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1.
J. Alexis P. Rodríguez Jeffrey S. Kargel David A. Crown Alberto G. Fairén Victor R. Baker Pat Candelaria 《Icarus》2011,213(1):150-194
Higher outflow channel dissection in the martian region of southern circum-Chryse appears to have extended from the Late Hesperian to the Middle Amazonian Epoch. These outflow channels were excavated within the upper 1 km of the cryolithosphere, where no liquid water is expected to have existed during these geologic epochs. In accordance with previous work, our examination of outflow channel floor morphologies suggests the upper crust excavated by the studied outflow channels consisted of a thin (a few tens of meters) layer of dry geologic materials overlying an indurated zone that extends to the bases of the investigated outflow channels (1 km in depth). We find that the floors of these outflow channels contain widespread secondary chaotic terrains (i.e., chaotic terrains produced by the destruction of channel-floor materials). These chaotic terrains occur within the full range of outflow channel dissection and tend to form clusters. Our examination of the geology of these chaotic terrains suggests that their formation did not result in the generation of floods. Nevertheless, despite their much smaller dimensions, these chaotic terrains are comprised of the same basic morphologic elements (e.g., mesas, knobs, and smooth deposits within scarp-bound depressions) as those located in the initiation zones of the outflow channels, which suggests that their formation must have involved the release of ground volatiles. We propose that these chaotic terrains developed not catastrophically but gradually and during multiple episodes of nested surface collapse. In order to explain the formation of secondary chaotic terrains within zones of outflow channel dissection, we propose that the regional Martian cryolithosphere contained widespread lenses of volatiles in liquid form. In this model, channel floor collapse and secondary chaotic terrain formation would have taken place as a consequence of instabilities arising during their exhumation by outflow channel dissection. Within relatively warm upper crustal materials in volcanic settings, or within highly saline crustal materials where cryopegs developed, lenses of volatiles in liquid form within the cryolithosphere could have formed, and/or remained stable.In addition, our numerical simulations suggest that low thermal conductivity, dry fine-grained porous geologic materials just a few tens of meters in thickness (e.g., dunes, sand sheets, some types of regolith materials), could have produced high thermal anomalies resulting in subsurface melting. The existence of a global layer of dry geologic materials overlying the cryolithosphere would suggest that widespread lenses of fluids existed (and may still exist) at shallow depths wherever these materials are fine-grained and porous. The surface ages of the investigated outflow channels and chaotic terrains span a full 500 to 700 Myr. Chaotic terrains similar in dimensions and morphology to secondary chaotic terrains are not observed conspicuously throughout the surface of Mars, suggesting that intra-cryolithospheric fluid lenses may form relatively stable systems. The existence of widespread groundwater lenses at shallow depths of burial has tremendous implications for exobiological studies and future human exploration. We find that the clear geomorphologic anomaly that the chaotic terrains and outflow channels of southern Chryse form within the Martian landscape could have been a consequence of large-scale resurfacing resulting from anomalously extensive subsurface melt in this region of the planet produced by high concentrations of salts within the regional upper crust. Crater count statistics reveal that secondary chaotic terrains and the outflow channels within which they occur have overlapping ages, suggesting that the instabilities leading to their formation rapidly dissipated, perhaps as the thickness of the cryolithosphere was reset following the disruption of the upper crustal thermal structure produced during outflow channel excavation. 相似文献
2.
