Comet 67P Research Articles

Gas Dynamic Models of the Interaction between the Solar Wind

Gas dynamic models of the interaction between the solar wind and cometary atmospheresare considered. Interest in the development of such models arose sharply after the beginning of the investigations of comets with the use of spacecraft launched at distances close to their surfaces. The instruments on this spacecraft gave the possibility to investigate experimentally the parameters of gas flow out from the cometary surfaces when the comets approach the Sun and its interaction with the solar wind plasma flow, which could not be made using only the spectral photometry. The beginning of such studies was started by almost instantaneous approaching of several space probes to Halley’s Comet on March 1986. Only after 28 years, the Rosetta spacecraft launched by the European Space Agency (ESA) along a complex trajectory have approached comet Churyumov–Gerasimenko and, maneuvering in the neighborhood of this comet during more than two years, it, in particular, have investigated the interaction of the cometary atmosphere and the solar wind

Isosceles tetrahedron and an equimomental system of a rigid body

The problem of equimomental systems of a rigid body is considered. It is shown that the system of four equal masses located at the vertices of an isosceles tetrahedron is equimomental to a given rigid body. A system of material points of equal masses located at the vertices of an isosceles tetrahedron, which is equimomental of cometary nuclei of 67P Churyumov-Gerasimenko, has been constructed.

Geodesy of irregular small bodies via neural density fields

Asteroids’ and comets’ geodesy is a challenging yet important task for planetary science and spacecraft operations, such as ESA’s Hera mission tasked to look at the aftermath of the recent NASA DART spacecraft’s impact on Dimorphos. Here we present a machine learning approach based on so-called geodesyNets which learns accurate density models of irregular bodies using minimal prior information. geodesyNets are a three-dimensional, differentiable function representing the density of a target irregular body. We investigate six different bodies, including the asteroids Bennu, Eros, and Itokawa and the comet Churyumov-Gerasimenko, and validate on heterogeneous and homogeneous ground-truth density distributions. Induced gravitational accelerations and inferred body shape are accurate, resulting in a relative acceleration error of less than 1%, also close to the surface. With a shape model, geodesyNets can even learn heterogeneous density fields and thus provide insight into the body’s internal structure. This adds a powerful tool to consolidated approaches like spherical harmonics, mascon models, and polyhedral gravity.

Observations of a Solar Energetic Particle Event From Inside and Outside the Coma of Comet 67P.

We analyze observations of a solar energetic particle (SEP) event at Rosetta's target comet 67P/Churyumov-Gerasimenko during 6-10 March 2015. The comet was 2.15AU from the Sun, with the Rosetta spacecraft approximately 70km from the nucleus placing it deep inside the comet's coma and allowing us to study its response. The Eastern flank of an interplanetary coronal mass ejection (ICME) also encountered Rosetta on 6 and 7 March. Rosetta Plasma Consortium data indicate increases in ionization rates, and cometary water group pickup ions exceeding 1keV. Increased charge exchange reactions between solar wind ions and cometary neutrals also indicate increased upstream neutral populations consistent with enhanced SEP induced surface activity. In addition, the most intense parts of the event coincide with observations interpreted as an infant cometary bow shock, indicating that the SEPs may have enhanced the formation and/or intensified the observations. These solar transient events may also have pushed the cometopause closer to the nucleus. We track and discuss characteristics of the SEP event using remote observations by SOHO, WIND, and GOES at the Sun, in situ measurements at Solar Terrestrial Relations Observatory Ahead, Mars and Rosetta, and ENLIL modeling. Based on its relatively prolonged duration, gradual and anisotropic nature, and broad angular spread in the heliosphere, we determine the main particle acceleration source to be a distant ICME which emerged from the Sun on 6 March 2015 and was detected locally in the Martian ionosphere but was never encountered by 67P directly. The ICME's shock produced SEPs for several days which traveled to the in situ observation sites via magnetic field line connections.

