The ''Viking 2'' mission was part of the American

Viking program The ''Viking'' program consisted of a pair of identical American space probes, ''Viking 1'' and ''Viking 2'' both launched in 1975, and landed on Mars in 1976. The mission effort began in 1968 and was managed by the NASA Langley Research Cent ...

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

, and consisted of an orbiter and a lander essentially identical to that of the ''

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 lan ...

'' mission. ''Viking 2'' was operational on Mars for sols (

days A day is the time period of a full rotation of the Earth with respect to the Sun. On average, this is 24 hours (86,400 seconds). As a day passes at a given location it experiences morning, afternoon, evening, and night. This daily cyc ...

; '). The ''Viking 2'' lander operated on the surface for days, or sols, and was turned off on April 12, 1980, when its batteries eventually failed. The orbiter worked until July 25, 1978, returning almost 16,000 images in 706 orbits around Mars.

Mission profile

The craft was launched on September 9, 1975. Following launch using a

Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...

Centaur A centaur ( ; ; ), occasionally hippocentaur, also called Ixionidae (), is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse that was said to live in the mountains of Thessaly. In one version o ...

launch vehicle and a 333-day cruise to Mars, the ''Viking 2''

Orbiter A spacecraft is a vehicle that is designed to fly and operate in outer space. Spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, planetary exploration, ...

began returning global images of Mars prior to orbit insertion. The orbiter was inserted into a 1,500 x 33,000 km, 24.6 h

Mars orbit Mars has an orbit with a semimajor axis of 1.524 astronomical units (228 million km) (12.673 light minutes), and an eccentricity of 0.0934.Jean Meeus, ''Astronomical Formulæ for Calculators''. (Richmond, VA: Willmann-Bell, 1988) 99. Elements b ...

on August 7, 1976, and trimmed to a 27.3 h site certification orbit with a

periapsis An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

of 1,499 km and an inclination of 55.2 degrees on August 9. The orbiter then began taking photographs of candidate landing sites, which were used to select the final landing site. The lander separated from the orbiter on September 3, 1976, at 22:37:50 UT and landed at

Utopia Planitia Utopia Planitia ( Greek and Latin: "Utopia Land Plain") is a large plain within Utopia, the largest recognized impact basin on Mars and in the Solar System with an estimated diameter of . It is the Martian region where the '' Viking 2'' lander t ...

. The normal procedure called for the structure connecting the orbiter and lander (the bioshield) to be ejected after separation. However, due to problems with the separation process, the bioshield remained attached to the orbiter. The orbit inclination was raised to 75 degrees on September 30, 1976.

Orbiter

The orbiter's primary mission ended on October 5, 1976, at the beginning of

solar conjunction Solar conjunction generally occurs when a planet or other Solar System object is on the opposite side of the Sun from the Earth. From an Earth reference, the Sun will pass between the Earth and the object. Communication with any spacecraft in sol ...

. The extended mission commenced on December 14, 1976, after the solar conjunction. On December 20, 1976, the periapsis was lowered to 778 km, and the inclination raised to 80 degrees. Operations included close approaches to

Deimos Deimos, a Greek word for ''dread'', may refer to: In general * Deimos (deity), one of the sons of Ares and Aphrodite in Greek mythology * Deimos (moon), the smaller and outermost of Mars' two natural satellites Fictional characters * Deimos (comi ...

in October 1977, and the periapsis was lowered to 300 km and the period changed to 24 hours on October 23, 1977. The orbiter developed a leak in its propulsion system that vented its

attitude control Spacecraft attitude control is the process of controlling the orientation of a spacecraft (vehicle or satellite) with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, ...

gas. It was placed in a 302 × 33,176 km orbit and turned off on July 25, 1978, after returning almost 16,000 images in about 700–706 orbits around Mars.

Lander

The lander and its

aeroshell An aeroshell is a rigid heat-shielded shell that helps decelerate and protects a spacecraft vehicle from pressure, heat, and possible debris created by drag during atmospheric entry. Its main components consist of a heat shield (the forebody) an ...

separated from the orbiter on September 3, 1976, at 19:39:59 UT. At the time of separation, the lander was orbiting at about 4 km/s. After separation, rockets fired to begin lander

deorbit Atmospheric entry (sometimes listed as Vimpact or Ventry) is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. Atmospheric entry may be ''uncontrolled entry ...

