An orphan block is a valid block that is not part of the main blockchain due to the absence of a recognized parent block, often resulting from two blocks being mined simultaneously.

Understanding Orphan Blocks

An orphan block is a valid block that, intriguingly, does not have a parent block within the main blockchain. Imagine it as a puzzle piece that fits perfectly but doesn’t connect to the existing picture. These blocks are also known as detached blocks, stale blocks, or extinct blocks.

How Orphan Blocks Occur

Blocks become orphaned through a process akin to a race. When two miners broadcast their newly found blocks simultaneously, the network is temporarily split, unsure of which block to continue building upon. Eventually, the network resolves this by choosing the chain that becomes longer, leaving the other as an orphan.

The Fate of Orphan Blocks

These blocks are not lost. They return to the mempool, a kind of waiting room for unconfirmed blocks, where they have another chance to join the main blockchain. However, the transactions they contain remain valid and are simply waiting to be included in a new block.

While typically a natural occurrence, orphan blocks can be exploited. Malicious actors may attempt to use them to conduct attacks on the network, such as the dreaded 51% attack. Thus, understanding orphan blocks is not just academic; it’s a security matter as well.