Condensation Ice Research Articles

Robust and Superhydrophobic Polydimethylsiloxane/Ni@Ti3C2Tx Nanocomposite Coatings with Assembled Eyelash-Like Microstructure Array: A New Approach for Effective Passive Anti-Icing and Active Photothermal Deicing.

To solve the problem of ice condensation and adhesion, it is urgent to develop new anti-icing and deicing technologies. This study presented the development of a highly efficient photothermal-enhanced superhydrophobic PDMS/Ni@Ti3C2Tx composite film (m-NMPA) fabricated cost-effectively and straightforwardly. This film was fabricated utilizing PDMS as a hydrophobic agent, adhesive, and surface protector, while Ni@Ti3C2Tx as a magnetic photothermal filler innovatively. Through a simple spraying method, the filler is guided by a strong magnetic field to self-assemble into an eyelash-like microstructure array. The unique structure not only imparts superhydrophobic properties to the surface but also constructs an efficient "light-capturing" architecture. Remarkably, the m-NMPA film demonstrates outstanding superhydrophobic passive anti-icing and efficient photothermal active deicing performance without the use of fluorinated chemicals. The micro-/nanostructure of the film forms a gas layer, significantly delaying the freezing time of water. Particularly under extreme cold conditions (-30 °C), the freezing time is extended by a factor of 7.3 compared to the bare substrate. Furthermore, under sunlight exposure, surface droplets do not freeze. The excellent photothermal performance is attributed to the firm anchoring of nickel particles on the MXene surface, facilitating effective "point-to-face" photothermal synergy. The eyelash-like microarray structure enhances light-capturing capability, resulting in a high light absorption rate of 98%. Furthermore, the microstructure aids in maintaining heat at the uppermost layer of the surface, maximizing the utilization of thermal energy for ice melting and frost thawing. Under solar irradiation, the m-NMPA film can rapidly melt approximately a 4 mm thick ice layer within 558 s and expel the melted water promptly, reducing the risk of secondary icing. Additionally, the ice adhesion force on the surface of the m-NMPA film is remarkably low, with an adhesion strength of approximately 4.7 kPa for a 1 × 1 cm2 ice column. After undergoing rigorous durability tests, including xenon lamp weathering test, pressure resistance test, repeated adhesive tape testing, xenon lamp irradiation, water drop impact testing, and repeated brushing with hydrochloric acid and particles, the film's surface structure and superhydrophobic performance have remained exceptional. The photothermal superhydrophobic passive anti-icing and active deicing technology in this work rely on sustainable solar energy for efficient heat generation. It presents broad prospects for practical applications with advantages such as simple processing method, environmental friendliness, outstanding anti-icing effects, and exceptional durability.

Relative humidity measurements of a thin-film humidity sensor in condensing conditions in the temperature range from −40 °C to 5 °C

In condensing conditions, metastable states such as supersaturation of water vapour and supercooling of liquid water are commonly observed in the free atmosphere. This study investigates the response of a polymeric thin-film humidity sensor under condensing conditions at various temperatures (−40 °C, −20 °C, −5 °C, and 5 °C) and different relative humidity (RH) levels. To ensure precise control of RH, a saturator-based humidity generator operating in a two-temperature mode is utilized. The condensing conditions are achieved in two ways: by increasing water vapour pressure (WVP) at a fixed temperature and by decreasing the temperature while maintaining a constant WVP. In general, when measuring RH under condensing conditions, the sensor indicates a temporary supersaturation state with an RH peak exceeding 100% before the onset of condensation. Subsequently, the RH value exhibits a delayed decrease when exposed to a non-condensing RH level. The experiments with a constant WVP demonstrate a lower likelihood of ice condensation compared to those with a constant temperature. This study demonstrates the measurement capability and behaviour of thin-film humidity sensors above 100% RH in the supersaturation states that are commonly observed in the free atmosphere at meteorologically-relevant temperatures.

