Northern Hemisphere Of Mars Research Articles

Geometric properties of Martian impact craters: Preliminary results from the Mars Orbiter Laser Altimeter

The Mars Orbiter Laser Altimeter (MOLA) acquired high spatial and vertical resolution topographic data for 18 tracks across the northern hemisphere of Mars during the Fall of 1997. It sampled 98 minimally degraded impact craters between the latitudes of 80°N and 12°S The best fitting depth (d) versus diameter (D) power‐law relationship for these craters is: d = 0.14 D0.90 for simple varieties, and d = 0.25 D0.49 for complex structures. The simple‐to‐complex transition diameter is 8 km (+/−0.5 km). The cross‐sectional “shape” of the crater cavities was determined by fitting a power‐function to each profile. Variation in the exponent (n) suggest the craters flatten with increasing diameter and impact energy. The ejecta thickness is skewed suggesting that use of existing empirical expressions for the expected radial decay of ejecta thickness is inappropriate for Mars in most cases.

Arabia Terra, Mars: Tectonic and Palaeoclimatic Evolution of a Remarkable Sector of Martian Lithosphere

A regional geologic study of Arabia Terra, a densely cratered area of Mars northern hemisphere, has revealed the individuality of this province. This is best expressed by an equatorial belt with a crater age distinctly younger as compared to the northern part of Arabia Terra and to Noachis Terra to the south. We interpret this as an incipient back-arc system provoked by the subduction of Mars lowlands under Arabia Terra during Noachian times. The regional fracture patterns are also best explained in this manner, making it unnecessary to appeal to a rotational instability of the planet, which is not supported by the palaeoclimatic indicators in the area. This model could be the first regional-scale confirmation of Sleep's (1994) hypothesis of a limited plate consumption as an explanation of the martian dichotomy.

The martian hemispheric dichotomy may be due to a giant impact

Mars is divided into two fundamentally different geological provinces of approximately hemispherical extent1–3. The more southerly province is heavily cratered, contains relatively old geological units, and superficially resembles the lunar and mercurian highlands. The northern province is relatively lightly cratered and contains younger geological units, including extensive plains, volcanic edifices, and volcanic calderas. Except for the Tharsis and Elysium regions and other large volcanoes, most of the younger, northern province consists of lowlands, which lie an average of 3 km below the highlands. Lowlands occupy about one-third of Mars. They are separated from the highlands by a distinct scarp or by a sloping transitional zone as much as 700km wide in which highland materials have been disrupted and partly replaced by lowland deposits (Fig. 1). The transition is characterized by a variety of landforms unknown on other planets. The highlands and lowlands are in isostatic equilibrium across the transitional zone4. No generally accepted explanation for the cause of the highland-lowland dichotomy has been proposed although thinning of the lithosph¨re in the northern hemisphere by internal processes has been suggested5. Large impacts, which were a feature of early Solar System history, have also been suggested as an important cause of such early planetary-surface heterogeneities3,6,7. Subcircular lowlands such as Argyre, Chryse, Hellas, and Isidis Planitia and the plains south of Tharsis occupy previously recognized impact basins8–10. We propose here that the largest expanse of lowlands also results from formation of a large impact basin early in Mars' history that has profoundly shaped the planet's surface.

Surface properties of ancient cratered terrain in the northern hemisphere of Mars

The hilly and cratered material of Scott and Carr [1978], interpreted to be the oldest extensively exposed surface of Mars, has been examined where it is covered by high‐resolution (16–62 km2) infrared data from the Viking IRTM. This allows spatial variations in observed properties to be associated directly with geologic features and an assessment to be made of the contribution to the remotely determined properties from the ancient rock unit. The measured nighttime temperatures at 20 and 11 μm indicate that from 0 to 20% of the surface consists of high thermal inertia ‘blocks’ (assumed to be I = 30 × 10−3 cal cm−2 s½ K−1) surrounded by lower thermal inertia ‘soil’ (I = 1.5 to 7.5). Block abundances are typically ∼9% within the Arabia low thermal inertia region (I = 1.5 to 3.0) identified from global mapping and increase away from Arabia, particularly to the south. Geologic features crossed by the IRTM data generally show no distinguishable difference from the regional properties with the exceptions of dark patch material and craters near 27°N, 338°W. The dark patch material, typically within craters, has block abundances (5–20%) and soil thermal inertias (5.0–7.0 for an albedo of 0.15) distinctly different from the Arabia material; nonunit emissivity for this material would make the block abundances upper limits and the soil thermal inertias lower limits. The effective grain diameter of the dark patch material (160 to 360 μm) is indicative of sand‐sized particles capable of saltation. Two craters near 27°N, 338°W have slightly higher soil thermal inertias (∼3.5, corresponding to ∼70 μm) and lower block abundances (0–5%) than the surrounding Arabia material, but no prominent dark patches are associated with them. Imaging data from within and around the Arabia region indicate that subdued surface morphology is not always associated with low thermal inertias. The extensive mantling of northern hemisphere locations of ancient cratered terrain by fine‐grained material does not allow thermal measurements to be directly related to rock unit properties, but less mantling may be present in southern hemisphere locations of this material.

