostok 1 was the first spaceflight in the Vostok program and the first human spaceflight in history. The Vostok 3KA spacecraft was launched on April 12, 1961. The flight took Yuri Gagarin, a cosmonaut from the Soviet Union, into space. The flight marked the first time that a human entered outer...
on April 12, 1961. The first man to walk on the surface of another Solar System body was Neil Armstrong
Neil Armstrong
Neil Alden Armstrong is an American former astronaut, test pilot, aerospace engineer, university professor, United States Naval Aviator, and the first person to set foot upon the Moon....
, who stepped onto the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
on July 21, 1969 during the Apollo 11
Apollo 11
In early 1969, Bill Anders accepted a job with the National Space Council effective in August 1969 and announced his retirement as an astronaut. At that point Ken Mattingly was moved from the support crew into parallel training with Anders as backup Command Module Pilot in case Apollo 11 was...
mission; five more Moon landings occurred through 1972. The United States' Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
, which debuted in 1981, is the only reusable spacecraft to successfully make multiple orbital flights. The five shuttles that have been built have flown a total of 121 missions, with two of the craft destroyed in accidents. The first orbital space station
Space station
A space station is a spacecraft capable of supporting a crew which is designed to remain in space for an extended period of time, and to which other spacecraft can dock. A space station is distinguished from other spacecraft used for human spaceflight by its lack of major propulsion or landing...
to host more than one crew was NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's Skylab
Skylab
Skylab was a space station launched and operated by NASA, the space agency of the United States. Skylab orbited the Earth from 1973 to 1979, and included a workshop, a solar observatory, and other systems. It was launched unmanned by a modified Saturn V rocket, with a mass of...
, which successfully held three crews from 1973 to 1974. The first true human settlement in space was the Soviet space station Mir
Mir
Mir was a space station operated in low Earth orbit from 1986 to 2001, at first by the Soviet Union and then by Russia. Assembled in orbit from 1986 to 1996, Mir was the first modular space station and had a greater mass than that of any previous spacecraft, holding the record for the...
, which was continuously occupied for close to ten years, from 1989 to 1999. It was decommissioned in 2001, and its successor, the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
, has maintained a continuous human presence in space since then. In 2004, SpaceShipOne became the first privately funded vehicle to reach space on a suborbital flight. That year, U.S. President George W. Bush
George W. Bush
George Walker Bush is an American politician who served as the 43rd President of the United States, from 2001 to 2009. Before that, he was the 46th Governor of Texas, having served from 1995 to 2000....
announced the Vision for Space Exploration
Vision for Space Exploration
The Vision for Space Exploration is the United States space policy which was announced on January 14, 2004 by President George W. Bush. It is seen as a response to the Space Shuttle Columbia disaster, the state of human spaceflight at NASA, and a way to regain public enthusiasm for space...
, which called for a replacement for the aging Shuttle, a return to the Moon and, ultimately, a manned mission to Mars.