Evidence for recent groundwater seepage and surface runoff on Mars.
(17/365)
Relatively young landforms on Mars, seen in high-resolution images acquired by the Mars Global Surveyor Mars Orbiter Camera since March 1999, suggest the presence of sources of liquid water at shallow depths beneath the martian surface. Found at middle and high martian latitudes (particularly in the southern hemisphere), gullies within the walls of a very small number of impact craters, south polar pits, and two of the larger martian valleys display geomorphic features that can be explained by processes associated with groundwater seepage and surface runoff. The relative youth of the landforms is indicated by the superposition of the gullies on otherwise geologically young surfaces and by the absence of superimposed landforms or cross-cutting features, including impact craters, small polygons, and eolian dunes. The limited size and geographic distribution of the features argue for constrained source reservoirs. (+info)
Folds on Europa: implications for crustal cycling and accommodation of extension.
(18/365)
Regional-scale undulations with associated small-scale secondary structures are inferred to be folds on Jupiter's moon Europa. Formation is consistent with stresses from tidal deformation, potentially triggering compressional instability of a region of locally high thermal gradient. Folds may compensate for extension elsewhere on Europa and then relax away over time. (+info)
Galileo magnetometer measurements: a stronger case for a subsurface ocean at Europa.
(19/365)
On 3 January 2000, the Galileo spacecraft passed close to Europa when it was located far south of Jupiter's magnetic equator in a region where the radial component of the magnetospheric magnetic field points inward toward Jupiter. This pass with a previously unexamined orientation of the external forcing field distinguished between an induced and a permanent magnetic dipole moment model of Europa's internal field. The Galileo magnetometer measured changes in the magnetic field predicted if a current-carrying outer shell, such as a planet-scale liquid ocean, is present beneath the icy surface. The evidence that Europa's field varies temporally strengthens the argument that a liquid ocean exists beneath the present-day surface. (+info)
Resistance of Bacillus endospores to extreme terrestrial and extraterrestrial environments.
(20/365)
Endospores of Bacillus spp., especially Bacillus subtilis, have served as experimental models for exploring the molecular mechanisms underlying the incredible longevity of spores and their resistance to environmental insults. In this review we summarize the molecular laboratory model of spore resistance mechanisms and attempt to use the model as a basis for exploration of the resistance of spores to environmental extremes both on Earth and during postulated interplanetary transfer through space as a result of natural impact processes. (+info)
Nonlinear simulations of Jupiter's 5-micron hot spots.
(21/365)
Large-scale nonlinear simulations of Jupiter's 5-micron hot spots produce long-lived coherent structures that cause subsidence in local regions, explaining the low cloudiness and the dryness measured by the Galileo probe inside a hot spot. Like observed hot spots, the simulated coherent structures are equatorially confined, have periodic spacing, propagate west relative to the flow, are generally confined to one hemisphere, and have an anticyclonic gyre on their equatorward side. The southern edge of the simulated hot spots develops vertical shear of up to 70 meters per second in the eastward wind, which can explain the results of the Galileo probe Doppler wind experiment. (+info)
Evidence that the reactivity of the martian soil is due to superoxide ions.
(22/365)
The Viking Landers were unable to detect evidence of life on Mars but, instead, found a chemically reactive soil capable of decomposing organic molecules. This reactivity was attributed to the presence of one or more as-yet-unidentified inorganic superoxides or peroxides in the martian soil. Using electron paramagnetic resonance spectroscopy, we show that superoxide radical ions (O2-) form directly on Mars-analog mineral surfaces exposed to ultraviolet radiation under a simulated martian atmosphere. These oxygen radicals can explain the reactive nature of the soil and the apparent absence of organic material at the martian surface. (+info)
Detection of daily clouds on Titan.
(23/365)
We have discovered frequent variations in the near-infrared spectrum of Titan, Saturn's largest moon, which are indicative of the daily presence of sparse clouds covering less than 1% of the area of the satellite. The thermodynamics of Titan's atmosphere and the clouds' altitudes suggest that convection governs their evolutions. Their short lives point to the presence of rain. We propose that Titan's atmosphere resembles Earth's, with clouds, rain, and an active weather cycle, driven by latent heat release from the primary condensible species. (+info)
Solar wind record on the moon: deciphering presolar from planetary nitrogen.
(24/365)
Ion microprobe analyses show that solar wind nitrogen associated with solar wind hydrogen implanted in the first tens of nanometers of lunar regolith grains is depleted in 15N by at least 24% relative to terrestrial atmosphere, whereas a nonsolar component associated with deuterium-rich hydrogen, detected in silicon-bearing coatings at the surface of some ilmenite grains, is enriched in 15N. Systematic enrichment of 15N in terrestrial planets and bulk meteorites relative to the protosolar gas cannot be explained by isotopic fractionation in nebular or planetary environments but requires the contribution of 15N-rich compounds to the total nitrogen in planetary materials. Most of these compounds are possibly of an interstellar origin and never equilibrated with the 15N-depleted protosolar nebula. (+info)