What Is an Orphan Block?

In terms of cryptocurrencies, orphan blocks, sometimes referred to as stale blocks, are blocks that are not accepted into the blockchain network due to a time lag in the reporting of the block in question (compared to a qualifying block) to the network of miners.

Orphan blocks are technically valid and verified blocks but have been rejected by the chain. They are also called detached blocks as they exist in isolation from the blockchain.

Key Takeaways

  • An orphan block is a block that has been solved within the blockchain network but was not accepted due to a lag within the network itself.
  • There can be two miners who solve for a block simultaneously. The miner who has a more detailed proof-of-work sheet is the one who is awarded the block's reward.
  • There is no reward for solving a block which is then determined to be an orphan block.

Understanding an Orphan Block

A blockchain consists of a series of blocks, which act as data storage units to store details of the various transactions occurring on the blockchain network. During the standard mining process, miners attempt to generate new blocks by solving the complex mathematical equations necessary for the blockchain network to function.

The first miner who is successful in finding a new block is entitled to the block reward and writes the first transaction on the new block they found. In order for the blockchain network to continue to function, the newly found block gets added as the new 'unit' on the blockchain.

However, it is possible that two miners produce a block at a similar time. This situation occurs because the acceptance of the blocks into the blockchain by the nodes of the blockchain network does not happen instantaneously.

This time lag in accepting a block may lead to another miner solving for the same exact block. It leads to a temporary mix-up on the blockchain network, as the nodes try to decide which block of the two newly identified blocks it wants to accept.

In such a situation, the block with the larger share of proof of work (PoW) gets accepted into the blockchain. The other block, with a smaller proof of work, is discarded from getting added to the blockchain and is termed an orphan block. Such blocks are essentially valid and verified blocks, but due to the network’s working mechanism and the lag time leading to delayed acceptance, one of the blocks is rejected, or orphaned.

Another way an orphaned block is created is when a hacker with sufficient hashing power attempts to reverse a few transactions that occurred earlier in the blockchain network.

Orphan blocks are most commonly linked to the popular Bitcoin cryptocurrency network. In the case of a valid transaction existing on an orphan block, it is added to the next valid block accepted on the blockchain.

Uncle blocks, which appear on Ethereum-based blockchains, are similar to Bitcoin orphans but have an integrated use, unlike their Bitcoin counterparts, which are rejected outright.

Special Considerations: Orphan Block Rewards

Although it may seem like the blockchain miner responsible for producing an orphan block should be compensated for their time and energy, they, in fact, receive no reward for solving the block and producing an orphan block.

There are many miners who find this practice unfair since they are not compensated in any way for producing exceptional work that is only not accepted because there was a lag in the blockchain acceptance network.