Modeling and analysis of ice condensation on bridge deck pavement surface based on heat transfer theory and finite element method

Bridge surfaces usually freeze more easily than road surfaces in wet and cold conditions, which is unfavorable to traffic safety. This study aims to develop an ice prediction model for bridge deck pavement structures by integrating external climatic factors and internal structure parameters, and to analyze the mechanism of ice condensation. This model adopted finite element analysis to deal with the heat transfer problem and the latent heat during the phase change process. A series of experiments were designed to validate the model, and the relative difference was around 10 %. Results shown that: among external climatic factors, the impact of changes in water accumulation on ice formation is not significant. Meanwhile, the air temperature has the greatest impact, and there is a non-linear relationship between wind speed and the initial freezing time. In the study on the effect of aging, it was found that aged asphalt concrete pavement would freeze earlier and melt later compared to new. When comparing different structures, it was observed that the initial freezing time of the bridge deck pavement structure was 0.8 h earlier than the road structure, and the total freezing time was 2.8 h shorter than the road structure. It was also found that the lower thermal conductivity would delay the occurrence of icing when the bridge deck pavement structure was in a cooling stage. Finally, it was observed that the vehicle speed played a critical role in determining the direction of the heat flow with a specific value, and the value would increase as the temperature difference decreased. This prediction model is useful for transportation agencies to understand the mechanism of pavement ice formation and ensure traffic safety in winter.

Fabrication of bioinspired closed chute structure on TC4 surface by double laser beam ablation for enhanced dynamic anti-icing performance

The dynamic behavior of water droplets plays an important role in anti-icing performance, as when they impact on superhydrophobic surfaces, the rebound process effectively removes potential ice crystal nuclei on the surface, thereby reducing ice condensation and accumulation, ultimately preventing ice formation. In this study, inspired by the cuticle structure of springtails and the tilted arrangement of pigeon feathers, a bionic superhydrophobic surface with closed chute structure is proposed. The closed chute structure reduces the adhesion force between the surface and water droplets, enhancing directional rebounding ability and accelerating water droplets' separation from the surface for enhanced anti-icing performance. Considering the morphology of hierarchical closed structures is difficult to be regulated by single laser beam ablation, the superhydrophobic surface with closed chute structure is successfully fabricated by double laser beam ablation. This method optimizes the spatial distribution of the laser energy field by adjusting the rotation angle of the half-wave plate (HWP). By combining the analysis of micromorphology, elemental distribution, dynamic and static anti-icing tests etc., it is verified that the superhydrophobic surface with closed chute structure can improve the dynamic anti-icing performance, which provides a new method for anti-icing design in engineering field.

Nanophase magnetite in matrix of anomalous EL3 chondrite Northwest Africa (NWA) 8785

AbstractNWA 8785 is a remarkable EL3 chondrite with a high abundance (~34 vol%) of an Fe‐rich matrix. This is the highest matrix abundance known among enstatite chondrites (ECs) and more similar to the matrix abundances in some carbonaceous and Rumuruti chondrites. X‐ray diffraction and TEM data indicate that the fine‐grained portion of the NWA 8785 matrix consists of nanoscale magnetite mixed with a noncrystalline silicate material and submicron‐sized enstatite and plagioclase grains. This is the first report of magnetite nanoparticles in an EL3. The Si content of the metal (0.7 wt%), presence of ferroan alabandite, and its O isotopic composition indicate NWA 8785 is EL3‐related. Having more abundant matrix than in other ECs, and that the matrix is rich in magnetite nanoparticles, which are not present in any other EC, suggest classification as an EL3 anomalous. Although we cannot completely exclude any of the mechanisms or environments for formation of the magnetite, we find a secondary origin to be the most compelling. We suggest that the magnetite formed due to hydrothermal activity in the meteorite parent body. Although ECs are relatively dry and likely formed within the nebular snow line, ices may have drifted inward from just beyond the snow line to the region where the EL chondrites were accreting, or more likely the snow line migrated inward during the early evolution of the solar system. This may have resulted in the condensation of ices and provided an ice‐rich region for accretion of the EL3 parent body. Thus, the EL3 parent body may have had hydrothermal activity and if Earth formed near the EC accretion zone, similar bodies may have contributed to the Earth's water supply. NWA 8785 greatly extends the range of known characteristics of ECs and EC parent body processes.

