This eye-catching astronaut photo shows the point where an ancient Patagonian lake has been split by a peculiar land bridge, creating two contrastingly colored bodies of water.

Lake Pueyrredón (on the left in the photo) is the Argentine half of a roughly 40-mile-long (65 kilometers) glacial lake, which stretches across the country's border with Chile in Patagonia — a region in South America that is well known for its diverse range of geographic features, including mountains, fjords, deserts and rainforests. The Chilean half of the lake is known as Lake Cochrane (not shown in this image). Both halves hold crystal-clear water that is up to 1,600 feet (500 meters) deep, giving Pueyrredón a deep blue hue when viewed from above.

Thousands of years ago, a thick sediment barrier formed across the southern section of Lake Pueyrredón, creating a new body of water known as Lake Posadas. This smaller body, which is roughly 5 miles (8 km) long, has a lighter, teal color due to its shallow water and a large influx of sediment from a nearby river, according to NASA's Earth Observatory.

Other rivers from nearby hills have previously dumped large quantities of sediment along the western shore of Lake Pueyrredón (bottom of the photo), creating a trio of fan-shaped landforms, known as deltas, that increase in size from north to south (left to right in the photo).

Wind-driven currents and waves have pushed some of this sediment from the outer edges of the two smaller deltas, creating long, thin strips of land, known as sandspits, pointing down-current.

The strip of land separating Pueyrredón and Posadas looks similar to the sandspits. However, it is most likely a moraine — a barrier of sediment and larger rocks that formed along the edge of a hefty iceberg or long-lost glacier, according to the Earth Observatory.

Eagle-eyed viewers may be able to spot a narrow airstrip on the smallest delta (running almost parallel with its sandspit). While the area is largely uninhabited, it is popular with tourists, who travel to the lakes to camp, hike, fish and kayak, according to a local travel site.

Lake Posadas is also home to a unique island with a massive rocky arch (see below) that is also popular with tourists.

The two lakes in the astronaut photo sit within a large valley, which was carved by a massive ice sheet that once covered the area. The last remnants of this ice sheet are located in northern Patagonia, around 20 miles (30 km) west of Lake Cochrane, and have also been snapped from space by astronauts.

Patagonia is home to dozens of similar valleys and fjords that were carved out by the same massive ice slab. Around 210 miles (340 km) southwest of Pueyrredón and Posadas, a trio of ravines converge to create a rare configuration where a lake, river and glacier "touch" each other at a single point.

See more Earth from space

Tiny fragments of ancient alien tech may be strewn across the surface of the moon, and it may be relatively easy to find these microscopic relics, scientists propose in a new study.

The theoretical study does not claim to have found any evidence of advanced alien civilizations; rather, it offers a new way to search for clues of their existence.

Unlike Earth, the moon has no functional atmosphere or magnetic field, so it is completely exposed to the vacuum of space. As a result, it is constantly bombarded by meteorites, as well as hit by a steady stream of microscopic particles from the rest of the solar system and beyond. Because the moon has no water or tectonic movements, this microscopic matter accumulates and remains on the surface, completely undisturbed.

In the new paper, uploaded June 23 to the preprint server arXiv, the researchers argue that some of this dust originates from star systems beyond our own and, therefore, may contain evidence of long-lost alien civilizations. They also propose a new experiment that could potentially find these microscopic fragments within samples collected over the next decade or more. (The study has not been published yet, but it has been submitted to the International Journal of Astrobiology.)

"The moon has been quietly accumulating material from space for billions of years, much of it likely billions of years older than the moon itself," study first author Lewis Pinault, a planetary scientist at University College London and an affiliate of the SETI Institute, said in a statement. "We're asking whether that ancient collection might contain microscopic traces of technologies that existed long before humans ever looked up at the sky."

Tiny technosignatures

Until now, the search for evidence of advanced alien civilizations, known as technosignatures, has focused mainly on radio signals that could be emitted from inhabited exoplanets or hypothetical megastructures, such as Dyson spheres. However, these signals would originate only from active civilizations, not those that died out long before we could spot them.

The authors of the new study argue that when a civilization dies, traces of its technology could survive and end up in space, either via the deterioration of megastructures and other smaller spacecraft or via powerful asteroid strikes on once-inhabited exoplanets. Once in space, tiny specks of metal or other artificial materials could be ejected from star systems by powerful gusts of stellar wind and eventually drift toward us.

Using computer models, the team predicted that pieces of tech up to 3 micrometers across (three-millionths of a meter, or about 3% the width of a human hair) could escape their star systems and travel across interstellar space for up to 1 billion years. Then, they estimated how much of this material could be reaching the solar system and how likely it would be to end up on the moon. (We already know that interstellar dust can penetrate the inner solar system because scientists found some within samples collected from the surface of Bennu, an asteroid that orbits between Earth and Mars and was visited by NASA's OSIRIS-REx probe in 2020.)

To date, no lunar samples have contained any technosignatures. However, the scientists who studied them were likely not looking for such particulates, and the samples were probably too small to yield meaningful results, the study authors argue.

The researchers believe that a sample of lunar regolith with a volume of 35 cubic feet (1 cubic meter) could be enough to find at least one technological fragment. The team also proposed ways of combing through the material using microscopy, industrial materials analysis and AI-assisted imaging.

However, if such a sample does not yield any results, this would not necessarily disprove the researchers' hypothesis and may instead mean their models are off and a greater sample size would be required, the team wrote.

"Eminently reasonable"

Several upcoming space missions will collect fresh samples from the lunar surface, including China's recently delayed Chang'e-7 mission and future missions in NASA's Artemis program. These samples could potentially hold technosignatures, although the volume of regolith collected will be far less than what the researchers are proposing.

Therefore, we may have to wait until humans establish a permanent moon base before astronauts can collect enough material to be analyzed properly. This may not be that far off, as both the U.S. and China are planning to construct lunar bases within the next decade. Researchers also think the samples could be analyzed on the moon rather than on Earth.

As a result, the SETI Institute, which leads the international hunt for technosignatures, views the new idea as very promising.

"The concept of searching the lunar regolith for microscopic technosignatures is at once extraordinarily original and eminently reasonable," Bill Diamond, president and CEO of the SETI Institute, who was not involved in the new study, said in the statement. "This is a novel addition to the search methodologies applied to seeking evidence of technology as a proxy for life and intelligence beyond our solar system and we are excited at the prospect of bringing this to fruition."

Extraterrestrials quiz: Are you an alien expert, or has your brain been abducted?