This stunning astronaut photo shows a rare phenomenon, known as a "sunglint", transforming a potential meteor crater lake into a giant silver mirror in the heart of Africa.
Lake Iro, known locally as Lac Iro, is an approximately 7-mile-wide (12 kilometers) body of water in Chad, located around 60 miles (100 km) north of the country's border with the Central African Republic. The lake lies in the heart of Africa's Sahel region — an extensive savannah that separates the Sahara Desert and the rainforests of Central Africa.
Iro is partly surrounded by Bahr Salamat, a roughly 125-mile-long (200 km) waterway that splits and feeds into the lake. The river is renowned for being exceptionally windy, especially where it bends around Iro's southern shore, according to NASA's Earth Observatory.
The lake and large sections of the river shine brightly in the image as sunlight reflects off their watery surfaces, giving them a metallic-like sheen. If you look closely, parts of its surface appear to have a whiter color than the rest. These areas are most likely reflections of the clouds hanging high over the lake.
This phenomenon is known as a sunglint, and only occurs when the observer is perfectly aligned with the sun, relative to the object reflecting the light. As a result, this effect is best observed from space.
Related: See all the best images of Earth from space
Astronauts are particularly well-suited to capturing sunglints because they can alter their angle relative to the reflecting object, unlike satellites that have a fixed view. In recent years, ISS inhabitants have also spotted a massive sunglint around a pair of Greek islands, which revealed several unusual oceanographic phenomena, and another that painted a "sea of clouds" in a volcanic lake nestled between nesting Russian volcanoes.
Suspected impact crater
Recent research suggests Lake Iro may lie within an ancient meteor impact crater leftover from when a sizable space rock slammed into Earth millions of years ago.
This theory was first put forward in the 1980s, when geologists discovered bits of ancient crystal in the rocks surrounding the lake, according to a 2014 study reviewing African impact structures.
In a more recent study, published in 2024, researchers investigated the geological features of Lake Iro. They noted that an impact may have significantly altered the shape and direction of Bahr Salamat, which may explain why there are so many twists and turns to the winding river.
Lake Iro is also highly cyclical, meaning that its depth fluctuates seasonally and can almost completely drain during periods of extreme drought, which is a common characteristic among other impact crater lakes.
Based on this evidence, the researchers of the most recent study wrote that Lake Iro "cannot be readily explained by any process other than [a meteor] impact."
More research is needed to confirm if this is the case, and this "should be a priority" due to its size. The researchers added that evidence of the impact may have been well preserved by the lake.