Aerosol Typology and Trajectories in the Metropolitan Region of Rio De Janeiro, Brazil

Aerosols are liquid or solid particles suspended in the atmosphere. Correct determination of the distribution of aerosol types in the atmosphere is of paramount importance for long-term climate predictions. The latest report of the International Panel on Climate Change (IPCC) addresses aerosols as representing the most significant uncertainties in the context of forcing climate sources. These particles can interfere with the climate directly, indirectly, or semi-directly. Directly, we can highlight the interaction of these particles with solar radiation through their scattering or absorption. Indirectly, the role of these aerosols as nuclei for the condensation of liquid and ice in clouds is significant. Depending on their quantity, these aerosols can form larger or smaller droplets, leading to changes in the cloud's albedo. As for semi-direct effects, we can emphasize the role of aerosols as radiation absorbers within clouds, consequently leading to changes in the stability of the air parcel. As a semi-direct effect, we can highlight changes in the life cycle and the ability to make convective clouds colder and more profound.

Analysis of Cloud Growth Phases When Nocturnal Hail Occurs (Case Study: Sekadau, 22 August 2020)

On August 22 2020, hail was reported in Sekadau, West Kalimantan at 21:23 WIB. The phenomenon of hail does not usually occur at night. So, further research is needed to find out how the cloud growth phase and Cumulonimbus (Cb) cloud structure are in this phenomenon. This research utilizes remote sensing instruments in the form of a C-Band type weather radar for the Supadio Meteorological Station and the Himawari 8 Satellite, as well as a radiosonde instrument that is closest to the time and location of the hail events. The results of satellite imagery show that nocturnal hail occurs before the clouds reach the mature phase, with the cloud top temperature at the time of hail less than -60 ºC. The maximum reflectivity detected by the radar using CMAX products shows a less significant value with an intensity of up to 52 dBZ. The VCUT product shows the maximum intensity altitude is at an altitude of 5 – 8 km. This shows that there is a process of ice condensation on the freezing level layer. The ZHAIL product image shows that there is a potential for hail in the Sekadau area with a probability of more than 80%. The occurrence of ice rain at Sekadau at night is caused by the presence of Cumulonimbus clouds with very cold peak temperatures and the mixing process above the freezing level which supports the formation of ice condensation in Cb clouds.

Research on Short Term Prediction Algorithm for Freeway Pavement Ice

This article focuses on the short-term prediction algorithm for ice condensation on highway pavement. Solar radiation, ground long wave radiation, and atmospheric inverse radiation are the main factors affecting road surface temperature changes. According to the principle of radiation heat transfer, there is a radiation balance relationship among these three factors. Therefore, based on the balance relationship between these three radiations and the physical heat formula, this article designs a short-term prediction algorithm for road icing. Based on the basic theory of radiation heat transfer, the energy balance between solar shortwave radiation, atmospheric inverse radiation, and ground longwave radiation is calculated to predict the temperature of highway road surfaces.

Informed Multi‐Scale Approach Applied to the British Columbia Fires of Late Summer 2017

AbstractPyrocumulonimbus (PyroCb) clouds have a complex origin dependent on fire dynamics and meteorological conditions. When a pyrocumulonimbus cloud develops and is maintained over a period of time, it can inject significant aerosol into the troposphere and lower stratosphere, resulting in a longer‐term (months to years) occurrence of aerosol in the stratosphere. In this work, we investigate the British Columbia wildfires on 12–13 August 2017 using a multi‐scale simulation framework. We use the output of a physics‐based wildfire model (FIRETEC) with parameterized energy, particle, and gas emissions to drive the upper atmospheric aerosol mass injection within a regional cloud resolving model (HIGRAD). We demonstrate that vertical motions produced by latent heat release of the condensation of ice and cloud particles within the PyroCbs induce another 5 km of lifting of the simulated aerosol plume. Primary black carbon and organic aerosols (OAs) alone may not be enough to explain the observed aerosol burden, thus we show that secondary OA produced via condensation of gases by the fires, ash, and possibly dust can enhance lofted aerosol mass. A simulation with all emission mechanisms active, driven by the observed fuel load and environmental conditions, reasonably reproduces an aerosol profile inferred from observational data.