. After a few hours, at about 300 km attitude, the lander was reoriented for entry. The aeroshell with its ablative

heat shield In engineering, a heat shield is a component designed to protect an object or a human operator from being burnt or overheated by dissipating, reflecting, and/or absorbing heat. The term is most often used in reference to exhaust heat management a ...

slowed the craft as it plunged through the atmosphere. PSP 001501 2280 RED VL-2 lander

The ''Viking 2'' lander touched down about 200 km west of the crater Mie in

at at an altitude of -4.23 km relative to a reference ellipsoid with an equatorial radius of 3,397.2 km and a

flattening Flattening is a measure of the compression of a circle or sphere along a diameter to form an ellipse or an ellipsoid of revolution (spheroid) respectively. Other terms used are ellipticity, or oblateness. The usual notation for flattening is f ...

of 0.0105 (

planetographic longitude A planetary coordinate system (also referred to as ''planetographic'', ''planetodetic'', or ''planetocentric'') is a generalization of the geographic, geodetic, and the geocentric coordinate systems for planets other than Earth. Similar coordina ...

) at 22:58:20 UT (9:49:05 a.m. local Mars time). Approximately of propellants were left at landing. Due to radar misidentification of a rock or highly reflective surface, the thrusters fired an extra time 0.4 seconds before landing, cracking the surface and raising dust. The lander settled down with one leg on a rock, tilted at 8.2 degrees. The cameras began taking images immediately after landing. The ''Viking 2'' lander was powered by radioisotope generators and operated on the surface until its batteries failed on April 12, 1980. In July 2001, the ''Viking 2'' lander was renamed the Gerald Soffen Memorial Station after

Gerald Soffen Gerald A. Soffen (February 7, 1926 – November 22, 2000) was a NASA scientist and educator who served in a wide variety of roles for the space agency, primarily dealing with either education or with life sciences—especially the search for life o ...

(1926–2000), the project scientist of the ''Viking'' program.

Results from the ''Viking 2'' mission

Landing site soil analysis

The regolith, referred to often as "soil," resembled those produced from the weathering of basaltic

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

s. The tested soil contained abundant

silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

and

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

, along with significant amounts of

magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...

aluminum Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...

, and

titanium Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...

. Trace elements,

strontium Strontium is a chemical element; it has symbol Sr and atomic number 38. An alkaline earth metal, it is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is exposed to ...

and

yttrium Yttrium is a chemical element; it has Symbol (chemistry), symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost a ...

, were detected. The amount of

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

was one-fifth of the average for the Earth's crust. Some chemicals in the soil contained sulfur and

chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...

that were like those remaining after the evaporation of seawater. Sulfur was more concentrated in the crust on top of the soil than in the bulk soil beneath. The sulfur may be present as

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...

s of

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

, magnesium, calcium, or iron. A

sulfide Sulfide (also sulphide in British English) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to large families o ...

of iron is also possible. The ''Spirit'' rover and the ''Opportunity'' rover both found sulfates on Mars. Minerals typical weathering products of

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

igneous rocks Igneous rock ( ), or magmatic rock, is one of the three main Rock (geology)#Classification, rock types, the others being sedimentary rock, sedimentary and metamorphic rock, metamorphic. Igneous rocks are formed through the cooling and solidifi ...

were found. All samples heated in the gas chromatograph-mass spectrometer (GCMS) gave off water. However, the way the samples were handled prohibited an exact measurement of the amount of water. But, it was around 1%. Studies with

magnets A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...

aboard the landers indicated that the soil is between 3 and 7 percent magnetic materials by weight. The magnetic chemicals could be

magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...

and

maghemite Maghemite (Fe2O3, γ-Fe2O3) is a member of the family of iron oxides. It has the same formula as hematite, but the same spinel ferrite structure as magnetite () and is also ferrimagnetic. It is sometimes spelled as "maghaemite". ''Maghemite'' ...

, which could come from the weathering of

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

rock. Subsequent experiments carried out by the Mars ''Spirit'' rover (landed in 2004) suggest that magnetite could explain the magnetic nature of the dust and soil on Mars.

Search for life

''Viking 2'' carried a biology experiment whose purpose was to look for life. The ''Viking 2'' biology experiment weighed and consisted of three subsystems: the

Pyrolytic Release In 1976 two identical Viking program landers each carried four types of biological experiments to the surface of Mars. The first successful Mars landers, ''Viking 1'' and ''Viking 2'', then carried out experiments to look for biosignatures of micr ...

