Nasa has admitted that a massive hole on Mars could be a "portal" leading to an underground world of alien life.
The American space agency shared an image of the 300-foot-wide opening in the Martian landscape as its Astronomy Picture of the Day.
Rather than leave people guessing, Nasa suggested the giant hole appears to lead to a mysterious "lower level" that may support life.
The perfectly rounded hole spans roughly 328 feet and is located in the upper-right portion of a satellite photo taken by the Mars Reconnaissance Orbiter in 2017.
The perfectly rounded hole spans roughly 328 feet and is located in the upper-right portion of a satellite photo taken by the Mars Reconnaissance Orbiter in 2017
NASA/JPL–Caltech/UArizona
The cavity is surrounded by a circular crater, making the discovery even more mysterious.
Nasa described the landscape as "Swiss cheese-like" with numerous holes showing "dusty, dark, Martian terrain beneath evaporating, light, carbon dioxide ice".
"Holes such as this are of particular interest because they might be portals to lower levels that extend into expansive underground caves," Nasa researchers said.
"If so, these naturally occurring tunnels are relatively protected from the harsh surface of Mars, making them relatively good candidates to contain Martian life," they added.
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Nasa also noted these pits are "prime targets for possible future spacecraft, robots, and even human interplanetary explorers."
Scientists believe Mars was once more Earth-like billions of years ago, but today's surface is hostile to life.
Mars lacks a strong magnetic field and thick atmosphere, leaving its surface bombarded by deadly levels of cosmic and solar radiation.
However, life may have survived below the soil in these caves and tubes, protected by natural shielding.
This means astronauts might find evidence or even fossils of living organisms in these underground environments.
America's experts on underground mysteries - the US Geological Survey (USGS) - were brought in to find these Martian caves.
In 2019, the USGS Astrogeology Science Center created a map showing over 1,000 potential cave entrances across Mars.
Glen Cushing, a space scientist from the centre, cautioned: "It is impossible to see how far any of them extend beneath the surface."
In 2019, the USGS Astrogeology Science Center created a map showing over 1,000 potential cave entrances across Mars
ESA/DLR/FU Berlin (G. Neukum)
Other missions, including the European Space Agency's Mars Express, have found evidence of ancient lava tubes beneath the planet's dormant volcanoes.
The soonest human explorers might see this enormous hole for themselves could be in 2028.
SpaceX founder Elon Musk recently accelerated the timeline for reaching the Red Planet during an appearance on the Joe Rogan Experience podcast.
Musk revealed that SpaceX's "default plan" is to "launch several Starships to Mars at the end of next year."
These uncrewed missions would test if the vehicles could successfully land on Mars, with hopes to launch five remote-controlled starships by 2026.
