Viking mars lander

Viking mars lander DEFAULT

Viking 1 and 2, NASA’s first Mars landers

When did Viking 1 and 2 launch?

Viking 1 launched on August 20, 1975. It arrived in Mars orbit on June 19, 1976 and the lander touched down on July 20, 1976.

Viking 2 launched less than a month after Viking 1 on September 9, 1975. The spacecraft arrived in orbit on August 7, 1976 and the lander touched down on September 3.

How much did the Viking missions cost?

The Viking missions cost $1.06 billion, which when adjusted for inflation is roughly $7.1 billion in 2020 dollars. Viking remains NASA's most expensive robotic planetary science mission of all time. More than half of Viking costs ($610 million) went to lander development, while the orbiters accounted for $217 million. Mission operations through 1982 cost $104 million.

How long did the Viking 1 and 2 missions last?

Both missions lasted far beyond their planned 90-day lifetimes. The Viking 2 orbiter mission ended July 25, 1978, while the Viking 1 orbiter lasted until August 7, 1980.

The Viking 2 lander operated until April 11, 1980, and the Viking 1 lander lasted two more years, ending on November 11, 1982.

Sours: https://www.planetary.org/space-missions/viking

Viking program

Pair of NASA landers and orbiters sent to Mars in 1976

This article is about the NASA Mars probes. For the Swedish spacecraft, see Viking (satellite).

Viking Orbiter releasing the lander.jpg

Artist impression of a Viking orbiter releasing a lander descent capsule

ManufacturerJet Propulsion Laboratory / Martin Marietta
Country of originUnited States
OperatorNASA / JPL
ApplicationsMars orbiter/lander
Launch mass3,527 kilograms (7,776 lb)
PowerOrbiters: 620 watts (solar array)
Lander: 70 watts (two RTG units)
RegimeAreocentric
Design lifeOrbiters: 4 years at Mars
Landers: 4–6 years at Mars
StatusRetired
Built2
Launched2
RetiredViking 1 orbiter
August 17, 1980[1]
Viking 1 lander
July 20, 1976[1] (landing) to November 13, 1982[1]

Viking 2 orbiter
July 25, 1978[1]
Viking 2 lander
September 3, 1976[1] (landing) to April 11, 1980[1]
Maiden launchViking 1
August 20, 1975[1][2]
Last launchViking 2
September 9, 1975[1][3]

The Viking program consisted of a pair of identical American space probes, Viking 1 and Viking 2, which landed on Mars in 1976.[1] Each spacecraft was composed of two main parts: an orbiter designed to photograph the surface of Mars from orbit, and a lander designed to study the planet from the surface. The orbiters also served as communication relays for the landers once they touched down.

The Viking program grew from NASA's earlier, even more ambitious, Voyager Mars program, which was not related to the successful Voyager deep space probes of the late 1970s. Viking 1 was launched on August 20, 1975, and the second craft, Viking 2, was launched on September 9, 1975, both riding atop Titan IIIE rockets with Centaur upper stages. Viking 1 entered Mars orbit on June 19, 1976, with Viking 2 following on August 7.

After orbiting Mars for more than a month and returning images used for landing site selection, the orbiters and landers detached; the landers then entered the Martian atmosphere and soft-landed at the sites that had been chosen. The Viking 1 lander touched down on the surface of Mars on July 20, 1976, more than two-weeks before Viking 2's arrival in orbit. Viking 2 then successfully soft-landed on September 3. The orbiters continued imaging and performing other scientific operations from orbit while the landers deployed instruments on the surface.

The project cost was roughly $1 billion at the time of launch,[4][5] equivalent to about 5 billion USD in 2019 dollars.[6] The mission was considered successful and is credited with helping to form most of the body of knowledge about Mars through the late 1990s and early 2000s.[7][8]

Science objectives[edit]

  • Obtain high-resolution images of the Martian surface
  • Characterize the structure and composition of the atmosphere and surface
  • Search for evidence of life on Mars

Viking orbiters[edit]

The primary objectives of the two Viking orbiters were to transport the landers to Mars, perform reconnaissance to locate and certify landing sites, act as communications relays for the landers, and to perform their own scientific investigations. Each orbiter, based on the earlier Mariner 9 spacecraft, was an octagon approximately 2.5 m across. The fully fueled orbiter-lander pair had a mass of 3527 kg. After separation and landing, the lander had a mass of about 600 kg and the orbiter 900 kg. The total launch mass was 2328 kg, of which 1445 kg were propellant and attitude control gas. The eight faces of the ring-like structure were 0.4572 m high and were alternately 1.397 and 0.508 m wide. The overall height was 3.29 m from the lander attachment points on the bottom to the launch vehicle attachment points on top. There were 16 modular compartments, 3 on each of the 4 long faces and one on each short face. Four solar panel wings extended from the axis of the orbiter, the distance from tip to tip of two oppositely extended solar panels was 9.75 m.

Propulsion[edit]

The main propulsion unit was mounted above the orbiter bus. Propulsion was furnished by a bipropellant (monomethylhydrazine and nitrogen tetroxide) liquid-fueled rocket engine which could be gimballed up to 9 degrees. The engine was capable of 1,323 N (297 lbf) thrust, providing a change in velocity of 1480 m/s. Attitude control was achieved by 12 small compressed-nitrogen jets.

Navigation and communication[edit]

An acquisition Sun sensor, a cruise Sun sensor, a Canopusstar tracker and an inertial reference unit consisting of six gyroscopes allowed three-axis stabilization. Two accelerometers were also on board. Communications were accomplished through a 20 WS-band (2.3 GHz) transmitter and two 20 WTWTAs. An X band(8.4 GHz)downlink was also added specifically for radio science and to conduct communications experiments. Uplink was via S band (2.1 GHz). A two-axis steerable parabolic dish antenna with a diameter of approximately 1.5 m was attached at one edge of the orbiter base, and a fixed low-gain antenna extended from the top of the bus. Two tape recorders were each capable of storing 1280 megabits. A 381-MHz relay radio was also available.

Power[edit]

The power to the two orbiter craft was provided by eight 1.57 × 1.23 m solar panels, two on each wing. The solar panels comprised a total of 34,800 solar cells and produced 620 W of power at Mars. Power was also stored in two nickel-cadmium 30-A·hbatteries.

The combined area of the four panels was 15 square meters (160 square feet), and they provided both regulated and unregulated direct current power; unregulated power was provided to the radio transmitter and the lander.

