scholarly journals Ammonium salts are a reservoir of nitrogen on a cometary nucleus and possibly on some asteroids

Science ◽  
2020 ◽  
Vol 367 (6483) ◽  
pp. eaaw7462 ◽  
Author(s):  
Olivier Poch ◽  
Istiqomah Istiqomah ◽  
Eric Quirico ◽  
Pierre Beck ◽  
Bernard Schmitt ◽  
...  
Keyword(s):  
Spectral Reflectance ◽  
Laboratory Experiments ◽  
Cometary Nucleus ◽  
Interstellar Cloud ◽  
Ammonium Salts ◽  
The Sun ◽  
Volatile Species ◽  
Refractory Organic Matter ◽  
Comet 67P ◽  
Absorption Features

The measured nitrogen-to-carbon ratio in comets is lower than for the Sun, a discrepancy which could be alleviated if there is an unknown reservoir of nitrogen in comets. The nucleus of comet 67P/Churyumov-Gerasimenko exhibits an unidentified broad spectral reflectance feature around 3.2 micrometers, which is ubiquitous across its surface. On the basis of laboratory experiments, we attribute this absorption band to ammonium salts mixed with dust on the surface. The depth of the band indicates that semivolatile ammonium salts are a substantial reservoir of nitrogen in the comet, potentially dominating over refractory organic matter and more volatile species. Similar absorption features appear in the spectra of some asteroids, implying a compositional link between asteroids, comets, and the parent interstellar cloud.

scholarly journals Thermal Evolution of the Nucleus of the Comet 67P for 120 Years: Numerical Simulations

2018 ◽  
Vol 27 (1) ◽  
pp. 175-182 ◽  
Author(s):  
Andrey V. Rusol ◽  
Vera A. Dorofeeva
Keyword(s):  
Thermal Evolution ◽  
Rotation Axis ◽  
Cometary Nucleus ◽  
Heat Propagation ◽  
The Sun ◽  
Rock Body ◽  
Cometary Nuclei ◽  
Orbital Cycles ◽  
Subsurface Layers ◽  
Comet 67P

Abstract The purpose of this paper is to estimate to what temperatures and to what depth the outer layers of the cometary nuclei are heated for several dozen revolutions around the Sun, and what changes in the composition of the volatiles occur in this case. This is important because it is not clear how much the experimentally obtained results on the composition of cometary comes depend on how long the comet is in the current orbit. Our approach to this problem is based on using 3D model of the geometry and dynamics of a cometary nucleus that takes into account the diurnal rotation and orientation of the rotation axis relative to the Sun to simulate the irradiance to take value of temperature the surface of the nucleus and 1D thermal model of the porous ice-rock body. The results of the numerical simulation of heat propagation in the subsurface layers of some points the MA’AT region of the 67P core, obtained for the 20 orbital cycles (close to 130 years), are presented in this paper.

Covering of cometary nucleus by refractory crust and its evolution into asteroid-like body

1999 ◽  
Vol 173 ◽  
pp. 365-370
Author(s):  
Kh.I. Ibadinov
Keyword(s):  
Laboratory Experiments ◽  
Cometary Nucleus ◽  
Sublimation Rate ◽  
Cometary Nuclei ◽  
Short Period Comet ◽  
Short Period ◽  
Brightness Decrease ◽  
Crust Thickness ◽  
Ice Sublimation ◽  
Period Comet

AbstractFrom the established dependence of the brightness decrease of a short-period comet dependence on the perihelion distance of its orbit it follows that part of the surface of these cometary nuclei gradually covers by a refractory crust. The results of cometary nucleus simulation show that at constant insolation energy the crust thickness is proportional to the square root of the insolation time and the ice sublimation rate is inversely proportional to the crust thickness. From laboratory experiments resulted the thermal regime, the gas productivity of the nucleus, covering of the nucleus by the crust, and the tempo of evolution of a short-period comet into the asteroid-like body studied.

The Role of Chlorine in Stratospheric Chemistry

1996 ◽  
Vol 68 (9) ◽  
pp. 1749-1756 ◽  
Author(s):  
M. J. Molina
Keyword(s):  
Laboratory Experiments ◽  
Stratospheric Ozone ◽  
The Sun ◽  
Plastic Foam ◽  
Model Calculations ◽  
Stratospheric Chemistry ◽  
Blowing Agents ◽  
Stratospheric Ozone Layer ◽  
The Earth

The chlorofluorocarbons (CFCs) are industrialchemicals used as solvents, refrigerants, plastic foam blowing agents,etc. These compounds are eventually released to the environment; theyslowly drift into the stratosphere, where they decompose, initiatinga catalytic process involving chlorine free radicals and leading toozone destruction. The stratospheric ozone layer is important for theearth's energy budget, and it shields the surface of the earth fromultraviolet radiation from the sun. Very significant depletion of theozone layer has been observed in the spring months over Antarctica duringthe last 10-15 years. Laboratory experiments, model calculations andfield measurements, which include several aircraft expeditions, haveyielded a wealth of information which clearly points to the CFCs asthe main cause of this depletion.

