Dust Ejection Research Articles

Localised ejection of dust and chunks on comet 67P/Churyumov-Gerasimenko: testing how comets work

Localised ejection of dust and chunks on comet 67P/Churyumov-Gerasimenko: testing how comets work

New evidence supporting past dust ejections from active asteroid (4015) Wilson–Harrington

Context. (4015) Wilson-Harrington (hereafter, WH) was discovered as a comet in 1949 but has a dynamical property consistent with that of a near-Earth asteroid. Although there is a report that the 1949 activity is associated with an ion tail, the cause of the activity has not yet been identified. Aims. This work aims to reveal the mysterious comet-like activity of the near-Earth asteroid. Methods. We conducted new polarimetric observations of WH from May 2022 to January 2023, reanalyses of the photographic plate images taken at the time of its discovery in 1949, and dust tail simulation modelings, where the dust terminal velocity and ejection epoch are taken into account. Results. We found that this object shows polarization characteristics similar to those of low-albedo asteroids. We derived the geometric albedo ranging from pV = 0.076 ± 0.010 to pV = 0.094 ± 0.018 from our polarimetry (the values vary depending on the data used for fitting and the slope-albedo relationship coefficients). In addition, the 1949 image showed an increase in brightness around the nucleus. Furthermore, we found that the color of the tail is consistent with sunlight, suggesting that the 1949 activity is associated with dust ejection. From the dust tail analysis, ~9 × 105 kg of material was ejected episodically at a low velocity equivalent to or even slower than the escape velocity. Conclusions. We conclude that WH is most likely an active asteroid of main belt origin and that the activity in 1949 was likely triggered by mass shedding due to fast rotation.

Modeling the Enceladus dust plume based on in situ measurements performed with the Cassini Cosmic Dust Analyzer

We analyzed data recorded by the Cosmic Dust Analyzer on board the Cassini spacecraft during Enceladus dust plume traversals. Our focus was on profiles of relative abundances of grains of different compositional types derived from mass spectra recorded with the Dust Analyzer subsystem during the Cassini flybys E5 and E17. The E5 profile, corresponding to a steep and fast traversal of the plume, has already been analyzed. In this paper, we included a second profile from the E17 flyby involving a nearly horizontal traversal of the south polar terrain at a significantly lower velocity. Additionally, we incorporated dust detection rates from the High Rate Detector subsystem during flybys E7 and E21. We derived grain size ranges in the different observational data sets and used these data to constrain parameters for a new dust plume model. This model was constructed using a mathematical description of dust ejection implemented in the software package DUDI. Further constraints included published velocities of gas ejection, positions of gas and dust jets, and the mass production rate of the plume. Our model employs two different types of sources: diffuse sources of dust ejected with a lower velocity and jets with a faster and more colimated emission. From our model, we derived dust mass production rates for different compositional grain types, amounting to at least 28 kg/s. Previously, salt-rich dust was believed to dominate the plume mass based on E5 data alone. The E17 profile shows a dominance of organic-enriched grains over the south polar terrain, a region not well constrained by E5 data. By including both E5 and E17 profiles, we find the salt-rich dust contribution to be at most 1<!PCT!> by mass. This revision also results from an improved understanding of grain masses of various compositional types that implies smaller sizes for salt-rich grains. Our new model can predict grain numbers and masses for future mission detectors during plume traversals.