Measurements of water vapor in Mars' Antarctic

A complete Mars year of measurements of atmospheric water vapor in the south arctic have been obtained from the Viking Orbiters. Analysis of the observations indicates that, except for the south remnant cap, the southern hemisphere of Mars is devoid of any substantial reservoirs of water in contact with the atmosphere, and that, in the summer time, the top layer of soil is desiccated. Small amounts of water ice are incorporated into the annual CO 2 cap; this water is released at the cap margin when it retreats in the spring. The first global dust storm resulted in heating of the south arctic atmosphere and a transport of water in from the equatorial region. The second global dust storm had a negligible effect on atmospheric water vapor; the dust contained little water.

Plains and channels in the Lunae Planum—Chryse Planitia Region of Mars

The Lunae Planum‐Chryse Planitia region provides the opportunity to study a sequence of channeling events and to determine their temporal and genetic relationships to plains units in the northern hemisphere of Mars. Two sets of small channels and four major channel systems can be divided into four periods of channeling by superposition and contact relationships to the plains. All of the channels are considered to have formed by water erosion. The first two channeling events occurred early in the history of this area and formed small, narrow channels within the old rugged terrain. These channel events were separated by deposition of a mantle unit. The small channels probably formed by runoff of surface water or by a sapping process. These channels preceded the emplacement of vast volcanic plains in both Lunae Planum and Chryse Planitia. Channels postdating the plains are Vedra, Maumee, Bahram, and Maja valles; the first three of these deposited a sedimentary unit on the western slope of Chryse Planitia that was eroded by Maja Vallis. These large‐scale channels were probably formed predominantly by catastrophic floods and may represent two periods of water release from Juventae Chasma. The origin of Bahram Vallis remains uncertain.

Thermal mapping of the northern equatorial and temperate latitudes of Mars

Using Viking infrared thermal mapping observations, nighttime temperatures have been mapped over the northern hemisphere of Mars. The latitude range from 10°S to 50°N was mapped near midnight local time in the northern spring and temperatures compared to those predicted by a uniform thermal model. As in earlier Viking thermal mapping, three large well‐defined regions are significantly cooler than expected. Four less well defined warm areas occur; two extend north beyond this coverage. Large variations of the temperature residual, −45 to +19 K, are related primarily to the thermal inertia of the surface. Although strong local correlations exist in some areas, there is no consistent regional‐scale correlation with elevation, albedo, geology, or geomorphology. Where studied in detail, the boundaries of the cool regions and some local thermal structures are found to be related to the occurrence of patches of dark material and streaks downwind of craters. High‐resolution imaging indicates that a mantling layer exists over at least one of the cool regions. A general hypothesis for the transport of loose material on the Martian surface invokes the stability of the smooth, fine grained surfaces to account for the bimodal thermal behavior observed. This hypothesis and thermal mapping suggest that large areas of the Martian surface are very different from those observed by the Viking landers.

Moderate resolution thermal mapping of Mars: The channel terrain around the Chryse Basin

Moderate resolution (∼30 km) thermal inertia estimates have been made for several regions in the northern hemisphere of Mars. Examples of these maps are presented here for the region 0°–45°N, 0°–90°W. The thermal inertia of Kasei Vallis is found to be significantly higher than that of the surrounding terrain. The assumption of a uniform grain size surface gives maximum diameters of 1.0 mm inside and 0.05 mm outside Kasei Vallis for the surface materials. High inertia regions are well correlated with low albedo (A ∼ 0.14) regions. Three large channels in the Oxia Palus quandrangle also have high inertia floors. There is some indication that the thermal inertia increases toward the mouth of one of these channels. The Chryse and Acidalia basins have uniform high inertia surfaces with no decrease in inertia as distance increases from the major channels. There are numerous craters in the region which have high inertia‐low albedo features on the crater floor. This correlation has been observed for many other craters on Mars, both from Mariner 9 and Viking data. A possible explanation is the accumulation of coarsegrained, windblown material within the craters. Average grain sizes of these materials range from 0.5 to 1.1 mm, corresponding to medium to coarse sand. The Viking 1 landing site is located in the lowest inertia region within the area studied which met the latitude and elevation capabilities of that vehicle.