ПЕРСПЕКТИВА ПРИМЕНЕНИЯ ГИБРИДНОГО ПОРОШКОВОГО МАТЕРИАЛА AgI-SiO2 В СОСТАВЕ ПРОТИВОГРАДОВОГО РАКЕТНОГО ТОПЛИВА

The work proposes new hybrid powder materials as sediment-converting reagents used in geoengineering technologies (technologies for artificial precipitation management). Hybrid powder materials AgI-SiO2 are mesophase mesoporous silicon dioxide with silver iodide. They were obtained through the “Paste Formation” process, which involves constant mixing of an aqueous condensed suspension of silicon dioxide of various types with the sequential addition of silver nitrate and potassium iodide. The characteristic features of the synthesized AgI-SiO2 hybrids were studied using instrumental methods of analysis: structural, textural and rheological parameters. The influence of hybrid powder material AgI-SiO2 (HPs) on the efficiency of anti-hail rocket fuel is shown using the TERRA software system for modeling phase and chemical equilibrium at high temperatures. It is certain that using HPs AgI-SiO2 as part of anti-hail rocket fuel leads to an increase in the amount of condensed phase, including active forms of silver iodide. This active form of AgI is required for the implementation of ice formation processes in the cloud. An increase in the amount of the β-form of AgI in the composition of the initial HPs was shown compared to pure silver iodide using X-ray phase (XRF) analysis and differential scanning calorimetry. It was established that silver iodide in the hybrid has greater thermal stability, as evidenced by the characteristic peaks of crystalline forms. HPs AgI-SiO2 will improve the efficiency of anti-hail rocket fuel by increasing the number of ice formation and condensation centers, because they exhibit several mechanisms of action on atmospheric moisture. The synthesized hybrid powders meet the requirements of the regulatory documents in force in the Russian Federation

Impacts of Organic Ice Condensation on the Optical Properties of Haze on Pluto

The flyby of the New Horizons spacecraft in 2015 July revealed an unexpected cold atmosphere of Pluto and confirmed the existence of its atmospheric haze. The observed and simulated vertical profiles of chemical species and microphysical processes suggest that the haze particles in Pluto’s middle and lower atmosphere may contain organic ice condensation. Such organic ice components can potentially affect Pluto’s haze chemistry and optical properties, as well as its energy budget. This study investigates the influence of the ice components on the scattering properties of Pluto’s haze by comparing New Horizons observations and simulated particle scattering properties. Comprehensive tests are performed for various haze particle parameters, including their size, chemical component, ice content, and morphology. Scattering properties of these ice-bearing haze particles are calculated by a discrete dipole approximation method and compared to multispectral observations obtained by four New Horizons instruments in spectral regions ranging from the ultraviolet to the near-infrared. The results indicate that the inclusion of the organic ice component leads to higher ratios of backscattering in the visible to extinction in the ultraviolet and provides better agreement with observations compared to monodispersed homogeneous aggregates. But it alone is not sufficient to explain the observed forward scattering values in the visible and near-infrared. Therefore, other scattering sources and/or mechanisms are still required to explain the full set of scattering observations. Further observations, as well as laboratory measurements and numerical tests, are anticipated to improve our understanding of the morphology and ice content of Pluto’s haze.