Postperihelion Cometary Activity on the Outer Main-belt Asteroid 2005 XR132

We report comet-like activity on the outer main-belt asteroid 2005 XR132 discovered by the Lulin One-meter Telescope in early 2021 April. A series of follow-up observations were triggered to characterize the morphology and brightness variation of 2005 XR132. Long-term photometric data of the 2020 perihelion return reveal a 2 mag fading in 120 days, starting 20 days postperihelion, attributed to decreased cometary activity. Even though no variation indicative of the rotational period can be found in our data, we infer an a/b axial ratio of 1.32, given that the lower limit of rotational amplitude is 0.3 mag. A visible spectrum and broadband color support that 2005 XR132 has a reflectance feature similar to a BR-type Centaur object. The syndyne and synchrone simulations reveal a low-speed dust ejecta consisting of millimeter-sized dust grains released shortly after the perihelion passage. We demonstrate that 2005 XR132 has a short dynamical lifetime of 0.12 Myr, with <5% of it in the near-Earth space. Due to the strong gravitational influence from Jupiter and Saturn, the asteroid has followed a random walk orbital migrating process. We also find that since 1550 CE, the perihelion distance of 2005 XR132 has gradually decreased from 2.8 to 2.0 au, likely due to the Kozai–Lidov effect, which potentially reactivated the dormant nucleus. All these dynamical properties support a cometary origin for 2005 XR132 rather than an ice-rich main-belt object kicked out from a stable orbit, although current observational evidence has yet to confirm repeating cometary activities.

The Asteroseismological Richness of RCB and dLHdC Stars

RCB stars are L ≈ 104 L ⊙ solar-mass objects that can exhibit large periods of extinction from dust ejection episodes. Many exhibit semi-regular pulsations in the range of 30–50 days with semi-amplitudes of 0.05–0.3 mag. Space-based photometry has discovered that solar-like oscillations are ubiquitous in hydrogen-dominated stars that have substantial outer convective envelopes, so we explore the hypothesis that the pulsations in RCB stars and the closely related dustless hydrogen-deficient carbon (dLHdC) stars, which have large convective outer envelopes of nearly pure helium, have a similar origin. Through stellar modeling and pulsation calculations, we find that the observed periods and amplitudes of these pulsations follows the well-measured phenomenology of their H-rich brethren. In particular, we show that the observed modes are likely of angular orders l = 0, 1, and 2 and predominantly of an acoustic nature (i.e., p-modes with low radial order). The modes with largest amplitude are near the acoustic cutoff frequency appropriately rescaled to the helium-dominated envelope, and the observed amplitudes are consistent with that seen in high-luminosity (L > 103 L ⊙) H-rich giants. We also find that for T eff ≳ 5400 K, an hydrogen-deficient carbon stellar model exhibits a radiative layer between two outer convective zones, creating a g-mode cavity that supports much longer period (≈100 days) oscillations. Our initial work was focused primarily on the adiabatic modes, but we expect that subsequent space-based observations of these targets (e.g., with TESS or Plato) are likely to lead to a larger set of detected frequencies that would allow for a deeper study of the interiors of these rare stars.

Main Results from the ISSI International Team “Characterization of 67P Cometary Activity”

The ESA/Rosetta mission accompanied the Jupiter Family Comet 67P/Churyumov-Gerasimenko and provided a huge amount of data which are providing important results about cometary activity mechanisms. We summarize the results obtained within the ISSI International Team Characterization of 67P cometary activity, which studied dust and gas ejection in different stages of the comet’s orbit, by means of a data fusion between instruments onboard the Rosetta orbiter, i.e., the OSIRIS camera, the VIRTIS imaging spectrometer, the GIADA dust detector, the MIDAS atomic force microscope, the COSIMA dust mass spectrometer, and the ROSINA gas mass spectrometer, supported by numerical models and experimental work. The team reconstructed the motion of the dust particles ejected from the comet surface, finding a correlation between dust ejection and solar illumination as well as larger occurrence of fluffy (pristine) particles in less processed and more pebble-rich terrains. Dust activity is larger in ice-rich terrains, indicating that water sublimation is the dominant activity process during the perihelion phase. The comparison of dust fluxes of different particle size suggests a link between dust morphology and ejection speed, generation of micrometric dust from fragmentation of millimetric dust, and homogeneity of physical properties of compact dust particles across the 67P surface. The comparison of fluxes of refractory and ice particles suggests the occurrence of a small amount of ice in fluffy particles, which is released when they are fragmented. A new model of cometary activity has been finally developed, according to which the comet nucleus includes Water-Ice-Enriched Blocks (WEBs), that, when exposed by CO2 activity, are the main sources of water sublimation and dust ejection.

