On 1st January 2019, Nasa's New Horizons probe notched up another historic first: the first ever Kuiper belt fly-by. Its target was 2014 MU69, a chunk of ice and rock about four billion miles (approximately 6.4 billion kilometres) from Earth, dubbed Ultima Thule, a Latin phrase meaning a distant, unknown region. It is the most distant fly-by in history, and it is believed the d...