Assimilation of global positioning system radio occultation refractivity for the enhanced prediction of extreme rainfall events in southern India

AbstractHere, we investigated the impact of assimilating the satellite‐based product of Global Positioning System (GPS) radio occultation (RO) refractivity profiles data on the simulation of selected extreme rainfall events in three states of southern India: Tamil Nadu, Telangana, and Kerala. We assimilated the GPS RO data into the weather research and forecasting model using a 3DVar assimilation technique and evaluated the results against unassimilated (control) simulations. Various observations (e.g., rainfall measurements from AWS/rain‐gauge) and observation‐based gridded rainfall were used. The assimilation of the data yielded improved prediction of the spatial distributions of extreme rainfall regions and the amounts of rainfall. The analysis of the simulated dynamical and thermodynamic processes indicated that the assimilation of the data enabled the model to simulate significantly deep convection, high instability, and strong vertical motions. A vorticity budget analysis confirmed the marginally strengthened low‐level convergence. The vertical motions because of assimilation facilitated an increased vertical advection of vorticity, which enhanced the extreme conditions in storms. Moreover, the assimilation of the data resulted in enhanced water vapor condensation and high levels of ice, cloud, and rain water in clouds, all of which contributed to extreme rainfall.

Microwave-assisted single-step synthesis of acid hydrazides from corresponding acids utilizing newly designed apparatus

Acid hydrazides are essential intermediates in organic synthesis. They conventionally require a two-step synthetic pathway; esterification and hydrazine hydrate treatment; to obtain the hydrazide. The microwave-assisted synthetic methodology was utilized as a greener and straightforward single-step approach for their synthesis in highly encouraging yields. Thus, the aim of the present work was to synthesize acid hydrazides of Diclofenac, Indomethacin, Ibuprofen, and Mefenamic acid using microwave radiation with the aid of a newly designed fit-in ice condenser. Esters of the selected compounds were firstly synthesized, and acid hydrazides were then synthesized utilizing both the conventional and the proposed microwave-assisted single-step methods. The developed technique was successfully yielded 86.7%, 40.9%, and 65.5% acid hydrazides of Diclofenac, Indomethacin, and Mefenamic acid in just 3 min., 10 min. and 3 min., respectively. In comparison to the conventional method, the developed method was simpler with a very short reaction time and quantified yields. The structures of the synthesized acid hydrazides were also confirmed using FT-IR and 1H-NMR. The proposed method with the modified fit-in ice condenser proved to be efficient, cost-effective, and time-saving in the synthesis of acid hydrazides understudy in a single step.

Effects of Haze Radiation and Eddy Heat Transport on the Thermal Structure of Pluto’s Lower Atmosphere

Abstract The temperature profile of Pluto’s atmosphere has generally been assumed in a radiative–conductive equilibrium. Recent studies further highlighted the importance of radiative heating and cooling effects by haze particles. In this study, we update results from Zhang et al. by taking into account the icy haze composition proposed by Lavvas et al., and find that radiation of such an icy haze could still dominate the energy balance in the middle and upper atmosphere and explain the cold temperature observed by New Horizons. However, additional considerations are needed to explain the rapid decrease in temperature toward the icy surface at altitudes <25 km. We propose that vertical eddy heat transport might help maintain radiative–diffusive equilibrium in the lower atmosphere. In this scenario, our radiative–conductive–diffusive model (including both gas and haze) would match observations if the eddy diffusivity is on the order of 103 cm2 s−1. Alternatively, if eddy heat transport is not effective on Pluto, in order to match observations, haze albedo must increase rapidly with decreasing altitude and approach unity near the surface. This is a plausible result of additional ice condensation and/or cloud formation. In this scenario, haze radiation might still dominate over gas radiation and heat conduction to maintain radiative equilibrium. Better constraints on haze albedo at ultraviolet and visible wavelengths would be a key to distinguish these two scenarios. Future mid-infrared observations from the James Webb Space Telescope could also constrain the thermal emission and haze properties in Pluto’s lower atmosphere.

