A spacecraft orbiting Earth has directly detected the atoms that make up the area of space just outside the Solar System. To scientists’ surprise, new data from NASA’s Interstellar Boundary Explorer (IBEX) craft, launched in 2008, indicates that the composition of this area of interstellar medium is not uniform across the galaxy, but is unexpectedly low in oxygen. The discovery offers fresh information about the fundamental make up of stars, planets and even people.
Astronomers had previously achieved a general feel for the composition of the interstellar medium across the galaxy by studying how light from distant stars is absorbed. The new IBEX results provide the most detailed picture yet of the interstellar medium just outside our Solar System, the ‘local cloud’.
The results were surprising, says David McComas, a heliophysicist at Southwest Research Institute in Texas, and principal investigator for IBEX. “The composition of the medium isn’t like the average measured throughout the galaxy — and that is important because the interstellar medium is the material from which stars, planets and all life form.”
IBEX’s main goal is to map the heliosphere, the part of space directly influenced by the Sun. Charged particles from the Sun — the solar wind — create this protective bubble, which extends through the Solar System, preventing electrically-charged particles outside it from entering. IBEX detects neutral atoms, which can pass through the heliosphere as they lack an electric charge.
A previous NASA mission, Ulysses, measured neutral helium atoms from outside the heliosphere. IBEX is the first to measure heavier elements, such as oxygen and neon, which were found to be entering the Solar System more slowly than expected — and from a different direction. “This discovery changes our understanding of the heliosphere itself, and of how it works to keep out those energetic charged particles,” says McComas.