10 most difficult satel­lite pho­tog­ra­phy riddles

The Richat Structure in Mauritania, also known as the Eye of the Sahara, was interpreted as an asteroid impact structure, but no evidence of shock metamorphism has been found. Today, scientists believe that it is a huge (40 km in diameter) and deeply eroded geologic dome.

Sable Island is believed to have formed from a terminal moraine deposited on the continental shelf near the end of the last Ice Age. It emerges from vast shoals and shallows which, in tandem with frequent fog and sudden storms, have caused over 350 recorded shipwrecks

Lake Balkhash is the 13th largest lake in the world. The lake is divided by a strait into two distinct parts. The western is a fresh water half, while the eastern half is saline.

Launched June 10, 2011, Aquarius is NASA’s first satellite instrument specifically designed to study the salt content of ocean surface waters. The complete first year dataset of NASA's Aquarius instrument reveals seasonal changes in the Amazon River's plume. Depending on the prevailing currents, the river's freshwater outflow heads east toward Africa or bends up north to the Caribbean.

Kinshasa (at the bottom of the photo) is an urban area with a 2013 population of over 9 million. It faces the capital of the neighbouring Republic of Congo, Brazzaville, which can be seen in the distance across the wide Congo River.

Lake Titicaca is surrounded by the Andes. It is often called the highest navigable lake in the world, with a surface elevation of 3,812 metres (12,507 ft).

This is an astronaut photo of the Al Khufrah Oasis in Libya. The circular shape of fields is characteristic of center pivot irrigation. These fields are approximately 0.6 mile (1 kilometer) in diameter. Lighter colors indicate fields that have been harvested recently or just planted.

The southwestern coast of Finland has a great many skerries; so many, in fact, that they form an archipelago. This characteristic shore makes Helsinki easily recognizable.

São Paulo is about 79 km (49 mi) from Santos, the busiest container port in Latin America - visible at the bottom of the photo.

The city is flanked by the main chain of the Andes to the east and the Chilean Coastal Range to the west. The mountains around Santiago are quite tall; the tallest is the Tupungato volcano at 6,570 m (21,555 ft).