Upcoming \gamma -ray satellites will search for Dark Matter annihilations in Milky Way substructures ( or ’ clumps ’ ) .
The prospects for detecting these objects strongly depend on the assumptions made on the distribution of Dark Matter in substructures , and on the distribution of substructures in the Milky Way halo .
By adopting simplified , yet rather extreme , prescriptions for these quantities , we compute the number of sources that can be detected with upcoming experiments such as GLAST , and show that , for the most optimistic particle physics setup ( m _ { \chi } = 40 GeV and annihilation cross section \sigma v = 3 \times 10 ^ { -26 } cm ^ { 3 } s ^ { -1 } ) , the result ranges from zero to \sim hundred sources , all with mass above 10 ^ { 5 } M \odot .
However , for a fiducial DM candidate with mass m _ { \chi } = 100 GeV and \sigma v = 10 ^ { -26 } cm ^ { 3 } s ^ { -1 } , at most a handful of large mass substructures can be detected at 5 \sigma , with a 1-year exposure time , by a GLAST-like experiment .
Scenarios where micro-clumps ( i.e .
clumps with mass as small as 10 ^ { -6 } M \odot ) can be detected are severely constrained by the diffuse \gamma -ray background detected by EGRET .