Two 30-amp-hour, nickel-cadmium, rechargeable batteries provided power when the spacecraft was not facing the Sun, during launch, while performing correction maneuvers and also during Mars occultation.[9]

Main findings[edit]

Mars image mosaic from the Viking 1orbiter

By discovering many geological forms that are typically formed from large amounts of water, the images from the orbiters caused a revolution in our ideas about water on Mars. Huge river valleys were found in many areas. They showed that floods of water broke through dams, carved deep valleys, eroded grooves into bedrock, and travelled thousands of kilometers. Large areas in the southern hemisphere contained branched stream networks, suggesting that rain once fell. The flanks of some volcanoes are believed to have been exposed to rainfall because they resemble those caused on Hawaiian volcanoes. Many craters look as if the impactor fell into mud. When they were formed, ice in the soil may have melted, turned the ground into mud, then flowed across the surface. Normally, material from an impact goes up, then down. It does not flow across the surface, going around obstacles, as it does on some Martian craters.[10][11][12] Regions, called "Chaotic Terrain," seemed to have quickly lost great volumes of water, causing large channels to be formed. The amount of water involved was estimated to ten thousand times the flow of the Mississippi River.[13] Underground volcanism may have melted frozen ice; the water then flowed away and the ground collapsed to leave chaotic terrain.

Viking landers[edit]

Background painting by Don Davis, Artist's concept of Mars' surface behind a Viking lander test article pictured at JPL. The "sandbox".

Each lander comprised a six-sided aluminium base with alternate 1.09 and 0.56 m (3 ft 7 in and 1 ft 10 in) long sides, supported on three extended legs attached to the shorter sides. The leg footpads formed the vertices of an equilateral triangle with 2.21 m (7 ft 3 in) sides when viewed from above, with the long sides of the base forming a straight line with the two adjoining footpads. Instrumentation was attached inside and on top of the base, elevated above the surface by the extended legs.[14]

Each lander was enclosed in an aeroshell heat shield designed to slow the lander down during the entry phase. To prevent contamination of Mars by Earth organisms, each lander, upon assembly and enclosure within the aeroshell, was enclosed in a pressurized "bioshield" and then sterilized at a temperature of 111 °C (232 °F) for 40 hours. For thermal reasons, the cap of the bioshield was jettisoned after the Centaur upper stage powered the Viking orbiter/lander combination out of Earth orbit.[15]

Entry, Descent and Landing (EDL)[edit]

Each lander arrived at Mars attached to the orbiter. The assembly orbited Mars many times before the lander was released and separated from the orbiter for descent to the surface. Descent comprised four distinct phases, starting with a deorbit burn. The lander then experienced atmospheric entry with peak heating occurring a few seconds after the start of frictional heating with the Martian atmosphere. At an altitude of about 6 kilometers (3.7 miles) and traveling at a velocity of 900 kilometers per hour (600 mph), the parachute deployed, the aeroshell released and the lander's legs unfolded. At an altitude of about 1.5 kilometers (5,000 feet), the lander activated its three retro-engines and was released from the parachute. The lander then immediately used retrorockets to slow and control its descent, with a soft landing on the surface of Mars.[16]

First "clear" image ever transmitted from the surface of Mars – shows rocksnear the Viking 1lander (July 20, 1976).

At landing (after using rocket propellant) the landers had a mass of about 600 kg.

Propulsion[edit]

Propulsion for deorbit was provided by the monopropellanthydrazine (N2H4), through a rocket with 12 nozzles arranged in four clusters of three that provided 32 newtons (7.2 lbf) thrust, translating to a change in velocity of 180 m/s (590 ft/s). These nozzles also acted as the control thrusters for translation and rotation of the lander.

Terminal descent (after use of a parachute) and landing utilized three (one affixed on each long side of the base, separated by 120 degrees) monopropellant hydrazine engines. The engines had 18 nozzles to disperse the exhaust and minimize effects on the ground, and were throttleable from 276 to 2,667 newtons (62 to 600 lbf). The hydrazine was purified in order to prevent contamination of the Martian surface with Earth microbes. The lander carried 85 kg (187 lb) of propellant at launch, contained in two spherical titanium tanks mounted on opposite sides of the lander beneath the RTG windscreens, giving a total launch mass of 657 kg (1,448 lb). Control was achieved through the use of an inertial reference unit, four gyros, a radar altimeter, a terminal descent and landing radar, and the control thrusters.

Power[edit]

Power was provided by two radioisotope thermoelectric generator (RTG) units containing plutonium-238 affixed to opposite sides of the lander base and covered by wind screens. Each Viking RTG was 28 cm (11 in) tall, 58 cm (23 in) in diameter, had a mass of 13.6 kg (30 lb) and provided 30 watts continuous power at 4.4 volts. Four wet cell sealed nickel-cadmium 8 Ah (28,800 coulombs), 28 volt rechargeable batteries were also on board to handle peak power loads.

Payload[edit]

Image from Mars taken by the Viking 2lander

Communications were accomplished through a 20-watt S-band transmitter using two traveling-wave tubes. A two-axis steerable high-gain parabolic antenna was mounted on a boom near one edge of the lander base. An omnidirectional low-gain S-band antenna also extended from the base. Both these antennae allowed for communication directly with the Earth, permitting Viking 1 to continue to work long after both orbiters had failed. A UHF(381 MHz) antenna provided a one-way relay to the orbiter using a 30 watt relay radio. Data storage was on a 40-Mbit tape recorder, and the lander computer had a 6000-word memory for command instructions.

The lander carried instruments to achieve the primary scientific objectives of the lander mission: to study the biology, chemical composition (organic and inorganic), meteorology, seismology, magnetic properties, appearance, and physical properties of the Martian surface and atmosphere. Two 360-degree cylindrical scan cameras were mounted near one long side of the base. From the center of this side extended the sampler arm, with a collector head, temperature sensor, and magnet on the end. A meteorology boom, holding temperature, wind direction, and wind velocity sensors extended out and up from the top of one of the lander legs. A seismometer, magnet and camera test targets, and magnifying mirror are mounted opposite the cameras, near the high-gain antenna. An interior environmentally controlled compartment held the biology experiment and the gas chromatograph mass spectrometer. The X-rayfluorescence spectrometer was also mounted within the structure. A pressure sensor was attached under the lander body. The scientific payload had a total mass of approximately 91 kg (201 lb).

Biological experiments[edit]

Main article: Viking biological experiments

The Viking landers conducted biological experiments designed to detect life in the Martian soil (if it existed) with experiments designed by three separate teams, under the direction of chief scientist Gerald Soffen of NASA. One experiment turned positive for the detection of metabolism (current life), but based on the results of the other two experiments that failed to reveal any organic molecules in the soil, most scientists became convinced that the positive results were likely caused by non-biological chemical reactions from highly oxidizing soil conditions.[17]

Dust dunes and a large boulder taken by the Viking 1 lander.

Trenches dug by the soil sampler of the Viking 1 lander.

