Space Weather & Heliophysics

MHD Simulations of the Space Weather in Proxima b: Habitability Conditions and Radio Emission

By Keith Cowing
Status Report
May 30, 2024
Filed under , , , , , , , , , , ,
MHD Simulations of the Space Weather in Proxima b: Habitability Conditions and Radio Emission
Sketch of the magnetospheric interaction in the starplanet system Proxima – Proxima b. The stellar wind velocity and the interplanetary magnetic field (IMF) streamlines (assumed to be radial–see text in Sect. 3) are drawn in green and red, respectively. Note that there are magnetic field lines from the star (yellow circle) that are connected to the exoplanet Proxima b (purple circle). The density distribution is shown as a color scale, normalized to the value of the stellar wind density, ρsw = µmpnsw (see Table 1). The sketch represents a super-Alfvénic case, where the ram pressure of the wind dominates over the stellar wind magnetic field pressure, so a bow shock is formed at the dayside of the planet. The Proxima star is beyond the limits of our simulation domain. — astro-ph.EP

The habitability of exoplanets hosted by M-dwarf stars dramatically depends on their space weather. We present 3D magneto-hydrodynamic simulations to characterise the magneto-plasma environment and thus the habitability of the Earth-like planet Proxima b when it is subject to both calm and extreme (CME-like) space weather conditions.

We study the role of the stellar wind and planetary magnetic field, and determine the radio emission arising from the interaction between the stellar wind of Proxima and the magnetosphere of its planet Proxima b. We find that if Prox b has a magnetic field similar to that of the Earth (Bp=B≈0.32 G) or larger, the magnetopause standoff distance is large enough to shield the surface from the stellar wind for essentially any planetary tilt but the most extreme values (close to 90∘), under a calm space weather.

Even if Proxima b is subject to more extreme space weather conditions, the planet is well shielded by an Earth-like magnetosphere (Bp≈B; ≈23.5), or if it has tilt smaller than that of the Earth. For calm space weather conditions, the radio emission caused by the day-side reconnection regions can be as high as 7×1019 erg s−1 in the super-Alfvénic regime, and is on average almost an order of magnitude larger than the radio emission in the sub-Alfvénic cases, due to the much larger contribution of the bow shock.

We also find that the energy dissipation at the bow shock is independent of the angle between the planet’s magnetic dipole and the incident stellar wind flow. If Prox b is subject to extreme space weather conditions, the radio emission is more than two orders of magnitude larger than under calm space weather conditions. This result yields expectations for a direct detection–from Earth–in radio of giant planets in close-in orbits.

Plots of density distribution (coloured scale, in particles cm−3 ) for simulations under calm space weather conditions (top and middle panels), and under a CME (bottom panels), for two different magnetic field intensity values of the exoplanet Proxima b. Green and red lines are as described in Fig. 2. — astro-ph.EP

Plots of density distribution (coloured scale, in particles cm−3 ) for two sub-Alfvénic (top) and super-Alfvénic (bottom) cases of our PLUTO simulations. Green lines correspond to streamlines of the stellar wind velocity, and red lines to magnetic field lines of both the stellar wind and the planet. In both cases, Bp = 0.32 G and the tilt of the planet is i = 0 deg, i.e., Bp is perpendicular to Bimf). In the sub-Alfvénic case, no bow shock is formed, and the resulting radio emission originates only from the reconnecting region of the exoplanet magnetosphere. In the super-Alfvénic case, a bow shock is formed. The radio emission originates both from the reconnecting region of the magnetosphere and from the bow shock (see Sect. 5). [Movies of those simulations, from beginning to end, when a steady solution is reached, can be downloaded from here.] — astro-ph.EP

Luis Peña-Moñino, Miguel Pérez-Torres, Jacobo Varela, Philippe Zarka

Comments: Accepted for publication in A&A (main journal). 14 pages, 8 figures. Videos showcasing the results of the simulation available at this https URL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2405.19116 [astro-ph.EP] (or arXiv:2405.19116v1 [astro-ph.EP] for this version)
Submission history
From: Luis Peña-Moñino
[v1] Wed, 29 May 2024 14:24:35 UTC (10,626 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