A photon burst clears the earliest dusty galaxies: modelling dust in high-redshift galaxies from ALMA to JWST

ABSTRACT The generation and evolution of dust in galaxies are important tracers for star formation, and can characterize the rest-frame ultraviolet to infrared emission from the galaxies. In particular understanding dust in high-redshift galaxies are important for observational cosmology, as they would be necessary to extract information on star formation in the early Universe. We update the public semi-analytical model Ancient Stars and Local Observables by Tracing Halos (a-sloth) to model the evolution of dust, focusing on high-redshift star-forming galaxies with stellar masses of ∼108–1010 M⊙ observed by ALMA (z ≈ 7) and JWST (z ≈ 11). We find that these galaxies should qualitatively differ in their star formation properties; while the samples in ALMA are explained by dust growth in normal star-forming galaxies, the lack of dust in the samples by JWST requires dust ejection by radiation pressure due to recent highly efficient star formation within a few 10 Myr, with order 100 times higher efficiency than normal galaxies calibrated by a-sloth. Depending on where the JWST galaxies locate on the luminosity function, their bursty star formation histories inferred from our model can have impacts for rates of star formation, supernova explosion, stellar feedback, and detectability of dusty, mature galaxies in the very early Universe.

Linking meteorites to their asteroid parent bodies: The capabilities of dust analyzer instruments during asteroid flybys

AbstractLinking meteorites to their asteroid parent bodies remains an outstanding issue. Space‐based dust characterization using impact ionization mass spectrometry is a proven technique for the compositional analysis of individual cosmic dust grains. Here we investigate the feasibility of determining asteroid compositions via cation mass spectrometric analyses of their dust ejecta clouds during low (7–9 km s−1) velocity spacecraft flybys. At these speeds, the dust grain mass spectra are dominated by easily ionized elements and molecular species. Using known bulk mineral volume abundances, we show that it is feasible to discriminate the common meteorite classes of carbonaceous chondrites, ordinary chondrites, and howardite–eucrite–diogenite achondrites, as well as their subtypes, relying solely on the detection of elements with ionization efficiencies of ≤700 or ≤800 kJ mol−1, applicable to low (~7 km s−1) and intermediate (~9 km s−1) flyby speed scenarios, respectively. Including the detection of water ion groups enables greater discrimination between certain meteorite types, and flyby speeds ≥10 km s−1 enhance the diagnostic capabilities of this technique still further. Although additional terrestrial calibration is required, this technique may allow more unequivocal asteroid‐meteorite connections to be determined by spacecraft flybys, emphasizing the utility of dust instruments on future asteroid missions.

Optical monitoring of the dust environment at lunar surface exploration sites

Lessons from the Apollo program showed that dust perturbed by human activities on the lunar surface can significantly interfere with the operation of mechanical, thermal and optical systems. During the Artemis program, monitoring the local dust environment created by surface activities will be critical to understanding and mitigating problems associated with lunar dust. This could be accomplished at many locations using in situ dust detectors; however, a complementary, and arguably more comprehensive, approach would be to measure the intensity of scattered sunlight from dust. Such measurements could be obtained using modest cameras and yield the abundance of dust along an observer line-of-sight. Observations along several look-directions would reveal the dust spatial distribution and constrain the minimum grain size from the angular width of the forward scattering lobe. Perhaps most importantly, these measurements would constrain spatial and temporal variations in dust ejection and deposition rates. Using scattering properties for realistically shaped lunar dust grains, this study simulates spectral intensities for a plausible steady-state distribution of low-speed (∼ m s−1) dust around an exploration site. This is used to assess the feasibility of using commonly available wide-angle optics and commercial off-the-shelf (COTS) image sensors to create a notional dust monitoring camera. The dust detection sensitivity of cameras constructed using components with flight heritage is modeled; e.g., the PL1 image sensor aboard the Light Italian CubeSat for Imaging of Asteroids (LICIACube) part of NASA's Double Asteroid Redirect Test (DART) mission. Results indicate that a simple but well-baffled camera can successfully detect a steady-state dust cloud created by human (artificial) activity with a peak concentration of < 1 μg m−3 for a polar site on the Moon—well below what might be expected during Artemis operations.

