Thursday, March 31, 2011

IBEX Camera Sees a Ribbon in the Sky

The NASA IBEX (Interstellar Boundary Explorer) mission (the size of a kitchen table) was launched in 2008 to map the heliosphere that surrounds our solar system. It carries a High-Energy Neutral Atom (HENA) camera that images energetic neutral atoms, rather than photons, to create maps of the boundary region between our solar system and the rest of our galaxy.

The surprise result (so far) is that the energy and particles at the galactic boundary are confined to a "ribbon" structure that envelopes the heliosphere. For reference, the Voyager spacecraft are just now passing through the heliopause, at about 100 AUs, after more than 30 years of in-flight operation. Both the heliosphere and heliopause are shown below on a logarithmic scale.

For the first ten billion kilometres of its radius, the solar wind travels at over a million kilometers per hour. As it begins to drop out with the interstellar medium, it slows down before finally ceasing altogether. The point where the solar wind slows down is the termination shock; the point where the interstellar medium and solar wind pressures balance is called the heliopause; the point where the interstellar medium, traveling in the opposite direction, slows down as it collides with the heliosphere is the bow shock. [Source: Wikipedia]