Coronal Mass Ejection Magnetic Fields Drop Faster Near the Sun Than in Space


  • Coronal Mass Ejection (CME) is a huge explosion on the Sun where it throws out a massive cloud of plasma (hot gas made of charged particles) and magnetic field into space.


  • Coronal mass ejections magnetic field decreases with distance from the Sun in a very consistent and predictable way, following a power-law from about 0.07 au to 5 au from the sun. CME magnetic field decreases differently near the sun so researchers used a multipole type power law.

R is heliocentric distance

k= −1.57 for 0.07 au to 5 au from the sun.

k=  - 6 for near-Sun


  • The power law constants B0 and B1 are then determined using a Levenberg-Marquardt algorithm It is used to solve non linear least square problems.


Source: https://arxiv.org/html/2512.04730v1


Metal-poor stars in cluster Dolidze 25 accrete mass from their disks at rates very similar to those in normal-metallicity regions


  • Even though Dolidze 25 region has far fewer heavy elements, the stars still show normal levels of accretion — meaning gas is falling onto them from their disks at rates comparable to similar stars in richer environments. This suggests that low metallicity does not strongly change how young stars grow or how their disks evolve during the first couple of million years.


  • Mass-accretion rates tell us how fast material from the surrounding disk is falling onto the star. Low metallicity does not slow down the early growth of stars from their disks.

 

  • Lithium absorption lines (young stars still have lithium) and Hydrogen emission lines (Balmer emission) are measured here. From the emission lines, they estimated line luminosity and then calculated Mass accretion rate(how much mass each young star is accreting from its disk)

  • Lacc is luminosity,

R∗ is the stellar radius,
Rin​ is the inner radius of the disk

M∗​ is the stellar mass

 

Mars Mass Affects Earth’s long term Climate Rhythms(Milankovitch cycles)


  • The Earth’s 100,000-year eccentricity cycle and the 41,000-year axial tilt cycle change in strength and period as Mars becomes heavier or lighter. In extreme high-Mars mass cases the earth orbit becomes messy and chaotic rather than clean and periodic.


  • Even relatively small planets like Mars play an important role in keeping Earth’s orbital and climatic cycles stable over millions of years. In simple terms, the structure of Earth’s climate rhythms depends on the gravitational “architecture” of the Solar System..


  • The researchers used secular theory approximation. It is an analytical and computational method used to study the long-term (secular) evolution of orbital elements. And fourier analysis is also used.


https://arxiv.org/html/2512.02108v1



The Mass–orbit Relation of Helium WhiteDwarfs Depends Strongly on Low-Temperature Opacities


  • Opacity tells us how much a star’s material blocks light and heat from moving through it.


  • The final orbit means the orbit of the two stars in binary after mass transfer is over and the donor star has become a helium white dwarf.


  • Two objects orbiting each other—like a star and a planet, or two stars—each body has a region around it where its gravity is dominant. This region is called its Roche lobe. If gas reaches beyond the Roche lobe, the other object’s gravity can pull it away.


  • The study concludes that the relationship between a helium white dwarf’s mass and the final orbital period of its binary system depends strongly on low-temperature opacity in stellar models. It also depends on metallicity, angular momentum loss and how mass transfer happens.


  • The Freedman opacity is used here which consider molecular effects but not grain condensates. According to this, the predicted white dwarfs end up forming at slightly smaller radii during their red-giant phase, leading to shorter orbital periods.


Source: https://arxiv.org/html/2511.20147v1


Researchers found 3-planet giant system in a 4:2:1 Laplace resonance chain


  • TOI-7510, a star hosting three transiting giant planets. The planets orbit every 11.5, 22.6, and 48.9 days, forming a near 4:2:1 Laplace resonance chain. Their orbital periods are strongly gravitationally connected. Using transit timing variations and photodynamical modeling, the authors estimate that the planets are large- Jupiter sized but with different densities, an inner planet that is unusually low-density.


  • Photodynamical modeling: The researchers combine gravity-based orbital simulations and transit light-curve analysis into one unified model.


