Passage: Adrastea has an irregular shape and measures 20×16×14 km across. A surface area estimate would be between 840 and 1,600 (~1,200) km2. This makes it the smallest of the four inner moons. The bulk, composition and mass of Adrastea are not known, but assuming that its mean density is like that of Amalthea, around 0.86 g/cm3, its mass can be estimated at about 2 × 1015 kg. Amalthea's density implies that the moon is composed of water ice with a porosity of 10–15%, and Adrastea may be similar.No surface details of Adrastea are known, due to the low resolution of available images.

Question: what is the surace estimate
between 840 and 1,600