Multi-scale study of anti-freeze properties, anti-freeze mechanism and rheological properties of biological antifreeze protein (AFP) modified emulsified asphalt coating

In this study, biological modification technology was utilized to improve the frost resistance of pavement. By adding biological antifreeze protein to asphalt-based materials, a biomodified emulsified asphalt layer with active antifreeze qualities was created. The mixing mode and its anti-freezing efficacy were investigated using molecular dynamics (MD) simulations. The anti-freezing protein (AFP) was embedded on the asphalt surface, and the structure was completed with asphalt application in two phases. After AFP was attached to the surface of the asphalt binder, the structure remained stable at low temperatures, inhibiting icing and producing a thermal hysteresis differential. Hydrogen bonding and Van der Waals forces influence ice molecule aggregation, and AFP can reduce their effect and induce ice crystal melting. Scanning electron microscopy (SEM) and fluorescence microscopy (FM) revealed that the AFP surface was uneven and anchored to the asphalt surface. The overall structure was complete, with a two-phase distribution that corresponded with the MD results. The anti-icing test results demonstrated that the AFP-modified emulsified asphalt coating effectively inhibited ice condensation and could change the ice crystal growth pattern. The rheological test results revealed that AFP had a slightly negative effect on the high-temperature deformation resistance of the asphalt binder. Environment friendly AFP-modified emulsified asphalt can significantly improve the anti-freezing characteristics of the pavement.

The Nature and Composition of Jupiter’s Building Blocks Derived from the Water Abundance Measurements by the Juno Spacecraft

Abstract The microwave radiometer on board the Juno spacecraft provided a measurement of the water abundance found to range between ∼1 and 5.1 times the protosolar abundance of oxygen in the near-equatorial region of Jupiter. Here, we aim to combine this up-to-date oxygen determination, which is likely to be more representative of the bulk abundance than the Galileo probe subsolar value, with the other known measurements of elemental abundances in Jupiter, to derive the formation conditions and initial composition of the building blocks agglomerated by the growing planet, and that determine the heavy element composition of its envelope. We investigate several cases of formation of icy solids in the protosolar nebula (PSN), from the condensation of pure ices to the crystallization of mixtures of pure condensates and clathrates in various proportions. Each of these cases corresponds to a distinct solid composition whose amount is adjusted in the envelope of Jupiter to match the O abundance measured by Juno. The volatile enrichments can be matched by a wide range of planetesimal compositions, from solids exclusively formed from pure condensates or from nearly exclusively clathrates, the latter case providing a slightly better fit. The total mass of volatiles needed in the envelope of Jupiter to match the observed enrichments is within the ∼4.3–39 M ⊕ range, depending on the crystallization scenario considered in the PSN. A wide range of masses of heavy elements derived from our fits is found to be compatible with the envelope’s metallicity calculated from current interior models.

The history of ground ice at Jezero Crater Mars and other past, present, and future landing sites

Shallow subsurface water ice on Mars is currently stable poleward of about 45° latitude and unstable in the equatorial regions. Past climate cycles driven by orbital oscillations are expected to result in significant changes to this distribution of ground ice over geologic history. In the present study we model the 2.5-Myr history of ground ice at 11 past, present, and planned future landing sites, employing new views of the martian climate and new ground truth observations. We specifically evaluate the potential for detecting ground ice at current and future GPR-equipped-rover landing sites at Jezero Crater, Utopia Planitia, and Oxia Planum. We find that, while ground ice is stable at the past Phoenix and Viking Lander 2 sites, it is presently unstable at all others. However, ground ice would have been stable at all the landing sites for extended periods of 10's of kyrs when the obliquity exceeded about 29°–33°. The most recent such episode would have occurred about 500 kyrs ago. On thousand-year time scales water-vapor diffusion through porous soil and ice condensation are rapid enough to keep pace with these climate changes, such that the presence of ground ice can be equated with its stability. Prior to 5 Myr ago the obliquity is predicted to have experienced a secular shift to a higher average of ~36°. During this time extensive subsurface ice deposits may have formed that may persist unstably today as a relict of this past condition.