Jose A.P. Rodriguez Sho Sasaki James M. Dohm Hideaki Miyamoto Goro Komatsu Justin C. Ferris 《Icarus》2005,175(1):36-57
The undulating, warped, and densely fractured surfaces of highland regions east of Valles Marineris (located north of the eastern Aureum Chaos, east of the Hydraotes Chaos, and south of the Hydaspis Chaos) resulted from extensional surface warping related to ground subsidence, caused when pressurized water confined in subterranean caverns was released to the surface. Water emanations formed crater lakes and resulted in channeling episodes involved in the excavation of Ares, Tiu, and Simud Valles of the eastern part of the circum-Chryse outflow channel system. Progressive surface subsidence and associated reduction of the subsurface cavernous volume, and/or episodes of magmatic-driven activity, led to increases of the hydrostatic pressure, resulting in reactivation of both catastrophic and non-catastrophic outflow activity. Ancient cratered highland and basin materials that underwent large-scale subsidence grade into densely fractured terrains. Collapse of rock materials in these regions resulted in the formation of chaotic terrains, which occur in and near the headwaters of the eastern circum-Chryse outflow channels. The deepest chaotic terrain in the Hydaspis Chaos region resulted from the collapse of pre-existing outflow channel floors. The release of volatiles and related collapse may have included water emanations not necessarily linked to catastrophic outflow. Basal warming related to dike intrusions, thermokarst activity involving wet sediments and/or dissected ice-enriched country rock, permafrost exposed to the atmosphere by extensional tectonism and channel incision, and/or the injection of water into porous floor material, may have enhanced outflow channel floor instability and subsequent collapse. In addition to the possible genetic linkage to outflow channel development dating back to at least the Late Noachian, clear disruption of impact craters with pristine ejecta blankets and rims, as well as preservation of fine tectonic fabrics, suggest that plateau subsidence and chaos formation may have continued well into the Amazonian Period. The geologic and paleohydrologic histories presented here have important implications, as new mechanisms for outflow channel formation and other fluvial activity are described, and new reactivation mechanisms are proposed for the origin of chaotic terrain as contributors to flooding. Detailed geomorphic analysis indicates that subterranean caverns may have been exposed during chaos formation, and thus chaotic terrains mark prime locations for future geologic, hydrologic, and possible astrobiologic exploration. 相似文献
3.
Martin Miller 《中国天文和天体物理学报》2005,5(1):1-5
The first mapping observations of the bipolar HII region S106 in HCN J = 3 - 2 line were made by KOSMA submillimeter telescope in April, 2004. The results show that there is a bipolar outflow centered on the high-mass star S106 IRS4 and that the flat structure of molecular cloud core is perpendicular to the axis of the outflow. This image roughly corresponds to the optical image where a dark lane bisects the bipolar HII region. Together with the optical, infrared and radio data, we conclude that the central UC HII region and molecular outflow formed before the 相似文献
4.
《Planetary and Space Science》2007,55(3):315-332
Global recharge of the martian hydrologic system has traditionally been viewed as occurring through basal melting of the south polar cap. We conclude that regional recharge of a groundwater system at the large volcanic provinces, Elysium and Tharsis, is also very plausible and has several advantages over a south polar recharge source in providing a more direct, efficient supply of water to the outflow channel source regions surrounding these areas. This recharge scenario is proposed to have operated concurrently with and within the context of a global cryosphere–hydrosphere system of the subsurface characteristic of post-Noachian periods. To complement existing groundwater flow modeling studies, we examine geologic evidence and possible mechanisms for accumulation of water at high elevations on the volcanic rises, such as melting snow, infiltration, and increased effective permeability of the subsurface between the recharge zone and outflow source. Evidence for the presence of large Amazonian-aged cold-based piedmont glaciers on the Tharsis Montes has been well documented. Climate modeling predicts snow accumulation on high volcanic rises at obliquities thought to be typical over much of martian history. Thermal gradients causing basal melting of snowpack over 1 km thick could provide several kg m−2 yr−1 of water, charging a volume equivalent to the pore space in a square meter column of subsurface in less than 1.5×105 yr. In order to account for estimated outflow channel volumes, the subsurface volume above the elevation of the outflow channels must be charged several times over the area of Tharsis. Complete aquifer recharge can be accomplished in ∼0.3–2 My through the snowpack melting mechanism at Tharsis and in ∼5×104 years for channel requirements at Elysium. Abundant radial dikes emanating from large martian volcanic rises can crack and/or melt the cryosphere, initiating water outflow and creating anisotropies that can channel subsurface water from a high-elevation groundwater reservoir to outflow sources. In this model, snow accumulation, infiltration of meltwater, and increased effective permeabilities are a consequence of the geologic, thermal, and climatic environment at Elysium and Tharsis, and may have had a genetic influence on the preferential distribution of outflow channels around volcanic rises on Mars. 相似文献
5.
