Abstract numerical framework to calculate the height and potential of the vacuum inner
gap of pulsars is presented here. The results demonstrate that small mountains on a pulsar’s
polar cap tend to significantly influence the properties of the inner vacuum gap, making it easier for sparks to form. In this scenario, the magnetospheric activity observed from the pulsars
PSR J0250+5854 and PSR J2144−3933 which lie below the traditional pulsar death line, and some single-pulse modulation
phenomena could also then be understood. Furthermore, the presence of small mountains
should depend on the puzzling state of supranuclear matter inside pulsars. In order to sustain
stable mountains on the surface, pulsars might be made of solid strangeon matter, which is
favoured by both the charge neutrality and the flavour symmetry of quarks.

Mapping textures of polar ice cores using 3D laboratory X-ray microscopy

Abstract Polar amplification (PA) is a robust feature of contemporary climate change, but its state‐dependence across different climate conditions is poorly understood despite potential relevance to paleoclimate records and future projections. Here we examine the state‐dependence of PA across a wide range of climate states in an idealized moist general circulation model. We generate a phase space of climate states with different global‐mean surface temperatures and equator‐to‐pole surface temperature contrasts then perturb each with longwave radiative forcing. We find that the state‐dependence of PA is largely a superposition of two effects. Firstly, as a consequence of moist thermodynamics, latent energy transport drives stronger PA in climates with higher global‐mean surface temperatures and stronger meridional surface temperature gradients. On top of this, the ice‐albedo feedback amplifies PA in climates where the climatological ice edge sits within the polar cap.

Abstract Velocity distribution functions (VDFs) are an essential observable for studying kinetic and wave–particle processes in solar wind plasmas. To experimentally distinguish modes of heating, acceleration, and turbulence in the solar wind, precise representations of particle phase-space VDFs are needed. In the first paper of this series, we developed the Slepian basis reconstruction (SBR) method to approximate fully agyrotropic continuous distributions from discrete measurements of electrostatic analyzers (ESAs). The method enables accurate determination of plasma moments, preserves kinetic features, and prescribes smooth gradients in phase space. In this paper, we extend the SBR method by imposing gyrotropic symmetry (g-SBR). Incorporating this symmetry enables high-fidelity reconstruction of VDFs that are partially measured, as from an ESA with a limited field of view (FOV). We introduce three frameworks for g-SBR, the gyrotropic SBR: (A) 1D angular Slepian functions on a polar cap, (B) 2D Slepian functions in a Cartesian plane, and (C) a hybrid method. We employ model distributions representing multiple anisotropic ion populations in the solar wind to benchmark these methods, and we show that the g-SBR method produces a reconstruction that preserves kinetic structures and plasma moments, even with a strongly limited FOV. For our choice of model distribution, g-SBR can recover ≥​​​​​​90% of the density when only 20% is measured. We provide the package gdf for open-source use and contribution by the heliophysics community. This work establishes direct pathways to bridge particle observations with kinetic theory and simulations, facilitating the investigation of gyrotropic plasma heating phenomena across the heliosphere.

Abstract. This paper describes instrumentation and procedures developed to measure H2 and Ne in polar ice core samples. Gases are extracted from ice core samples by melting under vacuum. Measurements are conducted by gas chromatographic separation with detection by a pulsed helium ionization detector (He-PDD). The analytical system was developed for field analysis of ice core samples immediately after drilling. This minimizes the potential for exchange of these highly permeable gases between the ice core and the modern atmosphere. The design, operation, and performance of the instrument are discussed using data from the initial deployment to Summit, Greenland. The results demonstrate the feasibility of ice core analysis of H2 and Ne with precision of 8.6 % and 10.2 % (1σ) respectively.

