More than 70 original NASA photographs including a celebrated image of Buzz Aldrin's moon walk taken by Neil Armstrong were sold at auction in Copenhagen on Wednesday for more than 155,000 euros ($172,000).

The Aldrin image, which fetched 5,373 euros, shows the astronaut on the surface of the moon in July 1969 during the first manned lunar landing. It was famously used on the cover of LIFE magazine.

Armstrong, the first man to step onto the Moon, can be seen in the reflection of Aldrin's visor.

A total of 74 NASA photographs were put up for sale including 26 taken on the Moon during the Apollo missions in the 1960s and 1970s.

In the 21st century, planetary scientists have become increasingly aware that subsurface oceans consisting of liquid water exist within objects throughout the solar system. Because water is a universal requirement for life on Earth, these bodies—mostly moons—are enticing targets in the search for extraterrestrial life.

A primary way of deducing the existence of an unseen ocean is through an induced magnetic field. These fields originate from a unique application of Faraday's law of induction, which states that a time-varying magnetic field creates an electric current when applied to a circuit. Water that is salty enough to remain liquid in cold space environments is very conductive; at the same time, a moon's orbit through a planet's rotating magnetic field exposes the moon to a field strength that varies with time.

In Steven Spielberg's 1977 film "Close Encounters of the Third Kind," extraterrestrials communicate with humans through a catchy five-note sequence. In Spielberg's 1982 blockbuster "E.T.," a diminutive alien learns basic English from a children's TV show. More recently, in 2016's "Arrival," squid-like visitors use pictograms to make themselves understood to American scientists wielding whiteboards with words.