Monthly Notices of the Royal Astronomical Society, 2017
One of the most surprising measurements of the Rosetta Orbiter Spectrometer for Ion and Neutral A... more One of the most surprising measurements of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument on the comet 67P/Churyumov-Gerasimenko was the detection of O 2 along with N 2 and noble gases which were measured for the first time in comets, along with the major constituents, water, CO, and CO 2. The O 2 high abundance of 1-10 per cent relative to H 2 O was calculated, with an average value of 3.80 ± 0.85 per cent (Bieler et al. 2015). The strong correlation of molecular oxygen abundance with water, suggests the formation of O 2 by radiolysis or photolysis of water molecules and the trapping of O 2 in the amorphous ice, together with the other gases while the comet was formed. In this study, we present new experimental results for trapping O 2 with N 2 and Ar in amorphous ice in order to understand the direct measurements of the Rosetta spacecraft. The discovery of O 2 in comets challenges our understanding of the composition of the volatiles in the outskirts of the young solar system and their delivery to the Earth's atmosphere.
Water vapor, when deposited as ice on a cold surface, in the presence of gases such as CO, can tr... more Water vapor, when deposited as ice on a cold surface, in the presence of gases such as CO, can trap considerable amounts of the gas, as a function of the gas properties and temperature of deposition. The amount of trapped gas drops exponentially when the temperature is raised (Bar-Nun and Kleinfeld, 1989). Thus, we have a cosmochemical thermometer to determine at which temperature the ice grains of a comet were formed. CO, the major gas (except H 2 O vapor) in cometary comea, could be a strong indicator of the formation temperature of the ice grains which agglomerated to form comets Halley, Hyakutake and Hale-Bopp. The CO/H 2 O ratios measured in the cometary comea (directly from the nucleus) are: 0.07 in Halley
Following the tracing of jets emanating from Comet Wild-2 to depressions in the ice by Brownlee e... more Following the tracing of jets emanating from Comet Wild-2 to depressions in the ice by Brownlee et al. [2004. The Stardust—A successful encounter with the remarkable Comet Wild 2. Lunar Planet. Sci. 35. Abstract 1981], we demonstrated experimentally the formation of depressions and chaotic terrain on comet analogs when gas is released from underlying ice pockets. We also demonstrated experimentally the ejection of ice grains into the experimental cometary “coma.”
The findings of Deep Impact on the structure and composition of Tempel-1 are compared with our ex... more The findings of Deep Impact on the structure and composition of Tempel-1 are compared with our experimental results on large (20 cm diameter and up to 10 cm high) samples of gas-laden amorphous ice. The mechanical ∼tensile strength inferred for Tempel-1: ∼65 Pa is 30 to 60 times smaller than our experimental findings of 2–4 kPa. This means that Tempel-1 is even fluffier than our very fluffy, talcum like, ice sample. The thermal inertia: I100 WK−1m−2s1/2 is very close to our value of 80. The density of 620+470/−330 kgm−3, is close to our value of 250–300 kg m−3, taking into account an ice/silicate ratio of 1 in the comet, while we study pure ice. Surface morphological features, such as non-circular depressions, chaotic terrain and smooth surfaces, 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 135 K 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.
The isotopic enrichment in argon, krypton, and xenon, when trapped in water ice, was studied expe... more The isotopic enrichment in argon, krypton, and xenon, when trapped in water ice, was studied experimentally. The isotopes were found to be enriched according to their (m 1 /m 2) 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.
It is demonstrated experimentally that the CO/H 2 O, CH 4 / the low density form in the temperatu... more It is demonstrated experimentally that the CO/H 2 O, CH 4 / the low density form in the temperature range of 38-80 K (Jenniskens H 2 O, and C 2 H 6 /H 2 O ratios found by Mumma et al. (1996) in et al. 1995) might also play a role in gas trapping in the water ice. These Comet Hyakutake could be obtained by the trapping of these factors determine the temperature dependent residence time of the gas gases in water ice which was formed at 64-66 K. The formation in the open channels and cracks in the forming water ice, until incoming of the ice particles which formed comets, either in the warm water molecules freeze and close these openings, thus trapping the gas inside the water ice. Another factor is the macroscopic porosity of the outskirts of the interstellar cloud or in the outer part of the water ice, which decreases as the temperature is raised. In trying to solar nebula, is discussed. C 3 H 8 is predicted to exist in comets compare the experimental results with the findings of Mumma et al.
