Brother mortgaged our family property without my consent?

I just found out that my brother has mortgaged our ancestral property in Chennai without informing me. The property is jointly owned by both of us, inherited from our parents. I am worried as I was out of town for a few months and never signed any papers. Can he do this legally without my consent? What are my rights to contest this and protect my share? Please advise, I feel completely betrayed and helpless.