I couldn’t find anything about Mendes by Galeano, but I did find this song by Sepultura about him: https://youtu.be/10OWU-wxuGc?si=vO1LRuJ-dbOR664H

Edit: Galeano wrote an article about Mendes: https://vermelho.org.br/2019/02/13/galeano-explica-chico-mendes-militancia-ecologica-com-luta-social/

The lack of attention this issue gets outside of astronomy communities is symptomatic of colonial capitalist state society’s othering and exploitation of the natural world. For the vast majority of human history, everyone lived by the stars, to navigate and to plan agricultural, ceremonial, hunting, foraging, and migration cycles. Many indigenous people around the world still do. But if you stop thinking of the stars as living guides who impart their wisdom and start thinking of them as future platinum mines and colonies, you don’t pay as much attention to them and you don’t notice their disappearance until it’s too late. Most settlers see more stars on TV programs about pop sci than actually looking up at them. We are a part of the universe, after all, not some outside observer unaffected by it. We should at least care about that.