| The Tharsis hemisphere of Mars. The 4 giant volcanoes are marked by clouds and the western half of Valles Marineris is seen at proper. Picture credit score: NASA. |
In 1977-1978, the Jet Propulsion Laboratory (JPL) Mars Program studied a low-cost “minimal” Mars Pattern Return (MSR) mission as a possible follow-on to the Viking missions. Late in 1978, JPL Mars Program engineers known as upon the NASA-sponsored Mars Science Working Group (MSWG) for help in defining science necessities to assist information MSR spacecraft design and operations planning.
The MSWG scientists divided into Web site Choice and Pattern Acquisition groups. The groups held two joint workshops and produced 10 detailed stories earlier than the center of 1979. Edited by JPL’s Neil Nickle, they didn’t see print till November 1980.
Publication was delayed partly as a result of Mars planning at JPL slowed markedly in early 1979. It might not start to emerge from the doldrums once more till the next 12 months, after President Jimmy Carter’s NASA Administrator, theoretical physicist Robert Frosch, created the Photo voltaic System Exploration Committee in an (in the end profitable) effort to revitalize the house company’s flagging robotic exploration program.
As a result of the MSWG stories have been primarily based on restricted knowledge, they might seem archaic to some readers. However, they continue to be essential, for they seize snapshots of the state of Mars science because the busy first period of robotic Mars exploration ended and the lengthy hole started between the Viking missions, which reached Mars in 1976, and Mars Pathfinder and Mars International Surveyor, which arrived on the planet in 1997.
The primary MSWG report, which checked out polar touchdown websites for the minimal MSR mission, was authored by J. Cutts, Ok. Blasius, W. Roberts, and Ok. Pang of the Planetary Science Institute (PSI) of Science Purposes, Inc., and A. Howard of the College of Virginia (UV). They submitted their report back to JPL on 30 April 1979.
The PSI/UV crew started by mentioning that people had already explored Mars’s poles for greater than a decade. Mariner 7 had begun close-up martian polar exploration by imaging your entire southern ice cap at low decision throughout its August 1967 flyby. Mariner 9 imaged each caps from Mars orbit throughout 1971-1972, and the Viking 2 orbiter started high-resolution polar imaging in 1976.
In lots of respects, polar MSR websites constituted a particular case, the PSI/UV crew wrote. Whereas missions to the opposite MSR websites would focus primarily on rock samples, the polar MSR mission would purchase meter-long core samples of ice or mud and ice. Rock samples could be “an unplanned bonus.”
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| The north pole of Mars. Picture credit score: NASA. |
The 5 scientists checked out two MSR websites close to Mars’s north pole (picture at high of publish). Web site A, at 86.5° north (N), 105° west (W), included huge “featureless” expanses of undulating perennial ice underlain by layered deposits. Core samples of perennial ice may present knowledge on ice cap formation processes and time scale, martian local weather historical past, and natural compounds trapped within the ice. They’d set up “floor fact” for deciphering polar knowledge from orbital spacecraft.
They assumed {that a} touchdown may safely happen wherever inside a goal ellipse 25 kilometers huge by 40 kilometers lengthy, and calculated {that a} lander that set down within the ellipse would stand a minimum of a 99% probability of touchdown on perennial ice. Because of this, no mobility (that’s, no rover) could be required at Web site A.
The second polar website, Web site B (84.5° N, 105° W), included perennial ice and “partially defrosted” terraced troughs. The latter, the PSI/UV scientists defined, would “type home windows by means of the layered deposits and cross-sections by means of martian historical past.” The 25-kilometer-by-40-kilometer Web site B goal ellipse would additionally overlap the sting of the everlasting ice cap.
Deciding on such a different space would, they warned, scale back the likelihood of touchdown on perennial ice to between 60% and 90%. If, nevertheless, the Web site B mission included a short-range (about 10 kilometers) rover, then the likelihood of sampling multiple terrain and of sampling perennial ice would enhance to better than 90%.
In discussing the engineering issues of a polar MSR mission, the PSI/UV crew cited Purdue College’s 1976-1977 Mars Polar Ice Pattern Return examine (see “For Extra Info,” under), however in any other case left engineering to the engineers. Potential issues recognized included acquisition and preservation of ice and permafrost cores, mechanical operations at extraordinarily low temperatures, and water and carbon dioxide frost accumulation and evaporation that may impede a rover.
