Explore the vast range of titles available.

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.

In situ measurement of O 2 in the coma of comet 67P/Churyumov–Gerasimenko shows local abundances ranging from one per cent to ten per cent relative to H 2 O; the spatial and temporal uniformity of the O 2 /H 2 O ratio suggests that primordial O 2 was incorporated into the nucleus during the comet’s formation. Molecular oxygen on comet 67P Molecular oxygen (O 2 ) has been detected on icy bodies in the Solar System, including the moons of Jupiter and Saturn, but until now it has not been detected in a comet. Andre Bieler et al . report the detection and in situ measurement of O 2 in the coma of 67P/Churyumov–Gerasimenko, made by the Rosetta spacecraft's ROSINA instrument between September 2014 and March 2015. The data reveal local abundances of O 2 between 1% to 10% relative to H 2 O. The O 2 /H 2 O ratio is consistent throughout the coma and does not change systematically with distance from the Sun, suggesting that primordial O 2 was incorporated into the nucleus during the comet's formation. Current Solar System formation models do not predict conditions that would allow this to occur. The composition of the neutral gas comas of most comets is dominated by H 2 O, CO and CO 2 , typically comprising as much as 95 per cent of the total gas density 1 . In addition, cometary comas have been found to contain a rich array of other molecules, including sulfuric compounds and complex hydrocarbons. Molecular oxygen (O 2 ), however, despite its detection on other icy bodies such as the moons of Jupiter and Saturn 2 , 3 , has remained undetected in cometary comas. Here we report in situ measurement of O 2 in the coma of comet 67P/Churyumov–Gerasimenko, with local abundances ranging from one per cent to ten per cent relative to H 2 O and with a mean value of 3.80 ± 0.85 per cent. Our observations indicate that the O 2 /H 2 O ratio is isotropic in the coma and does not change systematically with heliocentric distance. This suggests that primordial O 2 was incorporated into the nucleus during the comet’s formation, which is unexpected given the low upper limits from remote sensing observations 4 . Current Solar System formation models do not predict conditions that would allow this to occur.

The origin of cometary matter and the potential contribution of comets to inner-planet atmospheres are long-standing problems. During a series of dedicated low-altitude orbits, the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) on the Rosetta spacecraft analyzed the isotopes of xenon in the coma of comet 67P/Churyumov-Gerasimenko. The xenon isotopic composition shows deficits in heavy xenon isotopes and matches that of a primordial atmospheric component. The present-day Earth atmosphere contains 22 ± 5% cometary xenon, in addition to chondritic (or solar) xenon.

Comets contain the best-preserved material from the beginning of our planetary system. Their nuclei and comae composition reveal clues about physical and chemical conditions during the early solar system when comets formed. ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) onboard the Rosetta spacecraft has measured the coma composition of comet 67P/Churyumov-Gerasimenko with well-sampled time resolution per rotation. Measurements were made over many comet rotation periods and a wide range of latitudes. These measurements show large fluctuations in composition in a heterogeneous coma that has diurnal and possibly seasonal variations in the major outgassing species: water, carbon monoxide, and carbon dioxide. These results indicate a complex coma-nucleus relationship where seasonal variations may be driven by temperature differences just below the comet surface.

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.

Establishing the mechanisms by which the solar wind enters Earth's magnetosphere is one of the biggest goals of magnetospheric physics, as it forms the basis of space weather phenomena such as magnetic storms and aurorae 1 . It is generally believed that magnetic reconnection is the dominant process, especially during southward solar-wind magnetic field conditions when the solar-wind and geomagnetic fields are antiparallel at the low-latitude magnetopause 2 . But the plasma content in the outer magnetosphere increases during northward solar-wind magnetic field conditions 3 , 4 , contrary to expectation if reconnection is dominant. Here we show that during northward solar-wind magnetic field conditions—in the absence of active reconnection at low latitudes—there is a solar-wind transport mechanism associated with the nonlinear phase of the Kelvin–Helmholtz instability 5 . This can supply plasma sources for various space weather phenomena.

