We've known about coronal rain for a long time, but its motion has foxed solar physicists. For some reason, coronal rain falls very slowly, a lot slower than we'd expect for plasma falling toward a gravitational bully like the sun.
"The sun's gravity should be pulling the material down much faster than it actually moves. What's slowing the descent?" he asks.
With thanks to the SDO, Schrijver finally has an answer.
"The rain appears to be buoyed by a ‘cushion' of hot gas," he says. "Previous observatories couldn't see it, but it is there."
The sun's lower corona is a confused forest of magnetic field lines and turbulent plasma of different temperatures. Using its temperature-sensitive instruments, the SDO can see that below the falling coronal rain is plasma at million degree temperatures, many times hotter than the coronal rain itself. The presence of this very hot gas exerts a pressure on the falling "rain," slowing it down.
This is an elegant answer to a beautiful solar phenomena, a very early success for what promises to be a very fruitful mission.
WATCH VIDEO: See the SDO video of coronal rain in action (produced by Jorge Ribas, narration: me):