The following table is a list of

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...

orbiter A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, pl ...

s, consisting of

space probes Space is the boundless three-dimensional extent in which objects and events have relative position and direction. In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually conside ...

which were launched from Earth and are currently orbiting

. As of February 2021, there have been 18 spacecraft missions operating in Mars' orbit, 8 of which are currently active. In 2022, contact was lost to India's

Mars Orbiter Mission The Mars Orbiter Mission (MOM), also called ''Mangalyaan'', was a space probe orbiting Mars since 24 September 2014. It was launched on 5 November 2013 by the Indian Space Research Organisation (ISRO). It was India's first interplanetary missio ...

. So with that loss, 7 orbiters remain active.

History

20th century

The

Soviets Soviet people ( rus, сове́тский наро́д, r=sovyétsky naród), or citizens of the USSR ( rus, гра́ждане СССР, grázhdanye SSSR), was an umbrella demonym for the population of the Soviet Union. Nationality policy in th ...

Mars program The Mars program was a series of uncrewed spacecraft launched by the Soviet Union between 1960 and 1973. The spacecraft were intended to explore Mars, and included flyby probes, landers and orbiters. Early Mars spacecraft were small, and launche ...

and the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

Mariner program The Mariner program was conducted by the American space agency NASA to explore other planets. Between 1962 and late 1973, NASA's Jet Propulsion Laboratory (JPL) designed and built 10 robotic interplanetary probes named Mariner to explore the in ...

became the two first successful space programs that intended to explore

through

Mars 2 The Mars 2 was an uncrewed space probe of the Mars program, a series of uncrewed Mars landers and orbiters launched by the Soviet Union beginning 19 May 1971. The Mars 2 and Mars 3 missions consisted of identical spacecraft, each with an orbit ...

Mars 3 Mars 3 was a robotic space probe of the Soviet Mars program, launched May 28, 1971, nine days after its twin spacecraft Mars 2. The probes were identical robotic spacecraft launched by Proton-K rockets with a Blok D upper stage, each consisting ...

and

Mariner 9 Mariner 9 (Mariner Mars '71 / Mariner-I) was a robotic spacecraft that contributed greatly to the exploration of Mars and was part of the NASA Mariner program. Mariner 9 was launched toward Mars on May 30, 1971 from LC-36B at Cape Canaveral Air ...

were all launched into space in May 1971, and all entered Mars’ orbit that same year. NASA's Mariner 9 reached the planet's orbit first on November 14, narrowly beating the Soviet's spacecraft amid the

space race The Space Race was a 20th-century competition between two Cold War rivals, the United States and the Soviet Union, to achieve superior spaceflight capability. It had its origins in the ballistic missile-based nuclear arms race between the tw ...

, and subsequently became the first spacecraft to orbit another planet. Contact with all eight Mars orbiters launched during the 20th century has been lost. NASA's four spacecraft are conjectured to remain in Mars' orbit. Mariner 9, ''

Viking 1 ''Viking 1'' was the first of two spacecraft, along with ''Viking 2'', each consisting of an orbiter and a lander, sent to Mars as part of NASA's Viking program. The lander touched down on Mars on July 20, 1976, the first successful Mars land ...

'' and ''

Viking 2 The ''Viking 2'' mission was part of the American Viking program to Mars, and consisted of an orbiter and a lander essentially identical to that of the ''Viking 1'' mission. ''Viking 2'' was operational on Mars for sols ( days; '). The ''Vik ...

'' are expected to lower down into the Martian atmosphere by 2022 and either burn up or crash into the planet's surface. ''

Mars Global Surveyor ''Mars Global Surveyor'' (MGS) was an American robotic space probe developed by NASA's Jet Propulsion Laboratory and launched November 1996. MGS was a global mapping mission that examined the entire planet, from the ionosphere down through the a ...

'' is expected to crash onto the surface of the planet by 2047. The fate of the Soviet's three Mars program orbiters and

Phobos 2 ''Phobos 2'' was the last space probe designed by the Soviet Union. It was designed to explore the moons of Mars, Phobos and Deimos. It was launched on 12 July 1988, and entered orbit on 29 January 1989. ''Phobos 2'' operated nominally throug ...

remains unclear, but they are still presumed to be in orbit. In 1999 the

Mars Climate Orbiter The ''Mars Climate Orbiter'' (formerly the Mars Surveyor '98 Orbiter) was a robotic space probe launched by NASA on December 11, 1998, to study the Martian climate, Martian atmosphere, and surface changes and to act as the communications re ...

impacted the Martian atmosphere.

