This past week, two separate Bitcoin miners pulled off the improbable, if not impossible: mining a solo block.

On Tuesday, a single miner with 120 TH/s solved a single block, worth 6.25 BTC or about $270,000 as of writing. It was quickly followed on Thursday by yet another solo miner who was able to mine a block with only 116 TH/s. Impressively, the second miner was only hashing for less than two days, according to Solo Miner developer Dr. Con Kolivas.

For context, your odds of winning the Powerball are around one in 292 million, while the probability of winning a solo block for each miner is one in 1.4 million, according to BTC Archive on Twitter. So how’d it happen?

Solo mining

When mining Bitcoin, the higher your hashrate, the higher odds you have of finding a block.

Miners typically “pool” their hashrate together in order to have a better chance of finding the reward. Conceptually, pools act like giant ASICs with better chances of finding a block than smaller ASICs. That block reward is then spread evenly across the pool's members.

Pool mining is contrasted with solo mining, where a lone miner guesses to find the next block by themself. The math is fairly simple and the same for pools and solo miners alike: the hashrate of the miner under management divided by the hashrate of the network indicates the likelihood of winning a reward, over time.

Read: What is hashrate under management?

The math may be simple, but solo mining remains not so. Solo miners are competing by themselves against hundreds of thousands of other machines, losing almost all likelihood of profitability.

In this case, two miners accomplished a feat not only incredibly rare, but more and more unlikely as network hashrate grows.

Photo by Waldemar Brandt on Unsplash