Huygens' GCMS found ^36Ar and ^40Ar mixing ratios of 2.8x10^-7 and 4.3x10^-7 respectively, or... more Huygens' GCMS found ^36Ar and ^40Ar mixing ratios of 2.8x10^-7 and 4.3x10^-7 respectively, or 7x10^-3 and 3.6x10^-3 of their abundances in Earth's atmosphere. Our experiments on the UV photolysis of gas mixtures containing N [2]:CH[4]:C[2]H[2]:HCN=550:105:40:4 torr demonstrated the formation of long chain polymers with an elemental composition of C:H:N=1:1:0.007. These polymers aggregate to form aerosol particles which, during their formation
The UV photolysis of gas mixtures containing C 2 H 2 , C 2 H 4 and HCN, diluted in N 2 and CH 4 w... more The UV photolysis of gas mixtures containing C 2 H 2 , C 2 H 4 and HCN, diluted in N 2 and CH 4 was studied experimentally. At the onset of irradiation, a pale yellow aerosol appeared, similar to Titan's
Whenever large fluxes of gas are released from gas pockets below an ice layer, they shatter the o... more Whenever large fluxes of gas are released from gas pockets below an ice layer, they shatter the overlying ice layer and propel ice grains. Grain ejection operates on Comets, Enceladus' south polar plume, Triton's N2 plumes and on Mars' Polar Regions during their spring. Fig. 1- Ice grains ejection upon warming up a thin ice sample: 100 µm ice layer, covered by 100 µm frozen CO2 and finally by a 100 µm ice layer. Fig. 2 - Three stages of coverage of the surface of a large ice sample by ice grains.
In a unique machine, the first of its kind, large (200 cm 2 ϫ 10 cm) samples of gas-laden amorpho... more In a unique machine, the first of its kind, large (200 cm 2 ϫ 10 cm) samples of gas-laden amorphous ice were prepared at 80 K and 10 Ϫ5 Torr. The sample consisted of a fluffy agglomerate of 200-m ice grains, similar to what is presumed to be the structure of comet nuclei. The sample was heated from above by IR radiation. The properties studied were gas content in the ice and its emanation from the ice upon warming and bearing on the gas/water vapor ratio observed in cometary comae vs this ratio in cometary nuclei and the effect of internal trapped gas on the thermal conductivity of the ice and the density and mechanical properties of pure ice vs gas-laden ice. These findings might have significance for the interpretation of comet observations, the forthcoming ESA's Rosetta space mission to Comet 46P/Wirtanen in 2012, and to other comet missions.
Monthly Notices of the Royal Astronomical Society, 2017
One of the most surprising measurements of the Rosetta Orbiter Spectrometer for Ion and Neutral A... more One of the most surprising measurements of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument on the comet 67P/Churyumov-Gerasimenko was the detection of O 2 along with N 2 and noble gases which were measured for the first time in comets, along with the major constituents, water, CO, and CO 2. The O 2 high abundance of 1-10 per cent relative to H 2 O was calculated, with an average value of 3.80 ± 0.85 per cent (Bieler et al. 2015). The strong correlation of molecular oxygen abundance with water, suggests the formation of O 2 by radiolysis or photolysis of water molecules and the trapping of O 2 in the amorphous ice, together with the other gases while the comet was formed. In this study, we present new experimental results for trapping O 2 with N 2 and Ar in amorphous ice in order to understand the direct measurements of the Rosetta spacecraft. The discovery of O 2 in comets challenges our understanding of the composition of the volatiles in the outskirts of the young solar system and their delivery to the Earth's atmosphere.
Water vapor, when deposited as ice on a cold surface, in the presence of gases such as CO, can tr... more Water vapor, when deposited as ice on a cold surface, in the presence of gases such as CO, can trap considerable amounts of the gas, as a function of the gas properties and temperature of deposition. The amount of trapped gas drops exponentially when the temperature is raised (Bar-Nun and Kleinfeld, 1989). Thus, we have a cosmochemical thermometer to determine at which temperature the ice grains of a comet were formed. CO, the major gas (except H 2 O vapor) in cometary comea, could be a strong indicator of the formation temperature of the ice grains which agglomerated to form comets Halley, Hyakutake and Hale-Bopp. The CO/H 2 O ratios measured in the cometary comea (directly from the nucleus) are: 0.07 in Halley
Following the tracing of jets emanating from Comet Wild-2 to depressions in the ice by Brownlee e... more Following the tracing of jets emanating from Comet Wild-2 to depressions in the ice by Brownlee et al. [2004. The Stardust—A successful encounter with the remarkable Comet Wild 2. Lunar Planet. Sci. 35. Abstract 1981], we demonstrated experimentally the formation of depressions and chaotic terrain on comet analogs when gas is released from underlying ice pockets. We also demonstrated experimentally the ejection of ice grains into the experimental cometary “coma.”