In the environments of the North and South Poles, ice floe drifts lead to excessive errors in the GPS and real-time kinematic (RTK) signals of the unmanned aerial vehicle (UAV)-based cross-domain collaborative monitoring systems deployed on these floes, which makes it impossible to complete related tasks such as UAV return and landing. Moreover, deep learning-based target detection methods suffer from insufficient accuracy and real-time performance when addressing low-contrast, fog- and snow-obscured, and high-elevation polar images. Therefore, this study integrates transformer-based convolution (TransConv) into You Only Look Once (YOLO)v11 to strengthen the ability of the network to model the global information contained in fog- and snow-obscured images and to achieve improved target detection performance in complex environments. A mist global feature pyramid network (MistGFPN) is designed to focus on the ability to extract features from small targets to improve the target detection performance achieved at high altitudes. An efficient asymmetric detection head (EADH) is proposed to improve the frames per second (FPS) and real-time detection performance of the target detection model. Finally, several comparative experiments are designed to verify the effectiveness and real-time performance of the proposed model. The experimental results obtained on homemade datasets show that the proposed model (YOLO-TME) improves the accuracy, recall, average accuracy, and F1 score metrics by 4.2%, 5.8%, 5.5%, and 5.1%, respectively, over those of the original YOLOv11 model, which indicates that YOLO-TME provides substantially improved detection accuracy while maintaining high detection speed, thus satisfying the real-time landing sign detection requirements imposed in polar environments.

Abstract Recent developments in the study of pulsar radio emission revealed that the microphysics of quantum electrodynamic pair cascades at pulsar polar caps may be responsible for generating the observed coherent radio waves. However, modeling the pair cascades in the polar cap region poses significant challenges, particularly under conditions of high plasma multiplicity. Traditional particle-in-cell (PIC) methods often face rapidly increasing computational costs as the multiplicity grows exponentially. To address this issue, we present a new simulation code using the Vlasov method, which efficiently simulates the evolution of charged particle distribution functions in phase space without a proportional increase in computational expense at high multiplicities. We apply this code to study e ± pair cascades in 1D, incorporating key physical processes such as curvature radiation, radiation reaction, and magnetic pair production. We study both the Ruderman–Sutherland and the space-charge-limited flow regimes, and find quasiperiodic gap formation and pair production bursts in both cases. These features produce strong electric field oscillations, potentially enabling coherent radio emission. We construct a unified analytic model that describes the key features of the polar cap cascade, which can be used to estimate the return current heating rate that can be used to inform X-ray hotspot models. Spectral analysis shows that a significant amount of energy is carried in superluminal modes—collective excitations that could connect to observed radio features. Our results align with previous PIC studies while offering enhanced fidelity in both dense and rarefied regions.

Abstract Direct remote-sensing observations of the solar poles have been hindered by the restricted view obtained from the ecliptic plane. For the first time ever, Solar Orbiter with its remote-sensing instruments observed the poles of the Sun from out of the ecliptic in the spring of 2025. Here, we report the first measurements of the magnetic field of the solar poles taken when Solar Orbiter was at heliographic latitudes ranging between 14 . ° 9 and 16 . ° 7. The data sets were collected by the High Resolution Telescope of the Polarimetric and Helioseismic Imager on board Solar Orbiter (SO/PHI-HRT). Two sets of observations, approximately one month apart, for the south and north pole are considered in this work. The magnetic flux and flux density measured during these campaigns are reported as a function of the heliographic latitude observed by SO/PHI-HRT. The net fluxes show a different latitudinal distribution for the two polar caps. We also discuss the observed dependence of the measured fluxes on the viewing angle. These first results highlight the importance of high-resolution direct measurements of the polar field, paving the way for the high-latitude observations planned for SO/PHI-HRT in the coming years.

Abstract Since the early days of Mars exploration it was evident that water played an important role in the geologic and climate evolution of the planet. In the decades following the conclusion of the Viking missions, determining the current amount, distribution and state of water, either liquid or solid, came to be considered one of the key investigations to understand Mars’ past. An orbiting ground penetrating radar was included in the payload of Mars Express: The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) was designed to probe the subsurface down to depths of a few kilometres to search for ice, water and dielectric interfaces outlining large-scale stratigraphy. MARSIS successfully probed both polar caps, providing unique insights on their structure and composition. In addition, MARSIS probed the widespread and unique Medusae Fossae Formation, revealing that it could contain a large amount of water ice. MARSIS provided the first evidence of a stable body of liquid brine beneath the South Polar Layered Deposits. In the coming years, new operative modes and improved processing methods hold the promise of providing new detailed information on the Martian subsurface at a vertical resolution of about 100 m and a horizontal resolution of a few to several kilometres.