Sub-mm/mm optical properties of real protoplanetary matter derived from Rosetta/MIRO observations of comet 67P

ABSTRACT Optical properties are required for the correct understanding and modelling of protoplanetary and debris discs. By assuming that comets are the most pristine bodies in the Solar system, our goal is to derive optical constants of real protoplanetary material. We determine the complex index of refraction of the near-surface material of comet 67P/Churyumov–Gerasimenko by fitting the sub-millimetre/millimetre observations of the thermal emission of the comet’s sub-surface made by the Microwave Instrument for the Rosetta Orbiter with synthetic temperatures derived from a thermophysical model and radiative-transfer models. According to the two major formation scenarios of comets, we model the sub-surface layers to consist of pebbles as well as of homogeneously packed dust grains. In the case of a homogeneous dusty surface material, we find a solution for the length-absorption coefficient of α ≈ 0.22 cm−1 for a wavelength of 1.594 mm and α ≥ 3.84 cm−1 for a wavelength of 0.533 mm and a constant thermal conductivity of 0.006 W m−1 K−1. For the pebble scenario, we find for the pebbles and a wavelength of 1.594 mm a complex refractive index of $n = (1.074 \!-\! 1.256) + \mathit{i} \, (2.580 \!-\! 7.431)\times 10^{-3}$ for pebble radii between 1 and 6 mm. Taking into account other constraints, our results point towards a pebble make-up of the cometary sub-surface with pebble radii between 3 and 6 mm. The derived real part of the refractive index is used to constrain the composition of the pebbles and their volume filling factor. The optical and physical properties are discussed in the context of protoplanetary and debris disc observations.

Searching for outbursts in the ground-based photometry of 67P/Churyumov–Gerasimenko

ABSTRACT 67P/Churyumov–Gerasimenko is a Jupiter-family comet that was the target of the Rosetta mission, the first mission to successfully orbit and land a probe on a comet. This mission was accompanied by a large ground-based observing campaign. We have developed a pipeline to calibrate and measure photometry of comet 67P during its 2016 perihelion passage, making use of all visible wavelength broad-band imaging collected across a wide range of facilities. The pipeline calibrates the brightness of the comet to a common photometric system (Pan-STARRS 1) using background stars within the field allowing for compilation and comparison of multiple data sets. Results follow the predictions based on previous apparitions: 67P shows no obvious change in activity levels from orbit-to-orbit and coma colours remain constant throughout the apparition. We detected an outburst on 2015 August 22 of ∼0.14 mag. The brightness and estimated mass of this outburst puts it in line with the outbursts directly observed on the nucleus by Rosetta. An in situ outburst was observed at the same time as the one seen from the ground; however, linking these two events directly remains challenging.

Ion‐Ion Cross‐Field Instability of Lower Hybrid Waves in the Inner Coma of Comet 67P

AbstractWe show that an ion‐ion cross‐field streaming instability between cold newborn cometary ions and heated heavy ions that were picked up upstream is likely a contributing source of observed lower hybrid (LH) waves in the inner coma of comet 67P/Churyumov‐Gerasimenko. Electric field oscillations in the LH frequency range are common here, and have previously been attributed mainly to the lower‐hybrid drift instability, driven by gradients associated with observed local density fluctuations. However, the observed wave activity is not confined to such gradients, nor is it always strongest there. Thus, other instabilities are likely needed as well to explain the observed wave activity. Several previous works have shown the existence of multiple populations of cometary ions in the inner coma of 67P, distinguished by differences in mass, energy and/or flow direction. We here examine two selected time intervals in October and November 2015, with substantial wave activity in the LH frequency range, where we identify two distinct cometary ion populations: a bulk population of locally produced, predominantly radially outflowing ions, and a more tenuous population picked up further upstream and accelerated back toward the comet by the solar wind electric field. These two populations exhibit strong relative drifts (∼20 km/s, or about five times the pickup ion thermal velocity), and we perform an electrostatic dispersion analysis showing that conditions should be favorable for LH wave generation through the ion‐ion cross‐field instability.

