According to the Daily Express, the 2.4-kilometre wide slab of space rock is one of 17 being closely monitored by Nasa and other astronomy experts due to its proximity to earth. Scientists now believe this asteroid could be even bigger than calculated as it is thought part of its mass may have been shrouded in darkness. The news has further fuelled rumours by conspiracy theorists that a mysterious Planet X four times the size of Jupiter will pass the Earth this month.