In situ mass spectrometry has been a powerful tool in many space missions to investigate atmospheres and exospheres of different bodies in the solar system. Applying new technologies, the mass spectrometers have become increasingly more sensitive. In this study, we show that spacecraft outgassing, which can never be completely prevented, will be the limiting factor in future missions that investigate very tenuous atmospheres and exospheres of moons, asteroids, or comets at large heliocentric distances. The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument on the European Space Agency Rosetta mission has monitored spacecraft outgassing for 6 years during the cruise phase with unprecedented instrument sensitivity. It is shown that diffusion of gas from materials and from the spacecraft interior plays an important role in maintaining a relatively permanent thin gas cloud around the spacecraft for many years. The density and composition of this gas cloud depends on location on the spacecraft, maneuvers, and payload activity. The main contaminants are water, which is adsorbed on cold surfaces, and organics from the spacecraft structure, electronics, and insulations. Decomposed lubricant material can give a significant contribution to the total background. Fortunately for Rosetta, outgassing of the spacecraft will play a minor role when the comet is close to perihelion; only in the early phase of the mission the outgassing may be larger than the cometary signature.

We examine traversals on 20 November 2001 of the equatorial magnetopause boundary layer simultaneously at ∼1500 magnetic local time (MLT) by the Geotail spacecraft and at ∼1900 MLT by the Cluster spacecraft, which detected rolled‐up MHD‐scale vortices generated by the Kelvin‐Helmholtz instability (KHI) under prolonged northward interplanetary magnetic field conditions. Our purpose is to address the excitation process of the KHI, MHD‐scale and ion‐scale structures of the vortices, and the formation mechanism of the low‐latitude boundary layer (LLBL). The observed KH wavelength (>4 × 104 km) is considerably longer than predicted by the linear theory from the thickness (∼1000 km) of the dayside velocity shear layer. Our analyses suggest that the KHI excitation is facilitated by combined effects of the formation of the LLBL presumably through high‐latitude magnetopause reconnection and compressional magnetosheath fluctuations on the dayside, and that breakup and/or coalescence of the vortices are beginning around 1900 MLT. Current layers of thickness a few times ion inertia length ∼100 km and of magnetic shear ∼60° existed at the trailing edges of the vortices. Identified in one such current sheet were signatures of local reconnection: Alfvénic outflow jet within a bifurcated current sheet, nonzero magnetic field component normal to the sheet, and field‐aligned beam of accelerated electrons. Because of its incipient nature, however, this reconnection process is unlikely to lead to the observed dusk‐flank LLBL. It is thus inferred that the flank LLBL resulted from other mechanisms, namely, diffusion and/or remote reconnection unidentified by Cluster.

Issue Title: Rosetta: Mission to Comet 67P/Churyumov-Gerasimenko The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) will answer important questions posed by the mission's main objectives. After Giotto, this will be the first time the volatile part of a comet will be analyzed in situ. This is a very important investigation, as comets, in contrast to meteorites, have maintained most of the volatiles of the solar nebula. To accomplish the very demanding objectives through all the different phases of the comet's activity, ROSINA has unprecedented capabilities including very wide mass range (1 to >300 amu), very high mass resolution (m/Δ m > 3000, i.e. the ability to resolve CO from N^sub 2^ and ^sup 13^C from ^sup 12^CH), very wide dynamic range and high sensitivity, as well as the ability to determine cometary gas velocities, and temperature. ROSINA consists of two mass spectrometers for neutrals and primary ions with complementary capabilities and a pressure sensor. To ensure that absolute gas densities can be determined, each mass spectrometer carries a reservoir of a calibrated gas mixture allowing in-flight calibration. Furthermore, identical flight-spares of all three sensors will serve for detailed analysis of all relevant parameters, in particular the sensitivities for complex organic molecules and their fragmentation patterns in our electron bombardment ion sources.[PUBLICATION ABSTRACT]

Vector magnetic field observations of the martian crust were acquired by the Mars Global Surveyor (MGS) magnetic field experiment/electron reflectometer (MAG/ER) during the aerobraking and science phasing orbits, at altitudes between ∼100 and 200 kilometers. Magnetic field sources of multiple scales, strength, and geometry were observed. There is a correlation between the location of the sources and the ancient cratered terrain of the martian high-lands. The absence of crustal magnetism near large impact basins such as Hellas and Argyre implies cessation of internal dynamo action during the early Naochian epoch (∼4 billion years ago). Sources with equivalent magnetic moments as large as 1.3 × 10$^{17}$ ampere-meter$^2$ in the Terra Sirenum region contribute to the development of an asymmetrical, time-variable obstacle to solar wind flow around Mars.