Abstract Dust storms near Mars' South Pole during the perihelion and summer solstice seasons ( L s ∼ 250–290°) are phenomenologically distinct from martian dust storms in other locations and seasons. While they have previously been observed to increase atmospheric dust loading and warm the south polar atmosphere, they have no notable impact on the middle latitudes, tropics, or northern hemisphere. Here, we use a combination of multiple remote sensing instruments, atmosphere reanalyses, and general circulation modeling to study the evolution of dust storms near the Martian South Pole during Mars Year 30 (a prototypical year for such storms). Dust lifting preferentially occurs in the eastern hemisphere (180°–320°E) and follows the retreating seasonal CO 2 polar cap to higher latitudes as the season progresses—implicating the strong cap edge thermal forcing and katabatic flows as well as surface dust availability in driving dust lifting. Dust remains confined to the high southern latitudes during this season with strong diurnal variability in both latitudinal and vertical extents. Dust is entrained in the southern circumpolar jet stream, creating filamentation and longitudinal mixing and controlling the flow of dust back onto the polar cap. The diurnally varying atmospheric circulation (Ferrel cell) limits the mixing of dust to lower latitudes and prevents a global thermal response.

Abstract The Regolith and Ice Drill for Exploration of New Terrains (TRIDENT) is a 1 m class drill developed for capturing regolith and ice during the Volatiles Investigating Polar Exploration Rover (VIPER) and the Polar Resources Ice Mining Experiment (PRIME-1) lander missions to the south pole of the Moon. The drill employs decoupled rotation and percussion mechanisms to allow for three modes: rotation, percussion, and rotation–percussion, depending on operational goals and the material strength. TRIDENT can be operated in such a way that it can characterize subsurface material and deliver cuttings to the surface for characterization by other instruments. TRIDENT includes a drill-bit-integrated temperature sensor and an auger-integrated heater with a colocated temperature sensor 35 cm above the bit for thermal conductivity measurement. The heater can also be used in cases of ice adherence (freezing in) and to enhance the sublimation of ice from the cuttings pile. TRIDENT collects and delivers subsurface regolith onto the surface using a “bite” sampling approach: cuttings are captured in the auger flutes, the auger is retracted after drilling a 10 cm bite, and then 10 cm worth of cuttings are deposited onto the surface, forming a cuttings cone. This regolith cone is then analyzed by instruments Mass Spectrometer Observing Lunar Operations (MSOLO) and NIRVSS on the VIPER and MSOLO on the PRIME-1 missions. The drilling activity creates a seismic signal that can be detected on any associated inertial measurement unit that is turned on during the activity, which enables seismic science. TRIDENT represents two decades of technology development for planetary applications and could be deployed on any future missions to other solar system bodies. TRIDENT on the PRIME-1 mission has been successfully deployed in horizontal orientation (this orientation was due to the lander being in an off nominal landing orientation). All actuators, sensors, and heaters worked as designed. Even though the drill did not penetrate regolith, it was covered in regolith that fell onto the drill during the landing operation. VIPER is scheduled to launch to the Moon at the end of 2027 on Blue Origin’s Mk1 lander.

Abstract The Endurance sounding rocket, launched in May 2022 at an altitude of 768 km, provided the first observations of plasma waves in the sunlit polar cap on a sounding rocket. Despite the quiet geomagnetic conditions required for the primary mission science, Endurance observed a variety of interesting electric field and plasma density waves. This work presents observations of novel ion Bernstein waves ordered by the proton cyclotron frequency with unusual polarization characteristics. These waves are most prominent at harmonics n > 6 up to the lower hybrid frequency and from 250 to 600 km altitude, but also as weak modulations of very low frequency hiss at higher frequencies. At low altitudes near the F‐region density peak, their temporal profile strongly follows that of the lower hybrid frequency, indicating that the plasma density, in addition to the magnetic field, controls wave properties. While these waves share similarities with ion Bernstein waves previously reported in the auroral region, they exhibit left‐hand elliptical polarization rather than the expected linear polarization. In addition, a previously unreported extension of certain harmonic bands to altitudes <250 km is observed, with a particularly strong enhancement near 125 km altitude coinciding with an increase in E‐region plasma density. We present observations and analysis of the ion Bernstein waves and suggest that they may represent signatures of ion upflow.

