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.)
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.