arXiv subjects

Riku Jarvinen

Publications and source records attributed to Riku Jarvinen.

7 recordsLinked to original sources

arXiv2026

Atmospheric Escape Rates from Mars - If it Orbited an Old M-Dwarf Star

Atmospheric escape is an important process that influences the evolution of planetary atmospheres. A variety of physical mechanisms can contribute to escape from an atmosphere, including thermal escape, ion escape, photochemical escape, and sputtering. Here we estimate escape rates via each of these processes for a hypothetical Mars-like exoplanet orbiting Barnard's star (an old, inactive M dwarf star). We place the planet at an orbital distance that receives the same total stellar flux as it does in our solar system. We use the measured stellar extreme ultraviolet (EUV) spectrum and assumptions on the star's magnetic field to determine both the high-energy radiation and the stellar wind environment around the planet. This information is used to model the response of the planet's thermosphere, exosphere and magnetosphere using a variety of models that have been validated against solar system observations. We find overall escape rates that are dominated by thermal processes and elevated by 2-5 orders of magnitude relative to present-day Mars, suggesting that a Mars-like planet orbiting Barnard's star would not retain a significant atmosphere for more than 10's of millions of years. Recently reported planets around Barnard's star should also not have retained significant atmospheres. By extension, Mars-like planets orbiting any M dwarf near the 'Habitable Zone' should not retain atmospheres for extended periods of time.

astro-ph.EP↗

arXiv2025

Temporal Substepping Scheme for Magnetohydrodynamics with Cell-based Adaptive Mesh Refinement on Staggered Grid

We present a new algorithm for numerical magnetohydrodynamics on staggered meshes preserving $\nabla \cdot B = 0$. Our algorithm is based on the constrained transport method and supports both cell-based adaptive mesh refinement and temporal substepping. We handle resolution changes directly on the logically Cartesian grid without needing interpolation or projection between nested or neighboring grids, nor coupling the solution between refinement levels.

physics.space-ph↗

arXiv2025

Unveiling the Mixing and Transport Processes of Solar Wind and Planetary Ions in the Magnetopause Boundary Layer

Kelvin-Helmholtz (KH) vortices are widely observed in astrophysics and heliophysics, including at Jovian and terrestrial magnetopauses, the Martian sheath-ionosphere boundary, the heliopause, and within stellar accretion disks. These vortices play a critical role in transporting mass, momentum, and energy across boundary layers. Magnetized planets such as Earth exhibit a higher incidence of fully rolled-up, nonlinear KH vortices compared to non-magnetized planets like Mars. In contrast to previous magnetohydrodynamic (MHD) studies, this work adopts a kinetic point of view to quantify ion mixing rates using three-dimensional global hybrid simulations, with Earth as a representative case. This approach enables automated identification of the KH-modulated, corrugated magnetopause. For the first time, we provide a quantitative assessment of how solar wind conditions control solar wind entry and subsequent mixing with magnetospheric ions via KH waves. We find that under northward interplanetary magnetic field (IMF) conditions, the flux of particles crossing the dayside magnetopause increases with solar wind dynamic pressure and peaks in the KH region. Notably, the KH-modulated low-latitude boundary layer thins as the dynamic pressure increases. Under southward IMF conditions, coupled reconnection and KH structures further enhance solar wind injection and boost magnetospheric ion escape in the dayside, especially near the subsolar point where reconnection intensifies this exchange. These results also shed light on the evolution of space environments and mass transport at magnetized planets in the heliosphere and beyond.

physics.space-ph↗

arXiv2023

Auroral imaging with combined Suomi 100 nanosatellite and ground-based observations: A case study

Auroras can be regarded as the most fascinating manifestation of space weather and they are continuously observed by ground-based and, nowadays more and more, also by space-based measurements. Investigations of auroras and geospace comprise the main research goals of the Suomi 100 nanosatellite, the first Finnish space research satellite, which has been measuring the Earth's ionosphere since its launch on Dec. 3, 2018. In this work, we present a case study where the satellite's camera observations of an aurora over Northern Europe are combined with ground-based observations of the same event. The analyzed image is, to the authors' best knowledge, the first auroral image ever taken by a cubesat. Our data analysis shows that a satellite vantage point provides complementary, novel information of such phenomena. The 3D auroral location reconstruction of the analyzed auroral event demonstrates how information from a 2D image can be used to provide location information of auroras under study. The location modelling also suggests that the Earth's limb direction, which was the case in the analyzed image, is an ideal direction to observe faint auroras. Although imaging on a small satellite has some large disadvantages compared with ground-based imaging (the camera cannot be repaired, a fast moving spinning satellite), the data analysis and modelling demonstrate how even a small 1-Unit (size: 10 cm x 10 cm x 10 cm) CubeSat and its camera, build using cheap commercial off-the-shelf components, can open new possibilities for auroral research, especially, when its measurements are combined with ground-based observations.

