A dramatic difference in temperature between the near and far side of the mantle has long been hypothesised, but our study provides the first evidence using real samples." They show us that the differences between the near and far side are not only at the surface but go deep into the interior." In their paper, the researchers noted that the far side of the interior may have been cooler due to having fewer heat-producing elements - elements such as uranium, thorium and potassium, which release heat due to radioactive decay. They then used several techniques to estimate the temperature of the sample while at different stages of its past when it was deep in the moon's interior. The pattern of these X-rays can be analysed to identify the elements that make up the sample.