Proceedings of the 20th Lwwr and Planetary Science Co nference, pp. 54 1-55 54 1 Lunar and Planetary Institute, Houston, 1990 Geologic Setting of Diverse Volcanic Materials in Nlrthern Elysium Planitia, Mars P.J. Mouginis-Mark Plnnetary Geosciences Division, Hawaii Institute of Geophysics, Universi of Hawaii, Honolulu, HI 96822 Geologic mapping of high-resolution (30-50 m/ pixel) VIking Orbiter images Jnorth ern Elysium Planitia has identified seven sites where current problems in martian volcanolo'Y, chronology, and stratigraphy can be resolved. These sites, which are discussed in the context of a wtential Mars rover/ sample return mission, would permit the foU owing investigations: ( 1 ) the dating o Lower Amazonian lava flows from Elysium Mons (thereby providing absolute calibration for global crater size/ frequency relative chronologies, ( 2) the petrologic investigation of long run-out lava flows, ( 3) the geologic interpretation of materials that may either be lava flows or lahar deposits, ( 4) the balysis of materials believed to be ash deposits produced by explosive eruptions of Hecates Tholus, and f5) the investigation of the stratigraphy of fractured terrain along the boundary between northern Elysium t;'lanitia and southern Utopia Planitia. I INTRODUCfiON frequency curves derived from orbital data can be absolutely calibr.tted, (2) to permit petrologic studies of Elysium Mons For more than a decade, analyses of the Viking Orbiter image lava flows, ( 3) the geologic!interpretation of materials that may data set have revealed the diversity of volcanic materials on either be lava flows or lahar deposits, ( 4) to study the physical Mars from scales ranging from < 1 km to >1 OOOs km. Global properties (the degree of cementation and particle size mapping at 1:25M (Scott and Carr, 1978) and 1:15M (Scott distribution of the surfaoe, stratigraphic relationships, and and Tanaka, 1986; Greeley and Guest, 1987), as weU as microtopography) of the volcano Hecates Tholus in order to numerous regional geological studies at 1:2M, have motivated better define its eruptive history, and ( 5) to study stratigr.tphic detailed mapping at 1:SOOK under NASA's Mars Geologic sections of the boundary arp that separates Elysium Mons Mappers Program in order to resolve local geologic relation­ lava flows from the northern plains. ships. One of several areas identified as important to the interpretation of the volcanic history of Mars is northern ASSUMED ROVER CAPABILITIES Elysium Planitia. Materials resulting from both lava-producing and explosive volcanic eruptions are believed to exist here For the purpose of this · vestigation, it is assumed that the (Mouginis-Mark et al., 1982, 1984; K. L. Tanaka, M.G. rover will land at the same locality as the sample renu-n vehicle Chapman, and D. H. Scott, unpublished data, 1989), as weU as and that selected samples can be renu-ned to Earth in addition the products of complex interactions between volcanic to the rover performing in situ investigations. Alternative materials and subsurface volatiles (Mouginis-Mark, 1985). To configurations have also been di.scussed (Blanchard et al., the west and north of the volcano Hecates Tholus, numerous 1985; Mars Study Team, 1987; Gooding et al., 1989), but lava flows from Elysium Mons, coUapse features, plains units, these configurations would not significantly affect the science and possible melt water deposits have been identified by these objectives as they are deS<tribed here, provided that the rover mapping efforts. In addition, the morphology of Hecates Tholus landed within - 10 km of the sample renu-n vehicle. In this indicates that explosive volcanism (rather than the eruption analysis the rover is assumed to have the foUowing capabilities: of lava flows) most likely dominated the eruptive history of 1. The spacecraft will have the ability to land a roving the volcano (Mouginis-Mark et al., 1982); many valley vehicle within a target ellipse approximately 10 X 6 km in size. networks and the absence of weU-preserved lava flows make As with the site selection procedure for the Viking Landers this volcano significantly different from those found within the (Masursky and Graybill, ~ 976a,b ), possible hazards within the Tharsis region (d. Carr et al., 1977a). landing site ellipse are c@nsidered here to be either craters By virtue of the variety of volcanic materials, northern and their ejecta blankets, steep slopes, or areas of differential Elysium should be considered as a candidate landing site for erosion (stripping, mant~g, and texturing). From the analysis a funu-e Mars rover mission. Only by the in situ investigation of 40 m/pixel Vtking Orbtter images, it is assumed that areas of surface phenomena, and by the renu-n of samples to Earth that are free of resolvable impact craters and other hazardous for dating and petrologic study, can details of the emplacement features represent "safe" landing sites. However, as