Study on the dust migration law and a spray dust suppression scheme in transportation roadway

To solve the problem of excessive dust concentration in the belt transportation roadway of the mine. Numerical simulations were used to study the dust migration in the belt transportation roadway under 1.5m/s ventilation conditions. The simulation results show the process of dust ejection from the inflow chute to contamination of the whole belt transportation roadway, and the spatial distribution of dust velocity. A comprehensive dust reduction scheme of "central suppression and bilateral splitting" was designed according to the dust distribution, with simultaneous control of the infeed chute and the roadway. In practical application, pneumatic spraying greatly reduces the amount of dust in the guide chute. The misting screen has a significant effect on dust collection and segregation. The solution effectively controls the dust in the space of 20m on both sides of the transfer point, and the dust removal efficiency reaches more than 90%.

Perihelion Activity of (3200) Phaethon is Not Dusty: Evidence from STEREO/COR2 Observations

We present an analysis of asteroid (3200) Phaethon using coronagraphic observations from 2008 to 2022 by the COR2 cameras onboard the twin Solar TErrestrial RElations Observatory spacecraft. Although undetected in individual images, Phaethon was visible in stacks combined from the same perihelion observations, yet only at small (≲30°) but not large (≳150°) phase angles. The observations are in line with the contribution from a bare nucleus, thereby seriously contradicting the interpretation based on HI-1 observations that attributes the perihelion activity to the ejection of μm-sized dust. We obtained an upper limit to the effective cross section of μm-sized dust to be ≲105 m2, at least three orders of magnitude smaller than earlier estimates based on HI-1 data. On the contrary, the COR2 observations cannot rule out the existence of mm-sized or larger debris around Phaethon. However, the fact that no postperihelion debris tail has ever been detected for Phaethon suggests the unimportance of such dust in the perihelion activity. We thus conclude that the perihelion activity of Phaethon is highly unlikely relevant to the ejection of dust. Rather, we deduce that the activity is associated with gas emissions, possibly Fe i and/or Na D lines. To verify our conjecture and to fully understand the perihelion activity of Phaethon, more observations at small heliocentric distances are desired. We compile a list of observing windows ideal for the search of gas emissions of the asteroid from ground telescopes. The best opportunities will be during total solar eclipses.

Blue monsters. Why are JWST super-early, massive galaxies so blue?

ABSTRACT The recent James Webb Space Telescope tentative discovery of a population of super-early (redshift z &amp;gt; 10), relatively massive (stellar mass M* = 108–109M⊙) and evolved (metallicity Z ≈ 0.1 Z⊙) galaxies, which nevertheless show blue (β ≃ −2.6) spectra, and very small dust attenuation (AV ≲ 0.02), challenges our interpretation of these systems. To solve the puzzle, we propose two solutions in which dust is either (a) ejected by radiation pressure, or (b) segregated with respect to UV-emitting regions. We clarify the conditions for which the two scenarios apply, and show that they can be discriminated by ALMA observations, such as the recent non-detection of the 88μm dust continuum in GHZ2 (z ≃ 12) favouring dust ejection.

Dust processing in protoplanetary envelopes as the origin of hot minerals in comets

ABSTRACT Crystalline silicates are found in a large number of comets. These pose a long-standing conundrum for Solar system formation models as they can only be created in the inner hot disc at temperatures higher than 800 K, and there is no obvious mechanism to transport them out into the comets formation region. Here, we propose that these particles could have formed inside the hydrostatic envelopes surrounding young protoplanets still embedded in the protoplanetary disc. Using a simplified 1D model we investigate the thermal structure of these envelopes, and find that for core masses ranging from 0.08 to 1.5 M⊕, located anywhere between 1 and 30 au, the temperature and pressure at the base of the envelopes are high enough to quickly vapourize silicate particles of various sizes. Moreover, if the grain abundance is atleast solar, these envelopes become fully convective, allowing for dust ejection across the Bondi radius back into the disc. Amorphous silicates are hence thermally processed into crystalline particles in these envelopes, and then transported back to disc through convective diffusion to be finally incorporated into the cometary building blocks.

