A NASA satellite scanning the outer limits of the solar system has found an unexpected dense "ribbon" of gas there.

Data from the IBEX satellite shows a dense ribbon of particles coming from the heliosphere. The locations of the two Voyager spacecraft, V1 and V2, are also shown. Data from the IBEX satellite shows a dense ribbon of particles coming from the heliosphere. The locations of the two Voyager spacecraft, V1 and V2, are also shown. (SwRI) NASA's Interstellar Boundary Explorer satellite, called IBEX, is mapping the edge of the solar system, where charged particles from the sun, the solar wind, meets gas from the rest of the galaxy.

The boundary where the pressure from the solar wind and the interstellar medium are at the same pressure, 16 billion kilometres from Earth, forms a giant bubble called the heliopause, and it's nothing like what scientists predicted it to be.

The heliopause doesn't emit light, so it can't be seen with conventional cameras. Particles called energetic neutral atoms (ENAs) are produced in interactions between charged particles at the heliopause.

IBEX orbits the Earth in an elongated orbit and gathers ENAs as they fly past at incredible speeds, up to four million km/h.

CBC Radio's Quirks & Quarks will have an interview with principal investigator David McComas on Oct. 24.

IBEX found that ENAs aren't coming from the heliopause in a uniform way, but are concentrated in a narrow ribbon. The ENA emissions from the ribbon are two to three times higher than the rest of the sky.

"We have discovered an arc-shaped ribbon of high-pressure material that looks to be piled-up material from the sun. The IBEX maps and the discovery of the ribbon are completely different from what we thought it should look like," wrote study author Herbert Funsten.

NASA's Voyageur spacecraft, launched in 1977 and currently in the region where the ENAs are created, have also studied the heliopause and failed to detect the ribbon.

"The most astounding feature in the IBEX sky maps — the bright narrow ribbon — snakes through the sky between the Voyager spacecraft, where it remained completely undetected until now," said David McComas of the Southwest Research Institute, the principal investigator for IBEX.

The IBEX results are the subject of six different papers in this week's issue of Science.