Orphan Block

What Is an Orphan Block?

In blockchain terms, orphan blocks are blocks mined at the same time as another block but not accepted by the blockchain. Most of the time, this is because there are not enough blocks generated from that block for the network to recognize it as the longest fork. The Bitcoin blockchain discards orphan blocks; however, other blockchains may use them for different purposes.

Technically, orphan blocks are called stale blocks, but because most people refer to them as orphaned, the name orphan block has stuck.

Key Takeaways

  • An orphan block is a block that has been solved within the blockchain network but was not accepted by the network.
  • There can be two miners who solve valid blocks simultaneously. The network uses both blocks until one chain has more verified blocks than the other. Then, the blocks in the shorter chain are orphaned.
  • Orphan blocks are a regular occurrence in a distributed blockchain such as Bitcoin and Ethereum.

Understanding Orphan Blocks

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 hash—the hexadecimal number that stores the block's information.

The first miner who successfully opens a new block is entitled to the block reward and writes the first transaction on the new block. The newly opened block stores information about the previous blocks and new transactions, and is mined to open another block.

How Does a Block Become Orphaned?

The series of blocks that create a blockchain are related in that they receive information from the blocks that preceded them. When a block is closed, its data is encoded and passed on to the next block. These two blocks are a parent and child block. If two blocks are opened from the same parent block simultaneously, there are two child blocks. Only one of them can be integrated into the chain.

The blockchain decides which block and fork to integrate based on the longest number of validated blocks.

The network nodes, which validate blocks, decide which block to use by allowing a small fork between the two child blocks. Then, the nodes determine what block they want to accept by reaching a validation consensus.

Each block will have subsequent blocks created, initiating a race to verify the most blocks. The fork with more verified blocks—through proof of work (PoW)—gets accepted into the blockchain. Any verified blocks within the shorter chain are discarded.

The discarded block is called an orphan block (in technical documents, it's called a stale block). Any blocks generated from the orphaned block go back to the memory pool to be validated and added to the new chain.

How Are Orphan Blocks Different From Stale Blocks?

As mentioned previously, many people call blocks rejected by the network orphan blocks. In technical terms, this is not the block relationship. Because blocks are referred to by ancestral relationships for easy reference, an orphan block would technically be a block with unknown parent blocks.

The parent-child relationship in a blockchain stems from its database roots where data from the parent is included in the child blocks so that values are linked.

This would mean that the block hash was incomplete. The block hash is an encrypted number and a snapshot of the complete blockchain at the moment the block was created. Parent block information would be included in this hash, so an orphan block would be a strange occurrence in a network that relies on validation and verification of all preceding blocks. A true orphan block without any parental block information is likely a block that has been tampered with.

A stale block is what most people are referring to when they talk about a block rejected by the blockchain network.

Is a Bitcoin a Block?

A block is an encrypted record of all transactions within that block. Bitcoin is the cryptocurrency rewarded for solving the hash—the encrypted hexadecimal number that stores the previous block's information.

What Happens to Orphaned Bitcoin?

Bitcoin is the cryptocurrency awarded for opening a new block in the blockchain. Blocks can become orphaned, but a bitcoin cannot. Orphaned (stale) blocks are discarded.

Is There a Reward for Mining Stale Blocks?

Generally, there is no reward for mining a stale block. However, some blockchains might allow for stale block rewards. Ethereum awards miners who created ommer blocks (its stale block equivalent) with smaller rewards and transaction fees—at least until it switches to a proof-of-stake consensus mechanism.

Investing in cryptocurrencies and other Initial Coin Offerings (“ICOs”) is highly risky and speculative, and this article is not a recommendation by Investopedia or the writer to invest in cryptocurrencies or other ICOs. Since each individual's situation is unique, a qualified professional should always be consulted before making any financial decisions. Investopedia makes no representations or warranties as to the accuracy or timeliness of the information contained herein. As of the date this article was written, the author does not own Bitcoin or Ethereum.

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