physics.space-ph↗

arXiv2022

First Radar -- CubeSat Transionospheric HF Propagation Observations: Suomi 100 Satellite and EISCAT HF Facility

Radio waves provide a useful diagnostic tool to investigate the properties of the ionosphere because the ionosphere affects the transmission and properties of High Frequency (HF) electromagnetic waves. We have conducted a transionospheric HF-propagation research campaign with a nanosatellite on a low-Earth polar orbit and the EISCAT HF transmitter facility in Tromsø, Norway, in December 2020. In the active measurement, the EISCAT HF facility transmitted sinusoidal 7.953 MHz signal which was received with the HEARER radio spectrometer onboard 1 Unit (size: 10 cm x 10 cm x 10 cm) Suomi 100 space weather nanosatellite. Data analysis showed that the EISCAT HF signal was detected with the satellite's radio spectrometer when the satellite was the closest to the heater along its orbit. Part of the observed variations seen in the signal was identified to be related to the heater's antenna pattern and to the transmitted pulse shapes. Other observed variations can be related to the spatial and temporal variations of the ionosphere and its different responses to the used transmission frequencies and to the transmitted O- and X-wave modes. Some trends in the observed signal may also be associated to changes in the properties of ionospheric plasma resulting from the heater's electromagnetic wave energy. This paper is, to authors' best knowledge, the first observation of this kind of "self-absorption" measured from the transionospheric signal path from a powerful radio source on the ground to the satellite-borne receiver.

physics.space-ph↗

arXiv2019

Planetary Magnetic Field Control of Ion Escape from Weakly Magnetized Planets

Intrinsic magnetic fields have long been thought to shield planets from atmospheric erosion via stellar winds; however, the influence of the plasma environment on atmospheric escape is complex. Here we study the influence of a weak intrinsic dipolar planetary magnetic field on the plasma environment and subsequent ion escape from a Mars sized planet in a global three-dimensional hybrid simulation. We find that increasing the strength of a planet's magnetic field enhances ion escape until the magnetic dipole's standoff distance reaches the induced magnetosphere boundary. After this point increasing the planetary magnetic field begins to inhibit ion escape. This reflects a balance between shielding of the southern hemisphere from ``misaligned" ion pickup forces and trapping of escaping ions by an equatorial plasmasphere. Thus, the planetary magnetic field associated with the peak ion escape rate is critically dependent on the stellar wind pressure. Where possible we have fit power laws for the variation of fundamental parameters (escape rate, escape power, polar cap opening angle and effective interaction area) with magnetic field, and assessed upper and lower limits for the relationships.

astro-ph.EP↗

arXiv2019

Stellar Influence on Heavy Ion Escape from Unmagnetized Exoplanets

Planetary habitability is in part determined by the atmospheric evolution of a planet; one key component of such evolution is escape of heavy ions to space. Ion loss processes are sensitive to the plasma environment of the planet, dictated by the stellar wind and stellar radiation. These conditions are likely to vary from what we observe in our own solar system when considering a planet in the habitable zone around an M-dwarf. Here we use a hybrid global plasma model to perform a systematic study of the changing plasma environment and ion escape as a function of stellar input conditions, which are designed to mimic those of potentially habitable planets orbiting M-dwarfs. We begin with a nominal case of a solar wind experienced at Mars today, and incrementally modify the interplanetary magnetic field orientation and strength, dynamic pressure, and Extreme Ultraviolet input. We find that both ion loss morphology and overall rates vary significantly, and in cases where the stellar wind pressure was increased, the ion loss began to be diffusion or production limited with roughly half of all produced ions being lost. This limit implies that extreme care must be taken when extrapolating loss processes observed in the solar system to extreme environments.

astro-ph.EP↗