Radial distribution of plasma at comet 67P

Context. The Rosetta spacecraft followed comet 67P/Churyumov-Gerasimenko (67P) for more than two years at a slow walking pace (~1 m s−1) within 1500 km from the nucleus. During one of the radial movements of the spacecraft in the early phase of the mission, the radial distribution of the plasma density could be estimated, and the ionospheric density was found to be inversely proportional to the cometocentric distance r from the nucleus (a 1/r distribution). Aims. This study aims to further characterise the radial distribution of plasma around 67P throughout the mission and to expand on the initial results. We also aim to investigate how a 1/r distribution would be observed during aflyby with a fast (~10’s km s−1) spacecraft, such as the upcoming Comet Interceptor mission, when there is also an asymmetry introduced to the outgassing over the comet surface. Methods. To determine the radial distribution of the plasma, we used data from the Langmuir probe and Mutual Impedance instruments from the Rosetta Plasma Consortium during six intervals throughout the mission, for which the motion of Rosetta was approximately radial with respect to the comet. We then simulated what distribution a fast flyby mission would actually observe during its passage through a coma when there is a 1/r plasma density distribution as well as a sinusoidal variation with a phase angle (and then a sawtooth variation) multiplied to the outgassing rate. Results. The plasma density around comet 67P is found to roughly follow a 1/r dependence, although significant deviations occur in some intervals. If we normalise all data to a common outgassing rate (or heliocentric distance) and combine the intervals to a radial range of 10–1500 km, we find a 1/r1.19 average distribution. The simulated observed density from a fast spacecraft flying through a coma with a 1/r distribution and an asymmetric outgassing can, in fact, appear anywhere in the range from a 1/r distribution to a 1/r2 distribution, or even slightly outside of this range. Conclusions. The plasma density is distributed in such a way that it approximately decreases in a manner that is inversely proportional to the cometocentric distance. This is to be expected from the photoionisation of a collision-less, expanding neutral gas at a constant ionisation rate and expansion speed. The deviation from a pure 1/r distribution is in many cases caused by asymmetric outgassing over the surface, additional ionisation sources being present, electric fields accelerating plasma, and changing upstream solar wind conditions. A fast flyby mission can observe a radial distribution that deviates significantly from a 1/r trend if the outgassing is not symmetric over the surface. The altitude profile that will be observed depends very much on the level of outgassing asymmetry, the flyby velocity, the comet rotation rate, and the rotation phase. It is therefore essential to include data from both the inbound and outbound legs, as well as to compare plasma density to neutral density to get a more complete understanding of the radial distribution of the plasma.

The Nature of Low-albedo Small Bodies from 3 μm Spectroscopy: One Group that Formed within the Ammonia Snow Line and One that Formed beyond It

We present evidence, via a large survey of 191 new spectra along with previously published spectra, of a divide in the 3 μm spectral properties of the low-albedo asteroid population. One group (“sharp types,” or STs, with band centers <3 μm) has a spectral shape consistent with carbonaceous chondrite meteorites, while the other group (“not sharp types,” or NSTs, with bands centered >3 μm) is not represented in the meteorite literature but is as abundant as the STs among large objects. Both groups are present in most low-albedo asteroid taxonomic classes, and, except in limited cases, taxonomic classifications based on 0.5–2.5 μm data alone cannot predict whether an asteroid is an ST or NST. Statistical tests show that the STs and NSTs differ in average band depth, semimajor axis, and perihelion at confidence levels ≥98% while not showing significant differences in albedo. We also show that many NSTs have a 3 μm absorption band shape like comet 67P and likely represent an important small-body composition throughout the solar system. A simple explanation for the origin of these groups is formation on opposite sides of the ammonia snow line, with the NST group accreting H2O and NH3 and the ST group only accreting H2O, with subsequent thermal and chemical evolution resulting in the minerals seen today. Such an explanation is consistent with recent dynamical modeling of planetesimal formation and delivery and suggests that much more outer solar system material was delivered to the main asteroid belt than would be thought based on the number of D-class asteroids found today.