We present results of our morphologic and stratigraphic investigations in the Amenthes region for which our observations suggest a complex spatial and temporal interrelation between volcanic and possibly water-related processes. We have produced a series of self-consistent geological maps and a stratigraphic correlation chart that show the spatial and temporal distribution of volcanic, fluvial and tectonic processes.The Amenthes region consists of a broad trough-like topographic depression that has served as a path for the supply of materials from Hesperia Planum to Isidis Planitia. It is most likely that Hesperia Planum and, in particular the area north of Hesperia Planum, including Tinto Vallis, Palos crater and the surrounding dissected highlands have acted as a source region for materials that were transported into the Amenthes trough and farther into the Isidis basin. The Amenthes trough, as well as the graben of Amenthes Fossae were formed after the Isidis impact in the Noachian and represent likely the oldest features in the Amenthes region. Dendritic valley networks, that bear evidence for surface runoff, have dissected the highlands adjacent to Amenthes Planum and within the Tinto Vallis and Palos crater region before ∼3.7 Ga. The ridged volcanic plains located near the Palos crater and Tinto Vallis region, within Amenthes Planum as well as within the Isidis transitional plains were formed between ∼3.5 and 3.2 Ga and represent the volcanic activity which resulted in the flooding of the Amenthes trough. The sinuous channel of Tinto Vallis was formed in the Hesperian (?3.5 Ga) and shows characteristics, which are consistent with both ground water sapping and igneous processes. The Palos crater outflow channel was formed nearly at the same time as Tinto Vallis, between ∼3.5 Ga and ∼3.2 Ga and postdates the volcanic flooding of the Amenthes trough in the Hesperian. Small valleys (∼3.4-2.8 Ga) incised into the ridged plains of Amenthes Planum appear also within the transitional plains located between the Amenthes plains and the Isidis interior plains. Our model ages show that Tinto Vallis, the Palos crater outflow channel as well as the small valleys are unlikely formed at the same time and by the same processes as the dendritic valley networks and represent an episode that clearly postdates the volcanic activity. 相似文献
6.
The plains materials that form the martian northern lowlands suggest large-scale sedimentation in this part of the planet. The general view is that these sedimentary materials were transported from zones of highland erosion via outflow channels and other fluvial systems. The study region, the northern circum-polar plains south of Gemini Scopuli on Planum Boreum, comprises the only extensive zone in the martian northern lowlands that does not include sub-basin floors nor is downstream from outflow channel systems. Therefore, within this zone, the ponding of fluids and fluidized sediments associated with outflow channel discharges is less likely to have taken place relative to sub-basin areas that form the other northern circum-polar plains surrounding Planum Boreum. Our findings indicate that during the Late Hesperian sedimentary deposits produced by the erosion of an ancient cratered landscape, as well as via sedimentary volcanism, were regionally emplaced to form extensive plains materials within the study region. The distribution and magnitude of surface degradation suggest that groundwater emergence from an aquifer that extended from the Arabia Terra cratered highlands to the northern lowlands took place non-catastrophically and regionally within the study region through faulted upper crustal materials. In our model the margin of the Utopia basin adjacent to the study region may have acted as a boundary to this aquifer. Partial destruction and dehydration of these Late Hesperian plains, perhaps induced by high thermal anomalies resulting from the low thermal conductivity of these materials, led to the formation of extensive knobby fields and pedestal craters. During the Early Amazonian, the rates of regional resurfacing within the study region decreased significantly; perhaps because the knobby ridges forming the eroded impact crater rims and contractional ridges consisted of thermally conductive indurated materials, thereby inducing freezing of the tectonically controlled waterways associated with these features. This hypothesis would explain why these features were not completely destroyed. During the Late Amazonian, high-obliquity conditions may have led to the removal of large volumes of volatiles and sediments being eroded from Planum Boreum, which then may have been re-deposited as thick, circum-polar plains. Transition into low obliquity ∼5 myr ago may have led to progressive destabilization of these materials leading to collapse and pedestal crater formation. Our model does not contraindicate possible large-scale ponding of fluids in the northern lowlands, such as for example the formation of water and/or mud oceans. In fact, it provides a complementary mechanism involving large-scale groundwater discharges within the northern lowlands for the emplacement of fluids and sediments, which could have potentially contributed to the formation of these bodies. Nevertheless, our model would spatially restrict to surrounding parts of the northern plain either the distribution of the oceans or the zones within these where significant sedimentary accumulation would have taken place. 相似文献
7.
