This study evaluates how a future Tianwen-Titan orbiter could improve Titan gravity-field and tidal Love-number recovery when combined with a Cassini-based simulated tracking baseline. A multi-arc covariance framework implemented with the Tudat astrodynamics toolbox is used to compare two representative orbiter geometries: a 40° mid-inclination orbit for repeated low- and mid-latitude sampling and a 90° polar orbit for global latitudinal coverage. For periapsis altitudes of 1500 and 1000 km, the lower-altitude cases extend the recoverable gravity spectrum from 10°–11° to 12°–15°. At 1500 km, the 40° configuration reduces the formal uncertainty of k2 from about 0.067–0.070 in the Cassini baseline to approximately 0.002 and improves C22 to about 0.0025 × 10–6. The 90° configuration more strongly constrains odd zonal harmonics, reducing J3 and J5 uncertainties by factors of about 10 and 24. These results indicate that mid-inclination and polar orbiters provide complementary sensitivity for future Titan gravity science and interior structure interpretation.
Suprathermal particles form in the Earth’s upper atmosphere with energies an order of magnitude greater than the average kinetic energy of surrounding gas particles. In the polar regions, the main mechanism for the formation of such particles is due to the precipitation of auroral electrons of magnetospheric origin. Intense formation of suprathermal oxygen atoms Oh during geomagnetic storms can cause additional braking of low-Earth orbiting (LEO) satellites in polar orbits due to the high accommodation of these atoms with the satellite surface. During extreme solar events, these processes can significantly reduce the accuracy of LEO satellite dynamics forecasts based on empirical upper-atmosphere models. Therefore, theoretical calculations using kinetic models are particularly relevant when analyzing such events. In this paper, we evaluate the contribution of suprathermal oxygen atoms to the atmospheric drag of LEO satellite in polar orbits during extreme geomagnetic storms. To this end, (a) the kinetics of Oh formation and transport in the upper atmosphere are calculated and (b) the motion of LEO satellite in the disturbed atmosphere is modeled. Based on calculation results, it has been established for the first time that, due to the influence of suprathermal oxygen atoms produced in large quantities during extreme geomagnetic storms, the positions of LEO satellite at altitudes of 400–800 km can deviate from those predicted by empirical models by up to 5 m in altitude and up to 350 m along the orbit. These deviations amount to 40
Based on data from the MGNS neutron detector on board the BepiColombo spacecraft from 2019 to 2024, we analyzed the neutron flux produced by the interaction of galactic cosmic ray (GCR) protons with the spacecraft materials. A comparison was made with data from the HEND detector on board the Mars Odyssey spacecraft and the LEND detector on board the Lunar Reconnaissance Orbiter (LRO). It has been shown that as solar activity increased, the flux of secondary neutrons from the Moon and Mars decreased by 50
The aim of this study is to determine the polarimetric and photometric characteristics of the interstellar comet 3I/2025 N1 (ATLAS), as well as to model the physical properties of particles in its coma. Observations of the comet were carried out using the POLSHAKH polarimeters on the 2.6-m telescope of the Crimean Astrophysical Observatory, the telescope Zeiss-2000 of shared research facility “Terskol observatory” of Institute of Astronomy of the RAS, and the SCORPIO-2 instrument on the 6-m telescope of the Special Astrophysical Observatory during the period from November 18, 2025 to January 26, 2026. The following main results were obtained. • Among all comets observed to date, comet 3I/ATLAS showed the highest absolute values of the degree of linear polarization on the negative and positive branches of the phase curve. The following parameters of the polarization phase curve were determined: Pmin = –3.01 • The spectral polarization gradient ΔP(λ)/Δλ = 0.004 ± 0.001 ( • In November 2025, the B–V, V–R, and R–I colors were ≈0.4m, and g–r = 0.71m. • Dust productivity Afρ amounted to 5461 ± 70 cm for the r‑sdss filter and a coma diameter of 22696 km at a heliocentric distance of 1.710 AU. • The best fit to the observed polarization phase curve is achieved by modeling conjugate random Gaussian particles with roughness G_50^7( 0.5) for a particle mixture consisting of 95
The mechanism of explosive mutations of pathogenic viruses during low solar activity at the minima of various solar cycles is examined, coupled with the low effectiveness of virus pandemic social lockdowns. A hypothesis is proposed for atmospheric circulation and virus mutations linked to solar activity and cosmic ray cycles. Several stages of viral migration and mutation are proposed: the ascent of viruses with aero plankton into the atmosphere to altitudes of up to 11–15 km, their mutation under the influence of cosmic rays and shortwave solar radiation, and the subsequent precipitation of mutated viruses to the Earth’s surface via rain at distances of up to 2500–3000 km from the initial outbreak virus site. At an altitude of 5 km, the bioefficiency and mutational impact of cosmic rays increases tenfold, and at altitudes of 11 km, it increases 100-fold. At the same time, localized long-lived areas with increased virus concentrations (or stable fluxes) arise in the troposphere layers of the atmosphere and the tropopause, subject to the constant active mutational impact of solar and galactic cosmic rays, as well as ultraviolet and X-ray radiation from the Sun. The cyclical nature of mutations is tied to solar cycle extrema: peaks in solar cosmic rays and shortwave solar radiation at the solar cycle maximum and peaks in galactic cosmic rays at the solar cycle minimum. Subsequent concentration of moisture on aeroplankton during cloud formation facilitates subsequent precipitation, which carries mutated virus and bacterial colonies in the upper troposphere back into the near-surface atmosphere, soil, and water bodies. This mechanism ensures atmospheric circulation and mutations of viruses/aeroplankton and triggers the emergence of viral pandemics at any solar activity extrema, including the minima of solar activity cycles of various scales, from the 11-year cycle to the centennial one. The atmospheric circulation of pathogenic viruses and their mutations explains the low effectiveness of social terrestrial lockdowns during viral pandemics. The discussed mechanism of atmospheric circulation transport, cyclicity, and mutations of atmospheric bioplankton may be highly promising for constructing models of a possible atmospheric biosphere on Venus, and for the development of the Russian Venera-D space mission. The Venusian atmosphere has a wide range of pressures and temperatures, structured, stable macrocirculation, and a distinct separation of the boundaries of different environments, which allows for the effective, sustainable formation, development, and transfer of diverse ecological niches within the planet’s atmosphere.
