Helioseismology from An Off-Sun-Earth Vantage Point

Most of our knowledge about the Sun's interior, including dynamics and structures on both global and local scales, has been gained through observations on Earth, near Earth, or along the Sun-Earth line. Observations from vantage points off the Sun-Earth line will help us better monitor the Sun and better understand its internal dynamics. Here, I outline four helioseismology research topics that can greatly benefit from such observations from a different vantage point. First, helioseismology routinely maps active regions on the Sun's far side before they rotate into the Earth's view; however, the accuracy of these helioseismic maps and the quantitative relationship between helioseismic phase shifts and magnetic field can only be evaluated with an off-Sun-Earth observation. Second, our current detection of the deep solar interior is limited by the surface area we can use for acoustic measurements; off-Sun-Earth observations will allow us to analyze waves passing through the solar core, greatly enhancing our capability of investigating the Sun's deep interior. Third, current studies on the Sun's internal meridional circulation are significantly complicated by a systematic center-to-limb effect; an off-Sun-Earth vantage point will help us understand the physical cause of the effect, and hopefully result in a more robust method to remove the effect. Fourth, due to the Wilson Depression in sunspots and the inclined magnetic field lines in sunspot penumbrae, the observed line-of-sight oscillatory signals from sunspots are therefore from different atmospheric heights and are only a component of the complicated oscillations; an observation from a different vantage point will likely help us disentangle the complexity of the observed oscillations.