Water ortho-to-para ratio in the coma of comet 67P/Churyumov-Gerasimenko

Context. Abundance ratios of the nuclear-spin isomers of H2O and NH3 have been measured in about two dozen comets, with a mean value corresponding to a nuclear-spin temperature of ~30 K. The real meaning of these unequilibrated nuclear-spin abundance ratios is still debated. However, an equilibrated water ortho-to-para ratio of 3 is also commonly observed. Aims. The H channel of the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS-H) on board Rosetta provided high-resolution 2.5–2.9 μm spectra of H2O vapour in the coma of comet 67P/Churyumov-Gerasimenko (67P), which are suitable for the determination of the ortho-to-para ratio (OPR) of water in this comet. Methods. A large dataset of VIRTIS-H spectra obtained in limb-sounding viewing geometry was analysed, covering heliocentric distances from 1.24 to 2.73 au and altitudes from a few hundred metres to &gt; 100 km. The OPR, together with the H2O rotational temperature and column density, were derived for each spectra using a database of fluorescence synthetic spectra that include both fundamental and hot vibrational water bands. The weak lines of the v1, v1 + v3 − v1 and v2 + v3 − v2 bands in the 2.774–2.910 μm range were used to calculate by how much the strong v3 band centred at 2.67 μm is attenuated due to optical depth effects, expressed by the attenuation factor fatten. Results. Most ortho-to-para ratio determinations are strongly affected by opacity effects, as demonstrated by the observed anti-correlation between the OPR and the column density, and the correlation between the OPR and attenuation factor fatten. Based on both radiative transfer calculations and OPR values obtained in low-opacity conditions, we derive an OPR of 2.94 ± 0.06 for comet 67P. Measured water rotational temperatures show a decrease in gas kinetic temperature with increasing altitude caused by adiabatic cooling. Heliocentric variations are also observed, with warmer temperatures near perihelion. Conclusions. The water ortho-to-para ratio measured in the coma of 67P is consistent with laboratory experiments showing that water vapour that has thermally desorbed from water ice has a statistical value of 3, regardless of the past formation process of water ice.

Underground reservoir of oxygen in comet 67P

Underground reservoir of oxygen in comet 67P

Evidence for thermokarst depressions on comet 67P/Churyumov-Gerasimenko: An interplanetary comparison

Aims. The nucleus of comet 67P/Churyumov-Gerasimenko (67P) is ice rich and shows evidence of morphologies driven by sublimation processes. In particular, the fine-particle deposits (FPD) that cover its surface reveal depressions of many tens of meters. A detailed analysis of these morphologies and of the properties of the fine-particle deposits could help to constrain the amount of water ice in the subsurface. The aim of this paper is to characterize these depressions and constrain their formation and evolution by a detailed quantitative study of their morphometry and thermal environment, and through a comparison with similar morphologies on Earth and Mars. Methods. To study the cometary depressions, we constructed a database of morphometrical parameters for 131 depressions on 67P, 50 alases on Earth, and 200 scalloped depressions on Mars. We measured these parameters manually with the ArcGIS software. We used the images of the Narrow Angle Camera for 67P (down to a resolution of 1 m pixel−1), of the USGC-Digital Orthophoto Quadrangle for the Earth (5 m pixel−1), and of the High Resolution Imaging Science Experiment for Mars (25 cm pixel−1). We also used the digital elevation models associated with these images. In addition, we performed a study of the thermal environment of each depression on 67P to estimate the maximum temperature, the total erosion, and the total energy received from the Sun during one revolution. The morphometrical and thermal environment parameters were then used together for a comparative study of the depressions on 67P, the Earth, and Mars. Results. Our results show that depressions on 67P are geological analogs to alases on Earth and scalloped depressions on Mars; we call them cometary thermokarst depressions. They have been formed by a thermokarst process (i.e., permafrost thawing that causes a subsidence) triggered by water-ice sublimation. The cometary thermokarst depressions on 67P are distributed throughout the nucleus, without preferential distribution for a particular hemisphere or region. They are exclusively located in the fine-particle deposit layer, which is a few meters thick and is thought to have to contain a volume fraction of water ice of about 50% for the subsidence to occur. The formation and evolution of the depressions is driven by the Sun; the side facing the dominant insulation is the preferential direction of erosion. Our results contribute to a better understanding of the periglacial system on comet 67P and of the erosion processes on the nucleus.

