Jean-Jacques Berthelier

67P/Churyumov-Gerasimenko, a Jupiter family comet with a high D/H ratio

The provenance of water and organic compounds on Earth and other terrestrial planets has been discussed for a long time without reaching a consensus. One of the best means to distinguish between different scenarios is by determining the deuterium-to-hydrogen (D/H) ratios in the reservoirs for comets and Earth’s oceans. Here, we report the direct in situ measurement of the D/H ratio in the Jupiter family comet 67P/Churyumov-Gerasimenko by the ROSINA mass spectrometer aboard the European Space Agency’s Rosetta spacecraft, which is found to be (5.3 ± 0.7) × 10−4—that is, approximately three times the terrestrial value. Previous cometary measurements and our new finding suggest a wide range of D/H ratios in the water within Jupiter family objects and preclude the idea that this reservoir is solely composed of Earth ocean–like water.

Molecular nitrogen in comet 67P/Churyumov-Gerasimenko indicates a low formation temperature

Making comets in the cold The speciation of nitrogen compounds in comets can tell us about their history. Comets are some of the most ancient bodies in the solar system and should contain the nitrogen compounds that were abundant when they formed. Using the ROSINA mass spectrometer aboard the Rosetta spacecraft orbiting comet 67P/Churyumov-Gerasimenko, Rubin et al. found molecular nitrogen at levels that are depleted compared to those in the primordial solar system. Depletion of such a magnitude suggests that the comet formed either from the low-temperature agglomeration of pristine amorphous water ice grains or from clathrates. Science, this issue p. 232 Direct measurements of N2 by instruments aboard the Rosetta spacecraft provide clues about the comet’s long history. Molecular nitrogen (N2) is thought to have been the most abundant form of nitrogen in the protosolar nebula. It is the main N-bearing molecule in the atmospheres of Pluto and Triton and probably the main nitrogen reservoir from which the giant planets formed. Yet in comets, often considered the most primitive bodies in the solar system, N2 has not been detected. Here we report the direct in situ measurement of N2 in the Jupiter family comet 67P/Churyumov-Gerasimenko, made by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis mass spectrometer aboard the Rosetta spacecraft. A N2/CO ratio of (5.70±0.66)×10−3 (2σ standard deviation of the sampled mean) corresponds to depletion by a factor of ~25.4 ± 8.9 as compared to the protosolar value. This depletion suggests that cometary grains formed at low-temperature conditions below ~30 kelvin.

Abundant molecular oxygen in the coma of comet 67P/Churyumov-Gerasimenko

The composition of the neutral gas comas of most comets is dominated by H2O, CO and CO2, typically comprising as much as 95 per cent of the total gas density. In addition, cometary comas have been found to contain a rich array of other molecules, including sulfuric compounds and complex hydrocarbons. Molecular oxygen (O2), however, despite its detection on other icy bodies such as the moons of Jupiter and Saturn, has remained undetected in cometary comas. Here we report in situ measurement of O2 in the coma of comet 67P/Churyumov–Gerasimenko, with local abundances ranging from one per cent to ten per cent relative to H2O and with a mean value of 3.80 ± 0.85 per cent. Our observations indicate that the O2/H2O ratio is isotropic in the coma and does not change systematically with heliocentric distance. This suggests that primordial O2 was incorporated into the nucleus during the comet’s formation, which is unexpected given the low upper limits from remote sensing observations. Current Solar System formation models do not predict conditions that would allow this to occur.

Radiation belt electron precipitation due to VLF transmitters: Satellite observations

In the Earth’s inner magnetosphere, the distribution of energetic electrons is controlled by pitch-angle scattering by waves. A category of Whistler waves originates from powerful ground-based VLF transmitter signals in the frequency range 10–25 kHz. These transmissions are observed in space as waves of very narrow bandwidth. Here we examine the significance of the VLF transmitter NWC on the inner radiation belt using DEMETER satellite global observations at low altitudes. We find that enhancements in the 100–600 keV drift-loss cone electron fluxes at L values between 1.4 and 1.7 are linked to NWC operation and to ionospheric absorption. Waves and particles interact in the vicinity of the magnetic equatorial plane. Using Demeter passes across the drifting cloud of electrons caused by the transmitter; we find that 300 times more 200 keV electrons are driven into the drift-loss cone during NWC transmission periods than during non-transmission periods. The correlation between the flux of resonant electrons and the Dst index shows that the electron source intensity is controlled by magnetic storm activity.

Comparison of 3D kinetic and hydrodynamic models to ROSINA-COPS measurements of the neutral coma of 67P/Churyumov-Gerasimenko

67P/Churyumov-Gerasimenko (hereafter 67P) is a Jupiter-family comet and the object of investigation of the European Space Agency mission Rosetta. This report presents the first full 3D simulation results of 67P’s neutral gas coma. In this study we include results from a direct simulation Monte Carlo method, a hydrodynamic code, and a purely geometric calculation which computes the total illuminated surface area on the nucleus. All models include the triangulated 3D shape model of 67P as well as realistic illumination and shadowing conditions. The basic concept is the assumption that these illumination conditions on the nucleus are the main driver for the gas activity of the comet. As a consequence, the total production rate of 67P varies as a function of solar insolation. The best agreement between the model and the data is achieved when gas fluxes on the night side are in the range of 7% to 10% of the maximum flux, accounting for contributions from the most volatile components. To validate the output of our numerical simulations we compare the results of all three models to in situ gas number density measurements from the ROSINA COPS instrument. We are able to reproduce the overall features of these local neutral number density measurements of ROSINA COPS for the time period between early August 2014 and January 1 2015 with all three models. Some details in the measurements are not reproduced and warrant further investigation and refinement of the models. However, the overall assumption that illumination conditions on the nucleus are at least an important driver of the gas activity is validated by the models. According to our simulation results we find the total production rate of 67P to be constant between August and November 2014 with a value of about 1 × 1026 molecules s−1.

