Publications (13) View all
-
Chapter: How Well Do Experimental Results on Large Samples of Gas-Laden Amorphous Ice Duplicate Deep Impact’s Findings?
[show abstract] [hide abstract]
ABSTRACT: The findings of Deep Impact on the structure and composition of Tempel-1 are compared with our experimental results on large (20cm diameter and up to 10cm high) samples of gas-laden amorphous ice which does not contain dust. The mechanical ∼tensile strength inferred for Tempel-1: up to 12kPa is close to our experimental findings of 2–4kPa. This means that Tempel-1 is as fluffy as our very fluffy, talcum like, ice sample. The thermal inertia: 30<I<100W K−1 m−2 s1/2 is close to our value of80. The density of 350±250kg m−3, is close to our value of 250–300kg m−3, taking into account an ice/silicate ratio of1 in the comet, while we study pure ice. Surface morphological features, such as non-circular depressions and chaotic terrain, were observed in our experiments. The only small increase in the gas/water vapor ratio pre- and post-impact, suggest that in the area excavated by the impactor, the 135K front did not penetrate deeper than a few meters. Altogether, the agreement between the findings of Deep Impact and our experimental results point to a loose agglomerate of ice grains (with a silicate-organic core), which was formed by a very gentle aggregation of the ice grains, without compaction.09/2008: pages 199-205; -
Article: An experimental study of the isotopic enrichment in Ar, Kr, and Xe when trapped in water ice.
[show abstract] [hide abstract]
ABSTRACT: The isotopic enrichment of argon, krypton, and xenon, when trapped in water ice, was studied experimentally. The isotopes were found to be enriched according to their (m1/m2)1/2 ratio. These enrichment factors could be useful for comparison among the uncertain cosmic or solar isotopic ratios, the hopeful in situ cometary ratio, and those in Earth's atmosphere, in the context of cometary delivery of volatiles to Earth.Icarus 12/1999; 142(1):298-300. · 3.38 Impact Factor -
Article: Gas release from comets.
[show abstract] [hide abstract]
ABSTRACT: Water ice was shown experimentally to retain trapped gases beyond the transformation temperature of amorphous ice to cubic ice. The amount of retained gases, which emerge during the transformation of cubic ice to hexagonal ice and when the ice evaporates, depends linearly on the thickness of the ice layer. Implications to comets are discussed.Icarus 02/1991; 89:411-3. · 3.38 Impact Factor -
Article: Structure and dynamics of amorphous water ice.
[show abstract] [hide abstract]
ABSTRACT: Further insight into the structure and dynamics of amorphous water ice, at low temperatures, was obtained by trapping in it Ar, Ne, H2, and D2. Ballistic water-vapor deposition results in the growth of smooth, approximately 1 x 0.2 micrometer2, ice needles. The amorphous ice seems to exist in at least two separate forms, at T < 85 K and at 85 < T < 136.8 K, and transform irreversibly from one form to the other through a series of temperature-dependent metastable states. The channels formed by the water hexagons in the ice are wide enough to allow the free penetration of H2 and D2 into the ice matrix even in the relatively compact cubic ice, resulting in H2-(D2-) to-ice ratios (by number) as high as 0.63. The larger Ar atoms can penetrate only into the wider channels of amorphous ice, and Ne is an intermediate case. Dynamic percolation behavior explains the emergence of Ar and Ne (but not H2 and D2) for the ice, upon warming, in small and big gas jets. The big jets, each containing approximately 5 x 10(10) atoms, break and propel the ice needles. Dynamic percolation also explains the collapse of the ice matrix under bombardment by Ar , at a pressure exceeding 2.6 dyn cm-2, and the burial of huge amounts of gas inside the collapsed matrix, up to an Ar-to-ice of 3.3 (by number). The experimental results could be relevant to comets, icy satellites, and icy grain mantles in dense interstellar clouds.Physical review. B, Condensed matter 12/1987; 36(17):9219-27. -
Article: Trapping of gases by water ice and implications for icy bodies.
[show abstract] [hide abstract]
ABSTRACT: The trapping of various gases by water ice at low temperatures (20-80K) and their release from the ice upon warming, was studied experimentally. The results of these experiments, together with a computation of the thermal evolution of a cometary nucleus, can explain the gas and dust jets which were observed to emanate from the nucleus of P/Halley. The experimental results are important also to the gas content of Titan.Advances in Space Research 02/1987; 7(5):45-7. · 1.18 Impact Factor