3D Radiative-transfer Simulations of the Ejecta Plume Anticipated from DART Impact

We present a modeling approach that allows the reconstruction of detailed images of the ejecta plume produced by the DART impact on asteroid Dimorphos. The approach is based on the 3D radiative-transfer technique and uses the publicly available HYPERION software package. The modeling automatically includes all interactions of light with the asteroid and ejecta plume, including transmission of the light through a hollow cone, reflection from the asteroid, and second transmission through the ejecta for each point within the ejecta plume and asteroid surface. The results of the modeling are the FITS images of the asteroid and ejecta as they will be seen by the LEIA camera on board LICIACube for any specific moments after impact. The parameters of the modeling are preimpact assumptions regarding Dimorphos’ shape and composition, the presumed impact location, and the planned flyby trajectory of LICIACube. The results of the modeling show the readiness of our modeling tools to simulate the realistic ejecta plume after impact with the purpose to model the LICIACube images at different moments after impact and estimate the properties of the dust ejecta particles and the ejecta mass.

Toward a population synthesis of disks and planets

Context. Millimeter astronomy provides valuable information on the birthplaces of planetary systems. In order to compare theoretical models with observations, the dust component has to be carefully calculated. Aims. Here, we aim to study the effects of dust entrainment in photoevaporative winds, and the ejection and drag of dust due to the effects caused by radiation from the central star. Methods. We improved and extended the existing implementation of a two-population dust and pebble description in the global Bern/Heidelberg planet formation and evolution model. Modern prescriptions for photoevaporative winds were used and we accounted for settling and advection of dust when calculating entrainment rates. In order to prepare for future population studies with varying conditions, we explored a wide range of disk, photoevaporation, and dust parameters. Results. If dust can grow to pebble sizes, that is, if they are resistant to fragmentation or turbulence is weak, drift dominates and the entrained mass is small but larger than under the assumption of no vertical advection of grains with the gas flow. For the case of fragile dust shattering at velocities of 1m s−1 – as indicated in laboratory experiments –, an order of magnitude more dust is entrained, which becomes the main dust removal process. Radiation pressure effects disperse massive, dusty disks on timescales of a few hundred Myr. Conclusions. These results highlight the importance of dust entrainment in winds as a solid-mass removal process. Furthermore, this model extension lays the foundations for future statistical studies of the formation of planets in their birth environment.

Hot exozodis: cometary supply without trapping is unlikely to be the mechanism

ABSTRACT 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 very unlikely to be responsible for hot exozodis. We model the trajectory and size evolution of dust grains released by star-grazing comets, to establish the dust and comet properties required to reproduce hot-exozodi observations. We find that cometary supply alone can only reproduce observations if dust ejecta has an extremely steep size distribution upon release, and the dust-deposition rate is extraordinarily high. These requirements strongly contradict our current understanding of cometary dust and planetary systems. Cometary supply is therefore unlikely to be solely responsible for hot exozodis, so may need to be combined with some dust-trapping mechanism (such as gas or magnetic trapping) if it is to reproduce observations.