Paul D. Komar 《Icarus》1979,37(1):156-181
Comparisons are undertaken between the hydraulics of channelized water flows on Mars, large terrestrial rivers, deep-sea turbidity currents, and the catastrophic flow of Lake Missoula floods. Expected bottom shear stresses, velocities and discharges, flow powers, and other parameters are computed for each. Sand transport rates and the times required for channel erosion are estimated for Mangala Channel. These calculations indicate that the turbidity currents and Lake Missoula floods were similar to channelized water flow on Mars in their flow characteristics and in their abilities to erode and transport sediments. Like the Lake Missoula floods, deep-sea turbidity currents are catastrophic in character, being formed by the slumping of large masses of sediment trapped in submarine canyons or deposited on the continental slope. The repeated flows originating from submarine canyons have formed deep-sea channels similar in scale and overall morphology to the Martian outflow channels. The submarine canyon can be viewed as the counterpart of the chaotic terrain or crater which serves as sources for many Martian channels. Like most Martian outflow channels, the deep-sea channels generally lack tributaries or have only minor tributaries, instead consisting of a single pronounced channel extending for several hundred kilometers from its origin at the submarine canyon to deep abyssal depths. The channels vary considerably in dimensions, but most commonly have widths in the range 2 to 15 km with reliefs of 50 to 450 meters, again similar in scale to the Martian channels. Other similarities include sections of anastomosing channels, a general lack of pronounced meandering, and a lack of an apparent “delta” where the transported sediments are deposited. The similarities of channel morphology and flow hydraulics indicate the deep-sea channels and turbidity currents can be useful in furthering our understanding of the Martian outflow channels. Physical processes in the deep-sea occur under a reduced effective gravity because of the overlying water with its buoyancy. The deep-sea channels provide another set of Earth-based channels which can be studied to determine the effects of gravity on such factors as channel meandering and anastomosing characteristics. 相似文献
8.
A number of martian outflow channels were carved by discharges from large dilational fault zones. These channels were sourced by groundwater, not surface water, and when observed on high-standing plateaus they provide indicators of elevated paleo-groundwater levels. We identify three outflow channels of Hesperian age that issued from a 750-km-long fault zone extending from Candor Chasma to Ganges Chasma. Two of these channels, Allegheny Vallis and Walla Walla Vallis, have sources >2500 m above the topographic datum, too high to be explained by discharge from a global aquifer that was recharged solely in the south polar region. The indicated groundwater levels likely required regional sources of recharge at low latitudes. The floodwaters that erupted from Ophir Cavus to form Allegheny Vallis encountered two ridges that restricted the flow, forming temporary lakes. The flow probably breached or overtopped these obstructions quickly, catastrophically draining the lakes and carving several scablands. After the last obstacle had been breached, a single main channel formed that captured all subsequent flow. We performed hydrologic analyses of this intermediate phase of the flooding, prior to incision of the channel to its present depth. Using floodwater depths of 30-60 m, we calculated flow velocities of 6-15 m s−1 and discharges in the range of . Locally higher flow velocities and discharges likely occurred when the transient lakes were drained. Variable erosion at the channel and scabland crossing of MOLA pass 10644 suggests that the upper 25-30 m may consist of poorly consolidated surface materials underlain by more cohesive bedrock. We infer that an ice-covered lake with a surface elevation >2500 m probably existed in eastern Candor Chasma because this canyon is intersected by the Ophir Catenae fault system from which Allegheny Vallis and Walla Walla Vallis originated. We introduce a new hydrology concept for Mars in which the groundwater system was augmented by recharge from canyon lakes that were formed when water was released by catastrophic melting of former ice sheets in Tharsis by effusions of flood basalts. This model could help to reconcile the expected presence of a thick cryosphere during the Hesperian with the abundant evidence for groundwater as a source for some of the circum-Chryse outflow channels. 相似文献
9.
O. V. Antyufeyev V. M. Shulga I. I. Zinchenko 《Kinematics and Physics of Celestial Bodies》2016,32(6):276-282
The high-mass star-forming region IRAS 17333-3606 has been mapped in the 13CO (J = 2–1) and C18O (J = 2–1) lines in the submillimeter wavelength range using the APEX (Chile) radio telescope. The analysis of the low-velocity part of the molecular outflow has been carried out, and the main parameters of the outflow have been determined. We have used a novel approach for calculating parameters of the low-velocity part of bipolar molecular outflows in molecular clouds. The approach excludes the influence of the surrounding cloud on the parameters of the outflow. The mass of the low-velocity part is much greater than that of the high-velocity part of the molecular outflow, while their energies are comparable. The core of the young stellar object is significantly deformed by the impact of the bipolar outflow. 相似文献
10.