Although there was a pronouncement by NASA during the mission saying that the Viking lander results did not demonstrate conclusive biosignatures in soils at the two landing sites, the test results and their limitations are still under assessment. The validity of the positive 'Labeled Release' (LR) results hinged entirely on the absence of an oxidative agent in the Martian soil, but one was later discovered by the Phoenix lander in the form of perchlorate salts.[18][19] It has been proposed that organic compounds could have been present in the soil analyzed by both Viking 1 and Viking 2, but remained unnoticed due to the presence of perchlorate, as detected by Phoenix in 2008.[20] Researchers found that perchlorate will destroy organics when heated and will produce chloromethane and dichloromethane, the identical chlorine compounds discovered by both Viking landers when they performed the same tests on Mars.[21]

The question of microbial life on Mars remains unresolved. Nonetheless, on April 12, 2012, an international team of scientists reported studies, based on mathematical speculation through complexity analysis of the Labeled Release experiments of the 1976 Viking Mission, that may suggest the detection of "extant microbial life on Mars."[22][23] In addition, new findings from re-examination of the Gas Chromatograph Mass Spectrometer (GCMS) results were published in 2018.[24]

Camera/imaging system[edit]

The leader of the imaging team was Thomas A. Mutch, a geologist at Brown University in Providence, Rhode Island. The camera uses a movable mirror to illuminate 12 photo diodes. Each of the 12 silicon diodes are designed to be sensitive to different frequences of light. Several diodes are placed to focus accurately at distances between six and 43 feet away from the lander.

The cameras scanned at a rate of five vertical scan lines per second, each composed of 512 pixels. The 300 degree panorama images were composed of 9150 lines. The cameras’ scan was slow enough that in a crew shot taken during development of the imaging system several members show up several times in the shot as they moved themselves as the camera scanned.[25][26]

Control systems[edit]

The Viking landers used a Guidance, Control and Sequencing Computer (GCSC) consisting of two Honeywell HDC 402 24-bit computers with 18K of plated-wire memory, while the Viking orbiters used a Command Computer Subsystem (CCS) using two custom-designed 18-bit serial processors.[27][28][29]

Financial cost of the Viking program[edit]

The two orbiters cost US$217 million (at the time), which is about 1 billion USD in year-2019 dollars.[30][31] The most expensive single part of the program was the lander's life-detection unit, which cost about 60 million then or 300 million USD in 2019 year-dollars.[30][31] Development of the Viking lander design cost US$357 million.[30] This was decades before NASA's "faster, better, cheaper" approach, and Viking needed to pioneer unprecedented technologies under national pressure brought on by the Cold War and the aftermath of the Space Race, all under the prospect of possibly discovering extraterrestrial life for the first time.[30] The experiments had to adhere to a special 1971 directive that mandated that no single failure shall stop the return of more than one experiment—a difficult and expensive task for a device with over 40,000 parts.[30]

The Viking camera system cost US$27.3 million to develop, or about 100 million in 2019 year-dollars.[30][31] When the Imaging system design was completed, it was difficult to find anyone who could manufacture its advanced design.[30] The program managers were later praised for fending off pressure to go with a simpler, less advanced imaging system, especially when the views rolled in.[30] The program did however save some money by cutting out a third lander and reducing the number of experiments on the lander.[30]

Overall NASA says that US$1 billion in 1970s dollars was spent on the program,[4][5] which when inflation-adjusted to 2019 dollars is about 5 billion USD.[31]

Mission end[edit]

The craft all eventually failed, one by one, as follows:[1]

CraftArrival dateShut-off dateOperational lifetimeCause of failure
Viking 2 orbiterAugust 7, 1976July 25, 19781 year, 11 months, 18 daysShut down after fuel leak in propulsion system.
Viking 2 landerSeptember 3, 1976April 11, 19803 years, 7 months, 8 daysShut down after battery failure.
Viking 1 orbiterJune 19, 1976August 17, 19804 years, 1-month, 19 daysShut down after depletion of attitude control fuel.
Viking 1 landerJuly 20, 1976November 13, 19826 years, 3 months, 22 daysShut down after human error during software update caused the lander's antenna to go down, terminating power and communication.

The Viking program ended on May 21, 1983. To prevent an imminent impact with Mars the orbit of Viking 1 orbiter was raised on August 7, 1980, before it was shut down 10 days later. Impact and potential contamination on the planet's surface is possible from 2019 onwards.[4]

The Viking 1 lander was found to be about 6 kilometers from its planned landing site by the Mars Reconnaissance Orbiter in December 2006. [32]

Message artifact[edit]

(See also List of extraterrestrial memorials and Category:Message artifacts)

Each Viking lander carried a tiny dot of microfilm containing the names of several thousand people who had worked on the mission.[33] Several earlier space probes had carried message artifacts, such as the Pioneer plaque and the Voyager Golden Record. Later probes also carried memorials or lists of names, such as the Perseverance rover which recognizes the almost 11 million people who signed up to include their names on the mission.

Viking lander locations[edit]

See also[edit]

References[edit]