ESA's Cometary Mission Rosetta-Re-Characterization of the COSAC Mass Spectrometry Results.

The most pristine material of the Solar System is assumed to be preserved in comets in the form of dust and ice as refractory matter. ESA's mission Rosetta and its lander Philae had been developed to investigate the nucleus of comet 67P/Churyumov–Gerasimenko in situ. Twenty‐five minutes after the initial touchdown of Philae on the surface of comet 67P in November 2014, a mass spectrum was recorded by the time‐of‐flight mass spectrometer COSAC onboard Philae. The new characterization of this mass spectrum through non‐negative least squares fitting and Monte Carlo simulations reveals the chemical composition of comet 67P. A suite of 12 organic molecules, 9 of which also found in the original analysis of this data, exhibit high statistical probability to be present in the grains sampled from the cometary nucleus. These volatile molecules are among the most abundant in the comet's chemical composition and represent an inventory of the first raw materials present in the early Solar System.

On positively charged dust in the coma of comet 67P

ABSTRACT Moment analysis of ion spectrograms measured by the Ion Composition Analyser (ICA) in the coma of comet 67P typically produces an ion number density estimate markedly lower than the number density of free electrons as measured by the Mutual Impedance Probe and the dual Langmuir Probe. While there are good reasons to distrust the ion density moment estimate in these circumstances, the issue cannot yet be considered fully understood and it is of interest to see whether any natural non-instrumental cause is possible. An obvious such cause would be whether a significant fraction of the positive charge density resides in positively charged dust grains that are not measured by the ICA. Here, we show that this scenario is highly unlikely, even near perihelion where photoemission is the strongest. In our semi-analytical grain charging model, we balance the current contributions to grains of photoelectron emission and electron attachment so as to find the expected charge state for a grain of a given radius. The charge state is affected by the ambient electron number density, the electron temperature, and the heliocentric distance. While at times the bulk of the dust population around comet 67P could be charged positive, dust charging, including photoelectron emission, should have a negligible influence on the overall ionization balance in the cometary coma simply because the dust particles are not ubiquitous enough.

Development of a cometosheath at comet 67P/Churyumov-Gerasimenko

Context. The ionosphere of a comet is known to deflect the solar wind through mass loading, but the interaction is dependent on cometary activity. We investigate the details of this process at comet 67P using the Rosetta Ion Composition Analyzer. Aims. This study aims to compare the interaction of the solar wind and cometary ions during two different time periods in the Rosetta mission. Methods. We compared both the integrated ion moments (density, velocity, and momentum flux) and the velocity distribution functions for two days, four months apart. The velocity distribution functions were projected into a coordinate system dependent on the magnetic field direction and averaged over three hours. Results. The first case shows highly scattered H+ in both ion moments and velocity distribution function. The He2+ ions are somewhat scattered, but less so, and appear more like those of H2O+ pickup ions. The second case shows characteristic evidence of mass-loading, where the solar wind species are deflected, but the velocity distribution function is not significantly changed. Conclusions. The distributions of H+ in the first case, when compared to He2+ and H2O+ pickup ions, are indicative of a narrow cometosheath on the scale of the H+ gyroradius. Thus, He2+ and H2O+, with larger gyroradii, are largely able to pass through this cometosheath. An examination of the momentum flux tensor suggests that all species in the first case have a significant non-gyrotropic momentum flux component that is higher than that of the second mass-loaded case. Mass loading is not a sufficient explanation for the distribution functions and momentum flux tensor in the first case, and so we assume this is evidence of bow shock formation.