Alberto G. Fairén James M. Dohm Miguel A. de Pablo Javier Ruiz Robert C. Anderson 《Icarus》2003,165(1):53-67
Throughout the recorded history of Mars, liquid water has distinctly shaped its landscape, including the prominent circum-Chryse and the northwestern slope valleys outflow channel systems, and the extremely flat northern plains topography at the distal reaches of these outflow channel systems. Paleotopographic reconstructions of the Tharsis magmatic complex reveal the existence of an Europe-sized Noachian drainage basin and subsequent aquifer system in eastern Tharsis. This basin is proposed to have sourced outburst floodwaters that sculpted the outflow channels, and ponded to form various hypothesized oceans, seas, and lakes episodically through time. These floodwaters decreased in volume with time due to inadequate groundwater recharge of the Tharsis aquifer system. Martian topography, as observed from the Mars Orbiter Laser Altimeter, corresponds well to these ancient flood inundations, including the approximated shorelines that have been proposed for the northern plains. Stratigraphy, geomorphology, and topography record at least one great Noachian-Early Hesperian northern plains ocean, a Late Hesperian sea inset within the margin of the high water marks of the previous ocean, and a number of widely distributed minor lakes that may represent a reduced Late Hesperian sea, or ponded waters in the deepest reaches of the northern plains related to minor Tharsis- and Elysium-induced Amazonian flooding. 相似文献
11.
L. I. Matveyenko V. A. Demichev A. V. Ipatov A. E. Melnikov I. F. Surkis 《Astronomy Letters》2012,38(12):764-770
Polarization measurements of the H2O maser emission from the active region in Orion KL were carried out at epoch 2011?C2012 on the Svetloe-Zelenchukskaya radio interferometer. The bipolar outflow structure and polarized emission parameters have been determined. The emission from the components at v = 7.6 and 7.0 km s?1 dominates in the line profile; the relative contribution of the former component has increased. The velocity of the bipolar outflow ejector region is almost equal to that of the local standard of rest v LSR = 7.65 km s?1, while the velocity of the remote component is v = 7.0 km s?1. The emission from the bipolar outflow is observed at a distance up to 11 mas from the ejector. Its diameter does not exceed 0.3 mas. The outflow orientation in the plane of the sky is ?37°. The outflow velocity components along the line of sight differ by ??v = 0.3 km s?1. The polarization levels of the bipolar outflow and the remote component reach m = 62 and 39%, respectively. 相似文献
12.
Nigel R. Minchin Derek Ward-Thompson Glenn J. White 《Astrophysics and Space Science》1995,224(1-2):203-209
Comparison of submillimetre continuum observations of the L1204/S140 complex with previous high resolution CS, NH3 and CI observations provides evidence that, for the first time, demonstrates the PDR and outflow are intimately linked. The only scenario that is able to explain all of the available molecular and atomic emission line data and our submillimetre continuum data, is one in which the outflow has expanded towards the edge of the molecular cloud and the edge of the blueshifted outflow lobe is now bounded by the expanding HII region. The NH3 and continuum emission emanate from the inner edge of the outflow lobe, shielded from the external UV field. 相似文献
13.