experiment (PR), the Labeled Release experiment (LR), and the Gas Exchange experiment (GEX). In addition, independent of the biology experiments, ''Viking 2'' carried a Gas Chromatograph/Mass Spectrometer (GCMS) that could measure the composition and abundance of organic compounds in the Martian soil. The results were unusual and conflicting: the GCMS and GEX gave negative results, while the PR and LR gave positive results. Viking scientist Patricia Straat stated in 2009, "Our (LR) experiment was a definite positive response for life, but a lot of people have claimed that it was a false positive for a variety of reasons." Many scientists believe that the data results were attributed to inorganic chemical reactions in the soil. However, this view may be changing due to a variety of discoveries and studies since Viking. These include the discovery of near-surface ice near the Viking landing zone, the possibility of perchlorate destruction of organic matter, and the reanalysis of GCMS data by scientists in 2018. Some scientists still believe the results were due to living reactions. The formal declaration at the time of the mission was that the discovery of organic chemicals was inconclusive. Mars has almost no ozone layer, unlike the Earth, so UV light sterilizes the surface and produces highly reactive chemicals such as peroxides that would oxidize any organic chemicals.Hartmann, W. 2003. A Traveler's Guide to Mars. Workman Publishing. NY NY. The ''Phoenix'' Lander discovered the chemical

perchlorate A perchlorate is a chemical compound containing the perchlorate ion, , the conjugate base of perchloric acid (ionic perchlorate). As counterions, there can be metal cations, quaternary ammonium cations or other ions, for example, nitronium cat ...

in the Martian soil. Perchlorate is a powerful oxidizing agent, which could have eradicated any organic material on the surface. Perchlorate is now considered widespread on Mars, making it hard to detect any organic compounds on the Martian surface.

''Viking 2'' lander image gallery

File:First Color Image of the Viking Lander 2 Site.jpg, First color image (''Viking 2'' lander Camera 2 sol , September 5, 1976) 14:36 File:22g144 netoyee.jpg, ''Viking 2'' lander Camera 2 22G144 (Low Resolution Color) Sol 552 19:16 File:Mars Viking 22e169.png, Frost on Mars. File:22i067 FROST.png, ''Viking 2'' lander Camera 2 FROST (Low Resolution Color) Sol 955 12:13 File:Mars Viking 21i093.png, Frost at the landing site. (false color) File:21i090 21i093 21d224-225-226 LOW RESOLUTION COLOR.jpg, ''Viking 2'' lander Camera 1 FROST (Low Resolution Color) Sol 960 14:14 File:21i091 HIGH RESOLUTION COLOR.jpg, ''Viking 2'' lander Camera 1 FROST HIGH RESOLUTION (With Low Resolution Color) Sol 959 14:39 File:SKY-AT-SUNRISE-(22b023).jpg, ''Viking 2 '' lander Camera 2 SKY AT SUNRISE (Low Resolution Color) Sol 34 04:22 File:SKY-AT-SUNRISE(22h093).jpg, ''Viking 2'' lander Camera 2 SKY AT SUNRISE (Low Resolution Color) Sol 631 04:00

Orbiter results

Viking program

The Viking Orbiters led to significant discoveries about the presence of water on Mars. Huge river valleys were found in many areas. They showed that water floods carved deep valleys, eroded grooves into bedrock, and traveled thousands of kilometers. In the southern hemisphere, the presence of branched stream areas suggests that there was once rainfall.Moore, P. et al. 1990. ''The Atlas of the Solar System''. Mitchell Beazley Publishers NY, NY. The images below are mosaics of many small, high-resolution images. Image:Streamlined_Islands_in_Maja_Valles.jpg, Streamlined islands seen by Viking showed that large floods occurred on Mars. Image is located in

Lunae Palus quadrangle The Lunae Palus quadrangle is one of a series of list of quadrangles on Mars, 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The quadrangle (geography), quadrangle is also referred to ...

. Image:Viking Teardrop Islands.jpg, Tear-drop shaped islands caused by flood waters from

Maja Valles The Maja Valles are a large system of ancient outflow channels in the Lunae Palus quadrangle on Mars. About Their location is 12.6° north latitude and 58.3° west longitude. The name is a Nepali word for "Mars". The Maja Valles begin at Juv ...

, as seen by Viking Orbiter. Image is located in

Oxia Palus quadrangle The Oxia Palus quadrangle is one of a series of list of quadrangles on Mars, 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Oxia Palus quadrangle is also referred to as MC-11 (Mars ...

. The islands are formed in the ejecta of

Lod Lod (, ), also known as Lydda () and Lidd (, or ), is a city southeast of Tel Aviv and northwest of Jerusalem in the Central District of Israel. It is situated between the lower Shephelah on the east and the coastal plain on the west. The ci ...