21st century

PIA07944 Mars Express Seen by Mars Global Surveyor, Figure 1

PIA07944 Mars Express Seen by Mars Global Surveyor

2001 Mars Odyssey ''2001 Mars Odyssey'' is a robotic spacecraft orbiting the planet Mars. The project was developed by NASA, and contracted out to Lockheed Martin, with an expected cost for the entire mission of US$297 million. Its mission is to use spectr ...

'' was launched April 7, 2001 on a

Delta II Delta II was an expendable launch system, originally designed and built by McDonnell Douglas. Delta II was part of the Delta rocket family and entered service in 1989. Delta II vehicles included the Delta 6000, and the two later Delta 7000 va ...

rocket and currently holds the record for the longest-surviving continually active spacecraft in orbit around a planet other than Earth at . In 2003, the

European Space Agency , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1205 ...

(ESA) launched their first planetary mission with

Mars Express ''Mars Express'' is a space exploration mission being conducted by the European Space Agency (ESA). The ''Mars Express'' mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally ref ...

to conduct reconnaissance and exploration of Mars from orbit. On 12 August 2005, NASA launched ''

Mars Reconnaissance Orbiter ''Mars Reconnaissance Orbiter'' (MRO) is a spacecraft designed to study the geology and climate of Mars, provide reconnaissance of future landing sites, and relay data from surface missions back to Earth. It was launched on August 12, 2005, an ...

'' (MRO). As MRO entered orbit in 2006, it joined three other active spacecraft which were in Mars' orbit:

(MGS), Mars Express, and ''2001 Mars Odyssey''; at the time, this set a record for the most operational spacecraft in the immediate vicinity of Mars. MGS has since ceased to function. On November 5, 2013, the

(''Mangalyaan-1'') was launched by the

Indian Space Research Organisation The Indian Space Research Organisation (ISRO; ) is the national space agency of India, headquartered in Bengaluru. It operates under the Department of Space (DOS) which is directly overseen by the Prime Minister of India, while the Chairman ...

(ISRO) as a "technology demonstrator" project. Its secondary goal is to analyze the Martian atmosphere and topography. The orbiter reached Mars orbit on September 24, 2014. Through this mission, ISRO became the first space agency to succeed in its first attempt at a Mars orbiter. The mission is the first successful Asian interplanetary mission. Ten days after ISRO's launch, NASA launched their seventh Mars orbiter

MAVEN MAVEN is an American spacecraft orbiting Mars to study the loss of its atmospheric gases to space, providing insight into the history of the planet's climate and water. The spacecraft name is an acronym for "Mars Atmosphere and Volatile Evolu ...

to study the

Martian atmosphere The atmosphere of Mars is the layer of gases surrounding Mars. It is primarily composed of carbon dioxide (95%), molecular nitrogen (2.8%), and argon (2%). It also contains trace levels of water vapor, oxygen, carbon monoxide, hydrogen, and no ...

. Its goals include determining how the planet's

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

and

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

, presumed to have once been substantial, were lost over time.

Fate

After achieving orbit, functional or not, Mars orbiters have been predicted to remain in orbit for a certain amount of time. *''

'' orbiter, likely to be in orbit until 2019 (It is likely to be still in orbit however.) *

is expected to remain in orbit until approximately 2022, when the spacecraft is projected to enter the Martian atmosphere and either burn up or crash into the planet's surface. *

, around 2046 (1996+50 years) Besides decaying to Mars, a collision with a moon or other spacecraft is also a possibility. In March 2017, ''

'' had to change its orbit to avoid colliding with Phobos, and with an increasing number of spacecraft at Mars this risk increases. The ''

'' is still being tracked, although it is no longer functioning.

Table of objects

Note that days active category does not necessarily equate to time in orbit, for example Mars Global Surveyor is expected remain in Mars orbit for 50 years after its arrival. The detection of derelict spacecraft in Mars orbit has some interest due to the minute risk of collision with such a spacecraft. One example of this is a proposal to use the Optical Navigation Camera on the Mars Reconnaissance Orbiter to search for small moons, dust rings, and old orbiters.M. Adler, et al. – Use of MRO Optical Navigation Camera .. (2012)
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References

{{DEFAULTSORT:Mars orbiters Missions to Mars * Space probes Lists of spacecraft