Magnetic energy fluxes in sub-Alfvénic planet star and moon planet interactions

Saur, Joachim; Grambusch, T.; Duling, Stefan; Neubauer, F. M.; Simon, Sven

doi:10.1051/0004-6361/201118179

Cited by 176 publications

(350 citation statements)

References 103 publications

(204 reference statements)

Supporting

Mentioning

335

Contrasting

Order By: Relevance

“…Therefore, any future models attempting to explain the early UV observation need to include planetary gas in their simulations. The modeling described here does not provide any additional constraints on whether a bow shock exists around close-in exoplanets (see Saur et al 2013 and VJH11a for conflicting arguments) but does show that the bow shock does not produce any observable signature in the UV and optical.…”

Section: Discussionmentioning

confidence: 80%

Investigation of the environment around close-in transiting exoplanets using cloudy

Turner

Christie

Arras

et al. 2016

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

It has been suggested that hot stellar wind gas in a bow shock around an exoplanet is sufficiently opaque to absorb stellar photons and give rise to an observable transit depth at optical and UV wavelengths. In the first part of this paper, we use the CLOUDY plasma simulation code to model the absorption from X-ray to radio wavelengths by 1-D slabs of gas in coronal equilibrium with varying densities (10 4 − 10 8 cm −3 ) and temperatures (2000 − 10 6 K) illuminated by a solar spectrum. For slabs at coronal temperatures (10 6 K) and densities even orders of magnitude larger than expected for the compressed stellar wind (10 4 − 10 5 cm −3 ), we find optical depths orders of magnitude too small (> 3 × 10 −7 ) to explain the ∼ 3% UV transit depths seen with Hubble. Using this result and our modeling of slabs with lower temperatures (2000 − 10 4 K), the conclusion is that the UV transits of WASP-12b and HD 189733b are likely due to atoms originating in the planet, as the stellar wind is too highly ionized. A corollary of this result is that transport of neutral atoms from the denser planetary atmosphere outward must be a primary consideration when constructing physical models. In the second part of this paper, additional calculations using CLOUDY are carried out to model a slab of planetary gas in radiative and thermal equilibrium with the stellar radiation field. Promising sources of opacity from the X-ray to radio wavelengths are discussed, some of which are not yet observed.

show abstract

Section: Discussionmentioning

confidence: 80%

Investigation of the environment around close-in transiting exoplanets using cloudy

Turner

Christie

Arras

et al. 2016

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

show abstract

“…Saur et al [2013] found the Enceladus interaction to be nearly saturated; i.e., the incident plasma is decelerated to almost complete stagnation, and the currents in the interaction region are at their maximum strength (see Table 1 in that work). Hence, there are two possible explanations for the weakness of the observed magnetic field jumps: on the one hand, it is very likely that Cassini has not yet crossed those regions of the flux tube where the hemisphere coupling currents are strongest.…”

Section: Impact Of the Anti-hall Effectmentioning

confidence: 92%

“…Subsequently, Saur et al [2007], Simon et al [2011b], and Kriegel et al [2011] applied this method to analyze various aspects of the magnetic field perturbations and the asymmetric flow deflection near the plume of Enceladus. Based on the analytical expressions for the electromagnetic fields, Saur et al [2013] and Simon et al [2013] calculated the Poynting flux generated by sub-Alfvénic moon-plasma interactions and by the electromagnetic coupling of exoplanets to their host stars. Saur [2004] also succeeded in solving equation (4) for an elliptically shaped obstacle with constant conductances.…”

Section: Simon Model Of Moon-plasma Interactions 7211mentioning

confidence: 99%

An analytical model of sub‐Alfvénic moon‐plasma interactions with application to the hemisphere coupling effect

Simon

2015

JGR Space Physics

View full text Add to dashboard Cite

We develop a new analytical model of the Alfvén wing that is generated by the interaction between a planetary moon's ionosphere and its magnetospheric environment. While preceding analytical approaches assumed the obstacle's height‐integrated ionospheric conductivities to be spatially constant, the model presented here can take into account a continuous conductance profile that follows a power law. The electric potential in the interaction region, determining the electromagnetic fields of the Alfvén wing, can then be calculated from an Euler‐type differential equation. In this way, the model allows to include a realistic representation of the “suspension bridge”‐like conductance profile expected for the moon's ionosphere. The major drawback of this approach is its restriction to interaction scenarios where the ionospheric Pedersen conductance is large compared to the Hall conductance, and thus, the Alfvénic perturbations are approximately symmetric between the planet‐facing and the planet‐averted hemispheres of the moon. The model is applied to the hemisphere coupling effect observed at Enceladus, i.e., to the surface currents and the associated magnetic discontinuities that arise from a north‐south asymmetry of the obstacle to the plasma flow. We show that the occurrence of this effect is very robust against changes in the conductance profile of Enceladus' plume, and we derive upper limits for the strength of the magnetic field jumps generated by the hemisphere coupling effect. During all 11 reported detections of the hemisphere coupling currents at Enceladus, the observed magnetic field jumps were clearly weaker than the proposed limits. Our findings are also relevant for future in situ studies of putative plumes at the Jovian moon Europa.

