Pope Francis washes the feet of a prisoner at the Casal Del Marmo Youth Detention Center during the mass of the Lord's Supper on Thursday in Rome. L'Osservatore Romano/Getty Images hide caption

itoggle caption L'Osservatore Romano/Getty Images

A computer simulation of the formation of large-scale structures in the Universe, showing a patch of 100 million light-years and the resulting coherent motions of galaxies flowing towards the highest mass concentration in the centre. The snapshot refers to an epoch about 10 billion years back in time. Klaus Dolag/VIMOS-VLT Deep Survey/ESO hide caption

itoggle caption Klaus Dolag/VIMOS-VLT Deep Survey/ESO

Coprates Chasma in the Valles Marineris on Mars, photographed by the Mars Express spacecraft. Appearing in the top half of this image, it ranges from 60-100 km wide and drops 8-9 km below the surrounding plains. G. Neukum/ESA/DLR/FU Berlin hide caption

itoggle caption G. Neukum/ESA/DLR/FU Berlin