  • Transit-timing variations (TTVs):in multi-planet systems, a planet does not pass in front of its star at perfectly regular intervals, because gravity from other nearby planets slightly speeds up or slows down its orbit. By measuring these small timing changes, astronomers can determine how strongly the planets interact, estimate their masses, and understand their orbital shapes.


Sub-Neptunes Evolve From Hydrogen–Helium to Water-Rich Atmospheres


  • The study shows that many hot sub-Neptunes slowly lose their original H-He atmosphere because of strong X-ray UV radiation from their star. 


  • The atmosphere gets replaced by gases released from the interior, especially hydrogen and water — but not helium, because there is very little helium in the interior. So the planet’s atmosphere becomes helium-poor and water-rich, forming a secondary atmosphere.


  • This explains why many small exoplanets do not show helium in observations. Many small planets (<2.5 Earth radii) have already transitioned to secondary atmospheres and lost most of their helium.


  • Larger sub-Neptunes tend to retain more of their original H-He atmospheres, which means they keep higher helium abundances and therefore show higher helium escape rates.


  • Here the Atmospheric Escape Method is used. The researchers calculated how the atmosphere escapes due to strong X-ray and UV radiation (XUV) from the host star:

  • FXUV​ = stellar XUV radiation hitting the planet

RXUV​ = effective radius where XUV is absorbed

M˙esc = mass-loss rate


Source: https://www.arxiv.org/pdf/2511.15903



Eccentricity shows that giant planets slowly turn into brown-dwarf as mass increases — not suddenly


  • Lower-mass giant planets (1–3 Jupiter masses) usually form by core accretion, their orbit eccentricity is less. Brown dwarfs (mass> 13 Jupiter mass) have high eccentricity, they are formed by gravitational instability. The eccentricity changes slowly and smoothly with mass.


  • Radial velocity with Hipparcos + Gaia Astrometric accelerations astrometry is used here which gives the tilt of the orbit. That allows them to measure the actual masses.


  • Low-mass giant planets are common. As mass increases, planets become rarer

So occurrence rate decreases smoothly with mass increase.


  • The giant planets and brown dwarfs do not form two separate, sharply divided populations. Instead, their properties—eccentricity, occurrence rate, and host star metallicity—change continuously and gradually as mass increases from about 1 to 80 Jupiter masses. Eccentricity rises steadily, indicating a transition from core-accretion formation to gravitational-instability processes, but this shift is smooth rather than abrupt.


  • Hierarchical Bayesian Modeling of Eccentricity Distributions is used in the article.


How Rotation Changes Fingering Convection Inside Planetary Cores


  • Fingers refers to narrow, tube-like streams of fluid that move upward or downward inside the planetary core.


  • The study uses hydrodynamical simulations within a rotating spherical shell geometry to model fingering convection, by solving the Boussinesq approximation of the Navier-Stokes equations. The equations are solved using a pseudo-spectral method. Variables are expanded in spherical harmonics for the angular components and a second-order finite difference scheme is used for the radial direction.


  • The ratio of the squared buoyancy frequency to the squared rotation rate is calculated here. It indicates the relative importance of buoyancy (vertical stratification) versus rotation (Coriolis forces) in a fluid system.


Rotation changes the direction and shape of the fingers:

  • When the planetary core rotates very fast, the Coriolis force becomes more important than buoyancy. As a result fingers no longer rise straight up/down (radially), instead they align with the rotation axis, forming long columns. This creates powerful east-west flowing zonal winds inside the core.


  • Intermediate regimes: These are highly anisotropic and drift slowly towards the equator over time.


  • Weakly-Rotating Regime: The fingers align with gravity and the mixing becomes more homogeneous laterally, causing the strong zonal flows to weaken and eventually disappear.


  • When the stratification is very strong, the fingers group together into small clusters, and only weak, slow changes in density appear on large scales. These density patterns are surrounded by big, donut-shaped circulating flows (toroidal gyres) in the upper part of the layer. This may affect the magnetic field.


This  helps for study of the Mercury core.


Source: https://arxiv.org/html/2511.11442v1



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