The findings of Deep Impact on the structure and composition of Tempel-1 are compared with our ex... more The findings of Deep Impact on the structure and composition of Tempel-1 are compared with our experimental results on large (20 cm diameter and up to 10 cm high) samples of gas-laden amorphous ice. The mechanical ∼tensile strength inferred for Tempel-1: ∼65 Pa is 30 to 60 times smaller than our experimental findings of 2–4 kPa. This means that Tempel-1 is even fluffier than our very fluffy, talcum like, ice sample. The thermal inertia: I100 WK−1m−2s1/2 is very close to our value of 80. The density of 620+470/−330 kgm−3, is close to our value of 250–300 kg m−3, taking into account an ice/silicate ratio of 1 in the comet, while we study pure ice. Surface morphological features, such as non-circular depressions, chaotic terrain and smooth surfaces, 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 135 K 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.
The isotopic enrichment in argon, krypton, and xenon, when trapped in water ice, was studied expe... more The isotopic enrichment in argon, krypton, and xenon, when trapped in water ice, was studied experimentally. The isotopes were found to be enriched according to their (m 1 /m 2) 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.
It is demonstrated experimentally that the CO/H 2 O, CH 4 / the low density form in the temperatu... more It is demonstrated experimentally that the CO/H 2 O, CH 4 / the low density form in the temperature range of 38-80 K (Jenniskens H 2 O, and C 2 H 6 /H 2 O ratios found by Mumma et al. (1996) in et al. 1995) might also play a role in gas trapping in the water ice. These Comet Hyakutake could be obtained by the trapping of these factors determine the temperature dependent residence time of the gas gases in water ice which was formed at 64-66 K. The formation in the open channels and cracks in the forming water ice, until incoming of the ice particles which formed comets, either in the warm water molecules freeze and close these openings, thus trapping the gas inside the water ice. Another factor is the macroscopic porosity of the outskirts of the interstellar cloud or in the outer part of the water ice, which decreases as the temperature is raised. In trying to solar nebula, is discussed. C 3 H 8 is predicted to exist in comets compare the experimental results with the findings of Mumma et al.
Huygens' GCMS found ^36Ar and ^40Ar mixing ratios of 2.8x10^-7 and 4.3x10^-7 respectively, or... more Huygens' GCMS found ^36Ar and ^40Ar mixing ratios of 2.8x10^-7 and 4.3x10^-7 respectively, or 7x10^-3 and 3.6x10^-3 of their abundances in Earth's atmosphere. Our experiments on the UV photolysis of gas mixtures containing N [2]:CH[4]:C[2]H[2]:HCN=550:105:40:4 torr demonstrated the formation of long chain polymers with an elemental composition of C:H:N=1:1:0.007. These polymers aggregate to form aerosol particles which, during their formation
The UV photolysis of gas mixtures containing C 2 H 2 , C 2 H 4 and HCN, diluted in N 2 and CH 4 w... more The UV photolysis of gas mixtures containing C 2 H 2 , C 2 H 4 and HCN, diluted in N 2 and CH 4 was studied experimentally. At the onset of irradiation, a pale yellow aerosol appeared, similar to Titan's
Whenever large fluxes of gas are released from gas pockets below an ice layer, they shatter the o... more Whenever large fluxes of gas are released from gas pockets below an ice layer, they shatter the overlying ice layer and propel ice grains. Grain ejection operates on Comets, Enceladus' south polar plume, Triton's N2 plumes and on Mars' Polar Regions during their spring. Fig. 1- Ice grains ejection upon warming up a thin ice sample: 100 µm ice layer, covered by 100 µm frozen CO2 and finally by a 100 µm ice layer. Fig. 2 - Three stages of coverage of the surface of a large ice sample by ice grains.
In a unique machine, the first of its kind, large (200 cm 2 ϫ 10 cm) samples of gas-laden amorpho... more In a unique machine, the first of its kind, large (200 cm 2 ϫ 10 cm) samples of gas-laden amorphous ice were prepared at 80 K and 10 Ϫ5 Torr. The sample consisted of a fluffy agglomerate of 200-m ice grains, similar to what is presumed to be the structure of comet nuclei. The sample was heated from above by IR radiation. The properties studied were gas content in the ice and its emanation from the ice upon warming and bearing on the gas/water vapor ratio observed in cometary comae vs this ratio in cometary nuclei and the effect of internal trapped gas on the thermal conductivity of the ice and the density and mechanical properties of pure ice vs gas-laden ice. These findings might have significance for the interpretation of comet observations, the forthcoming ESA's Rosetta space mission to Comet 46P/Wirtanen in 2012, and to other comet missions.
Uploads
Papers by D. Laufer