121 research outputs found
Fast outflow of neutral and ionized gas from the radio galaxy 3C 293
We detect a fast outflow of neutral and ionized gas with velocities up to
about 1000 km/s from the central region of radio galaxy 3C 293. With optical
spectroscopy we locate the bulk of the ionized gas outflow at the position of a
bright radio hot-spot in the inner radio jet, about 1 kpc east of the nucleus.
Given the presence of large amounts of cold gas and the distorted morphology of
the radio jet in this region, we argue that the ISM is pushed out by a severe
interaction with the radio plasma. The similarity of the outflow of HI with the
ionized gas outflow that we see at the position of the radio hot-spot suggests
that despite the high energies involved in the jet-ISM interaction, part of the
gas stays, or becomes again, neutral. In this paper we also present the
detection of HI emission in three nearby companions of 3C 293.Comment: 8 pages, 4 figures. Proceedings of the "Extra-planar Gas" conference,
Dwingeloo, the Netherlands, June 7-11, 2004. To appear in ASP Conference
Series, ed. R. Brau
Remote Sensing of Chiral Signatures on Mars
We describe circular polarization as a remote sensing diagnostic of chiral
signatures which may be applied to Mars. The remarkable phenomenon of
homochirality provides a unique biosignature which can be amenable to remote
sensing through circular polarization spectroscopy. The natural tendency of
microbes to congregate in close knit communities would be beneficial for such a
survey. Observations of selected areas of the Mars surface could reveal chiral
signatures and hence explore the possibility of extant or preserved biological
material. We describe a new instrumental technique that may enable observations
of this form.Comment: 14 pages, 3 figures; to be published in Planetary and Space Scienc
In situ detection of boron by ChemCam on Mars
We report the first in situ detection of boron on Mars. Boron has been detected in Gale crater at levels Curiosity rover ChemCam instrument in calcium-sulfate-filled fractures, which formed in a late-stage groundwater circulating mainly in phyllosilicate-rich bedrock interpreted as lacustrine in origin. We consider two main groundwater-driven hypotheses to explain the presence of boron in the veins: leaching of borates out of bedrock or the redistribution of borate by dissolution of borate-bearing evaporite deposits. Our results suggest that an evaporation mechanism is most likely, implying that Gale groundwaters were mildly alkaline. On Earth, boron may be a necessary component for the origin of life; on Mars, its presence suggests that subsurface groundwater conditions could have supported prebiotic chemical reactions if organics were also present and provides additional support for the past habitability of Gale crater
Stability of liquid saline water on present day Mars
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94901/1/grl26441.pd
Dwarf galaxy populations in present-day galaxy clusters: I. Abundances and red fractions
We compare the galaxy population in the Virgo, Fornax, Coma and Perseus
cluster to a state-of-the-art semi-analytic model, focusing on the regime of
dwarf galaxies with luminosities from approximately 10^8 L_sun to 10^9 L_sun.
We find that the number density profiles of dwarfs in observed clusters are
reproduced reasonably well, and that the red fractions of model clusters
provide a good match to Coma and Perseus. On the other hand, the red fraction
among dwarf galaxies in Virgo is clearly lower than in model clusters. We argue
that this is mainly caused by the treatment of environmental effects in the
model. This explanation is supported by our finding that the colours of central
("field") dwarf galaxies are reproduced well, in contrast to previous claims.
Finally, we find that the dwarf-to-giant ratio in model clusters is too high.
This may indicate that the current model prescription for tidal disruption of
faint galaxies is still not efficient enough.Comment: 20 pages, 10 figures. Accepted by MNRAS. Includes the modifications
after referee report. Main results unchanged, interpretation slightly change
Seasonal melting and the formation of sedimentary rocks on Mars, with predictions for the Gale Crater mound
A model for the formation and distribution of sedimentary rocks on Mars is
proposed. The rate-limiting step is supply of liquid water from seasonal
melting of snow or ice. The model is run for a O(10^2) mbar pure CO2
atmosphere, dusty snow, and solar luminosity reduced by 23%. For these
conditions snow only melts near the equator, and only when obliquity >40
degrees, eccentricity >0.12, and perihelion occurs near equinox. These
requirements for melting are satisfied by 0.01-20% of the probability
distribution of Mars' past spin-orbit parameters. Total melt production is
sufficient to account for aqueous alteration of the sedimentary rocks. The
pattern of seasonal snowmelt is integrated over all spin-orbit parameters and
compared to the observed distribution of sedimentary rocks. The global
distribution of snowmelt has maxima in Valles Marineris, Meridiani Planum and
Gale Crater. These correspond to maxima in the sedimentary-rock distribution.
Higher pressures and especially higher temperatures lead to melting over a
broader range of spin-orbit parameters. The pattern of sedimentary rocks on
Mars is most consistent with a Mars paleoclimate that only rarely produced
enough meltwater to precipitate aqueous cements and indurate sediment. The
results suggest intermittency of snowmelt and long globally-dry intervals,
unfavorable for past life on Mars. This model makes testable predictions for
the Mars Science Laboratory rover at Gale Crater. Gale Crater is predicted to
be a hemispheric maximum for snowmelt on Mars.Comment: Submitted to Icarus. Minor changes from submitted versio
Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars
Hellas basin acts as a major sink for the southern highlands of Mars and is likely to have recorded several episodes of sedimentation and erosion. The north-western part of the basin displays a potentially unique Amazonian landscape domain in the deepest part of Hellas, called “banded terrain”, which is a deposit characterized by an alternation of narrow band shapes and inter-bands displaying a sinuous and relatively smooth surface texture suggesting a viscous flow origin. Here we use high-resolution (HiRISE and CTX) images to assess the geomorphological interaction of the banded terrain with the surrounding geomorphologic domains in the NW interior of Hellas to gain a better understanding of the geological evolution of the region as a whole. Our analysis reveals that the banded terrain is associated with six geomorphologic domains: a central plateau named Alpheus Colles, plain deposits (P1 and P2), reticulate (RT1 and RT2) and honeycomb terrains. Based on the analysis of the geomorphology of these domains and their cross-cutting relationships, we show that no widespread deposition post-dates the formation of the banded terrain, which implies that this domain is the youngest and latest deposit of the interior of Hellas. Therefore, the level of geologic activity in the NW Hellas during the Amazonian appears to have been relatively low and restricted to modification of the landscape through mechanical weathering, aeolian and periglacial processes. Thermophysical data and cross-cutting relationships support hypotheses of modification of the honeycomb terrain via vertical rise of diapirs such as ice diapirism, and the formation of the plain deposits through deposition and remobilization of an ice-rich mantle deposit. Finally, the observed gradual transition between honeycomb and banded terrain suggests that the banded terrain may have covered a larger area of the NW interior of Hellas in the past than previously thought. This has implications on the understanding of the evolution of the deepest part of Hellas
Ancient hydrothermal seafloor deposits in Eridania basin on Mars
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