As a “subsequent logical step” towards a polar MSR mission, the PSI/UV scientists really helpful institution of a science working group with “substantial participation by earth scientists concerned with research of terrestrial sedimentary data[,] notably these pertaining to local weather change.” They didn’t advocate an MSR precursor mission; that’s, they judged that the Viking missions had offered knowledge satisfactory for planning a minimal MSR mission to Mars’s north pole.
Arizona State College (ASU) geologists R. Greeley, A. Ward, A. Peterfreund, D. Snyder, and M. Womer submitted the second of the ten MSWG stories to JPL in March 1979. Their quest for a younger volcanic MSR website was hampered, they defined, by a dearth of high-resolution (higher than 50 meters per pixel) orbital pictures. However, they situated six candidate websites that volcanic and had few craters, signifying youth. (Planetary scientists rely craters to estimate terrain age; the extra densely craters pock a panorama, the older it’s more likely to be.)
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| Arsia Mons (proper of middle) is southernmost of the 4 nice Tharsis volcanoes. ASU’s “Arsia Mons West” MSR website is situated close to the middle of the left (west) half of the picture. Picture credit score: NASA. |
The ASU geologists picked Arsia Mons West, situated at 8.5° south (S), 132.5° W, 500 kilometers from Arsia Mons, the southernmost of the 4 nice Tharsis volcanoes, as a result of the location gave the impression to be each very younger and comparatively homogenous geologically. The latter, they defined, was a fascinating high quality as a result of it could facilitate interpretation of pattern knowledge.
The Arsia Mons West website, which had been imaged by the Viking orbiters at 34-meters-per-pixel decision, included eight overlapping lava flows. The flows measured from eight to 35 kilometers huge and averaged 51 meters thick.
The ASU crew discovered room for 2 goal ellipses 80 kilometers lengthy by 50 kilometers huge on both aspect of a five-kilometer crater at their website’s middle. They calculated {that a} rover with a 14-kilometer vary would have a “full assure” of reaching an outcrop of younger volcanic rock.
At JPL’s request, the ASU geologists additionally assessed Viking 1’s Chryse Planitia touchdown website as a possible MSR touchdown website. The volcanic rocks have been outdated at Chryse, a smooth-floored basin on the confluence of a number of giant flood-carved channels. Based mostly on the in-situ proof offered by Viking 1 lander pictures, it was clear that no mobility could be wanted to amass a rock pattern.
The ASU crew famous, nevertheless, that the “worth of a returned pattern [would be] severely diminished as a result of it could be not possible to find out if the fabric represents native [lava] flows. . .[or] if it has been deposited from the floods that eroded the channels.” The ASU crew added that “[w]ithout mobility of a minimum of 200 to 300 kilometers, the [Chryse Planitia] website [would be a] a poor option to reply fundamental scientific questions on Mars.” For neither website did they advocate an MSR precursor mission.
A Younger-Lavas Touchdown Web site Northwest of the Volcano Apollinaris Patera and a Touchdown Web site on the Historical Terrain Southeast of the Schiaparelli Basin, had a single writer: Brown College geologist P. Mouginis-Mark. He argued for mobility at his younger Elysium Lavas (5° S, 190° W) and Historical Terrain (8° S, 336° W) minimal MSR websites. The previous, 150 kilometers from the Apollinaris Patera volcano, comprised rolling plains with scattered volcanic domes and shields, stratovolcanoes, and recent affect craters. He recognized a ridge working by means of the middle of the 80-by-50-kilometer goal ellipse because the characteristic more than likely to yield a “good pattern” (that’s, a well-preserved volcanic rock consultant of the location).
Mouginis-Mark calculated that with out mobility the likelihood of acquiring a great pattern could be nil, whereas the likelihood of touchdown on a sand dune and acquiring no pattern in any respect could be as excessive as 22%. The likelihood of acquiring a great pattern would enhance to 91%, nevertheless, if the mission included a rover with a round-trip vary of 20 kilometers.
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| The graceful-floored crater Schiaparelli (high of picture, good of middle). Mouginis-Mark’s “Historical Terrain” MSR website is situated close to the middle of the picture. Picture credit score: NASA. |
Mobility could be much more essential at Mouginis-Mark’s heavily-cratered Historical Terrain website, situated 150 kilometers from the 400-kilometer-diameter crater Schiaparelli. The location, which dated from the Noachian, the earliest recognized period of martian geological historical past, included extremely eroded giant craters buried underneath ejecta from Schiaparelli’s violent formation.
