6,853 research outputs found
Localized precipitation and runoff on Mars
We use the Mars Regional Atmospheric Modeling System (MRAMS) to simulate lake
storms on Mars, finding that intense localized precipitation will occur for
lake size >=10^3 km^2. Mars has a low-density atmosphere, so deep convection
can be triggered by small amounts of latent heat release. In our reference
simulation, the buoyant plume lifts vapor above condensation level, forming a
20km-high optically-thick cloud. Ice grains grow to 200 microns radius and fall
near (or in) the lake at mean rates up to 1.5 mm/hr water equivalent (maximum
rates up to 6 mm/hr water equivalent). Because atmospheric temperatures outside
the surface layer are always well below 273K, supersaturation and condensation
begin at low altitudes above lakes on Mars. In contrast to Earth lake-effect
storms, lake storms on Mars involve continuous precipitation, and their
vertical velocities and plume heights exceed those of tropical thunderstorms on
Earth. Convection does not reach above the planetary boundary layer for lakes
O(10^2) mbar. Instead, vapor is
advected downwind with little cloud formation. Precipitation occurs as snow,
and the daytime radiative forcing at the land surface due to plume vapor and
storm clouds is too small to melt snow directly (<+10 W/m^2). However, if
orbital conditions are favorable, then the snow may be seasonally unstable to
melting and produce runoff to form channels. We calculate the probability of
melting by running thermal models over all possible orbital conditions and
weighting their outcomes by probabilities given by Laskar et al., 2004. We
determine that for an equatorial vapor source, sunlight 15% fainter than at
present, and snowpack with albedo 0.28 (0.35), melting may occur with 4%(0.1%)
probability. This rises to 56%(12%) if the ancient greenhouse effect was
modestly (6K) greater than today.Comment: Submitted to JGR Planet
USSR Space Life Sciences Digest, issue 21
This is the twenty-first issue of NASA's USSR Space Life Sciences Digest. It contains abstracts of 37 papers published in Russian language periodicals or books or presented at conferences and of a Soviet monograph on animal ontogeny in weightlessness. Selected abstracts are illustrated with figures and tables from the original. A book review of a work on adaptation to stress is also included. The abstracts in this issue have been identified as relevant to 25 areas of space biology and medicine. These areas are: adaptation, biological rhythms, body fluids, botany, cardiovascular and respiratory systems, cytology, developmental biology, endocrinology, enzymology, equipment and instrumentation, exobiology, gravitational biology, habitability and environmental effects, hematology, human performance, life support systems, mathematical modeling, metabolism, microbiology, musculoskeletal system, neurophysiology, operational medicine, perception, psychology, and reproductive system
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
Impact of Space Weather on Climate and Habitability of Terrestrial Type Exoplanets
The current progress in the detection of terrestrial type exoplanets has
opened a new avenue in the characterization of exoplanetary atmospheres and in
the search for biosignatures of life with the upcoming ground-based and space
missions. To specify the conditions favorable for the origin, development and
sustainment of life as we know it in other worlds, we need to understand the
nature of astrospheric, atmospheric and surface environments of exoplanets in
habitable zones around G-K-M dwarfs including our young Sun. Global environment
is formed by propagated disturbances from the planet-hosting stars in the form
of stellar flares, coronal mass ejections, energetic particles, and winds
collectively known as astrospheric space weather. Its characterization will
help in understanding how an exoplanetary ecosystem interacts with its host
star, as well as in the specification of the physical, chemical and biochemical
conditions that can create favorable and/or detrimental conditions for
planetary climate and habitability along with evolution of planetary internal
dynamics over geological timescales. A key linkage of (astro) physical,
chemical, and geological processes can only be understood in the framework of
interdisciplinary studies with the incorporation of progress in heliophysics,
astrophysics, planetary and Earth sciences. The assessment of the impacts of
host stars on the climate and habitability of terrestrial (exo)planets will
significantly expand the current definition of the habitable zone to the
biogenic zone and provide new observational strategies for searching for
signatures of life. The major goal of this paper is to describe and discuss the
current status and recent progress in this interdisciplinary field and to
provide a new roadmap for the future development of the emerging field of
exoplanetary science and astrobiology.Comment: 206 pages, 24 figures, 1 table; Review paper. International Journal
of Astrobiology (2019
Arctic underwater noise transients from sea ice deformation: characteristics, annual time series, and forcing in Beaufort Sea