Martian extratropical cyclones

VIKING Orbiter 1 has recently photographed two cloud formations in the northern hemisphere of Mars which closely resemble satellite pictures of terrestrial extratropical cyclones. The pictures, (Figs 1 and 2) were acquired during the summer season and are the first evidence that baroclinic waves, prevalent during other seasons, also occur in summer. Physical properties of these systems deduced from the vidicon images and from the IR thermal mapping experiment (IRTM) are discussed here.

A Martian yellow cloud—July 1971

A short-term yellow cloud was observed in the southern hemisphere of Mars from July 10 to 22, 1971. The initial cloud was first photographed on the morning limb at 7:45 am local Martian sun time in the Serpentis-Hellespontus region (315°W; 27°S), 74 Earth days (72 Martian days) prior to the onset of the September major yellow storm. Historical observations from the Lowell Observatory archives indicate that prestorm yellow clouds of limited extent are not uncommon. Positional measurement and photographic differential photometry of the July yellow cloud were possible throughout its entire evolution because Mars was favorably situated and photographic coverage by the International Planetary Patrol was adequate. Maps showing the cloud's initial location, hourly and diurnal behavior, apparent motion, and areal coverage by haze are presented. The similarities between the July cloud and other southern hemisphere yellow clouds are summarized. Its relationships to classical albedo features and Mariner 9 topographic data are discussed. Photographic photometry indicates that the enhanced contrast between the yellow cloud and its surroundings is probably due more to the brightening of the cloud-covered areas than to any darkening of contiguous areas.

Close Approach of Mars

MARS was in opposition with the sun on July 23, and was nearest the earth, at a distance of 36 million miles and with an angular diameter of 24·1”, on July 28. Despite the closeness of the approach, the apparition is a most unfavourable one for observation in high northern latitudes. This is because of the planet's very large south declination. In May its declination ranged between -22½° and -23°; by the end of June it increased to -24°; and it is now -27°. Thus, since observations began, the altitude above the horizon in the latitude of Greenwich has never exceeded 16° and is now less than 12°. It follows that observers in Great Britain and in most northern observatories cannot expect to get good views of the planet during the present apparition. We shall have to rely almost entirely for our results on observers in the southern hemisphere. Astronomers in northern latitudes may look forward confidently to the next apparition in 1941; for then the planet will be high in their skies and not very much farther away from the earth. During the present apparition, the southern hemisphere of Mars is tilted towards the earth, the latitude of the centre of the disk being -12° at the beginning of June and -7° at the end of August. The spring equinox of Mars’ southern hemisphere occurred on June 1; the summer solstice will occur on October 24.

Astronomical Topics

Astronomical Notes for February. Jupiter, Mars and Neptune are all near opposition, and are observable for most of the night. The northern hemisphere of Mars is turned towards us; this is less well known than the southern hemisphere, being turned to us at aphelion oppositions. The diameter of Mars increases during February from 12″ to nearly 14″. There is an eclipse of Jupiter IV on February 12; the disappearance is at 8.11 p.M. when Jupiter will be too low; but the re-appearance at 11.54 P.M. is observable. Two stars in the Pleiades are occulted by the moon on February 3, disappearing at 8.43 and 9.34 P.M.

