Context: Remote light scattering and thermal infrared observations provide clues about the physical properties of cometary and interplanetary dust particles. Identifying these properties will lead to a better understanding of the formation and evolution of the Solar System. Aims: We present a numerical solution for the radiative and conductive heat transport in a random particulate medium enclosed by an arbitrarily shaped surface. The method will be applied to study thermal properties of cometary dust particles. Methods: The recently introduced incoherent Monte Carlo radiative transfer method developed for scattering, absorption, and propagation of electromagnetic waves in dense discrete random media is extended for radiative heat transfer and thermal emission. The solution is coupled with the conductive Fourier transport equation that is solved with the finite-element method. Results: The proposed method allows the synoptic analysis of light scattering and thermal emission by large cometary dust particles consisting of submicrometer-sized grains. In particular, we show that these particles can sustain significant temperature gradients resulting in the superheating factor phase function observed for the coma of comet 67P/Churyumov-Gerasimenko.
The first known interstellar object, 1I/2017 U1 'Oumuamua, displayed such unusual properties that its origin remains a subject of much debate. We propose that 'Oumuamua's properties could be explained as those of a fractal dust aggregate (a "dust bunny") formed in the inner coma of a fragmenting exo-Oort cloud comet. Such fragments could serve as accretion sites by accumulating dust particles, resulting in the formation of a fractal aggregate. The fractal aggregate eventually breaks off from the fragment due to hydrodynamic stress. With their low density and tenuously bound orbits, most of the…
The CoPhyLab (Cometary Physics Laboratory) project is designed to study the physics of comets through a series of earth-based experiments. For these experiments, a dust analogue was created with physical properties comparable to those of the non-volatile dust found on comets. This "CoPhyLab dust" is planned to be mixed with water and CO$_2$ ice and placed under cometary conditions in vacuum chambers to study the physical processes taking place on the nuclei of comets. In order to develop this dust analogue, we mixed two components representative for the non-volatile materials present in cometa…
Cometary meteoroid trails exist in the vicinity of comets, forming fine structure of the interplanetary dust cloud. The trails consist predominantly of cometary particles with sizes of approximately 0.1 mm to 1 cm which are ejected at low speeds and remain very close to the comet orbit for several revolutions around the Sun. When re-analysing the Helios dust data measured in the 1970s, Altobelli et al. (2006) recognized a clustering of seven impacts, detected in a very narrow region of space at a true anomaly angle of 135 deg, which the authors considered as potential cometary trail particles.…
Context. Cometary dust particles are subjected to various forces after being lifted off the nucleus. These forces define the dynamics of dust, trajectories, alignment, and fragmentation, which, in turn, have a significant effect on the particle distribution in the coma. Aims. We develop a numerical thermophysical model that is applicable to icy cometary dust to study the forces attributed to the sublimation of ice. Methods. We extended the recently introduced synoptic model for ice-free dust particles to ice-containing dust. We introduced an additional source term to the energy balance equatio…
Excess near-infrared emission is detected around one fifth of main-sequence stars, but its nature is a mystery. These excesses are interpreted as thermal emission from populations of small, hot dust very close to their stars (`hot exozodis'), but such grains should rapidly sublimate or be blown out of the system. To date, no model has fully explained this phenomenon. One mechanism commonly suggested in the literature is cometary supply, where star-grazing comets deposit dust close to the star, replenishing losses from grain sublimation and blowout. However, we show that this mechanism alone is…
Comets provide unique information about the physical and chemical properties of the environment in which the Solar system was formed. Understanding how cometary dust and ice evolve under the effect of sunlight is essential for constraining nuclear structure and triggering mechanism of comet activity. In this paper, we first study rotational disruption of dust grains lifted by outgassing from comet nuclei by radiative torques (RATs). We find that composite grains could be rapidly disrupted into small fragments by the Radiative Torque Disruption (RATD) mechanism. We then study rotational desorpt…
We present a possible correlation between the properties of scattered and thermal radiation from dust and the principal dust characteristics responsible for this relationship. To this end, we use the NASA/PDS archival polarimetric data on cometary dust in the Red (0.62--0.73 $μ$m) and K (2.00--2.39 $μ$m) domains to leverage the relative excess of the polarisation degree of a comet to the average trend at the given phase angle ($P_{\rm excess}$) as a metric of the dust's scattered light characteristics. The flux excess of silicate emissions to the continuum around 10 $μ$m ($F_{\rm Si}/F_{\rm co…