International audienceA 13-month time series of Arctic Ocean noise from the marginal ice zone of Eastern Beaufort Sea is analyzed to detect under-ice acoustic transients isolated from ambient noise with a dedicated algorithm. Noise transients due to ice cracking, fracturing, shearing, and ridging are sorted out into 3 categories: broadband impulses, frequency modulated (FM) tones, and high-frequency broadband noise. Their temporal and acoustic characteristics over the 8-month ice covered period, from November 2005 to mid-June 2006, are presented and their generation mechanisms are discussed. Correlations analyses showed that the occurrence of these ice transients responded to large-scale ice motion and deformation rates forced by meteorological events, often leading to opening of large-scale leads at main discontinuities in the ice cover. Such a sequence, resulting in the opening of a large lead, hundreds by tens km in size, along the margin of landfast ice and multiyear ice plume in Beaufort-Chukchi seas is detailed. These ice transients largely contribute to the soundscape properties of the Arctic Ocean, for both its ambient and total noise components. Some FM tonal transients can be confounded with marine mammal songs, especially when they are repeated, with periods similar to wind generated waves
On the habitability of Mars: An approach to planetary ecosynthesis
The possibility of utilizing Mars as a habitat for terrestrial life, including man, is examined. Available data, assumptions, and speculations on the climate, physical state, and chemical inventory of Mars are reviewed and compared with the known requirements and environmental limits of terrestrial life. No fundamental, insuperable limitation of the ability of Mars to support a terrestrial ecology is identified. The lack of an oxygen-containing atmosphere would prevent the unaided habitation of Mars by man. The present strong ultraviolet surface irradiation is an additional major barrier. The creation of an adequate oxygen and ozone-containing atmosphere on Mars may be feasible through the use of photosynthetic organisms. The time needed to generate such an atmosphere, however, might be several millions of years. This period might be drastically reduced by the synthesis of novel, Mars-adapted, oxygen producing photosynthetic strains by techniques of genetic engineering, and modifying the present Martian climate by melting of the Martian polar caps and concomitant advective and greenhouse heating effects
Combined Airborne Wind and Photovoltaic Energy System for Martian Habitats
Generating renewable energy on Mars is technologically challenging. Firstly, because, compared to Earth, key energy resources such as solar and wind are weak as a result of very low atmospheric pressure and low solar irradiation. Secondly, because of the harsh environmental conditions, the required high degree of automation, and the exceptional effort and cost involved in transporting material to the planet. Like on Earth, it is crucial to combine complementary resources for an effective renewable energy solution. In this work, we present the results of a design synthesis exercise, a 10 kW microgrid solution, based on a pumping kite power system and photovoltaic solar modules to power the construction and subsequent use of a Mars habitat. To buffer unavoidable energy fluctuations and balance seasonal and diurnal resource variations, the two energy systems are combined with a compressed gas storage system and lithium-sulphur batteries. The airborne wind energy solution was selected because of its low weight-to-wing-surface-area ratio, compact packing volume, and high capacity factor which enables it to endure strong dust storms in an airborne parking mode. The surface area of the membrane wing is 50 m2 and the mass of the entire system, including the kite control unit and ground station, is 290 kg. The performance of the microgrid was assessed by computational simulation using available resource data for a chosen deployment location on Mars. The projected costs of the system are €8.95 million, excluding transportation to Mars
Research Opportunities in Nutrition and Metabolism in Space
The objectives of the Life Sciences Research Office (LSRO) study on nutrient requirements for meeting metabolic needs in manned space flights are as follows: review extant knowledge on the subject; identify significant gaps in knowledge; formulate suggestions for possible research; and produce a documented report of the foregoing items that can be used for program planning. In accordance with NASA's request for this study, the report focuses on issues of nutrition and metabolism that relate primarily to the contemplated United States Space Station, secondarily to the Shuttle Program as an orbital test bed for operational studies, and incidentally to scenarios for future long-term space flights. Members of the LSRO ad hoc Working Group on Nutrition and Metabolism were provided with pertinent articles and summaries on the subject. At the meeting of the Working Group, presentations were made by NASA Headquarters program staff on past experiences relative to space-flight nutrition and metabolism, as well as scenarios for future flights. The discussions of the ad hoc Working Group focused on the following: (1) metabolic needs related to work and exercise; (2) nutrients required to meet such needs; (3) food types, management, and records; and (4) nutritional amelioration or prevention of space-related physiological and behavioral changes
The detection of climate change due to the enhanced greenhouse effect
The greenhouse effect is accepted as an undisputed fact from both theoretical and observational considerations. In Earth's atmosphere, the primary greenhouse gas is water vapor. The specific concern today is that increasing concentrations of anthropogenically introduced greenhouse gases will, sooner or later, irreversibly alter the climate of Earth. Detecting climate change has been complicated by uncertainties in historical observations and measurements. Thus, the primary concern for the GEDEX project is how can climate change and enhanced greenhouse effects be unambiguously detected and quantified. Specifically examined are the areas of: Earth surface temperature; the free atmosphere (850 millibars and above); space-based measurements; measurement uncertainties; and modeling the observed temperature record
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