Abstract Understanding the long-term evolution of lunar orbit is an essential task in astronomy and astrophysics because lunar and planetary ephemerides are indispensable in many important applications, such as spacecraft navigation and reference frame transformations. Recently, it has been suggested that climate dynamics, particularly sea level change due to melting of polar ice sheets, can subtly modulate ocean tides, thus altering the tidal dissipation and lunar recession rate by ∼2.6% in the 21st century. In our study, we provide a correction to standard models of lunar orbital evolution relevant for astrophysical applications. We use the reconstructed history of ice thickness, paleotopography, and sea level change since the last glacial cycle (∼122,000 yr ago) and adopt a revised tidal dissipation model to argue that the climate-induced changes in the lunar orbit might not be negligible and have likely altered the Earth–Moon distance by variable rates as large as ∼0.9 mm yr −1 , which occur on top of the background trend of ∼38.3 mm yr −1 . However, this is currently absent from dynamical models of lunar evolution. Our results suggest that lunar orbit ephemerides might need to be revised by at least ∼1.5%–2.3% in order to obtain a more accurate representation of the tidal dynamics and orbital motions. The model proposed in this paper might also be relevant for other astrophysical bodies, such as exoplanetary satellites.

We report on follow-up observations with the instrument at the and FAST, aiming to characterise the nature of five thermally emitting isolated neutron star (INS) candidates recently discovered from searches in the footprint of the All-sky Survey. We find that the X-ray spectra are predominantly thermal and can be described by low-absorbed blackbody models with effective temperatures ranging from 50 to 210 eV. In two sources, the spectra also show narrow absorption features at $300 - 400$ eV. Additional non-thermal emission components are not detected in any of the five candidates. The soft X-ray emission, the absence of optical counterparts in four sources, and the consequent large X-ray-to-optical flux ratios $>3000 - 5400$ confirm their INS nature. For the remaining source the available data do not allow a confident exclusion of an active galactic nucleus nature. However, if the source is Galactic, the small inferred X-ray emitting region is reminiscent of a heated pulsar polar cap, possibly pointing to a binary pulsar nature. X-ray timing searches do not detect significant modulations in all candidates, implying pulsed fraction upper limits of 13 -- 19% ($0.001-13.5$ Hz). The absence of pulsations in the FAST observations targeting and excludes periodic magnetospheric emission at 1 -- 1.5 GHz with an $8σ$ significance down to 4.08 µJy and 2.72 µJy, respectively. The long-term X-ray emission of all sources does not imply significant variability. Additional observations are warranted to establish exact neutron star types. At the same time, the confirmation of the predominantly thermal neutron star nature in four additional sources highlights the power of to complement the Galactic INS population.

Abstract Anomalously bright radar reflections from the base of Mars' south polar cap raise the tantalizing possibility of present‐day liquid water. Orosei et al. (2018, https://doi.org/10.1126/science.aar7268 ) first reported bright subsurface echoes from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) prompting studies of whether the high reflectivity, stems from liquid water or dry scattering interfaces. A key challenge has been the prior inability of the higher‐frequency Shallow Radar (SHARAD) to detect this basal zone, hindering potential diagnostic cross‐frequency comparisons. Due to a novel spacecraft maneuver, SHARAD has now obtained a basal return associated with the putative body of water. Modeling of the radar response is not consistent with the liquid water explanation, instead suggesting a localized, low roughness region of dry rock/dust beneath the ice could explain the SHARAD response. Reconciling the divergent responses of SHARAD and MARSIS remains essential to determine the nature of this anomalous south polar region.

The Atlantic meridional overturning circulation (AMOC) and polar ice sheets are coupled tipping elements, allowing for potential cascading tipping events in which tipping is facilitated by their mutual interactions. However, while an AMOC destabilization driven by Greenland ice sheet (GIS) meltwater release is well documented, the consequences of a West Antarctic ice sheet (WAIS) tipping on the AMOC remain unclear. In the Earth system model of intermediate complexity CLIMBER-X, we perform experiments where meltwater fluxes representing plausible tipping trajectories of the GIS and WAIS are applied. We find that WAIS meltwater input can increase or decrease the AMOC resilience to GIS meltwater. Also, we find that it can completely prevent an AMOC collapse, confirming in a comprehensive model what was previously found in conceptual frameworks. Moreover, we find this stabilization to occur for ice sheet tipping trajectories that are relevant under high future greenhouse gas emission scenarios.