First Images of Phosphorus Molecules toward a Protosolar Analog

Abstract The chemistry of phosphorus in star- and planet-forming regions is poorly understood, despite the central role of phosphorus in terrestrial biochemistry. We present Atacama Large Millimeter/submillimeter Array band 3 and 4 observations of PO and PN toward the Class I protostar B1-a, representing the first spatially resolved observations of phosphorus carriers toward a solar-type star-forming region. The phosphorus molecules emit from two distinct clumps, which coincide with regions where the protostellar outflow (traced by SiO) interacts with a filament of dense gas (traced by CCS). Thus, the gas-phase phosphorus seems to originate from the shocking of dense interstellar clumps. Based on the observed emission patterns, PO and PN appear to be daughter products of a solid phosphorus carrier with an intermediate volatility between ices and silicate grains. Interstellar shocks may therefore play an important role in converting semi-refractory phosphorus to a more volatile form prior to incorporation into cometary ices. Indeed, the (PO+PN)/CH3OH ratio is similar in B1-a and comet 67P, implying a comparable reservoir of volatile phosphorus. The PO/PN ratio ranges from ∼1–8 across B1-a. The northern emission clump exhibits a lower PO/PN ratio and weaker 13CH3OH emission than southern clump, indicating distinct shock physics and chemistry at the two positions. Resolved observations of P carriers toward additional sources are needed to better understand what regulates such variations in the PO/PN ratio in protostellar environments.

Upstream solar wind speed at comet 67P

Context.Rosetta followed comet 67P at heliocentric distances from 1.25 to 3.6 au. The solar wind was observed for much of this time, but was significantly deflected and to some extent slowed down by the interaction with the coma.Aims.We use the different changes in the speed of H+and He2+when they interact with the coma to estimate the upstream speed of the solar wind. The different changes in the speed are due to the different mass per charge of the particles, while the electric force per charge due to the interaction is the same. A major assumption is that the speeds of H+and He2+were the same in the upstream region. This is investigated.Methods.We derived a method for reconstructing the upstream solar wind from H+and He2+observations. The method is based on the assumption that the interaction of the comet with the solar wind can be described by an electric potential that is the same for both H+and He2+. This is compared to estimates from the Tao model and to OMNI and Mars Express data that we propagated to the observation point.Results.The reconstruction agrees well with the Tao model for most of the observations, in particular for the statistical distribution of the solar wind speed. The electrostatic potential relative to the upstream solar wind is derived and shows values from a few dozen volts at large heliocentric distances to about 1 kV during solar events and close to perihelion. The reconstructed values of the solar wind for periods of high electrostatic potential also agree well with propagated observations and model results.Conclusions.The reconstructed upstream solar wind speed during the Rosetta mission agrees well with the Tao model. The Tao model captures some slowing down of high-speed streams as compared to observations at Earth or Mars. At low solar wind speeds, below 400 km s−1, the agreement is better between our reconstruction and Mars observations than with the Tao model. The magnitude of the reconstructed electrostatic potential is a good measure of the slowing-down of the solar wind at the observation point.