W. H. McCutcheon G. Sandell H. E. Matthews T. B. H. Kuiper E. C. Sutton W. C. Danchi T. Sato 《Monthly notices of the Royal Astronomical Society》2000,316(1):152-164
The northern section of the molecular cloud complex NGC 6334 has been mapped in the CO and CS spectral line emission and in continuum emission at a wavelength of 1300 μm. Our observations highlight the two dominant sources, I and I(N), and a host of weaker sources. NGC 6334 I is associated with a cometary ultracompact H ii region and a hot, compact core ≤10 arcsec in size. Mid-infrared and CH3 OH observations indicate that it is also associated with at least two protostellar sources, each of which may drive a molecular outflow. For region I we confirm the extreme high-velocity outflow first discovered by Bachiller & Cernicharo and find that it is very energetic with a mechanical luminosity of 390 L⊙ . A dynamical age for the outflow is ∼3000 yr. We also find a weaker outflow originating from the vicinity of NGC 6334 I. In CO and CS this outflow is quite prominent to the north-west, but much less so on the eastern side of I, where there is very little molecular gas. Spectral survey data show a molecular environment at position I which is rich in methanol, methyl formate and dimethyl ether, with lines ranging in energy up to 900 K above the ground state. NGC 6334 I(N) is more dense than I, but cooler, and has none of the high-excitation lines observed toward I. I(N) also has an associated outflow, but it is less energetic than the outflow from I. The fully sampled continuum map shows a network of filaments, voids and cores, many of which are likely to be sites of star formation. A striking feature is a narrow, linear ridge which defines the western boundary. It is unclear if there is a connection between this filament and the many potential sites of star formation, or if the filament existed prior to the star formation activity. 相似文献
14.
P. S. Teixeira C. McCoey M. Fich C. J. Lada 《Monthly notices of the Royal Astronomical Society》2008,384(1):71-76
We present new infrared imaging of the NGC 2264 G protostellar outflow region, obtained with the InfraRed Array Camera (IRAC) onboard the Spitzer Space Telescope . A jet in the red outflow lobe (eastern lobe) is clearly detected in all four IRAC bands and, for the first time, is shown to continuously extend over the entire length of the red outflow lobe traced by CO observations. The redshifted jet also extends to a deeply embedded Class 0 source, Very Large Array (VLA) 2, confirming previous suggestions that it is the driving source of the outflow ( Gómez et al. 1994 ). The images show that the easternmost part of the redshifted jet exhibits what appear to be multiple changes of direction. To understand the redshifted jet morphology, we explore several mechanisms that could generate such apparent changes of direction. From this analysis, we conclude that the redshifted jet structure and morphology visible in the IRAC images can be largely, although not entirely, explained by a slowly precessing jet (period ≈8000 yr) that lies mostly on the plane of the sky. It appears that the observed changes in the redshifted jet direction may be sufficient to account for a significant fraction of the broadening of the outflow lobe observed in the CO emission. 相似文献
15.
Lei Zhu Yue-Fang Wu Yue Wei Department of Astronomy Peking University Beijing 《中国天文和天体物理学报》2006,6(1)
We report on a study of the molecular cloud S64 with observations at millimeter wavelengths of multiple molecular lines of CO isotopes.A weak outflow is found,and its physical parameters are estimated.The departure of the core of S64 from the S64 HII region indicates that there are still other star formation activities in that region. 相似文献
16.
Kenneth L. Tanaka Corey M. Fortezzo Rosalyn K. Hayward J.Alexis P. Rodriguez James A. Skinner 《Planetary and Space Science》2011,59(11-12):1128-1142
We present a preliminary photogeologic map of the Scandia region of Mars with the objective of reconstructing its resurfacing history. The Scandia region includes the lower section of the regional lowland slope of Vastitas Borealis extending about 500–1800 km away from Alba Mons into the Scandia sub-basin below ?4800 m elevation. Twenty mapped geologic units express the diverse stratigraphy of the region. We particularly focus on the materials making up the Vastitas Borealis plains and its Scandia sub-region, where erosional processes have obscured stratigraphic relations and made the reconstruction of the resurfacing history particularly challenging. Geologic mapping implicates the deposition, erosion, and deformation/degradation of geologic units predominantly during Late Hesperian and Early Amazonian time (～3.6–3.3 Ga). During this time, Alba Mons was active, outflow channels were debouching sediments into the northern plains, and basal ice layers of the north polar plateau were accumulating. We identify zones of regional tectonic contraction and extension as well as gradation and mantling. Depressions and scarps within these zones indicate collapse and gradation of Scandia outcrops and surfaces at scales of meters to hundreds of meters. We find that Scandia Tholi display concentric ridges, rugged peaks, irregular depressions, and moats that suggest uplift and tilting of layered plains material by diapirs and extrusion, erosion, and deflation of viscous, sedimentary slurries as previously suggested. These appear to be long-lived features that both pre-date and post-date impact craters. Mesa-forming features may have similar origins and occur along the southern margin of the Scandia region, including near the Phoenix Mars Lander site. Distinctive lobate materials associated with local impact craters suggest impact-induced mobilization of surface materials. We suggest that the formation of the Scandia region features potentially resulted from crustal heating related to Alba Mons volcanism, which acted upon a sequence of lavas, outflow channel sediments, and polar ice deposits centered within the Scandia region. These volatile-enriched sediments may have been in a state of partial volatile melt, resulting in the mobilization of deeply buried ancient materials and their ascent and emergence as sediment and mud breccia diapirs to form tholi features. Similar subsurface instabilities proximal to Alba Mons may have led to surface disruption, as suggested by local and regional scarps, mesas, moats, and knob fields. 相似文献
17.
