A Perfect Trio of Prehistoric Atolls Glow Like Tropical Jewels Off Australia's Coast – Earth From Space

Rowley Shoals is an Australian territory that includes three atolls: Imperieuse Reef (lower left), Clerk Reef (centre) and Mermaid Reef (upper right). (Image courtesy of NASA/ISS)

This stunning photograph by an astronaut shows an unusual chain of three atolls located next to each other off the coast of Australia. The oval-shaped islands were once part of a huge coral system that rivaled the Great Barrier Reef.

These three islands make up Rowley Shoals, an uninhabited Australian territory located in the Timor Sea about 180 miles (290 kilometers) off the coast of Western Australia. From southwest to northeast (left to right), they are called Imperieuse Reef, Clerk Reef, and Mermaid Reef.

All of these oval-shaped formations are atolls — rings of land surrounded by coral reefs that once framed an island that eventually sank beneath the waves. According to NASA's Earth Observatory, the atolls are arranged in a nearly perfect straight line, stretching about 60 miles (100 km) from one end to the other.