  1. ^ abcdefghijWilliams, David R. Dr. (December 18, 2006). "Viking Mission to Mars". NASA. Retrieved February 2, 2014.
  2. ^Nelson, Jon. "Viking 1". NASA. Retrieved February 2, 2014.
  3. ^Nelson, Jon. "Viking 2". NASA. Retrieved February 2, 2014.
  4. ^ abc"Viking 1 Orbiter spacecraft details". NASA Space Science Data Coordinated Archive. NASA. March 20, 2019. Retrieved July 10, 2019.
  5. ^ ab"Viking 1: First U.S. Lander on Mars". Space.com. Retrieved December 13, 2016.
  6. ^Thomas, Ryland; Williamson, Samuel H. (2020). "What Was the U.S. GDP Then?". MeasuringWorth. Retrieved September 22, 2020. United States Gross Domestic Product deflator figures follow the Measuring Worth series.
  7. ^"The Viking Program". The Center for Planetary Science. Retrieved April 13, 2018.
  8. ^"Viking Lander". California Science Center. July 3, 2014. Archived from the original on September 30, 2020. Retrieved April 13, 2018.
  9. ^"Sitemap – NASA Jet Propulsion Laboratory". Archived from the original on March 4, 2012. Retrieved March 27, 2012.
  10. ^Hugh H. Kieffer (1992). Mars. University of Arizona Press. ISBN . Retrieved March 7, 2011.
  11. ^Raeburn, P. 1998. Uncovering the Secrets of the Red Planet Mars. National Geographic Society. Washington D.C.
  12. ^Moore, P. et al. 1990. The Atlas of the Solar System. Mitchell Beazley Publishers NY, NY.
  13. ^Morton, O. 2002. Mapping Mars. Picador, NY, NY
  14. ^Hearst Magazines (June 1976). "Amazing Search for Life On Mars". Popular Mechanics. Hearst Magazines. pp. 61–63.
  15. ^Soffen, G. A., and C. W. Snyder, First Viking mission to Mars, Science, 193, 759–766, August 1976.
  16. ^"Viking". astro.if.ufrgs.br.
  17. ^BEEGLE, LUTHER W.; et al. (August 2007). "A Concept for NASA's Mars 2016 Astrobiology Field Laboratory". Astrobiology. 7 (4): 545–577. Bibcode:2007AsBio...7..545B. doi:10.1089/ast.2007.0153. PMID 17723090.
  18. ^Johnson, John (August 6, 2008). "Perchlorate found in Martian soil". Los Angeles Times.
  19. ^"Martian Life Or Not? NASA's Phoenix Team Analyzes Results". Science Daily. August 6, 2008.
  20. ^Navarro–Gonzáles, Rafael; Edgar Vargas; José de la Rosa; Alejandro C. Raga; Christopher P. McKay (December 15, 2010). "Reanalysis of the Viking results suggests perchlorate and organics at midlatitudes on Mars". Journal of Geophysical Research: Planets. 115 (E12010). Retrieved January 7, 2011.
  21. ^Than, Ker (April 15, 2012). "Life on Mars Found by NASA's Viking Mission". National Geographic. Retrieved April 13, 2018.
  22. ^Bianciardi, Giorgio; Miller, Joseph D.; Straat, Patricia Ann; Levin, Gilbert V. (March 2012). "Complexity Analysis of the Viking Labeled Release Experiments". IJASS. 13 (1): 14–26. Bibcode:2012IJASS..13...14B. doi:10.5139/IJASS.2012.13.1.14.
  23. ^Klotz, Irene (April 12, 2012). "Mars Viking Robots 'Found Life'". DiscoveryNews. Retrieved April 16, 2012.
  24. ^Guzman, Melissa; McKay, Christopher P.; Quinn, Richard C.; Szopa, Cyril; Davila, Alfonso F.; Navarro‐González, Rafael; Freissinet, Caroline (2018). "Identification of Chlorobenzene in the Viking Gas Chromatograph-Mass Spectrometer Data Sets: Reanalysis of Viking Mission Data Consistent With Aromatic Organic Compounds on Mars"(PDF). Journal of Geophysical Research: Planets. 123 (7): 1674–1683. Bibcode:2018JGRE..123.1674G. doi:10.1029/2018JE005544. ISSN 2169-9100.
  25. ^The Viking Lander Imaging Team (1978). "Chapter 8: Cameras Without Pictures". The Martian Landscape. NASA. p. 22.
  26. ^McElheny, Victor K. (July 21, 1976). "Viking Cameras Light in Weight, Use Little Power, Work Slowly". The New York Times. Retrieved September 28, 2013.
  27. ^Tomayko, James (April 1987). "Computers in Spaceflight: The NASA Experience". NASA. Retrieved February 6, 2010.
  28. ^Holmberg, Neil A.; Robert P. Faust; H. Milton Holt (November 1980). "NASA Reference Publication 1027: Viking '75 spacecraft design and test summary. Volume 1 – Lander design"(PDF). NASA. Retrieved February 6, 2010.
  29. ^Holmberg, Neil A.; Robert P. Faust; H. Milton Holt (November 1980). "NASA Reference Publication 1027: Viking '75 spacecraft design and test summary. Volume 2 – Orbiter design"(PDF). NASA. Retrieved February 6, 2010.
  30. ^ abcdefghiMcCurdy, Howard E. (2001). Faster, Better, Cheaper: Low-Cost Innovation in the U.S. Space Program. JHU Press. p. 68. ISBN .
  31. ^ abcdAs the Viking program was a government expense, the inflation index of the United States Nominal Gross Domestic Product per capita is used for the inflation-adjusting calculation.
  32. ^Chandler, David (December 5, 2006). "Probe's powerful camera spots Vikings on Mars". New Scientist. Retrieved October 8, 2013.
  33. ^"Visions of Mars: Then and Now". The Planetary Society.

Further reading[edit]

External links[edit]

Sours: https://en.wikipedia.org/wiki/Viking_program
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Viking Lander

The Viking 1 lander was the first US spacecraft ever to land successfully on Mars. Through the historic two missions of the Viking project, a total of over 50,000 images of Mars were collected (with 4,500 coming from the landers), with both orbiters and landers sending back information that changed everything scientists thought they knew about the Red Planet.

History

Carl Sagan, host of the original television series Cosmos, poses with a model of the Viking lander in Death Valley, California

Before the Viking launches in the mid-1970s, our knowledge of Mars was extremely limited. The team of scientists assembled for the Viking project had to figure out how to land and navigate a spacecraft on a planet with almost no prior knowledge of what the surface would be like. Prior to the Viking missions, the Soviets had tried to land spacecrafts on Mars, and although one of their crafts seems to have made it to the surface, it lost contact with Earth before landing and may have crashed.

The Viking project, however, was an amazing success. The Viking program, of which the lander was a part, gathered data and images about our nearest planetary neighbor that changed the way we see Mars. In fact, before Viking, scientists thought the Martian sky would be a deep blue, like our upper atmosphere, but early photos from Viking revealed Mars's salmon-colored sky for the first time.

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Made up of two sets of spacecraft, each including an orbiter and a lander, Vikings 1 and 2 together mapped about 97% of Mars from orbit and collected about 4,500 close-up images of the Martian surface. In addition to cameras, the landers carried equipment to analyze the Martian soil, wind and atmosphere and send the results back to Earth. Though the spacecraft were designed to function about 90 days once at Mars, they kept collecting and sending data for over six years. One of the main goals of the Viking program was to find out if life had ever existed on Mars. Though the missions didn't find evidence of life, they determined that many of the necessary ingredients for life were present on the planet, leaving the question tantalizingly unanswered.

Subsequent missions to Mars—including Pathfinder, the twin rovers Spirit and Opportunity, the rover Curiosity, the lander Insight, and the recently launched rover Perseverance—all build on the technology created for the Viking missions, as well as the information collected by the Viking orbiters and landers. Even 35 years later, data and results from the Viking missions are still being analyzed.

The Science Center's Viking Lander

The Viking lander on display at the Science Center is a full-scale engineering model, on loan to us from Lockheed Martin Corporation.

Sours: https://californiasciencecenter.org/exhibits/air-space/mission-planets/viking-lander
Viking First Views of Mars
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This is the proof test article of the Viking Mars Lander. For exploration of Mars, Viking represented the culmination of a series of exploratory missions that had begun in 1964 with Mariner 4 and continued with Mariner 6 and Mariner 7 flybys in 1969 and a Mariner 9 orbital mission in 1971 and 1972. The Viking mission used two identical spacecraft, each consisting of a lander and an orbiter. Launched on August 20, 1975 from the Kennedy Space Center in Florida, Viking 1 spent nearly a year cruising to Mars, placed an orbiter in operation around the planet, and landed on July, 20 1976 on the Chryse Planitia (Golden Plains). Viking 2 was launched on September 9, 1975 and landed on September 3, 1976. The Viking project's primary mission ended on November 15, 1976, 11 days before Mars's superior conjunction (its passage behind the sun), although the Viking spacecraft continued to operate for six years after first reaching Mars. The last transmission from the planet reached Earth on November 11, 1982.

While Viking 1 and 2 were on Mars, this third vehicle was used on Earth to simulate their behavior and to test their responses to radio commands. Earlier, it had been used to demonstrate that the landers could survive the stresses they would encounter during the mission.

NASA transferred this artifact to the Museum in 1979.

“Life as we know it with its humanity is more unique than many have thought.”—President Lyndon B. Johnson, “Remarks Upon Viewing New Mariner 4 Pictures from Mars,” July 29, 1965.