We report the discovery of the inner edge of the high velocity CO outflow associated with the bipolar jet originating from IRS 1 in Barnard 5 and the first ever resolution of its circumstellar disk in the 2.6 mm dust continuum and C18O. From high spatial resolution observations made with the Owens Valley Millimeter Array we are able to locate the origin of the outflow to within approximately 500 AU on either side of IRS 1 and apparently at the edge of, or possibly within, its circumstellar disk. The orientation of the continuum disk is perpendicular to the highly collimated jet outflow recently seen in optical emission at much farther distances. The disk has been detected in C18O giving a disk mass approximately 0.16 M (solar). Our HCO+ and HCN maps indicate significant chemical differentiation in the circumstellar region on small scales with HCO+ tracing an extended disk of material. The 12CO interferometer maps of the outflow show two conelike features originating at IRS 1, the blue one fanning open to the northeast and the red one to the southwest. The vertices of the cones are on either side of the circumstellar disk and have a projected opening angle of about 90 degrees. The intrinsic opening angle is in the range of 60 degrees-90 degrees which leads to significant interaction between outflow and infall. 相似文献
18.
The problem of effective transform of Poynting flux energy into the kinetic energy of relativistic plasma outflow in a magnetosphere
is considered. In this article we present an example of such acceleration. In order to perform it, we use the approach of
ideal axisymmetric magnetohydrodynamics (MHD). For highly magnetized plasma outflow we show that a linear growth of Lorentz
factor with a cylindrical distance from the rotational axis is a general result for any field configuration in the sub-magnetosonic
flow. In the far region the full magnetohydrodynamics problem for one-dimensional flow is considered. It turns out that the
effective plasma outflow acceleration is possible in the paraboloidal magnetic field. It is shown that such an acceleration
is due to the drift of charged particles in the crossed electric and magnetic field. The clear explanation of the absence
of acceleration in the monopole magnetic field if given.
相似文献
19.
Pulses of CO2 injected into the martian atmosphere more recently than 4 Ga can place the atmosphere into a stable, higher pressure, warmer greenhouse state. One to two bar pulses of CO2 added to the atmosphere during the past several billion years are sufficient to raise global mean temperatures above 240 or 250 K for tens to hundreds of millions of years, even when accounting for CO2 condensation. Over time, the added CO2 is lost to carbonates, the atmosphere collapses and returns to its buffered state. A substantial amount of water could be transported during the greenhouse periods from the surface of a frozen body of water created by outflow channel discharges to higher elevations, despite global temperatures well below freezing. This water, precipitated as snow, could ultimately form fluvial valleys if deposition sites are associated with localized heat sources, such as magmatic intrusions or volcanoes. Thus, if outflow channel discharges were accompanied by the release of sufficient quantities of CO2, a limited hydrological cycle could have resulted that would have been capable of producing geomorphic change sufficient for fluvial erosion and valley formation. Glacial or periglacial landforms would also be a consequence of such a mechanism. 相似文献
20.
S. Arribas E. Mediavilla B. Garcia-Lorenzo C. Del Burgo 《Astrophysics and Space Science》1997,248(1-2):159-166
From 2-D spectroscopy of the [O III] λλ 4959,5007 and [S III] λ 9069 lines we have studied the ionized gas-velocity field in the central regions of NGC 1068. The existence of a strong bipolar outflow of ionized gas is confirmed. The origin of this outflow, which is probably related to the active nucleus, is about 1.4″ NE of the optical nucleus; therefore, this region is a candidate to host the hidden nucleus of NGC 1068. 相似文献