* Astronomy

Title: An experimental study of the formation of an ice crust and migration of water vapour in a comet's upper layers
Authors: Pat-E, I.; Laufer, D.; Notesco, G.; Bar-Nun, A.

From recent close encounters with Comets Wild-2 and Tempel 1 we learned that their surfaces are very rugged and no simple uniform layers model can be applied to them. Rather, a glaciological approach should be applied for describing their surface features and behaviour. Such intrinsically rugged surface is formed in our large scale experiments, where an agglomerate of ~200 m gas-laden amorphous ice particles is accumulated to form a 20 cm diameter and few cm high ice sample. The density, tensile strength and thermal inertia of our ice sample were found to be very close to those found by Deep Impact for Comet Tempel 1: density 250 - 300 kg m^-3 vs DI 350 - 400 kg m^-3; tensile strength 2 - 4 kPa vs DI 1 - 10 kPa; thermal inertia 80 W K^-1 m^-2 s^½ vs <100 W K^-1 m^-2 s^½ and <50 W K^-1 m^-2 s^½. From the close agreement between the thermal inertias measured in our ice sample, which had no dust coverage and that of Comet Tempel 1, we deduce that the low thermal inertia is an intrinsic property of the fluffy structure of the ice as a result of its low density, with an addition by the broken terrain and not due to the formation of a dust layer. Upon warming up of the ice, water vapour migrates both outward into the coma and inward. Reaching cooler layers, the water vapour condenses, forming a denser ice crust, as we show experimentally. We also demonstrate the inward and outward flow of water vapour in the outer ice layers through the exchange between layers of D2O ice and H2O ice, to form HDO.

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Comets have always fascinated us. A mysterious appearance could mean a sure failure in battle, at least for one side. Now Tel Aviv University justifies our fascination - comets might have provided the elements for the emergence of life on our planet.
While investigating the chemical make-up of comets, Prof. Akiva Bar-Nun of the Department of Geophysics and Planetary Sciences at Tel Aviv University found they were the source of missing ingredients needed for life in Earth's ancient primordial soup.

"When comets slammed into the Earth through the atmosphere about four billion years ago, they delivered a payload of organic materials to the young Earth, adding materials that combined with Earth's own large reservoir of organics and led to the emergence of life" - Prof. Bar-Nun.

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Visiting aliens may be the stuff of legend, but if a scientific team working at the National Institute of Standards and Technology (NIST) is right, we may be able to find extraterrestrial life even before it leaves its home planet - by looking for left- (or right-) handed light.
The technique the team has developed for detecting life elsewhere in the universe will not spot aliens directly. Rather, it could allow spaceborne instruments to see a telltale sign that life may have influenced a landscape: a preponderance of molecules that have a certain "chirality," or handedness. A right-handed molecule has the same composition as its left-handed cousin, but their chemical behaviour differs. Because many substances critical to life favour a particular handedness, Thom Germer and his colleagues think chirality might reveal life's presence at great distances, and have built a device to detect it.

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The newly detected presence of two complex organic molecules in the Milky Way
Located close the center of the galaxy, the molecular cloud Sagittarius B2 is something akin to a galactic watering hole. A popular hangout for biologists and chemists looking for the building blocks of life in space, it contains a rich stew of materials in the process of being recycled into stars and planets.
suggests the building blocks for life may exist in space even before the formation of planets.

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Over the last four years, a team of researchers carefully analysed samples of meteorites with an abundance of carbon, called carbonaceous chondrites. They looked for the amino acid isovaline and discovered that three types of carbonaceous meteorites had more of the left-handed version than the right-handed variety - as much as a record 18 percent more in the often-studied Murchison meteorite.

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