Viking

Mars had long held a special fascination for humans who pondered the planets of the solar system—partly because of the possibility that life might either presently exist or at some time in the past have existed there. Astronomer Percival Lowell became interested in Mars during the latter part of the nineteenth century, and he built what became the Lowell Observatory near Flagstaff, Arizona, to study the planet. He argued that Mars had once been a watery planet and that the topographical features known as canals had been built by intelligent beings. The idea of intelligent life on Mars remained in the popular imagination for a long time, and only with the first photographs from Mars by Mariner 4 in 1965 were the hopes of many dashed that life might be present on Mars. This images showed a cratered, ­lunar-­like surface without structures and canals, nothing that even remotely resembled a pattern that intelligent life might produce. U.S. News and World Report announced at the time that “Mars is dead.”

Later spacecraft, especially Mariners 6 and 7, in 1969, reexcited curiosity and laid the groundwork for an eventual landing on the planet. Their pictures verified the Moon‑like appearance of Mars, but they also found that volcanoes had once been active on the planet, that the frost observed seasonally on the poles was made of carbon dioxide, and that huge plates indicated considerable tectonic activity in the planet’s past. Suddenly, Mars fascinated scientists, reporters, and the public once again, largely because of the possibility of past life that might have existed there.

The Viking mission that emerged from this excitement consisted of two identical spacecraft, each with a lander and an orbiter. Launched in 1975 from the Kennedy Space Center, Florida, Viking 1 spent nearly a year cruising to Mars, placed an orbiter in operation around the planet, and landed on July 20, 1976, on the Chryse Planitia (Golden Plains), with Viking 2 following in September 1976. These were the first sustained landings on another planet in the solar system. While one of the most important scientific activities of this project involved an attempt to determine whether there was life on Mars, the scientific data returned mitigated against the possibility. The two landers continuously monitored weather at the landing sites and found both exciting cyclical variations and an exceptionally harsh climate that prohibited the possibility of life. Atmospheric temperatures at the more southern Viking 1 landing site, for instance, was only as high as +7 degrees Fahrenheit at midday, but the predawn summer temperature was ‑107 degrees Fahrenheit. And the lowest predawn temperature was ‑184 degrees Fahrenheit, about the frost point of carbon dioxide.

Although the three biology experiments contained on the landers discovered unexpected and enigmatic chemical activity in the Martian soil, they provided no clear evidence for the presence of living microorganisms in soil near the landing sites. According to scientists, Mars was self‑sterilizing. They concluded that the combination of solar ultraviolet radiation that saturates the surface, the extreme dryness of the soil, and the oxidizing nature of the soil chemistry had prevented the formation of living organisms in the Martian soil.

The failure to find any evidence of life on Mars, past or present, devastated the optimism of scientists involved in the search for extraterrestrial life. Collectively, these missions led to the development of two essential reactions. The first was an abandonment by most scientists that life might exist elsewhere in the Solar System. Planetary scientist and JPL director Bruce Murray complained at the time of Viking about the lander being ballyhooed as a definite means of ascertaining whether or not life existed on Mars. The public expected to find it, and so did many of the other scientists involved in the project. Murray argued that “the extraordinarily hostile environment revealed by the Mariner flybys made life there so unlikely that public expectations should not be raised.” Murray believed that the legacy of failure to detect life, despite the billions spent and a succession of overoptimistic statements, would spark public disappointment and perhaps a public outrage. Murray was right. The immediate result was that NASA did not return to Mars for two decades. The Viking Program’s chief scientist, Gerald A Soffen, commented in 1992: “If somebody back then had given me 100 to 1 odds that we wouldn’t go back to Mars for 17 years, I would’ve said, ‘You’re crazy’.”

The second reaction, never accepted by scientists, found a powerful public life. Some asserted that a corrupt Federal government, and its mandarins of science, had found evidence of life beyond Earth but was keeping it from the public for reasons ranging from stupidity to diabolical plots. NASA has had to respond to these charges repeatedly thereafter. This issue first arose on 25 July 1976 when the Viking 1 orbiter took an image of the Cydonia region of Mars that looked like a human face. All evidence suggests that this was the result of shadows on the hills, and Gerry Soffen said so at a press conference, but some refused to accept this position. The “face” remains a sore point to the present, with Soffen being asked about it many times over the years. Always, he stated it was not the remnant of some ancient civilization but was a natural feature lit oddly in this one image but not in any others. As NASA stated officially in 2001, “The ‘Face on Mars’ has since become a pop icon. It has starred in a Hollywood film, appeared in books, magazines, radio talk shows—even haunted grocery store checkout lines for 25 years! Some people think the Face is bona fide evidence of life on Mars—evidence that NASA would rather hide, say conspiracy theorists. Meanwhile, defenders of the NASA budget wish there was an ancient civilization on Mars.”

The artifact in the National Air and Space Museum’s collection is a structural dynamics test article transferred from NASA.

Sours: https://airandspace.si.edu/collection-objects/viking-lander/nasm_A19790215000

Mars lander viking

Viking 1

robotic spacecraft sent to Mars

This article is about the mission to Mars. For other uses, see Viking One.

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.[3] The lander touched down on Mars on 20 July 1976, the first successful Mars lander in history. Viking 1 operated on Mars 2307 days (over 61⁄4 years)[3] or 2245 Martian solar days, the longest Mars surface mission[3] until the record was broken by the Opportunity rover on 19 May 2010.[7]

Mission[edit]

Following launch using a Titan/Centaur launch vehicle on 20 August 1975, and an 11-month cruise to Mars,[8] the orbiter began returning global images of Mars about 5 days before orbit insertion. The Viking 1 Orbiter was inserted into Mars orbit on 19 June 1976,[9] and trimmed to a 1513 x 33,000 km, 24.66 h site certification orbit on 21 June. Landing on Mars was planned for 4 July 1976, the United States Bicentennial, but imaging of the primary landing site showed it was too rough for a safe landing.[10] The landing was delayed until a safer site was found,[10] and took place instead on 20 July [9] the seventh anniversary of the Apollo 11 Moon landing.[11] The lander separated from the orbiter at 08:51 UTC and landed at Chryse Planitia at 11:53:06 UTC.[12] It was the first attempt by the United States at landing on Mars.[13]

Orbiter[edit]

The instruments of the orbiter consisted of two vidicon cameras for imaging (VIS), an infrared spectrometer for water vapor mapping (MAWD) and infrared radiometers for thermal mapping (IRTM).[14] The orbiter primary mission ended at the beginning of solar conjunction on 5 November 1976. The extended mission commenced on 14 December 1976, after solar conjunction.[citation needed] Operations included close approaches to Phobos in February 1977.[15] The periapsis was reduced to 300 km on 11 March 1977.[16] Minor orbit adjustments were done occasionally over the course of the mission, primarily to change the walk rate — the rate at which the areocentric longitude changed with each orbit, and the periapsis was raised to 357 km on 20 July 1979. On 7 August 1980, Viking 1 Orbiter was running low on attitude control gas and its orbit was raised from 357 × 33943 km to 320 × 56000 km to prevent impact with Mars and possible contamination until the year 2019. Operations were terminated on 17 August 1980, after 1485 orbits. A 2009 analysis concluded that, while the possibility that Viking 1 had impacted Mars could not be ruled out, it was most likely still in orbit.[17] More than 57,000 images were sent back to Earth.

