STEREO Observations Indicate That Sun's Corona Is Larger Than Expected

redOrbit Staff & Wire Reports – Your Universe Online

Astronomers using NASA’s Solar Terrestrial Relations Observatory (STEREO) have discovered that the atmosphere of solar particles surrounding the sun is larger than previously believed, extending out some five million miles above the surface, the US space agency announced on Wednesday.

The solar atmosphere, which is also known as the corona, consists of particles “through which magnetic fields swarm, solar flares erupt, and gigantic columns of material rise, fall and jostle each other around,” explained Karen C. Fox of NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

The discovery that the corona is larger than believed could have a tremendous impact on the upcoming Solar Probe Plus mission. Solar Probe Plus, which is due to launch in 2018, is expected to travel closer to the sun than any other piece of man-made technology in the history of space travel in an attempt to enhance our understanding of coronal heating, shed new light on the origins of solar wind, and answer other critical questions in heliophysics.

[ Animation of the future Heliophysics mission Solar Probe Plus ]

The new STEREO observations, which were published last month in The Astrophysical Journal, mark the first time that the inner boundary of the heliosphere has been directly measured. By combining these measurements with the outer boundary ones collected by Voyager 1, the entire extent of this large solar particle-filled bubble surrounding the sun and all of the planets has now been defined.

“We’ve tracked sound-like waves through the outer corona and used these to map the atmosphere,” said Craig DeForest of the Southwest Research Institute (SwRI) in Boulder, Colorado. “We can’t hear the sounds directly through the vacuum of space, but with careful analysis we can see them rippling through the corona.”

The authors of the new study analyzed magnetosonic waves, or waves that are a hybrid of sound waves and magnetic waves that are also known as Alfven waves. While sound waves on Earth oscillate hundreds of times per second, these waves are approximately 10 times the length of Earth and oscillate about once every four hours.

“Tracking magnetosonic waves showed DeForest and his team that the material throughout this extended space remained connected to the solar material much further in,” Fox explained. “That is to say that even out to 5 million miles from the sun, giant solar storms or coronal mass ejections can create ripple effects felt through the corona.”

Past that point, however, a steady stream of solar material known as the solar wind flows out from the sun. That material has separated from the star, and as such the corona cannot be affected by its movement. Since the Solar Probe Plus mission is expected to travel within four million miles of the sun, it could be greatly impacted by the discovery that the solar atmosphere extends out further than scientists had previously believed.

“This research provides confidence that Solar Probe Plus, as designed, will be exploring the inner solar magnetic system,” explained Marco Velli, a Solar Probe Plus scientist at the NASA Jet Propulsion Laboratory (JPL) in Pasadena, California. “The mission will directly measure the density, velocity and magnetic field of the solar material there, allowing us to understand how motion and heat in the corona and solar wind are generated.”

“Scientists knew the mission would be gathering information closer to the sun than ever before, but couldn’t be sure it would travel through the corona proper,” added Fox. “With direct access to the sun’s atmosphere, Solar Probe Plus will provide unprecedented information on how the solar corona is heated and revolutionize our knowledge of the origin and evolution of the solar wind.”