Rootstock is **not** a Bitcoin sidechain as per the sidechains whitepaper. It does **not** benefit from Bitcoin hashrate.

Satoshi consensus, based on proof-of-work, is the only consensus system that prevents the rewrite of blockchain history at a low cost. The academic community is advancing the knowledge and study of proof-of-stake as an alternative, but currently PoW provides the highest proven security. Merge mining is a technique that allows Bitcoin miners to mine other cryptocurrencies simultaneously with nearly zero marginal cost. The same mining infrastructure and setup they use to mine Bitcoins is reused to mine RSK simultaneously. This means that, as RSK rewards the miners with additional transaction fees, the incentive for merged mining becomes high.