First Map of the Sun’s Outer Boundary

Map of the Sun’s Outer Boundary. Credit CfA/ Melissa Weiss

Using NASA’s Parker Solar Probe and other spacecraft near Earth, scientists have created and confirmed the first two-dimensional map of the Sun‘s outer boundary.

The maps created by astronomers at the Center for Astrophysics, Harvard & Smithsonian, reveal for the first time how and where the Sun stops holding on to its outer atmosphere.

This illustration shows a boundary in the Sun’s atmosphere where the solar wind begins to move faster than magnetic waves can travel. At this point, solar material can no longer return to the Sun—it escapes into space for good.

The boundary changes shape over time, sometimes looking spiky and sometimes more bubbly. By combining close-up measurements from the Parker Solar Probe with observations from far away, scientists were able to follow how this boundary changes during the Sun’s activity cycle and map a region that had never been explored before.

“Parker Solar Probe data from deep below the Alfvén surface could help answer big questions about the Sun’s corona, like why it’s so hot. But to answer those questions, we first need to know exactly where the boundary is,” said Sam Badman, an astrophysicist at the CfA, and the lead author of the paper.