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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.

The European Rosetta mission has been following comet 67P/Churyumov-Gerasimenko for 2 years, studying the nucleus and coma in great detail. For most of these 2 years the Rosetta Orbiter Sensor for Ion and Neutral Analysis (ROSINA) has analysed the volatile part of the coma. With its high mass resolution and sensitivity it was able to not only detect deuterated water HDO, but also doubly deuterated water, D₂O and deuterated hydrogen sulfide HDS. The ratios for [HDO]/[H₂O], [D₂O]/[HDO] and [HDS]/[H₂S] derived from our measurements are (1.05 ± 0.14) × 10⁻³, (1.80 ± 0.9) × 10⁻² and (1.2 ± 0.3) × 10⁻³, respectively. These results yield a very high ratio of 17 for [D₂O]/[HDO] relative to [HDO]/[H₂O]. Statistically one would expect just 1/4. Such a high value can be explained by cometary water coming unprocessed from the presolar cloud, where water is formed on grains, leading to high deuterium fractionation. The high [HDS]/[H₂S] ratio is compatible with upper limits determined in low-mass star-forming regions and also points to a direct correlation of cometary H₂S with presolar grain surface chemistry. This article is part of the themed issue 'Cometary science after Rosetta'.

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.

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.

Organohalogens, a class of molecules that contain at least one halogen atom bonded to carbon, are abundant on the Earth where they are mainly produced through industrial and biological processes 1 . Consequently, they have been proposed as biomarkers in the search for life on exoplanets 2 . Simple halogen hydrides have been detected in interstellar sources and in comets, but the presence and possible incorporation of more complex halogen-containing molecules such as organohalogens into planet-forming regions is uncertain 3 , 4 . Here we report the interstellar detection of two isotopologues of the organohalogen CH 3 Cl and put some constraints on CH 3 F in the gas surrounding the low-mass protostar IRAS 16293–2422, using the Atacama Large Millimeter/submillimeter Array (ALMA). We also find CH 3 Cl in the coma of comet 67P/Churyumov–Gerasimenko (67P/C-G) by using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument. The detections reveal an efficient pre-planetary formation pathway of organohalogens. Cometary impacts may deliver these species to young planets and should thus be included as a potential abiotical production source when interpreting future organohalogen detections in atmospheres of rocky planets. Chloromethane (CH3Cl) has been observed towards a low-mass protostar and comet 67P, making it the first organohalogen detected in space. The species was previously considered to be a biomarker, but the authors suggest viable alternative abiotic formation routes.

The Framing Camera (FC) is the German contribution to the Dawn mission. The camera will map 4 Vesta and 1 Ceres through a clear filter and 7 band-pass filters covering the wavelengths from the visible to the near-IR. The camera will allow the determination of the physical parameters of the asteroids, the reconstruction of their global shape as well as local topography and surface geomorphology, and provide information on composition via surface reflectance characteristics. The camera will also serve for orbit navigation. The resolution of the Framing Camera will be up to 12 m per pixel in low altitude mapping orbit at Vesta (62 m per pixel at Ceres), at an angular resolution of 93.7 μrad px −1 . The instrument uses a reclosable front door to protect the optical system and a filter-wheel mechanism to select the band-pass for observation. The detector data is read out and processed by a data processing unit. A power converter unit supplies all required power rails for operation and thermal maintenance. For redundancy reasons, two identical cameras were provided, both located side by side on the + Z -deck of the spacecraft. Each camera has a mass of 5.5 kg.

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.

On 10 August 2021, the Mercury-bound BepiColombo spacecraft performed its second fly-by of Venus and provided a short-lived observation of its induced magnetosphere. Here we report results recorded by the Mass Spectrum Analyzer on board Mio, which reveal the presence of cold O + and C + with an average total flux of ~4 ± 1 × 10 4  cm −2  s −1 at a distance of about six planetary radii in a region that has never been explored before. The ratio of escaping C + to O + is at most 0.31 ± 0.2, implying that, in addition to atomic O + ions, CO group ions or water group ions may be a source of the observed O + . Simultaneous magnetometer observations suggest that these planetary ions were in the magnetosheath flank in the vicinity of the magnetic pileup boundary downstream. These results have important implications regarding the evolution of Venus’s atmosphere and, in particular, the evolution of water on the surface of the planet. Venus lacks a magnetic field, leading to interactions between the solar wind and its atmosphere. During its Venus fly-by, BepiColombo observed planetary C + and O + escape into space due to this interaction, which is important for understanding atmospheric evolution.