Lander[edit]

The lander and its aeroshell separated from the orbiter on 20 July at 08:51 UTC. At the time of separation, the lander was orbiting at about 5 kilometers per second (3.1 miles per second). The aeroshell's retrorockets fired to begin the lander de-orbit maneuver. After a few hours at about 300 kilometers (190 miles) altitude, the lander was reoriented for atmospheric entry. The aeroshell with its ablative heat shield slowed the craft as it plunged through the atmosphere. During this time, entry science experiments were performed by using a retarding potential analyzer, a mass spectrometer, as well as pressure, temperature, and density sensors.[14] At 6 km (3.7 mi) altitude, traveling at about 250 meters per second (820 feet per second), the 16 m diameter lander parachutes deployed. Seven seconds later the aeroshell was jettisoned, and 8 seconds after that the three lander legs were extended. In 45 seconds the parachute had slowed the lander to 60 meters per second (200 feet per second). At 1.5 km (0.93 mi) altitude, retrorockets on the lander itself were ignited and, 40 seconds later at about 2.4 m/s (7.9 ft/s), the lander arrived on Mars with a relatively light jolt. The legs had honeycomb aluminum shock absorbers to soften the landing.[14]

Documentary clip recounting the Viking 1landing with animation and video footage of the control centre

The landing rockets used an 18-nozzle design to spread the hydrogen and nitrogen exhaust over a large area. NASA calculated that this approach would mean that the surface would not be heated by more than one 1 °C (1.8 °F), and that it would move no more than 1 millimeter (0.04 inches) of surface material.[12] Since most of Viking's experiments focused on the surface material a more straightforward design would not have served.[citation needed]

The Viking 1 lander touched down in western Chryse Planitia ("Golden Plain") at 22°41′49″N312°03′00″E / 22.697°N 312.05°E / 22.697; 312.05[3][12] at a reference altitude of −2.69 kilometers (−1.67 mi) relative to a reference ellipsoid with an equatorial radius of 3,397 kilometers (2,111 mi) and a flatness of 0.0105 (22.480° N, 47.967° W planetographic) at 11:53:06 UTC (16:13 local Mars time).[18] Approximately 22 kilograms (49 lb) of propellants were left at landing.[12]

Transmission of the first surface image began 25 seconds after landing and took about four minutes (see below). During these minutes the lander activated itself. It erected a high-gain antenna pointed toward Earth for direct communication and deployed a meteorology boom mounted with sensors. In the next seven minutes the second picture of the 300° panoramic scene (displayed below) was taken.[19] On the day after the landing the first colour picture of the surface of Mars (displayed below) was taken. The seismometer failed to uncage, and a sampler arm locking pin was stuck and took five days to shake out. Otherwise, all experiments functioned normally.

The lander had two means of returning data to Earth: a relay link up to the orbiter and back, and by using a direct link to Earth. The orbiter could transmit to Earth (S-band) at 2,000 to 16,000 bit/s (depending on distance between Mars and Earth), and the lander could transmit to the orbiter at 16,000 bit/s.[20] The data capacity of the relay link was about 10 times higher than the direct link.[14]

First "clear" image ever transmitted from the surface of Mars – shows rocksnear the Viking 1Lander (20 July 1976). The haze on the left is possibly dust that had recently been kicked up by the landing rockets. Because of the "slow scan" facsimile nature of the cameras, the dust settled by mid-image.

The lander had two facsimile cameras; three analyses for metabolism, growth or photosynthesis; a gas chromatograph-mass spectrometer (GCMS); an x-ray fluorescence spectrometer; pressure, temperature and wind velocity sensors; a three-axis seismometer; a magnet on a sampler observed by the cameras; and various engineering sensors.[14]

The Viking 1 lander was named the Thomas Mutch Memorial Station in January 1981 in honour of Thomas A. Mutch, the leader of the Viking imaging team.[21] The lander operated for 2245 sols (about 2306 Earth days or 6 years) until 11 November 1982, (sol 2600), when a faulty command sent by ground control resulted in loss of contact. The command was intended to uplink new battery charging software to improve the lander's deteriorating battery capacity, but it inadvertently overwrote data used by the antenna pointing software. Attempts to contact the lander during the next four months, based on the presumed antenna position, were unsuccessful.[22] In 2006 the Viking 1 lander was imaged on the Martian surface by the Mars Reconnaissance Orbiter.[23]

Mission results[edit]

Search for life[edit]

Viking 1 carried a biology experiment whose purpose was to look for evidence of life. The Viking spacecraft biological experiments weighed 15.5 kg (34 lbs) and consisted of three subsystems: the pyrolytic release experiment (PR), the labeled release experiment (LR), and the gas exchange experiment (GEX). In addition, independent of the biology experiments, Viking carried a gas chromatograph-mass spectrometer (GCMS) that could measure the composition and abundance of organic compounds in the Martian soil.[24] The results were surprising and interesting: the GCMS gave a negative result; the PR gave a negative result, the GEX gave a negative result, and the LR gave a positive result.[25] 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."[26] Most scientists now believe that the data were due to inorganic chemical reactions of the soil; however, this view may be changing after the recent discovery of near-surface ice near the Viking landing zone.[27] Some scientists still believe the results were due to living reactions. No organic chemicals were found in the soil. However, dry areas of Antarctica do not have detectable organic compounds either, but they have organisms living in the rocks.[28] 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.[29] The Phoenix Lander discovered the chemical perchlorate in the Martian soil. Perchlorate is a strong oxidant so it may have destroyed any organic matter on the surface.[30] If it is widespread on Mars, carbon-based life would be difficult at the soil surface.

First panorama by Viking 1 lander[edit]

First panoramic view by Viking 1from the surface of Mars. Captured on 20 July 1976

Viking 1 image gallery[edit]

  • Launch of the Viking 1 probe (20 August 1975).

  • First image by the Viking 1 lander from the surface of Mars, showing lander's footpad.

  • Trenches dug by soil sampler device.

  • First colour image taken by the Viking 1 lander (21 July 1976).

  • Viking 1 lander site (11 February 1978).

  • Dunes and large boulder. Pole in the centre is an instrument boom.

