Reconstructing the Solar Wind From Its Early History to Current Epoch

Abstract

Stellar winds from active solar-type stars can play a crucial role in removal of stellar angular momentum and erosion of planetary atmospheres. However, major wind properties except for mass loss rates cannot be directly derived from observations. We employed a three-dimensional magnetohydrodynamic Alfvén wave driven solar wind model, ALF3D, to reconstruct the solar wind parameters including the mass loss rate, terminal velocity and wind temperature at 0.7, 2 and 4.65 Gyr. Our model treats the wind thermal electrons, protons and pickup protons as separate fluids and incorporates turbulence transport, eddy viscosity, turbulent resistivity, and turbulent heating to properly describe proton and electron temperatures of the solar wind. To study the evolution of the solar wind, we specified three input model parameters, the plasma density, Alfvén wave amplitude and the strength of the dipole magnetic field at the wind base for each of three solar wind evolution models that are consistent with observational constrains. Our model results show that the velocity of the paleo solar wind was twice as fast, ~ 50 times denser and 2 times hotter at 1 AU in the Sun's early history at 0.7 Gyr. The theoretical calculations of mass loss rate appear to be in agreement with the empirically derived values for stars of various ages. These results can provide realistic constraints for wind dynamic pressures on magnetospheres of (exo)planets around the young Sun and other active stars, which is crucial in realistic assessment of the Joule heating of their ionospheres and corresponding effects of atmospheric erosion.

Atmospheric loss from the dayside open polar region and its dependence on geomagnetic activity: implications for atmospheric escape on evolutionary timescales

“…In the young solar system, the Sun is believed to have been more active (e.g. Ribas et al, 2005;Güdel, 2007) with a higher EUV flux, higher solar wind dynamic pressure, and a more intense and active magnetic field (solar dynamo) due to faster rotation (Wood, 2006;Airapetian and Usmanov, 2016). This indicates that the young Earth experienced more intense geomagnetic activity compared to the present time (Krauss et al, 2012) and hence high escaping fluxes of ionospheric ions (Moore et al, 1999;Cully et al, 2003;Peterson et al, 2008).…”

The Lunar Paleo‐Magnetosphere: Implications for the Accumulation of Polar Volatile Deposits

“…Here, we employ the modeling results of Airapetian and Usmanov () to quantify, at least to first‐order, typical solar wind parameters at a solar age of ~2 Gyr. In particular, Airapetian and Usmanov () used a three‐dimensional, magnetohydrodynamic model of the solar wind with input conditions representative of three different solar epochs: 0.7, 2, and 4.65 Gyr (present day). For the 2‐Gyr heliospheric simulations, mean plasma parameters at 1 AU determined by the heliospheric magnetohydrodynamic model include a density of 30 cm ‐3 , solar wind speed of 550 km/s, particle temperatures of 17 eV, and interplanetary magnetic field strength of 30 nT (Airapetian & Usmanov, ; V. Airapetian, personal communication, November 2017).…”

The critical binary star separation for a planetary system origin of white dwarf pollution

“…Zendejas et al (2010) adopts ti = 0.1 Gyr, but in fact ti = 0.7 Gyr may be more realistic (Wood et al 2005;Airapetian & Usmanov 2016). For the Sun,ṀMS(t = ti) ≈ −2 × 10 −11 M⊙ yr −1 , a value we adopt here.…”

“…These properties are a function of that star's physical parameters, as well as age. Currently main sequence star winds are observationally poorly constrained, except for the Solar wind (Airapetian & Usmanov 2016). Consequently, we keep our treatment general in order to allow readers to insert their favoured values into the equations for future applications.…”