Mouginis-Mark anticipated {that a} good pattern may be discovered on the rim of a recent crater greater than two kilometers throughout, 5 of which occurred in Historical Terrain goal ellipse. He calculated {that a} rover round-trip vary of fifty kilometers could be wanted to realize a 90% likelihood of buying a great pattern.
For his or her contribution, USGS geologists H. Masursky, A. Dial, M. Strobell, G. Schaber, and M. Carr recycled 4 websites that they’d studied in 1977-1978 for a proposed Viking follow-on long-range rover mission. Masursky and Dial have been co-authors of the Viking ’79 traverse examine in 1974, whereas Carr led the Viking orbiter imaging crew (and thus was concerned in capturing the high-resolution pictures the minimal MSR Web site Choice Crew utilized in getting ready its stories).
The USGS websites represented two martian terrain varieties. Tyrrhena Terra and Iapgyia Terra included historical cratered terrain just like that at Mouginis-Mark’s Schiaparelli website, which is probably unsurprising provided that such terrain covers greater than 60% of Mars. The websites contained a jumble of overlapping craters and an intercrater mantle of outdated lava flows.
Samples collected in Tyrrhena and Iapgyia would allow age-dating of the oldest martian crustal materials, the USGS geologists wrote. This could allow calibration of the crater counts used for courting martian terrains. As well as, knowledge from the samples may “be in comparison with comparable analyses product of historical lunar crustal supplies returned by Apollo 16 and [to] historical terrestrial rocks so as to make interplanetary comparisons of [how rocks are formed], bodily and chemical properties, and age.”
Of the 2 websites, Tyrrhena was “superior as a possible pattern website in all respects,” the USGS crew wrote. They proposed that the minimal MSR lander set down the place the outdated lava flows gave the impression to be skinny, close to a six-kilometer-diameter crater – one giant sufficient, they judged, to have excavated historical crust buried beneath the flows. They calculated {that a} touchdown ellipse 30 kilometers lengthy and a rover with a 10-kilometer round-trip vary would attain solely outdated lava samples.
Acquiring an historical crustal rock pattern (“the first science goal”), then again, would demand a five-kilometer touchdown ellipse and a 14-kilometer round-trip rover. Reaching such touchdown accuracy implied that the minimal MSR lander could be able to automated steering and precision maneuvers throughout descent.
The opposite two USGS websites, Candor Chasma and Hebes Chasma, have been each a part of Valles Marineris, Mars’s nice equatorial canyon system. “These websites,” the USGS crew wrote, would “supply a novel alternative to pattern rock layers and their interbedded soils that will reveal the petrochemical historical past, age dates[,] and the historical past of environmental adjustments which will correlate with episodes of channel formation” on Mars. They may additionally yield natural materials (“if the current purple anorganic local weather didn’t exist at occasions prior to now”) and a document of “the historical past of photo voltaic variations.”
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| Martian Canyonlands: Candor Chasma. Picture credit score: NASA. |
At Candor, their most well-liked website, parallel rock layers have been uncovered within the sloping sides of a 1.3-kilometer-tall mesa standing on the backside of the four-kilometer-deep canyon. If the MSR lander may set down inside a five-kilometer touchdown ellipse atop the mesa, then a seven-kilometer round-trip traverse would allow sampling of among the layers. Recalling their 1977-1978 examine, which assumed a extra succesful (and extra expensive) rover, they famous {that a} “for much longer traverse — greater than 200 km — would permit the complete thickness of rock layers (~4 km) within the canyon partitions to be sampled.”
The MSWG’s fifth report, the primary of the six ready by members of the MSWG Pattern Acquisition Crew, seemed on the availability of rocks on Mars with emphasis on the equatorial Central Latitude Belt, which spanned between 30° N and 30° S. The report’s writer, College of Houston geologist E. King, defined that celestial mechanics and MSR lander engineering constraints would in all probability dictate that the Belt include the primary MSR touchdown website.
