The stars are not alone. In the disk of our Milky Way Galaxy about 10 percent of visible matter is in the form of gas, called the
interstellar medium (ISM). The ISM is
not uniform, and shows patchiness even near our
Sun. It can be quite difficult to detect the
local ISM because it is so tenuous and emits so little light. This mostly
hydrogen gas, however, absorbs some very specific colors that can be detected in the light of the
nearest stars. A working map of the local ISM within 20 light-years, based on ongoing observations and recent particle detections from the Earth-orbiting Interstellar Boundary Exporer satellite (
IBEX), is
shown above. These observations indicate that our Sun is moving through a
Local Interstellar Cloud as this cloud flows outwards from the
Scorpius-Centaurus Association star forming
region. Our Sun may exit the
Local Cloud, also called the Local Fluff, during the next 10,000 years. Much remains unknown about the local
ISM, including details of its distribution, its origin, and how it affects the
Sun and the Earth. Unexpectedly, recent
IBEX spacecraft measurements indicate that the
direction from which neutral
interstellar particles flow through our Solar System
is changing.