Societies and Academies

PARIS. Academy of Sciences, July 3.—M. Emile Bertin in the chair.—The president announced the death of Prince Albert of Monaco, foreign associate of the Academy.—P. A. Dangeard: The structure of the cell in the Iris. In a recent communication the author has given a detailed description of the plastidome and spherome in the leaves of Iris germanica: this is supplemented in the present paper by similar details for the same formations in the tissues, petals, sepals, stamens, ovary and ovules. The plastidome and spherome are independent formations and have an existence as general as the nucleus in the plant cell.—Andre Blondel: The unsymmetrical electric arc between carbon and metals.—M. Albert Recoura was elected correspondant for the section of Chemistry in the place of the late M. Ernest Solvay.—The Permanent Secretary announced the death of M. Otto Lehmann, correspondant for the section of Mineralogy.—Armand Cahen: Singular solutions of differential equations of the first order.—Miecislas Biernacki: The displacement of the zeros of integral functions by derivation.—R. Jarry-Desloges: Contribution to the study of the surface of planets. The systematic observation of the planetary surfaces, especially of Mars, commenced in 1907 at Revard, have been continued in May and June of this year at Setif, with the 37 cm. and 26 cm. refractors. The decoloration of certain dark areas in the southern hemisphere of Mars, observed in 1909 at Revard, has been seen again this year.—Jules Baillaud and Miles. Bonnet, Clavier, and Lhomme: Distribution of stars in the Paris zone of the astrophotographic catalogue.—Axel Lindh: The absorption spectrum of sulphur for the X-rays. An examination of sulphur compounds grouped according to the valency of the sulphur. As in the case of chlorine previously studied, the limits of the K absorption for sulphur are displaced towards the shortest wave-lengths for the higher valencies.—Albert Portevin: The thermal treatment of cast pieces, and especially of cast projectiles. Thermal treatment produces porosity in the metal.—Roger G. Boussu: The limit of inflammability of the vapours of the alcohol-petrol system and of a triple system containing as base alcohol and petrol.—C. Matignon and M. Frejacques: The transformation of gypsum into ammonium sulphate. Calcium sulphate was stirred with concentrated ammonium carbonate solution in approximately equimolecular proportions. Equilibrium was reached after five hours, about 96 per cent. being converted into ammonium sulphate.—Albert Granger and Pierre Bremond: The chemical composition of rock, supposed to be kaolin, from Djebel Debar, Algeria. This is formed of halloysite, associated with a hydrated aluminium silicate containing combined sulphuric acid.—Paul Thiery: The upper Bajocian of Lorraine.—G. Denizot: The last variations of the marine level on the coasts of Basse-Provence.—P. Bugnon: The basifuge acceleration in the hypocotyl.—G. Nicolas: A new host of Phyllosiphon. This parasite was found on Arum italicum near Toulouse. This resembles P. Arisari, and if not belonging to a different species, constitutes a different biological strain, since although Arisarum vulgare, carrying P. Arisari, grows in the neighbourhood of Arum italicum in Algeria, the latter plant has not been found attacked by the parasite.—Pierre Lesage: Experiments on the movement of liquids in cell masses.—Jacques de Vilmorin and Cazaubon: The catalase of seeds. The presence of catalase cannot be taken in all species as a proof of the vitality of the seed.—Marc Romieu and Fernand Obaton: Comparative spectroscopic study of the green pigment of the Chetoptera and the chlorophyll of the green alga, Ulva lactuca. The chetopterin is regarded as a pigment of extrinsic origin, and is a modified chlorophyll.—Mme. Danysz Michel and W. Koskowski: Study of some digestive functions in normal pigeons, fed with polished rice or kept without food. Comparative experiments made with pigeons on four different diets: normal diet, no food, polished rice only with and without daily injection of histamine. From the examination of the gastric juice and intestinal contents it is concluded that the observed facts can be explained without assuming the intervention of a vitamin.—J. Athanasiii: Nerve motor energy: electromyograms.—L. Garrelon, D. Santenoise, and R. Thuillant: The action of peptonic shock on the vago sympathetic nervous system.—P.. Wintrebert: The first manifestations of nervous co-ordination in the body movements of Scylliorhinus canicula—Pierre Girard: Remarks on a note of M. L. Lapicque on the mechanism of the exchanges between the cell and the surrounding medium.—W. R. Thompson: The theory of the action of entomophagous parasites. Increase in the proportion of hosts carrying parasites in cycle parasitism.—S. Metalnikow: An epizootic disease in the caterpillars of Galleria mellonella.— R. Cambier and E. Aubel: The culture of bacteria in a medium of definite chemical composition, with pyruvic acid as a base. The degradation of pyruvic acid. In these cultures the only source of carbon is sodium pyruvate. Three bacilli could be grown on this medium, the pyocyanic bacillus, Fliigge's fluorescent bacillus, and the coli bacillus. Acetic, lactic, and glycollic acids were isolated from the cultures.

The Northern Hemisphere of Mars

The Northern Hemisphere of Mars