The dual Viking landers had had hassle accumulating small rocks on Mars, King famous. This had led some to counsel that what seemed like rocks on the Viking websites have been in reality tender “clods” of martian grime. If appropriate, then this speculation would imply that rocks have been uncommon on Mars, which might in flip eradicate the first motivation for an MSR mission; that’s, to gather rocks.
King reported that his “analysis of the entire presently out there related knowledge” had eradicated this concern “fully” for giant components of Mars, together with for the Central Latitude Belt. Particularly encouraging have been knowledge from the Viking orbiter Infrared Thermal Mapping (IRTM) experiment, which mapped thermal inertia (that’s, how lengthy it takes a given floor to turn into cool at night time). Rocky surfaces want longer to chill down than do dusty surfaces.
Viking IRTM knowledge indicated that a lot of the Central Latitude Belt has thermal inertias as excessive as 12. “It is extremely tough to assemble an affordable mannequin of the martian floor that has a thermal inertia of greater than about 3 that doesn’t have a considerable proportion of the floor space lined with rocks,” King wrote.
He attributed the Vikings’ lack of ability to gather small rocks to inadequacies within the Viking sampler design. After it scooped a pattern containing small rocks, controllers on Earth commanded the sampler to show upside-down and shake for as much as two minutes to sieve out mud. King famous that shaking the sampler induced its lid to flap open as a lot as an inch. This could permit any pebbles it contained to flee.
He advocated accumulating rock samples within the type of drilled cores, since drilling may penetrate previous any weathered rock rinds. Drilling may additionally acquire uniform cylindrical samples that may very well be dealt with simply and saved effectively within the MSR spacecraft.
King was ambivalent concerning the want for mobility in an MSR mission; he wrote that, if the target of the mission have been to gather recent igneous rocks, and if the MSR touchdown website have been just like the Viking touchdown websites, then little mobility could be obligatory. He added that, whereas it may be prudent to “construct in some extra mobility as a margin of security and to afford extra potentialities for pattern assortment. . .such provisions [had to be] traded off towards lander science and returned pattern weight.”
USGS geologist H. Moore wrote the sixth MSWG report, which constituted a tour of the panorama inside view of the Viking 1 and Viking 2 lander cameras. Viking 2 landed in Utopia Planitia, close to the massive affect crater Mie, a area extra northerly than Viking 1’s website in Chryse Planitia. Like King, Moore wrote that Viking 1 rocks have been different (there have been 30 varieties) and tended to be smaller than Viking 2 rocks. The Viking 2 rock inhabitants, for its half, gave the impression to be dominated by ejecta from Mie.
Moore then described hypothetical rover traverses on the two websites. In every, the rover would go to 17 sampling stations, traverse about 100 meters, and vary as much as 20 meters from its lander.
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| The boulder named “Massive Joe” on the Viking 1 touchdown website in Chryse Planitia. Picture credit score: NASA. |
On the Viking 1 website, the rover would acquire samples of cloddy soil, crunchy “duricrust” materials, an energetic dune, and drift materials, in addition to 10-centimeter-long cores from bedrock outcrops, layered rocks, darkish and light-weight rocks, a pink rock, rocks shaped by asteroid impacts, and gray-hued “Massive Joe” (the biggest rock close to the lander). The rover on the Viking 2 website would acquire samples of “inter-rock drift” materials, a “drift dunelet,” thick crust close to a rock, and small rocks, together with cores from a coarsely pitted rock, planar and rounded rocks, a banded rock, the “large” and pitted ends of 1 angular rock, and a ventifact (a rock scratched and carved by wind-blown mud and sand).
Moore estimated that the rover would spend between six and eight days traversing and accumulating for every station. Every traverse would thus final from 102 to 136 days. The full mass of samples collected on every traverse would whole about two kilograms.
The seventh MSWG report sought to estimate the variety of crystalline rocks — that’s, volcanic rocks equivalent to basalt — on the Viking touchdown websites and to plan traverses that will adequately pattern them. Its authors, R. Arvidson, E. Guinness, S. Lee, and E. Strickland, geologists within the Division of Earth and Planetary Sciences at Washington College in St. Louis, Missouri, argued that any rock bigger than about 10 centimeters in diameter on the Viking websites was a great candidate for being crystalline.
