Scientists have discovered that the Sun has patches of “moss” on its surface. These small, bright, patchy structures made of plasma in the solar atmosphere were first spotted in 1999 by NASA’s TRACE mission. The moss grows around the center of sunspot groups, where magnetic conditions are strong, and is found between two layers of the Sun’s atmosphere called the chromosphere and corona.
The Sun’s Mysterious “Moss”
For a long time, scientists have been trying to understand how this mossy region is connected to the Sun’s lower atmospheric layers and how material there is heated from 10,000 degrees Fahrenheit up to nearly 1 million degrees Fahrenheit — 100 times hotter than the bright surface just below. Now, research using data from NASA’s High Resolution Coronal Imager (Hi-C) sounding rocket and NASA’s Interface Region Imaging Spectrograph (IRIS) mission have given scientists new insights into how the moss is superheated.
Superheating in the Solar Atmosphere
The observations from these instruments, combined with complex 3D simulations, have revealed that electrical currents may play a role in heating the moss. The region is filled with a tangle of magnetic field lines, like invisible spaghetti. This mess of magnetic spaghetti creates electrical currents that can help heat material to a wide range of temperatures from 10,000 to 1 million degrees Fahrenheit. This local heating in the moss seems to happen in addition to heat flowing from the hot, multi-million-degree overlying corona.
Electrical Currents Contribute to Heating
“Thanks to the high-resolution observations and our advanced numerical simulations, we’re able to figure out part of this mystery that’s stumped us for the past quarter of a century,” said author Souvik Bose, a research scientist at Lockheed Martin Solar and Astrophysics Laboratory and Bay Area Environmental Institute, NASA’s Ames Research Center in California’s Silicon Valley. “However, this is just a piece of the puzzle; it doesn’t solve the whole problem.”
The Quest for Understanding Continues
To fully understand how the corona and moss are heated, many more observations are needed. Some are coming soon: Hi-C is scheduled to launch again this month to capture a solar flare, and it may also capture another moss region together with IRIS. However, scientists and engineers are working to develop new instruments onboard the future MUlti-slit Solar Explorer (MUSE) mission to obtain observations that can fully address this mystery.
IRIS and TRACE are part of NASA’s Explorers Program.