Pumping Energy into the Solar Wind
The solar wind is ever enticing, providing as it does a highly variable stream of charged particles moving out from the Sun at speeds up to 800 kilometers per second. Finding ways to harness that energy for propulsive purposes is tricky, although a good deal of work has gone into designs like magsails, where a loop of superconducting wire creates the magnetic field needed to interact with this ‘wind.’ But given its ragged variability, the sail metaphor makes us imagine a ship constantly pummeled by gusts in varying degrees of intensity, constantly adjusting sail to maintain course and stability. And it’s hard to keep the metaphor working when we factor in solar flares or coronal mass ejections.
We can lose the superconducting loop if we create a plasma cloud of charged particles around the craft for the same purpose. Or maybe we can use an electric ‘sail,’ enabled by long tethers that deflect solar wind ions. All of these ideas cope with a solar wind that, near the Sun, may be moving at tens of kilometers per second but accelerating rapidly with distance, so that it can reach its highest speeds at 10 solar radii and more. Different conditions in the corona can produce major variations in these velocities.
Obviously it behooves us to learn as much as we can about the solar wind even as we continue to investigate less turbulent options like solar sails (driven by photon momentum) and their beam-driven lightsail cousins. A new paper in Science is a useful step in nailing down the process of how the solar wind is energized once it has left the Sun itself. The work comes out of the Smithsonian Astrophysical Observatory (SAO), which is part of the Center for Astrophysics | Harvard & Smithsonian (CfA), and it bores into the question of ‘switchbacks’ in the solar wind that have been thought to deposit energy.