  • Viking 1 Lander Camera 2 Sky at sunrise (Low Resolution Colour) Sol 379 07:50

Test of general relativity[edit]

Main article: Introduction to general relativity

High-precision test of general relativity by the Cassinispace probe (artist's impression)

Gravitational time dilation is a phenomenon predicted by the theory of general relativity whereby time passes more slowly in regions of lower gravitational potential. Scientists used the lander to test this hypothesis, by sending radio signals to the lander on Mars, and instructing the lander to send back signals, in cases which sometimes included the signal passing close to the Sun. Scientists found that the observed Shapiro delays of the signals matched the predictions of general relativity.[31]

Orbiter shots[edit]

Lander location[edit]

See also[edit]

References[edit]

  1. ^"45 years ago: Viking 1 Touches Down on Mars". NASA. July 20, 2021. Retrieved August 21, 2021.
  2. ^"Viking 1 Lander". National Space Science Data Center.
  3. ^ abcdefghWilliams, David R. Dr. (December 18, 2006). "Viking Mission to Mars". NASA. Retrieved February 2, 2014.
  4. ^"Viking 1". NASA Jet Propulsion Laboratory (JPL). NASA. October 19, 2016. Retrieved November 27, 2018.
  5. ^Shea, Garrett (September 20, 2018). "Beyond Earth: A Chronicle of Deep Space Exploration". NASA.
  6. ^Nelson, Jon. "Viking 1". NASA. Retrieved February 2, 2014.
  7. ^mars.nasa.gov. "Mars Exploration Rover". mars.nasa.gov.
  8. ^Loff, Sarah (August 20, 2015). "20 August 1975, Launch of Viking 1". NASA. Retrieved July 18, 2019.
  9. ^ abAngelo, Joseph A. (May 14, 2014). Encyclopedia of Space and Astronomy. Infobase Publishing. p. 641. ISBN .
  10. ^ abCroswell, Ken (October 21, 2003). Magnificent Mars. Simon and Schuster. p. 23. ISBN .
  11. ^Stooke, Philip J. (September 24, 2012). The International Atlas of Mars Exploration: Volume 1, 1953 to 2003: The First Five Decades. Cambridge University Press. ISBN .
  12. ^ abcd"Viking 1 Orbiter". National Space Science Data Center. Retrieved July 18, 2019.
  13. ^"Chronology of Mars Exploration". history.nasa.gov. Retrieved August 16, 2019.
  14. ^ abcdeSoffen, G.A.; Snyder, C.W. (August 1976). "The First Viking Mission to Mars". Science. New Series. 193 (4255): 759–766. Bibcode:1976Sci...193..759S. doi:10.1126/science.193.4255.759. JSTOR 1742875. PMID 17747776.
  15. ^R.E. Diehl, M.J. Adams; Rinderle, E.a. (March 1, 1979). "Phobos Encounter Trajectory and Maneuver Design". Journal of Guidance and Control. 2 (2): 123–129. Bibcode:1979JGCD....2..123.. doi:10.2514/3.55847. ISSN 0162-3192.
  16. ^Ulivi, Paolo; Harland, David M. (December 8, 2007). Robotic Exploration of the Solar System: Part I: The Golden Age 1957-1982. Springer Science & Business Media. p. 251. ISBN .
  17. ^Jefferson, David C; Demcak, Stuart W; Esposito, Pasquale B; Kruizinga, Gerhard L (August 10–13, 2009). An Investigation of the Orbital Status of Viking-1(PDF). AIAA Guidance, Navigation, and Control Conference. Archived from the original(PDF) on November 7, 2017.
  18. ^"Viking 1 Lander Mission Profile". Texas Space Grant Consortium. The University of Texas at Austin. Retrieved July 18, 2019.
  19. ^Mutch, T.A.; et al. (August 1976). "The Surface of Mars: The View from the Viking 1 Lander". Science. New Series. 193 (4255): 791–801. Bibcode:1976Sci...193..791M. doi:10.1126/science.193.4255.791. JSTOR 1742881. PMID 17747782. S2CID 42661323.
  20. ^Viking Mission to Mars JPL
  21. ^"NASA - NSSDCA - Spacecraft - Details". nssdc.gsfc.nasa.gov. Retrieved March 5, 2021.
  22. ^D. J. Mudgway (1983). "Telecommunications and Data Acquisition Systems Support for the Viking 1975 Mission to Mars"(PDF). NASAJet Propulsion Laboratory. Retrieved June 22, 2009.
  23. ^"NASA Mars Orbiter Photographs Spirit and Vikings on the Ground". NASA. 2006. Retrieved July 20, 2011.
  24. ^"Life on Mars". www.msss.com. Archived from the original on October 20, 2014.
  25. ^Viking Data May Hide New Evidence For Life. Barry E. DiGregorio, 16 July 2000.
  26. ^Viking 2 Likely Came Close to Finding H2O.Archived 30 September 2009 at the Wayback Machine Irene Klotz, Discovery News, 28 September 2009.
  27. ^Stuurman, C.M.; Osinski, G.R.; Holt, J.W.; Levy, J.S.; Brothers, T.C.; Kerrigan, M.; Campbell, B.A. (September 28, 2016). "SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars". Geophysical Research Letters. 43 (18): 9484–9491. Bibcode:2016GeoRL..43.9484S. doi:10.1002/2016gl070138.
  28. ^Friedmann, E. 1982. Endolithic Microorganisms in the Antarctic Cold Desert. Science: 215. 1045–1052.
  29. ^Hartmann, W. 2003. A Traveler's Guide to Mars. Workman Publishing. NY NY.
  30. ^Alien Rumors Quelled as NASA Announces Phoenix Perchlorate Discovery.Archived 4 September 2010 at the Wayback Machine A.J.S. Rayl, August 6, 2008.
  31. ^Reasenberg, R. D.; Shapiro, I. I.; MacNeil, P. E.; Goldstein, R. B.; Breidenthal, J. C.; Brenkle, J. P.; et al. (December 1979). "Viking relativity experiment – Verification of signal retardation by solar gravity". Astrophysical Journal Letters. 234: L219–L221. Bibcode:1979ApJ...234L.219R. doi:10.1086/183144.

External links[edit]

Wikimedia Commons has media related to Viking 1.
Sours: https://en.wikipedia.org/wiki/Viking_1
The Viking Mission

Viking Mars Landers

Viking 1 Lander

  • Launched on August 20, 1975
  • First mission to land on Mars
  • RTGs operated for over six years, until lander was shut down

Viking 2 Lander

  • Launched on September 9, 1975
  • RTGs operated for over four years until relay link (Viking orbiter) was lost

Powered by:

Photograph of a full-scale Viking lander model.

two SNAP-19 RTGs each

Goals:

NASA's Viking mission to Mars was composed of two pairs of spacecraft—Viking 1 and Viking 2—each consisting of an orbiter and a lander. The spacecraft were designed to take high-resolution images of the Martian surface, characterize the structure and composition of the atmosphere and surface, and search for evidence of life.

Accomplishments:

Viking 1 was the first successful mission to land on Mars (the Soviet Mars 3 lander survived for a few seconds after landing in 1971, but sent back no science data), operating on Chryse Planitia until November 1982. Viking 2 lander set down on Utopia Planitia and operated until April 1980.

Color image of the Martian surface taken by the Viking 1 lander 15 minutes before sunset.

The four Viking spacecraft provided numerous new insights into the nature and history of Mars, producing a vivid overall picture of a cold weathered surface with reddish volcanic soil under a thin, dry carbon dioxide atmosphere, clear evidence for the existence of ancient river beds and vast floods, and no detectable seismic activity.