show abstract

“…We therefore stress that r M here refers to a characteristic distance to the point where magnetic pressure equilibrium exists, which places an upper limit on the magnetospheric size, with the size at the nose being smaller if the stellar wind ram pressure is also taken into account. We note that the relative orientation of the stellar magnetic field with respect to the orientation of the planetary magnetic moment plays an important role in shaping the open-field-line region on the planet (e.g., Ip et al 2004;Zieger et al 2006;Kopp et al 2011;Sterenborg et al 2011;Saur et al 2013). Our purely magnetic pressure balance (Eq.…”

Section: Interaction Between the Planet And The Corona Of Its Host Starmentioning

confidence: 99%

“…On the stellar side, factors such as the thermal pressure, magnetic pressure (P B, ) and the ram pressure resulting from the relative motion between the planet and the coronal material can all contribute to setting the pressure equilibrium. The stellar-wind properties determine, for example, whether Earth-type magnetospheres surrounded by bow shocks or Ganymede-type magnetospheres with Alfvén wings are formed (Ip et al 2004;Zarka 2007;Kopp et al 2011;Sterenborg et al 2011;Saur et al 2013). To quantitatively evaluate this, the stellar wind density, temperature, magnetic field, and the relative velocity of the planet are required together with planetary magnetic characteristics.…”

Section: Interaction Between the Planet And The Corona Of Its Host Starmentioning

confidence: 99%

Effects of M dwarf magnetic fields on potentially habitable planets

Vidotto

Jardine

Morin

et al. 2013

A&A

152

161

View full text Add to dashboard Cite

We investigate the effect of the magnetic fields of M dwarf (dM) stars on potentially habitable Earth-like planets. These fields can reduce the size of planetary magnetospheres to such an extent that a significant fraction of the planet's atmosphere may be exposed to erosion by the stellar wind. We used a sample of 15 active dM stars, for which surface magnetic-field maps were reconstructed, to determine the magnetic pressure at the planet orbit and hence the largest size of its magnetosphere, which would only be decreased by considering the stellar wind. Our method provides a fast means to assess which planets are most affected by the stellar magnetic field, which can be used as a first study to be followed by more sophisticated models. We show that hypothetical Earth-like planets with similar terrestrial magnetisation (∼1 G) orbiting at the inner (outer) edge of the habitable zone of these stars would present magnetospheres that extend at most up to 6 (11.7) planetary radii. To be able to sustain an Earth-sized magnetosphere, with the exception of only a few cases, the terrestrial planet would either (1) need to orbit significantly farther out than the traditional limits of the habitable zone; or else, (2) if it were orbiting within the habitable zone, it would require at least a magnetic field ranging from a few G to up to a few thousand G. By assuming a magnetospheric size that is more appropriate for the young-Earth (3.4 Gyr ago), the required planetary magnetic fields are one order of magnitude weaker. However, in this case, the polar-cap area of the planet, which is unprotected from transport of particles to/from interplanetary space, is twice as large. At present, we do not know how small the smallest area of the planetary surface is that could be exposed and would still not affect the potential for formation and development of life in a planet. As the star becomes older and, therefore, its rotation rate and magnetic field reduce, the interplanetary magnetic pressure decreases and the magnetosphere of planets probably expands. Using an empirically derived rotation-activity/magnetism relation, we provide an analytical expression for estimating the shortest stellar rotation period for which an Earth-analogue in the habitable zone could sustain an Earth-sized magnetosphere. We find that the required rotation rate of the early-and mid-dM stars (with periods 37-202 days) is slower than the solar one, and even slower for the late-dM stars ( 63-263 days). Planets orbiting in the habitable zone of dM stars that rotate faster than this have smaller magnetospheric sizes than that of the Earth magnetosphere. Because many late-dM stars are fast rotators, conditions for terrestrial planets to harbour Earth-sized magnetospheres are more easily achieved for planets orbiting slowly rotating early-and mid-dM stars.

show abstract

Magnetic energy fluxes in sub-Alfvénic planet star and moon planet interactions

Cited by 176 publications

References 103 publications

Investigation of the environment around close-in transiting exoplanets using cloudy

Investigation of the environment around close-in transiting exoplanets using cloudy

An analytical model of sub‐Alfvénic moon‐plasma interactions with application to the hemisphere coupling effect

Effects of M dwarf magnetic fields on potentially habitable planets

Contact Info

Product

Resources

About