Improved Convective Ice Microphysics Parameterization in the NCAR CAM Model

AbstractPartitioning deep convective cloud condensates into components that sediment and detrain, known to be a challenge for global climate models, is important for cloud vertical distribution and anvil cloud formation. In this study, we address this issue by improving the convective microphysics scheme in the National Center for Atmospheric Research Community Atmosphere Model version 5.3 (CAM5.3). The improvements include: (1) considering sedimentation for cloud ice crystals that do not fall in the original scheme, (2) applying a new terminal velocity parameterization that depends on the environmental conditions for convective snow, (3) adding a new hydrometeor category, “rimed ice,” to the original four‐class (cloud liquid, cloud ice, rain, and snow) scheme, and (4) allowing convective clouds to detrain snow particles into stratiform clouds. Results from the default and modified CAM5.3 models were evaluated against observations from the U.S. Department of Energy Tropical Warm Pool‐International Cloud Experiment (TWP‐ICE) field campaign. The default model overestimates ice amount, which is largely attributed to the underestimation of convective ice particle sedimentation. By considering cloud ice sedimentation and rimed ice particles and applying a new convective snow terminal velocity parameterization, the vertical distribution of ice amount is much improved in the midtroposphere and upper troposphere when compared to observations. The vertical distribution of ice condensate also agrees well with observational best estimates upon considering snow detrainment. Comparison with observed convective updrafts reveals that current bulk model fails to reproduce the observed updraft magnitude and occurrence frequency, suggesting spectral distributions be required to simulate the subgrid updraft heterogeneity.

Haze Formation on Triton

Abstract The largest moon of Neptune, Triton, possesses a cold and hazy atmosphere. Since the discovery of the near-surface haze layer during the Voyager fly in 1989, the haze formation mechanism has not been investigated in detail. Here we provide the first haze microphysical model on Triton. Our model solves the evolution of both size and porosity distributions of haze particles in a self-consistent manner. We simulated the formation of sphere and aggregate hazes with and without condensation of the C2H4 ice. The haze particles can grow into fractal aggregates with mass-equivalent sphere sizes of ∼0.1–1 μm and fractal dimensions of D f = 1.8–2.2. The ice-free hazes cannot simultaneously explain both UV and visible observations of Voyager 2, while including the condensation of C2H4 ices provides two better solutions. For ice aggregates, the required total haze mass flux is ∼2 × 10−15 g cm−2 s−1. For the icy sphere scenario, the column-integrated C2H4 production rate is ∼8 × 10−15 g cm−2 s−1, and the ice-free mass flux is ∼6 × 10−17 g cm−2 s−1. The UV occultation observations at short wavelengths, <0.15 μm, may slightly favor the icy aggregates. Observations of the haze optical depth and the degree of forward scattering in UV and visible should be able to distinguish whether Triton’s hazes are icy spheres or ice aggregates in future Triton missions.

The influence of surface CO2 condensation on the evolution of warm and cold rocky planets orbiting Sun-like stars

ABSTRACT The habitable zone is the region around a star where standing bodies of liquid water can be stable on a planetary surface. Its width is often assumed to be dictated by the efficiency of the carbonate–silicate cycle, which has maintained habitable surface conditions on our planet for billions of years. This cycle may be inhibited by surface condensation of significant amounts of CO2 ice, which is likely to occur on distant planets containing high enough levels of atmospheric CO2. Such a process could permanently trap CO2 ice within the planet, threatening its long-term habitability. Recent work has modelled this scenario for initially cold and icy planetary bodies orbiting the Sun. Here, we use an advanced energy balance model to consider both initially warm and cold rapidly rotating planets orbiting F - K stars. We show that the range of orbital distances where significant surface CO2 ice condensation occurs is significantly reduced for warm start planets. Star type does not affect this conclusion, although surface CO2 ice condenses over a larger fraction of the habitable zone around hotter stars. The warm start simulations are thus consistent with 1D model predictions, suggesting that the classical habitable zone limits in those earlier models are still valid. We also find that the cold start simulations exhibit trends that are consistent with those of previous work for the Sun although we now extend the analysis to other star types.