has been processes and chronology be resolved (Gooding et al., 1989). shown by the analysis of iking Lander images ( cf. Mutch et This study therefore presents the geologic objectives that such al., 1977; Garoin et al., 11981) and the interpretation of very a rover misssion to northern Elysium Planitia would address. high resolution orbital images (Zimbelman, 1987), the The goals of this mission would be: ( 1 ) to provide an age for morphology of Mars appefJIS to be very different at the 50 m/ plains materials that are sufficiently extensive that crater size/ pixel, 10 m/pixel, and cehtimeter-scales. It is thus likely that 542 Proceedings of the 20th Lunar Planetary Science Conference Fig. 1. (a) Overview of the pro­ posed rover traverse site in north­ ern Elysium Planitia. Proposed landing site is marked by a star, and the six science stations are num­ bered I through 6. Portion of U.S. Geological Survey photomosaic MTM-35212. Width of image equi­ valent to 190 km, north is to the top. (b) Geologic map of the pro­ posed rover traverse site in north­ em Elysium Planitia (area shown is the same as that in a). Unit abbre­ B viations are as follows: "HT" - Hecates Tholus, "Fu" - undi.fferen­ tiad flows, "F1" - lobate fl ows, "Np" - Northern Plains materials, "UfB" - upper fractured boundary materials, "liB" - lower fracn1red boundary materials, and "Ce" - crater ejecta. Rim crests of meteor­ ite crdters are marked by barbed circles. Mouginis·M rk: Volcanic materials in Ely sium 543 candidate landing sites will have to come under greater Earth year life expectan should be planned for the rover. scrutiny for more detailed site selection dwjng the Mars Assuming 10 hours of tra erse time per martian day, and two Observer (MO) Mission, when such sites could be imaged at days spent at each sci I ce station and the landing site a resolution of - 1.5 m with the MO high-resolution camera. (including three visits to return samples), the rover would 2. A key aspect of the mission would be the return to Earth have to travel at a mean SReed of - 50 m/ hour when traversing of at least three selected samples that are obtained from the martian surface. I documented in situ localities. The rover must therefore be capable of visiting suitable localities identified either from orbit THE riNG SITE or from terminal-descent imaging. It is assumed here that each The landing site choseffor this study is located at 33.0° N, of these sample localities may be up to 10 km from the return 212.4°W and is devoid of eteorite craters larger than - 300m of the sapcecraft. An extended surface traverse will begin once in diameter (Fig. 1). Alth ugh no good estimates of absolute the collected samples are placed within the sample return elevation exist for this site, the elevation is believed to be about vehicle. 5 km (US. Geological Survey Map l-1120, 1978). However, 3. The rover vehicle must have a range capability of stereogrammetrically derived data for the area surrounding - 200 km over surfaces expected to locally J?Ossess a few Elysium Mons (Blasius nd Cutts, 1981) show that the meters of vertical relief (i.e., comparable to the topography on elevation of the proposed landing site may be less than 3 km terrestrial aa and pahoehoe flows; B. Campbell, S. H. Zisk, and above the 6.1 mb mean Mars datum (Earth-based radar P. Mouginis-Mark, unpublished data, 1989) and have boulder topography data of Downs et al. ( 1982) can be used to populations comparable to those seen at the Vtking Lander provide an absolute reference datum for the stereographically sites ( Garoin et al., 1981 ). The rover will also have the ability derived elevation]. to climb (or descend) slopes of - 2° -3° for traverses perhaps In addition to represen ing a safe landing site, the primary 10-15 km in horizontal extent and to communicate directly criterion for selecting t~ landing site is the collection and with Earth (i.e., there will be no need for the rover to return to Earth of a sample of the plains materials that underlie communicate with Earth via the landing craft). An alternative the lobate lava flows from northern Elysium Mons. The plains way to achieve this goal is for the rover to communicate with materials are interpreted to be undifferentiated lava flows of Earth via a Mars-orbiting relay station (Mars Study Team, Lower Amazonian age that form part of the Elysium formation 1987). (Unit Ael of Greeley and Guest, 1987) and have a crater 4. The instrument complement of the rover will depend 1 frequency of - 250 cratJ rs larger than 2-km diameter per upon the specific mission science requirements, but, as 6 2 10 km . Because these Unit Ael flows cover a large portion discussed by Singer ( 1988), it should carry suitable instru­ 1 of Elysium Planitia, obtaining a sample would enable an ments that will enable it both to navigate across the martian absolute age-calibration point to be added to the crater­ surface and to perform sample identification.