Martian corona: Nonthermal sources of hot heavy species

[1] We have studied the production of hot O and C atoms, and hot CO 2 and CO molecules in the Martian upper atmosphere and exosphere by dissociative recombination (DR) of O 2 + and CO + ions, and sputtering of the atmosphere by incident O + pick-up ions. Production and collisional thermalization of the hot particles in the upper atmosphere are described by using a unique Monte Carlo test particle approach to simulate both nonthermal processes. Velocity distributions, atmospheric loss rates, and density profiles are derived for suprathermal 0, C, CO, and CO 2 at low and high solar activity. At high solar activity the hot oxygen escape rate estimated from DR of O 2 + is found to be less than two times the sputtering rate. Sputtering is found to efficiently populate the corona with molecular species such as CO and CO 2 at high solar activity and also to produce a carbon escape rate that is comparable to that derived from the major photochemical sources. Dissociation of CO 2 molecules by the impacting pick-up ions flux are found to produce about 50% of the sputtered exospheric oxygen density at high solar activity. Collisions of the background atmospheric gas with hot O atoms produced by DR of O 2 + produce densities of hot CO 2 and CO molecules larger than 10 2 cm -3 for altitudes lower than 1000 km, at both high and low solar activity. Interestingly, the hot CO 2 density scale height is observed to be process dependent. The hot oxygen energy distributions associated with sputtering and DR near the exobase are also found to follow distinct decreasing energy laws. We suggest that the effects of the solar zenithal angle (SZA), crustal magnetic fields, and atmospheric tides on the ionospheric structure may produce exospheric signatures.

Power line harmonic radiation (PLHR) observed by the DEMETER spacecraft

Results of a systematic survey of Power Line Harmonic Radiation (PLHR) observed by a recently (June 2004) launched French spacecraft DEMETER are presented. In order to obtain a statistically significant number of events, an automatic identification procedure has been developed and all the available high-resolution data have been processed. Altogether, 58 events have been found in 865 hours of data recorded during the first year of operation. These events form three different classes: with frequency spacing of spectral lines of 50/100 Hz (10 events), with frequency spacing of 60/120 Hz (13 events), with other spacings/not clear cases (35 events). The first two classes of events are discussed in detail, showing that their origin is most probably connected with the radiation from the electric power systems which are magnetically conjugated with the place of observation. Additionally, in more than one half of the cases, the frequencies of PLHR lines well corresponded to the multiples of the power system frequency. The frequency drift of all the observed events was very slow, if observable. The events occurred without any significant preference for low or high geomagnetic activity, although more intense events were observed during disturbed times. Simultaneous observations of electric and magnetic components of PLHR suggest that the waves propagate in the electromagnetic right-hand polarized whistler mode.

Ground-based transmitter signals observed from space: Ducted or nonducted?

An image forming apparatus comprising (a) a photoreceptor comprising an endless transparent support having thereon a transparent conductive layer, a charge carrier generation layer and a charge carrier transport layer; (b) a charger for charging uniformly the outermost surface of the photoreceptor; (c) an exposing means for having the photoreceptor exposed to light from the side of the support to form an electrostatic latent image on the surface of the photoreceptor; (d) a developing means for developing the electrostatic latent image to form a toner image; (e) a transfer means for transferring the toner image onto a transfer material; and (f) a fixing means for fixing the toner image transferred, wherein a transmittance of the charge carrier generation layer is 20% or less with respect to exposing light emitted from the exposing means, and a carrier drift mobility in the charge carrier transport layer is 1x10-6 cm2/V.sec or more under an electric field intensity of 2x105 V/cm.

Detection of argon in the coma of comet 67P/Churyumov-Gerasimenko

ROSINA/DFMS shows that comets of type 67P/CG likely did not significantly contribute to Earth’s volatile budget. Comets have been considered to be representative of icy planetesimals that may have contributed a significant fraction of the volatile inventory of the terrestrial planets. For example, comets must have brought some water to Earth. However, the magnitude of their contribution is still debated. We report the detection of argon and its relation to the water abundance in the Jupiter family comet 67P/Churyumov-Gerasimenko by in situ measurement of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) mass spectrometer aboard the Rosetta spacecraft. Despite the very low intensity of the signal, argon is clearly identified by the exact determination of the mass of the isotope 36Ar and by the 36Ar/38Ar ratio. Because of time variability and spatial heterogeneity of the coma, only a range of the relative abundance of argon to water can be given. Nevertheless, this range confirms that comets of the type 67P/Churyumov-Gerasimenko cannot be the major source of Earth’s major volatiles.

Composition-dependent outgassing of comet 67P/Churyumov-Gerasimenko from ROSINA/DFMS. Implications for nucleus heterogeneity?

Early measurements of Rosetta’s target comet, 67P/Churyumov-Gerasimenko (67P), showed a strongly heterogeneous coma in H2O, CO, and CO2. Aims. The purpose of this work is to further investigate the coma heterogeneity of 67P, and to provide predictions for the near- perihelion outgassing profile based on the proposed explanations. Methods. Measurements of various minor volatile species by ROSINA/DFMS on board Rosetta are examined. The analysis focuses on the currently poorly illuminated winter (southern) hemisphere of 67P. Results. Coma heterogeneity is not limited to the major outgassing species. Minor species show better correlation with either H2O or CO2. The molecule CH4 shows a different diurnal pattern from all other analyzed species. Such features have implications for nucleus heterogeneity and thermal processing. Conclusions. Future analysis of additional volatiles and modeling the heterogeneity are required to better understand the observed coma profile.