The atmospheric concentrations of greenhouse gases, such as carbon dioxide ( ), methane , and nitrous oxide ( ) have a significant increase in the past 150 years. Carbon dioxide forces the earth’s energy out of balance by absorbing thermal infrared energy (heat) radiated by the surface, causing the ocean’s surface to warm, and melting more and more polar icecaps. Since polar icecaps help to regulate the earth’s climate system, the fate of the Arctic icecaps is critical to the future climate. This paper exhibits different mathematical models to predict rate of ice-depletion in Arctic Ocean, and to analyse the trend of the Arctic icecap. The prediction results shows that Artic ice cap will be free of ice by the year 2035.

The mechanical response and failure behavior of high-pressure frozen ice are essential to the technological progress in drilling thick polar ice sheets, but current research primarily focuses on non-pressure-frozen ice. In this paper, ice specimens with a cylindrical geometry were fabricated at −20 °C, applying freezing pressures across a range of 10 to 40 MPa with a 10 MPa interval. Their mechanical properties were investigated through triaxial compression tests under axial loading conditions and were compared with the results obtained at −10 °C. The results indicate that, with increasing freezing pressure, the samples transitioned from a failure state of interlaced cracking to a highly transparent state. The failure behavior observed in the specimens was characterized as ductile, as evidenced by the deviatoric stress–axial strain relationships. Moreover, the peak deviatoric stress exhibited a non-monotonic dependence on freezing pressure, with an initial rise from 9.59 MPa at 10 MPa to a peak of 14.37 MPa at 30 MPa and a subsequent decline to 10.12 MPa at 40 MPa. All specimens reached a relatively stable residual state at 5% axial strain, with residual deviatoric stresses ranging from 4.13 to 5.71 MPa. A reduction in freezing temperature from −10 °C to −20 °C can effectively enhance both the peak deviatoric stress and the residual stress of high-pressure frozen ice under triaxial shear conditions. All peak tangent modulus values, ranging from 1.61 to 2.93 GPa with an average of 2.2 GPa, were observed within 0.7% axial strain and exhibited mild fluctuations with increasing freezing pressure. These findings provide a more robust mechanical foundation for drilling research and operations in extremely thick polar ice caps.

Labeling ice cracks in Antarctic near-shore sea ice aerial orthophotos is critical for sea ice cargo route development; rapid, accurate identification and labeling of cracks in UAV imagery aids safe goods transfer between icebreakers and expedition stations, and studying ice crack distribution provides a key basis for assessing sea ice route reliability. Ice cracks have complex morphologies that traditional recognition methods struggle to handle, so this study proposes the ICI-YOLOv8 algorithm to improve sea ice crack detection near Antarctica’s Zhongshan Station, using crack density and fractal dimension to characterize spatial distribution and a Monte Carlo-based numerical model to quantify distribution probability. The algorithm achieves 0.628 accuracy and 0.662 mAP@0.5 (outperforming comparable methods in speed and accuracy) and reaches 0.933 accuracy and 0.657 mAP@0.5 with better generalization than similar models when tested on general remote sensing water datasets; a positive correlation exists between fractal dimension and ice crack density, and Monte Carlo simulation and probability distribution models verify their distribution properties. The proposed algorithm is suitable for rapid summer Antarctic near-shore sea ice crack identification, the numerical model effectively quantifies crack distribution to aid route development, and this study is important for understanding polar ice stability and sea ice route development.

Abstract Polar cap patches and polar cap arcs are two polar phenomena that typically occur under a southward and a northward interplanetary magnetic field (IMF), respectively. However, their morphology and plasma characteristics are significantly different due to completely different generation mechanisms. Here, we present multi‐instrument observations of coexisting polar cap patches and arcs (distance ∼500 km) in an all‐sky imager field of view as IMF Bz turns northward. When IMF Bz turns northward, the resulting sunward flow will prolong the evolution time of patches from the dayside to the nightside. A polar cap arc can form 1–2 hr after the northward turning, and it is driven by electron precipitation near the nightside poleward auroral boundary. As a consequence, both slow‐moving polar cap patches and polar cap arcs may appear at close proximity in the nightside polar cap. Statistical results show that such events generally occur under specific IMF conditions, such as the IMF turning from southward to northward, the northward to southward direction constantly jumping back and forth, etc. The polar cap arc is sometimes accompanied by increased auroral brightness and GNSS total electron content, although weaker than that when the patches exist alone. Simultaneous echoes from the Hankasalmi SuperDARN radar indicate the formation of ionospheric irregularities, where polar cap arcs may be a potential source for these irregularities (like patches).