, Bok, and

Gold Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...

craters. Image:Chryse Planitia Scour Patterns.jpg, Scour patterns, located in

, were produced by flowing water from Maja Valles, which lies just to the left of this mosaic. Detail of flow around Dromore crater is shown on the next image. Image:Detail of Maja Valles Flow.jpg, Great amounts of water were required to carry out the erosion shown in this Viking image. Image is located in

. The erosion shaped the ejecta around Dromore. Image:Vedra,_Maumee,_and_Maja_valles.jpg, Waters from

Vedra Valles The Vedra Valles are a set of channels in an ancient river valley in the Lunae Palus quadrangle of Mars, located at 19.4° N and 55.6° W. They are 115 km long and were named after an ancient river in Great Britain. Together with other ancient ...

Maumee Valles The Maumee Valles are a set of channels in an ancient river valley in the Lunae Palus quadrangle of Mars, located at 19.7° N and 53.2° W. They are long and were named after a North American river in Indiana and Ohio. Together with other anci ...

, and Maja Valles flowed from Lunae Planum on the left, to

Chryse Planitia Chryse Planitia (Greek, "''Golden Plain''") is a smooth circular plain in the northern equatorial region of Mars close to the Tharsis region to the west, centered at . Chryse Planitia lies partially in the Lunae Palus quadrangle, partially in t ...

on the right. Image is located in

and was taken by Viking Orbiter. Image:Kasei Valles topolabled.JPG, Area around northern Kasei Valles, showing relationships among

Kasei Valles The Kasei Valles are a giant system of canyons in Mare Acidalium and Lunae Palus quadrangles on Mars, centered at 24.6° north latitude and 65.0° west longitude. They are long and were named for the word for "Mars" in Japanese. This is one ...

Bahram Vallis Bahram Vallis is an ancient river valley in the Lunae Palus quadrangle of Mars at 20.7° north latitude and 57.5° west longitude. It is about 302 km long and was named after the word for 'Mars' in Persian. Bahram Vallis is located midway b ...

, and

. Map location is in

and includes parts of Lunae Planum and

. Image:Flow from Arandas Crater.jpg, The ejecta from Arandas crater acts like mud. It moves around small craters (indicated by arrows), instead of just falling down on them. Craters like this suggest that large amounts of frozen water were melted when the impact crater was produced. Image is located in

Mare Acidalium quadrangle The Mare Acidalium quadrangle is one of a series of list of quadrangles on Mars, 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Quadrangle (geography), quadrangle is located in t ...

and was taken by Viking Orbiter. Image:Alba Patera Channels.jpg, This view of the flank of

Alba Patera Alba Mons (formerly and still occasionally known as Alba Patera, a term that has since been restricted to the volcano's summit caldera; also initially known as the Arcadia ring) is a volcano located in the northern Tharsis region of the planet Ma ...

shows several channels/troughs. Some channels are associated with lava flows; others are probably caused by running water. A large trough or graben turns into a line of collapse pits. Image is located in

Arcadia quadrangle The Arcadia quadrangle is one of a series of list of quadrangles on Mars, 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The quadrangle (geography), quadrangle is located in the nort ...

and was taken by Viking Orbiter. Image:Branched Channels from Viking.jpg, Branched channels in

Thaumasia quadrangle The Thaumasia quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Thaumasia quadrangle is also referred to as MC-25 (Mars Chart-25). The name comes fr ...

, as seen by Viking Orbiter. Networks of channels like this are strong evidence for rain on Mars in the past. Image:Dissected Channels, as seen by Viking.jpg, The branched channels seen by Viking from orbit strongly suggested that it rained on Mars in the past. Image is located in

Margaritifer Sinus quadrangle The Margaritifer Sinus quadrangle is one of a series of list of quadrangles on Mars, 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Margaritifer Sinus quadrangle is also referred ...

. Image:Ravi Vallis.jpg, Ravi Vallis, as seen by Viking Orbiter.

Ravi Vallis Ravi Vallis is an ancient outflow channel, the source of which originates from the Aromatum Chaos depression, and is situated at the eastern end of Xanthe Terra, in the Margaritifer Sinus quadrangle (MC-19) region of Mars, located at . The Ravi V ...

was probably formed when catastrophic floods came out of the ground to the right (chaotic terrain). Image located in

. File:Deimos-viking1.jpg,

, photo taken in 1977.

Notes

References

External links

The Viking Mars Missions Education & Preservation Project, VMMEPP
online exhibit.
''Viking 2'' Mission Profile by NASA's Solar System Exploration

45 years ago: ''Viking'' 1 Touches Down on Mars
{{Portal bar, Solar System, Spaceflight Viking program 1975 in spaceflight Missions to Mars Derelict landers (spacecraft) Cebrenia quadrangle Nuclear-powered robots Spacecraft launched by Titan rockets Soft landings on Mars Spacecraft launched in 1975 1975 in Florida September 1975 in the United States 1976 on Mars