Antimatter belt found around the earth. Space travel fuel?

A wonderful story from the BBC.
A thin band of antimatter particles (anti-protons) has been spotted enveloping the earth, trapped between the Van Allen belts as predicted.  There may be enough for a scheme to fuel future spacecraft. The PAMELA satellite was launched in 2006 to look for this.

The anti-protons are sandwiched between the inner and outer
Van Allen belts. (Picture sourced from Wired Science.)

Earlier:  Positronium: Anti-matter turning up at the lab.  We've come a long way since 1928 when Dirac speculated such a thing might exist.
Added from Wired Science:  Not much has been detected but a few millionths of a gram may be enough to propel a spacecraft to velocities of 100 km/sec.