scholarly journals Models of Spots and Flares

1983 ◽  
Vol 71 ◽  
pp. 527-543
Author(s):  
D.J. Mullan
Keyword(s):  
Magnetic Fields ◽  
Laboratory Experiments ◽  
Equilibrium Structure ◽  
Stellar Atmosphere ◽  
Dark Spot ◽  
Quasi Equilibrium ◽  
The Sun ◽  
Convective Flows ◽  
Complex Interactions ◽  
Field Lines

MHD effects in stars are seen in their most spectacular form in the processes which are typical of flares. At first sight, it appears that the phenomena of dark spots (whose long lifetimes give an impression of quasi-equilibrium) are inevitably less interesting. However, this is not necessarily true. Laboratory experiments in recent years have shown that there are many more ways to drive a plasma out of equilibrium than to preserve equilibrium. In that sense, then, it is perhaps “easier to understand” why flares should occur in a stellar atmosphere (where convective jostling of field lines creates potential for driving a large number of instabilities) than why a long-lived feature such as a dark spot should persist. Various instabilities which may contribute to flares are discussed by Priest and Spicer (this volume). Here, we summarize work on the equilibrium structure of cool spots in the sun and stars. Since spots involve complex interactions between convective flows and magnetic fields, we need to refer to observations for help in identifying the dominant processes which should enter into the modelling. This summary therefore begins by discussing certain relevant properties of spots in the solar atmosphere.

scholarly journals A comparison between the two lobes of comet 67P/Churyumov–Gerasimenko based on D/H ratios in H2O measured with the Rosetta/ROSINA DFMS

2019 ◽  
Vol 489 (4) ◽  
pp. 4734-4740 ◽  
Author(s):  
Isaac R H G Schroeder ◽  
Kathrin Altwegg ◽  
Hans Balsiger ◽  
Jean-Jacques Berthelier ◽  
Michael R Combi ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
European Space Agency ◽  
Cometary Nucleus ◽  
The Other ◽  
Appreciable Difference ◽  
Space Agency ◽  
Close Proximity ◽  
Double Focusing ◽  
Comet 67P

ABSTRACT The nucleus of the Jupiter-family comet 67P/Churyumov–Gerasimenko was discovered to be bi-lobate in shape when the European Space Agency spacecraft Rosetta first approached it in 2014 July. The bi-lobate structure of the cometary nucleus has led to much discussion regarding the possible manner of its formation and on how the composition of each lobe might compare with that of the other. During its two-year-long mission from 2014 to 2016, Rosetta remained in close proximity to 67P/Churyumov–Gerasimenko, studying its coma and nucleus in situ. Based on lobe-specific measurements of HDO and H2O performed with the ROSINA Double Focusing Mass Spectrometer (DFMS) on board Rosetta, the deuterium-to-hydrogen (D/H) ratios in water from the two lobes can be compared. No appreciable difference was observed, suggesting that both lobes formed in the same region and are homogeneous in their D/H ratios.

scholarly journals Detection of Narrow C IV and Si IV Absorption Features in Spectra of Stars within 200 pc of The Sun

1984 ◽  
Vol 81 ◽  
pp. 185-188
Author(s):  
P. Molaro ◽  
J.E. Beckman ◽  
M. Franco ◽  
C. Morossi ◽  
M. Ramella
Keyword(s):  
Ambient Medium ◽  
The Sun ◽  
Probable Source ◽  
Absorption Features ◽  
Made In

AbstractDetection of narrow ( δλ< 0.5 A ) absorption features in C IV at λ λ 1548 and 1550 have been made in the spectra of 4 late B dwarfs within 200 pc of the sun; the Si IV doublet at λ λ 1393 and 1403 shows up in two of them. We argue that it is difficult to account for the strengths, widths, shapes , and C IV/Si IV ratios in terms consistent with a circumstellar origin except possibly for an asymmetric C IV component in one star (HD 135037). The most probable source is “semi-torrid” gas (cf. Bruhweiler et al. 1980) in the 50,000 K range forming the interfaces between cooler H I clouds and the ambient medium at coronal temperatures. Our technique, using late B rapid rotators, is useful for LISM probing of this kind.

scholarly journals Dielectronic Satellite Spectra in the Soft X-Ray Region

1972 ◽  
Vol 14 ◽  
pp. 655-664 ◽  
Author(s):  
A.H. Gabriel
Keyword(s):  
Steady State ◽  
Solar Flare ◽  
Resonance Line ◽  
Laboratory Experiments ◽  
Transient State ◽  
Dielectronic Recombination ◽  
The Sun ◽  
X Ray ◽  
Long Wavelength ◽  
Dielectronic Satellite