The Martian Moons Exploration (MMX) spacecraft is a JAXA mission to Mars and its moons Phobos and Deimos. MMX will carry the Circum-Martian Dust Monitor (CMDM) which is a newly developed light-weight ($\mathrm{650\,g}$) large area ($\mathrm{1\,m^2}$) dust impact detector. Cometary meteoroid streams (also referred to as trails) exist along the orbits of comets, forming fine structures of the interplanetary dust cloud. The streams consist predominantly of the largest cometary particles (with sizes of approximately $\mathrm{100\,μm}$ to 1~cm) which are ejected at low speeds and remain very close …
Here, we report the detection of phosphorus and fluorine in solid particles collected from the inner coma of comet 67P/Churyumov-Gerasimenko measured with the COmetary Secondary Ion Mass Analyser (COSIMA) instrument on-board the Rosetta spacecraft, only a few kilometers away from the comet nucleus. We have detected phosphorus-containing minerals from the presented COSIMA mass spectra, and can rule out e.g. apatite minerals as the source of phosphorus. This result completes the detection of life-necessary CHNOPS-elements in solid cometary matter, indicating cometary delivery as a potential sour…
Acceleration of cometary dust near the nucleus: Application to 67P/Churyumov-Gerasimenko
我们提出了一个模型的彗星尘埃能够模拟的动态范围内的彗星表面的前几十公里。罗塞塔上的GIADA和COSIMA仪器的最新测量表明，该核发出蓬松的尘埃颗粒，孔隙率超过50%，尺寸至少达到mm（Schulz et al. 2015，Rotundi et al. 2015，Fulle et al. 2015）。这些粒子的物理性质的检索需要一个有效的力量控制其动力学模型。在这里，我们提出了一个模型，能够模拟现实的，大的和多孔的颗粒使用分级聚集体，这表明以前的外推是不够的。我们的方法的主要优点是，我们可以模拟非常大的（毫米级）非球形团聚体，并可以准确地确定它们的1）有效截面和截面与质量的比率，2）气体阻力系数，和3）光散射特性。在实践中，我们发现，一个更详细的处理的尘埃结构的结果在3-5倍更高的速度为大的尘埃粒子在内部彗发比以前估计使用相同质量的球形粒子。我们将我们的模型应用于彗星67 P的核附近的尘埃动力学，并成功地再现了早期报告的尘埃速度，当时彗星距离太阳约3.5 AU。在这个阶段，我们采用一个简单的球形彗星核，我们的模型活动作为恒定速度的气体膨胀从一个均匀的活动表面，并使用米氏散射。我们讨论了未来改进这些简化的途径。
Cometary surface dust layers built out of millimetre-scale aggregates: dependence of modelled cometary gas production on the layer transport properties
In this work, we introduce a comet dust model that incorporates multiple dust morphologies along with inhomogeneous mixture of silicate minerals and carbonaceous materials under power-law size distribution, to replicate the standard polarization-phase curve observed in several comets in the narrow-band continuum. Following the results from Rosetta/MIDAS and COSIMA, we create high porosity Hierarchical Aggregates (HA) and low porosity (< 10$\%$) Solids in the form of agglomerated debris. We also introduce a moderate porosity structure with solids in the core, surrounded by fluffy aggregates cal…
Ammonium hydrosulphide has long since been postulated to exist at least in certain layers of the giant planets. Its radiation products may be the reason for the red colour seen on Jupiter. Several ammonium salts, the products of NH3 and an acid, have previously been detected at comet 67P/Churyumov-Gerasimenko. The acid H2S is the fifth most abundant molecule in the coma of 67P followed by NH3. In order to look for the salt NH4+SH-, we analysed in situ measurements from the Rosetta/ROSINA Double Focusing Mass Spectrometer during the Rosetta mission. NH3 and H2S appear to be independent of each …
The Morphological, Elastic, and Electric Properties of Dust Aggregates in Comets: A Close Look at COSIMA/Rosetta's Data on Dust in Comet 67P/Churyumov-Gerasimenko
Glass with embedded metal and sulfides (GEMS) is a major component of chondritic porous interplanetary dust particles. Although GEMS is one of the most primitive components in the Solar System, its formation process and conditions have not been constrained. We performed condensation experiments of gases in the system of Mg-Si-O (MgSiO3 composition) and of the S-free CI chondritic composition (Si-Mg-Fe-Na-Al-Ca-Ni-O system) in induction thermal plasma equipment. Amorphous Mg-silicate particles condensed in the experiments of the Mg-Si-O system, and their grain size distribution depended on the …
The optical properties of the second generation dust that we observe in debris disks remain quite elusive, whether it is the absorption efficiencies at millimeter wavelengths or the (un)polarized phase function at near-infrared wavelengths. Thankfully the same particles are experiencing forces that are size dependent (e.g., radiation pressure), and with high angular resolution observations we can take advantage of this natural spatial segregation. Observations at different wavelengths probe different ranges of sizes, and there is therefore a great synergy in multi-wavelength observations to be…
We study the development of activity in the incoming long-period comet C/2017 K2 over the heliocentric distance range 9 < r_H < 16 AU. The comet continues to be characterized by a coma of sub-millimeter and larger particles ejected at low velocity. In a fixed co-moving volume around the nucleus we find that the scattering cross-section of the coma is related to the heliocentric distance by a power law with heliocentric index $s = 1.14\pm0.05$. This dependence is significantly weaker than the inverse square variation of the insolation as a result of two effects. These are, first, the heliocentr…
Space Sciences Laboratory, University of California at Berkeley（加州大学伯克利分校空间科学实验室）；Centre for Astrophysics and Planetary Science, University of Kent（肯特大学天体物理与行星科学中心）；Washington University（华盛顿大学）
NASA's Stardust mission utilized a sample collector composed of aerogel and aluminum foil to return cometary and interstellar particles to Earth. Analysis of the aluminum foil begins with locating craters produced by hypervelocity impacts of cometary and interstellar dust. Interstellar dust craters are typically less than one micrometer in size and are sparsely distributed, making them difficult to find. In this paper, we describe a convolutional neural network based on the VGG16 architecture that achieves high specificity and sensitivity in locating impact craters in the Stardust interstellar…