The activity of comet C/2014 E2 (Jacques) from pre and post-perihelion images

We present ground-based optical and infrared imaging observations of long period comet C/2014 E2 (Jacques) before and after its perihelion passage. The aim of this work is to characterize the activity of the comet C/2014 E2 (Jacques) in its pre- and post-perihelion stages. Both from the morphological and photometric point of view, as well as its gas production (CO or CO2). We observed the comet with the 2.15 ​m telescope at CASLEO whit R broadband. For the analysis of the inner coma of the comet we used a series of enhancement filters in order to find dust structures. To estimate the dust production of the comet we made photometric measurements to calculate the Afρ parameter. To estimate the gas production we used NEOWISE infrared images of the comet. It was possible to identify two jet-like structures coming out from the nuclear region of the comet, one in the sun-ward direction (which is most likely the dust tail) and the other which probably is due to ejected dust from an active region in the nucleus. These two features were observed in pre- and post-perihelion observations. The A(0°)fρ values calculated for comet Jacques (in cm) were: 909 ​± ​47, 1014 ​± ​21, 706 ​± ​23 for pre-perihelion at ∼1.27au and 450 ​± ​21, 444 ​± ​20, 411 ​± ​18 for post-perihelion at ∼1.64au. The values derived for QCO (in molecules s−1) were: <5.24×1027,<5.92×1028,<1.41×1028. While for QCO2 (in molecules s−1) were: <4.62×1026,<5.21×1027,<1.24×1027. These values are upper limits since we can't discern between CO and CO2 emission.

Releasing Atmospheric Martian Dust in Sand Grain Impacts

Emission of dust up to a few microns in size by impacts of sand grains during saltation is thought to be one source of dust within the Martian atmosphere. To study this dust fraction, we carried out laboratory impact experiments. Small numbers of particles of about 200 μm in diameter impacted a simulated Martian soil (bimodal Mars Global Simulant). Impacts occurred at angles of ∼18° in vacuum with an impact speed of ∼1 m s−1. Ejected dust was captured on adjacent microscope slides and the emitted particle size distribution (PSD) was found to be related to the soil PSD. We find that the ejection of clay-sized dust gets increasingly harder the smaller these grains are. However, in spite of strong cohesive forces, individual impacts emit dust of 1 μm and less, i.e., dust in the size range that can be suspended in the Martian atmosphere. More generally, the probability of ejecting dust of a given size can be characterized by a power law in the size range between 0.5 and 5 μm (diameter).

Electrostatic dust ejection from asteroid (3200) Phaethon with the aid of mobile alkali ions at perihelion

The asteroid (3200) Phaethon is known to be the parent body of the Geminids, although meteor showers are commonly associated with the activity of periodic comets. What is most peculiar to the asteroid is its comet-like activity in the ejection of micrometer-sized dust particles at every perihelion passage, while the activity of the asteroid has never been identified outside the near-perihelion zone at 0.14au from the Sun. From the theoretical point of view, we argue that the activity of the asteroid is well explained by the electrostatic lofting of micrometer-sized dust particles with the aid of mobile alkali ions at high temperatures. The mass-loss rates of micrometer-sized particles from the asteroid in our model is entirely consistent with the values inferred from visible observations of Phaethon’s dust tail. For millimeter-sized particles, we predict three orders of magnitudes higher mass-loss rates, which could also account for the total mass of the Geminid meteoroid stream by the electrostatic lofting mechanism.

The case for a Themis asteroid family spacecraft mission

The last decade has highlighted the importance of icy asteroids as likely outer-solar-system planetesimals that brought organics and ices to the inner solar system. Better characterizing the relationship between these objects and other water-rich bodies throughout the solar system and their evolution as potential sources of organics has broad-ranging implications. Additionally, characterizing ice-rich bodies is important for understanding the evolution and diversity of Ocean Worlds. Observations and modeling have suggested that the Themis asteroid family likely represents the fragments of an icy protoplanet originally similar in size to (10) Hygeia (∼444 ​km), which was broken apart by a catastrophic collision and with (24) Themis possibly representing its core. While extensive observations have been made of the icy asteroid (1) Ceres, exploring the deep interior structure and processes is difficult when observing an intact planetary body. Thus, the many objects in the Themis family provide an opportunity to observe an interior cross-section of one of these protoplanetary objects. The Themis family contains a variety of members, including multiple Main Belt Comets (e.g., 133P/Elst-Pizarro) for which comet-like dust ejection (consistent with being driven by sublimation of volatile material) has been observed. In this paper, we present the science case for why the exploration of the Themis family is key to understanding icy objects in the solar system, and present three design-referenced mission architectures that would be plausible under the NASA Discovery mission cost cap that would address key science objectives pertaining to icy asteroids.