AbstractSatellite lines, situated on the long wavelength side of the helium-like ion resonance line, can be observed in highly-ionized ions both in laboratory sources and from the Sun. Although seen for more than 30 years, these lines have only recently been classified in detail as inner-shell transitions in lithium-like ions. Laboratory experiments have shown that under steady-state conditions these satellites are produced by dielectronic recombination, although in transient ionizing plasmas direct inner-shell excitation can be important. Detailed calculations have been carried out for high Z ions up to copper, and the results can be compared with solar flare spectra in iron. Such comparisons allow both the electron temperature and the transient state of the plasma to be determined. Laboratory spectra from such high-Z ions are different in appearance, and may be dominated by processes resulting from the transient ionizing state of the plasma.

scholarly journals The Visibility of Earth Transits

2004 ◽  
Vol 202 ◽  
pp. 445-447 ◽  
Author(s):  
T. Castellano ◽  
L. Doyle ◽  
D. McIntosh
Keyword(s):  
Laboratory Experiments ◽  
Ecliptic Plane ◽  
Solar Neighborhood ◽  
Geometric Condition ◽  
The Sun ◽  
Intrinsic Variability ◽  
Noise Sources ◽  
Photometric Detection ◽  
The Earth ◽  
Order Of Magnitude

The recent photometric detection of planetary transits of the solar-like star HD 209458 at a distance of 47 parsecs suggest that transits can reveal the presence of Jupiter-size planetary companions in the solar neighborhood (Charbonneau et al. 2000; Henry et al. 2000). Recent space-based transit searches have achieved photometric precision within an order of magnitude of that required to detect the much smaller transit signal of an earth-size planet across a solar-size star. Laboratory experiments in the presence of realistic noise sources have shown that CCDs can achieve photometric precision adequate to detect the 9.6 E-5 dimming of the Sun due to a transit of the Earth (Borucki et al. 1997; Koch et al. 2000). Space-based solar irradiance monitoring has shown that the intrinsic variability of the Sun would not preclude such a detection (Borucki, Scargle, Hudson 1985). Transits of the Sun by the Earth would be detectable by observers that reside within a narrow band of sky positions near the ecliptic plane, if the observers possess current Earth epoch levels of technology and astronomical expertise. A catalog of solar-like stars that satisfy the geometric condition for Earth transit visibility are presented.

scholarly journals Post-rendezvous radar properties of comet 67P/CG from the Rosetta Mission: understanding future Earth-based radar observations and the dynamical evolution of comets

2019 ◽  
Vol 489 (2) ◽  
pp. 1667-1683 ◽  
Author(s):  
Essam Heggy ◽  
Elizabeth M Palmer ◽  
Alain Hérique ◽  
Wlodek Kofman ◽  
M Ramy El-Maarry
Keyword(s):  
Large Scale ◽  
Structural Changes ◽  
Dynamical Evolution ◽  
Textural Properties ◽  
Building Blocks ◽  
Cometary Nucleus ◽  
Small Scale ◽  
Small Bodies ◽  
Radar Observations ◽  
Comet 67P

ABSTRACT Radar observations provide crucial insights into the formation and dynamical evolution of comets. This ability is constrained by our knowledge of the dielectric and textural properties of these small-bodies. Using several observations by Rosetta as well as results from the Earth-based Arecibo radio telescope, we provide an updated and comprehensive dielectric and roughness description of Comet 67P/CG, which can provide new constraints on the radar properties of other nuclei. Furthermore, contrary to previous assumptions of cometary surfaces being dielectrically homogeneous and smooth, we find that cometary surfaces are dielectrically heterogeneous ( εr′≈1.6–3.2), and are rough at X- and S-band frequencies, which are widely used in characterization of small-bodies. We also investigate the lack of signal broadening in CONSERT observations through the comet head. Our results suggest that primordial building blocks in the subsurface are either absent, smaller than the radar wavelength, or have a weak dielectric contrast (Δ εr′). To constrain this ambiguity, we use optical albedo measurements by the OSIRIS camera of the freshly exposed subsurface after the Aswan cliff collapse. We find that the hypothetical subsurface blocks should have |Δ εr′|≳0.15, setting an upper limit of ∼ 1 m on the size of 67P/CG's primordial building blocks if they exist. Our analysis is consistent with a purely thermal origin for the ∼ 3 m surface bumps on pit walls and cliff-faces, hypothesized to be high-centred polygons formed from fracturing of the sintered shallow ice-bearing subsurface due to seasonal thermal expansion and contraction. Potential changes in 67P/CG's radar reflectivity at these at X- and S-bands can be associated with large-scale structural changes of the nucleus rather than small-scale textural ones. Monitoring changes in 67P/CG's radar properties during repeated close-approaches via Earth-based observations can constrain the dynamical evolution of its cometary nucleus.

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