Cluster — Piers Anthony

"The CLUSTER series of SF adventures is set in a future focused on colonization of distant planets. Every living thing has a Kirlian aura that can be measured. Through transfer, a refinement of mattermission technology, the mind and personality of individuals with high aura can be sent to animate a body physically distant but a hosted aura fades at the rate of about 1 unit per Earth day and higher-Kirlian individuals last longer and thus have more freedom of movement. As CLUSTER opens, the alien envoy Pnotl of Sphere Knyfh seeks help from Sphere Sol in a shared galactic-level crisis: Galaxy Andromeda has discovered the secret of energy transfer and intends to use it to steal the basic energy of the Milky Way Galaxy. Knyfh offers the secret of aura transfer on the understanding that Sphere Sol will spread the technology to help create a galactic coalition to find and defeat agents of Andromeda. Sol's highest-Kirlian individual is Flint, a green-skinned native of Outworld, who has a Kirlian aura of 200, an eidetic memory (useful for memorizing the complex equations of Kirlian transfer that he will need to communicate to other spheres). He has extraordinary intelligence, and is highly adaptable. His mission is complicated, however, by the fact that he is pursued everywhere by a very high Kirlian female Andromedan agent and, somehow, the Andromedans are able to detect and trace Kirlian transfers."