Space physics. Tying up the solar system with a ribbon of charged particles.

Talk about rewriting the textbooks. Scientists thought they knew what the heliosphere looked like. The solar system’s enveloping pocket filled with the solar wind’s charged particles is plowing through the onrushing “galactic wind” of the interstellar medium in the shape of a comet, they all agreed. When NASA launched the Interstellar Boundary Explorer (IBEX) in October 2008, mission scientists expected it to confirm the textbooks. Instead, f ive papers published online in Science this week (www. sciencemag.org/cgi/content/abstract/ 1180906, 1180981, 1180927, 1180986, 1180971) report that IBEX revealed a sky-spanning “ribbon” of unexpectedly intense emissions of energetic neutral atoms (ENAs). No one knows what is creating the ENA ribbon, but everyone agrees that it means the textbook picture of the heliosphere is wrong. “I’m blown away completely,” says space physicist Neil Murphy of NASA’s Jet Propulsion Laboratory in Pasadena, California. “It’s amazing, it’s opened up a new kind of astronomy.” The meterwide, hexagonal IBEX monitors the edge of the solar system from Earth orbit by “seeing” the heliosphere’s outer boundary in the “light” of energetic neutral hydrogen atoms. They’re energetic because they are fast and neutral because they were once positive ions that lost their charge by picking up electrons. Those energetic parent ions l ie near the heliopause, the boundary where solar wind meets galactic wind more than 100 times Earth’s distance from the sun. Charged ions can’t reach Earth, buffeted as they are by the solar wind and its embedded magnetic field. But once an energetic ion picks up an electron from a neutral atom, it can fly straight and true just like light. IBEX’s two ENA detectors can then record the ENA glow from every direction. “The thing that’s really shocking is this ribbon,” says IBEX principal investigator David McComas of Southwest Research Institute in San Antonio, Texas. Researchers had expected gusts in the solar wind blowing against the boundary to create 20% or 30% variations in ENA emissions, but the ribbon is 10 Tying Up the Solar System With a Ribbon of Charged Particles SPACE PHYSICS