Dynamics of irregularly shaped cometary particles subjected to outflowing gas and solar radiative forces and torques

ABSTRACTThe dynamics of irregularly shaped particles subjected to the combined effect of gas drag and radiative forces and torques in a cometary environment is investigated. The equations of motion are integrated over distances from the nucleus surface up to distances where the gas drag is negligible. The aerodynamic forces and torques are computed assuming a spherically symmetric expanding gas. The calculations are limited to particle sizes in the geometric optics limit, which is the range of validity of our radiative torque calculations. The dynamical behaviour of irregular particles is quite different to those exhibited by non-spherical but symmetric particles such as spheroids. An application of the dynamical model to comet 67P/Churyumov–Gerasimenko, the target of the Rosetta mission, is made. We found that, for particle sizes larger than ∼10 μm, the radiative torques are negligible in comparison with the gas-driven torques up to a distance of ∼100 km from the nucleus surface. The rotation frequencies of the particles depend on their size, shape, and the heliocentric distance, while the terminal velocities, being also dependent on size and heliocentric distance, show only a very weak dependence on particle shape. The ratio of the sum of the particles projected areas in the sun-to-comet direction to that of the sum of the particles projected areas in any direction perpendicular to it is nearly unity, indicating that the interpretation of the observed u-shaped scattering phase function by Rosetta/OSIRIS on comet 67P coma cannot be linked to mechanical alignment of the particles.

VLT spectropolarimetry of comet 67P: dust environment around the end of its intense southern summer

Context.A cornucopia of Rosetta and ground-based observational data sheds light on the evolution of the characteristics of dust particles from comet 67P/Churyumov-Gerasimenko (hereafter 67P) with seasons, implying the different dust environments in the source regions on the surface of the comet.Aims.We aim to constrain the properties of the dust particles of 67P and therefrom diagnose the dust environment of its coma and near-surface layer at around the end of the southern summer of the comet.Methods.We performed spectropolarimetric observations for 67P dust over 4000–9000 Å using the ESO/Very Large Telescope from January–March 2016 (phase angle ranging from ~26° –5°). We examined the optical behaviours of the dust, which, together with Rosetta colour data, were used to search for dust evolution with cometocentric distance. Modelling was also conducted to identify the dust attributes compatible with the results.Results.The spectral dependence of the polarisation degree of 67P dust is flatter than that found in other dynamical groups of comets in similar observing geometry. The depth of its negative polarisation branch appears to be a bit shallower than in long-period comets and might be getting shallower as 67P repeats its apparitions. Its dust colour shows a change in slope around 5500 Å, (17.3 ± 1.4) and (10.9 ± 0.6)% (1000 Å)-1, shortward and longward of the wavelength, respectively, which are slightly redder but broadly consistent with the average of Jupiter-family comets.Conclusions.Observations of 67P dust in this study can be attributed to dust agglomerates of ~100 μm in size detected by Rosetta in early 2016. A porosity of 60% shows the best match with our polarimetric results, yielding a dust density of ~770 kg m-3. The compilation of Rosetta and our data indicates the dust’s reddening with increasing nucleus distance, which may be driven by water-ice sublimation as the dust moves out of the nucleus. We estimate the possible volume fraction of water ice in the initially ejected dust as ~6% (i.e. the refractory-to-ice volume ratio of ~14).

Extraction and analysis of planetary volatiles

<p indent="0mm">Planetary volatiles refer to material components that can be separated from a solid sample as a gas phase via physical processes such as impact and heating. On the one hand, these materials are crucial for studying the formation of the solar system and the evolution of planets and their satellites. On the other hand, they provide resources for deep space exploration. Along with the exploration of deep space in recent decades, the detection of volatiles has also advanced our understanding of the cosmos. For example, the discovery of the Moon’s polar ice has changed the impression that the Moon seriously lacks volatiles, the discovery of suspected biogenic methane on Mars has rekindled people’s hope that Mars may once have harbored life, and studies of the hydrogen isotopes in comet 67P have suggested that most of the water on Earth had come from asteroids instead of comets. The combination of pyrolysis in a high-temperature furnace with mass spectrometry is the main method used to extract and analyze volatiles from deep space. This paper summarizes the extraction methods used and the functional parameters of volatile extraction payloads in deep space exploration and compares the performance indexes of the mass spectrometers used for volatile analysis. Furthermore, this paper introduces some volatiles payloads that may be extracted and analyzed in future deep space exploration missions.