A stream of liquid water could be brimming beneath the craggy, tan rock crust on Mars, enough to make up a whole ocean, according to a NASA study, whose results were published on Monday in the Proceedings of the National Academy of Sciences (PNAS).

Here’s more about NASA’s latest discovery, and what it tells us about the potential of human settlements on the Red Planet in the future:

How did NASA find water on Mars?

NASA’s outer-space robotic explorer, the InSight Lander, touched down on Mars in 2018. It studied seismic waves on the planet, which read data from more than 1,300 marsquakes before shutting down two years ago.

InSight collected data from a plain near the planet’s equator called Elysium Planitia.

A group of researchers combined this data with computer models and speculated that underground water is the most likely explanation for the seismic readings.

While NASA found liquid saltwater on Mars in 2015, the latest discovery is significant because it indicates the large amount of water the planet possibly holds in fractures 11.5km (7.15 miles) to 20km (12.4 miles) underground.

The lead scientist of the research, Vashan Wright of the University of California San Diego’s Scripps Institution of Oceanography, said that if the InSight data collected at Elysium Planitia is representative of the rest of Mars, the water would be enough to fill a global ocean 1 to 2km (0.6 to 1.2 miles) deep.

Drills and other equipment will be needed to further investigate and confirm the presence of water.

It has long been discovered by scientists that Mars once had water, maybe even in ample amounts. Last year, China’s Mars rover also found that water may be more widespread than previously thought.

“There were thoughts that some of the water escaped when Mars lost its atmosphere,” Wright told Al Jazeera.

How did Mars lose its atmosphere?

Alastair Gunn, a radio astronomer at the Jodrell Bank Centre for Astrophysics at the University of Manchester, told the BBC that Mars used to have a strong magnetic field like Earth.

The motion of molten iron in Earth’s core generates the field, which protects from cosmic radiation and from the solar wind, which refers to energetic charged particles flowing from the sun.

However, Mars cooled internally and switched off this field. This solar wind stripped Mars of its atmosphere, turning it cold and dry.

Will there be human settlements on Mars?

A NASA rover called the Perseverance Rover, which was launched in 2020, has manufactured oxygen on Mars, Amitabha Ghosh, a space scientist who has worked with NASA, told Al Jazeera. “So we just need water in some form for human existence as well as making rocket fuel,” said Ghosh.

Plans for humans to inhabit Mars are not recent.

Billionaire and technology entrepreneur Elon Musk has been striving to colonise Mars for over a decade under SpaceX, his rocket company.

SpaceX employees have long been fleshing out the blueprint of a Martian city where humans roam, complete with dome habitats and spacesuits.

“Elon Musk is making a Starship which can carry 200 people to Mars in six months. It’s all coming together,” Ghosh added.

The SpaceX website deems Mars one of Earth’s closest habitable neighbours.

Musk is not the only one with Mars city dreams. The United Arab Emirates Space programme, particularly the Mohammed Bin Rashid Space Center, aims to establish a human settlement on Mars by 2117.

“In 10-15 years, it might not look like science fiction any more,” said Ghosh.

Who would live on Mars?

It is unlikely that most people will be able to afford to live on Mars, in case human settlements are established on the planet.

Space missions are priced very high. In 2011, Cirque Du Soleil billionaire Guy Laliberte paid $35m to go to space.

Las Vegas-based Bigelow Space Operations (BSO) said in 2019 that it would charge private astronauts $52m a seat to visit the International Space Station for a month or two.

Should humans live on Mars?

The prospect of humans living on the Red Planet has raised ethical questions: Some thinkers question whether it is right to move to a “backup planet” after wrecking environmental damage on Earth.

Ian Stoner, an instructor of the Department of Philosophy at Saint Paul College Minnesota, wrote an article arguing against establishing human settlements on Mars on moral grounds.

“Human presence on Mars, he argued in an article, is likely to constitute a significantly invasive or destructive investigation of the Martian environment.” Humans will impart bacteria, yeast and fungus on the environment of the planet, he added.

Earth is already marred by environmental damage due to warming temperatures which have resulted in rising sea levels, floods and droughts. A 2023 Pew Research Center survey asked 10,329 American adults about their top priorities for NASA missions. Sixty percent of respondents wanted NASA to monitor asteroids that could hit Earth.

For 50 percent of the respondents, the top priority was to monitor key parts of Earth’s climate system. Only 11 percent of respondents stated the exploration of Mars as their top priority.

Katharine Hayhoe, director of the Climate Science Center at Texas Tech University, rebuked the idea that Mars should be colonised instead of climate change on Earth being tackled, in an interview with US-based publication Aerospace America.

“If we do not take action to reduce and eventually eliminate our carbon emissions, they will overwhelm human civilisation as we know it, long before Mars is ready to be colonised by large numbers of people,” Hayhoe is quoted saying.

While space missions have been unearthing new details about the presence of water and oxygen on the Red Planet, Mars has not been explored by crewed space missions. There is not enough information about how long humans can sustainably survive on the planet.