Absurdly, mining testnet bitcoins is really expensive. Currently, it has a difficulty of 61681740.29071233 which means it has a target of:
0x0000000000000045a14a00000000000000000000000000000000000000000000
To be honest; I was wondering about mining tBTC myself a while back and I was astonished how the difficulty can be so high, even though there is no monetary reward for mining it. Is there any good reason why so many miners are apparently mining it? Or maybe it just has a different difficulty target / other parameters that were chosen?