EU citizens do not need a visa from the Embassy to go to Mexico. They should declare at their immigration entry point they come as tourist. That label covers specifically scientific conferences. More information below.
In case you will be needing an invitation to get a visa, please register, pay the fees, and then provide the following information to Francisco Hernández Quiroz (fhq at ciencias.unam.mx):
You will get the invitation by e-mail and also by post.