Although no traces of life were found, Viking found all elements essential to life on Earth—carbon, nitrogen, hydrogen, oxygen and phosphorus—were present on Mars.

More about Viking 1 ›

Images from Viking 1 lander ›

More about Viking 2 ›

Images from Viking 2 lander ›

Sours: https://rps.nasa.gov/missions/11/viking-mars-landers/

Similar news:

Life on Mars? 40 Years Later, Viking Lander Scientist Still Says 'Yes'

In 1976, NASA's twin Viking landers touched down on Mars in an attempt to answer a weighty question: Is there life on the Red Planet?

Gilbert Levin was the principal investigator of the Vikings' Labeled Release (LR) life-detection experiment. The instrument got positive responses at both landing locales. However, scientists did not reach a consensus on whether his results were proof of life.

In 1997, Levin concluded that the experiment had, indeed, detected life on Mars — and he has championed that viewpoint ever since. [The Search for Life on Mars: A Photo Timeline]

Call for follow-up

Now, more than four decades after the Viking landings — and with a lot more information about Mars in hand — Levin believes that NASA hasn't properly followed up on the Viking landers' results. 

"I am certain that NASA knows there is life on Mars," he said this past July on David Livingston's popular online program "The Space Show." 

Levin called for a re-examination of Viking LR data by an objective panel. But there's more.

Over the past 40 years, a succession of orbiters, landers and rovers has gathered evidence that life exists on Mars today, Levin said. 

There is "substantial and circumstantial evidence for extant microbial life on Mars," he said on "The Space Show."

Methane spikes

As an example, Levin noted that NASA's Curiosity rover has found cyclical and seasonal spikes in Mars methane. More than 90 percent of the methane in Earth's atmosphere is generated by microbes and other organisms.

"This is really hard to ignore as evidence for life," Levin said. 

However, water-rock chemistry can also produce methane, so it's not persuasive evidence of life, Curiosity mission team members and other scientists have said.  

Curiosity has also discovered organic molecules in 3-billion-year-old sedimentary rocks near the surface. Organics are the carbon-containing building blocks of life as we know it. But again, they're not convincing evidence of life by themselves; naturally occurring organics have also been spotted on asteroids, for example.

Water, water and more water

Then there's the July 2018 news from the European Space Agency's Mars Express mission: The orbiter apparently spotted an underground lake beneath a mile of ice near the Red Planet's south pole.  

Various spacecraft have found evidence of water on Mars over the years, Levin said, and now "we are deluged with an underground lake … so water is no longer the problem."

Levin also pointed to Curiosity imagery that can be interpreted as depicting fossilized stromatolites, structures that are built by colonial microbes here on Earth. There are intriguing similarities between ancient sedimentary rocks on Mars and structures shaped by microbes on Earth, he said.

Everything that we have learned about environmental conditions on Mars, Levin said, would permit terrestrial microorganisms to survive — and that includes the harsh radiation, the low pressure and the frigid temperatures. 

As for present-day life on the Red Planet, "it's getting to the point where the shoe is on the other foot," Levin said. "It's very hard to image a sterile Mars." [Ancient Mars Could Have Supported Life (Photos)]

More knowledge

Viking veteran Ben Clark, now a senior research scientist at the Space Science Institute in Boulder, Colorado, said "it's about time to start earnestly searching for signs of [Mars] life again." 

Clark developed a Viking-carried instrument that measured the composition of Martian soils.

"From what we have learned since Viking about the past history of Mars, it was even more eminently suited for the origin of life than we knew when the search began," Clark said. "A Viking lesson learned is that you had better understand the environment well before designing tests for biological activity."

Astrobiologist Dirk Schulze-Makuch, a professor at the Technical University Berliny, also said the Viking life-detection experiments were conducted before scientists really understood the Red Planet. 

"Life is intrinsically linked to its environment," Schulze-Makuch told Space.com. Not having that information in hand, we cannot home in on optimal search and life-detection strategies, and "that, of course, also applies to the icy moons," he added, referring to ocean-harboring worlds such as the Jupiter moon Europa and the Saturn satellite Enceladus.

"If it would have been known at the time of the Viking mission about Mars what is known today, they probably would have come up with the conclusion that microbial life likely exists on Mars," Schulze-Makuch said.

"I think the consensus is shifting more into the direction that the extraordinary claim would be that 'Mars is and was always lifeless,'" he added, referring to astronomer Carl Sagan's famous saying that "extraordinary claims need extraordinary evidence."

Nevertheless, Schulze-Makuch said that any declaration of life on Mars still requires overwhelming evidence before being scientifically saluted. "Just think about how long it took before it was accepted that there was and still is liquid water on Mars!" he said.

Better-informed instruments

John Rummel is familiar with Levin's steadfast life-on-Mars position.

"The Mars science community would have benefited greatly if Gil Levin had aspired to a leadership position in science after the Viking lander missions had completed their life-detection experiments," said Rummel, who twice served as NASA's planetary protection officer and is a former chair on planetary protection for the agency's Committee on Space Research.

New missions with better-informed instruments looking for life were possible then, Rummel said, but they needed a strong advocate who had the sort of data that Levin possessed. 

"Fundamentally, there is nothing new about Mars that wasn't possible with Viking, but it is a long way from Chryse or Utopia [the two Viking landing spots on Mars in 1976] to the sub-polar-cap lake now claimed by the Italians," Rummel, who's now based at the SETI (Search for Extraterrestrial Intelligence) Institute, told Space.com. "If Levin had stayed fully engaged, we might have already tried to go there."

Beyond the science debate

Astrobiologist Chris McKay, of NASA's Ames Research Center in Silicon Valley, is a longtime Mars investigator. 

The science community is in general agreement, McKay said, that the Viking LR experiment did not detect life. The reactions noted by that instrument and the other results from Viking can be explained by reactive chemicals called perchlorates, he said. 

Perchlorates were first detected in Martian soil by NASA's Phoenix lander in 2008, nearth the Red Planet's north pole. Further observations by other spacecraft strongly suggest that perchlorates are widespread throughout Mars.

That perchlorate explanation, however, is tentative, McKay said. "We cannot rule out that Gil Levin is correct and that there are dormant life-forms in the Martian soil," he said.

If so, that finding has implications beyond the science debated. "Are we confident enough that the Martian soil is lifeless to send astronauts … and then to bring those astronauts back to Earth? I say no," McKay said. "It seems to me that the standard of proof must be higher for these activities, and we have not reached that standard yet." 

But McKay thinks Levin is right in continuing to insist that the possibility of life be considered. 

"Life may not be the scientifically preferred explanation, but it cannot yet be disproven," McKay concluded.

Leonard David is author of "Mars: Our Future on the Red Planet," published by National Geographic. The book is a companion to the National Geographic Channel series "Mars." A longtime writer for Space.com, David has been reporting on the space industry for more than five decades. Follow us @Spacedotcom, Facebook or Google+. This version of the story published on Space.com.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected]

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