Such rocks, they added, cowl 9% of the Viking 1 website and 17% of the Viking 2 website. The previous, they wrote, included bedrock exposures and a minimum of 4 soil varieties, whereas the latter included two soil varieties and no bedrock. They identified that, whereas a sampler arm may in all probability attain a crystalline rock at both website, it could not be capable of pattern the entire out there supplies. For that motive, they proposed that MSR landers on the Viking websites ought to every deploy a “mini-rover.”
The Viking 1 website was “such an fascinating place,” the Washington College crew wrote, that they’d deliberate for it a 40-meter traverse with seven sampling stations (with an choice to increase to 50 meters and 10 stations). The fundamental traverse would acquire 10-centimeter core samples from three rocks and 4 soil samples. The prolonged traverse would pattern two extra rocks, together with Massive Joe, and would collect a complete of 5 soil samples, together with very purple soil from atop Massive Joe.
The Viking 2 website, in contrast, featured minimal selection, so the Washington College crew’s traverse there would cowl solely 25 meters and 7 stations. The mini-rover would acquire 4 soil samples and core samples from three rocks.
N. Nickle of JPL’s Flight Tasks Planning Workplace authored the eighth MSWG report, which was titled Necessities for Monitoring Samples. The report was printed initially as a JPL Interoffice Memorandum dated 20 October 1978. Nickle wrote that the “scientific integrity of the returned Martian samples is of prime significance.” “Scientific integrity,” he defined, meant “the preservation of the bodily and chemical state of the acquired samples.”
To keep up the scientific integrity of the samples collected through the minimal MSR mission, Nickle really helpful that they be stored 20° C cooler than the estimated minimal temperature they’d skilled on Mars, and that they be sealed inside a container with martian air at typical martian floor strain. As well as, he really helpful that the samples be uncovered to no extra galactic cosmic and photo voltaic radiation than they’d been on Mars, and to no magnetic subject stronger than Earth’s pure subject.
The minimal MSR mission sought to manage price partly by avoiding science instrumentation not required for pattern assortment. Within the MSWG’s ninth report, J. Warner of NASA’s Johnson Area Heart (JSC) in Houston, Texas, checked out low-mass, low-power MSR science devices designed to “present satisfactory info to pick out samples.”
His candidate instrument suite included a steerable imager, a reflectance spectrometer, a chemical analyzer on a increase, a boom-mounted densitometer, and a software for measuring hardness (this may, Warner urged, be made a operate of the pattern scoop; the Viking arm and claw had been used to scratch and chip at rocks to guage their hardness).
Warner additionally ready the tenth and final report of the Web site Choice and Pattern Acquisition Research, which he titled A Returned Martian Pattern. In it, he seemed on the type the minimal MSR pattern ought to take. He checked out two completely different touchdown website varieties: a Viking-like website “laden with a wide range of rocks and soils” and a hypothetical “{smooth} plains website.”
The JSC geologist cited Moore’s report when he wrote that, at a Viking-like website, an satisfactory pattern may very well be “obtained on a traverse of some hundred meters that by no means leaves the sector of view of the lander.” He estimated that an environment pattern, a soil core, 9 rock cores, 4 small rock fragments, two duricrust samples, and 6 scoops of soil would adequately characterize a Viking-like website. Collectively these samples would have a mass of 4.1 kilograms.
An eight-month, 15-station traverse may adequately pattern a rock-poor {smooth} plains website, Warner wrote. The rover would vary broadly over the graceful terrain. Sampling stations would happen at “obstructions” (for instance, craters). The rover would drill two or three rock cores and acquire one rock fragment at every station, scoop soil at each different station, and acquire duricrust at each fifth station. Including a soil core and an environment pattern would carry the entire pattern mass to five.7 kilograms if two rock cores have been collected and 6.9 kilograms if three cores have been collected.
Sources
Mars Pattern Return: Web site Choice and Pattern Acquisition Research, JPL Publication 80-59, Neil Nickle, editor, NASA Jet Propulsion Laboratory, 1 November 1980.
Detailed Studies of the Mars Pattern Return Web site Choice and Pattern Acquisition Research, JPL 715-23, Volumes I-X, Mars Science Working Group Mars Pattern Return Research Effort, NASA Jet Propulsion Laboratory, November 1980.
Extra Info
Mars Polar Ice Pattern Return (1976-1978)
Prelude to Mars Pattern Return: The Mars 1984 Mission (1977)
Safeguarding the Earth from Martians: The Antaeus Report (1978-1981)
